Merge branch 'master' of github.com:uwiger/gproc

Conflicts:
	test/gproc_tests.erl

Makefile

@@ -16,32 +16,32 @@
 ## IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 ## FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 ## THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-## LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
+## LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 ## FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 ## DEALINGS IN THE SOFTWARE.
 
 .PHONY: all compile clean eunit test eqc doc check dialyzer
 
-DIRS=src 
+DIRS=src
 
 all: compile eunit test doc
 
 check: compile dialyzer
 
 compile:
-	./rebar compile
+	rebar compile
 
 
 clean:
-	./rebar clean
+	rebar clean
 
 eunit:
-	./rebar eunit
+	rebar eunit
 
 test: eunit
 
 doc:
-	./rebar doc
+	rebar doc
 
 dialyzer:
-	./rebar skip_deps=true dialyze
+	rebar skip_deps=true dialyze

README.md

@@ -136,5 +136,6 @@ Freiburg 2007 ([Paper available here](http://github.com/esl/gproc/blob/master/do
 <tr><td><a href="http://github.com/esl/gproc/blob/master/doc/gproc_info.md" class="module">gproc_info</a></td></tr>
 <tr><td><a href="http://github.com/esl/gproc/blob/master/doc/gproc_init.md" class="module">gproc_init</a></td></tr>
 <tr><td><a href="http://github.com/esl/gproc/blob/master/doc/gproc_lib.md" class="module">gproc_lib</a></td></tr>
+<tr><td><a href="http://github.com/esl/gproc/blob/master/doc/gproc_monitor.md" class="module">gproc_monitor</a></td></tr>
 <tr><td><a href="http://github.com/esl/gproc/blob/master/doc/gproc_sup.md" class="module">gproc_sup</a></td></tr></table>
 

doc/README.md

@@ -136,5 +136,6 @@ Freiburg 2007 ([Paper available here](erlang07-wiger.pdf)).
 <tr><td><a href="gproc_info.md" class="module">gproc_info</a></td></tr>
 <tr><td><a href="gproc_init.md" class="module">gproc_init</a></td></tr>
 <tr><td><a href="gproc_lib.md" class="module">gproc_lib</a></td></tr>
+<tr><td><a href="gproc_monitor.md" class="module">gproc_monitor</a></td></tr>
 <tr><td><a href="gproc_sup.md" class="module">gproc_sup</a></td></tr></table>
 

doc/edoc-info

@@ -1,4 +1,4 @@
 {application,gproc}.
 {packages,[]}.
 {modules,[gproc,gproc_app,gproc_dist,gproc_info,gproc_init,gproc_lib,
-          gproc_sup]}.
+          gproc_monitor,gproc_sup]}.

doc/gproc.md

@@ -180,9 +180,12 @@ a = aggregate_counter
 
 
 
-<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#add_global_aggr_counter-1">add_global_aggr_counter/1</a></td><td>Registers a global (unique) aggregated counter.</td></tr><tr><td valign="top"><a href="#add_global_counter-2">add_global_counter/2</a></td><td>Registers a global (non-unique) counter.</td></tr><tr><td valign="top"><a href="#add_global_name-1">add_global_name/1</a></td><td>Registers a global (unique) name.</td></tr><tr><td valign="top"><a href="#add_global_property-2">add_global_property/2</a></td><td>Registers a global (non-unique) property.</td></tr><tr><td valign="top"><a href="#add_local_aggr_counter-1">add_local_aggr_counter/1</a></td><td>Registers a local (unique) aggregated counter.</td></tr><tr><td valign="top"><a href="#add_local_counter-2">add_local_counter/2</a></td><td>Registers a local (non-unique) counter.</td></tr><tr><td valign="top"><a href="#add_local_name-1">add_local_name/1</a></td><td>Registers a local (unique) name.</td></tr><tr><td valign="top"><a href="#add_local_property-2">add_local_property/2</a></td><td>Registers a local (non-unique) property.</td></tr><tr><td valign="top"><a href="#add_shared_local_counter-2">add_shared_local_counter/2</a></td><td>Registers a local shared (unique) counter.</td></tr><tr><td valign="top"><a href="#audit_process-1">audit_process/1</a></td><td></td></tr><tr><td valign="top"><a href="#await-1">await/1</a></td><td>Equivalent to <a href="#await-2"><tt>await(Key, infinity)</tt></a>.</td></tr><tr><td valign="top"><a href="#await-2">await/2</a></td><td>Wait for a local name to be registered.</td></tr><tr><td valign="top"><a href="#cancel_wait-2">cancel_wait/2</a></td><td></td></tr><tr><td valign="top"><a href="#default-1">default/1</a></td><td></td></tr><tr><td valign="top"><a href="#first-1">first/1</a></td><td>Behaves as ets:first(Tab) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#get_env-3">get_env/3</a></td><td>Equivalent to <a href="#get_env-4"><tt>get_env(Scope, App, Key, [app_env])</tt></a>.</td></tr><tr><td valign="top"><a href="#get_env-4">get_env/4</a></td><td>Read an environment value, potentially cached as a <code>gproc_env</code> property.</td></tr><tr><td valign="top"><a href="#get_set_env-3">get_set_env/3</a></td><td>Equivalent to <a href="#get_set_env-4"><tt>get_set_env(Scope, App, Key, [app_env])</tt></a>.</td></tr><tr><td valign="top"><a href="#get_set_env-4">get_set_env/4</a></td><td>Fetch and cache an environment value, if not already cached.</td></tr><tr><td valign="top"><a href="#get_value-1">get_value/1</a></td><td>Reads the value stored with a key registered to the current process.</td></tr><tr><td valign="top"><a href="#get_value-2">get_value/2</a></td><td>Reads the value stored with a key registered to the process Pid.</td></tr><tr><td valign="top"><a href="#give_away-2">give_away/2</a></td><td>Atomically transfers the key <code>From</code> to the process identified by <code>To</code>.</td></tr><tr><td valign="top"><a href="#goodbye-0">goodbye/0</a></td><td>Unregister all items of the calling process and inform gproc  
+<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#add_global_aggr_counter-1">add_global_aggr_counter/1</a></td><td>Registers a global (unique) aggregated counter.</td></tr><tr><td valign="top"><a href="#add_global_counter-2">add_global_counter/2</a></td><td>Registers a global (non-unique) counter.</td></tr><tr><td valign="top"><a href="#add_global_name-1">add_global_name/1</a></td><td>Registers a global (unique) name.</td></tr><tr><td valign="top"><a href="#add_global_property-2">add_global_property/2</a></td><td>Registers a global (non-unique) property.</td></tr><tr><td valign="top"><a href="#add_local_aggr_counter-1">add_local_aggr_counter/1</a></td><td>Registers a local (unique) aggregated counter.</td></tr><tr><td valign="top"><a href="#add_local_counter-2">add_local_counter/2</a></td><td>Registers a local (non-unique) counter.</td></tr><tr><td valign="top"><a href="#add_local_name-1">add_local_name/1</a></td><td>Registers a local (unique) name.</td></tr><tr><td valign="top"><a href="#add_local_property-2">add_local_property/2</a></td><td>Registers a local (non-unique) property.</td></tr><tr><td valign="top"><a href="#add_shared_local_counter-2">add_shared_local_counter/2</a></td><td>Registers a local shared (unique) counter.</td></tr><tr><td valign="top"><a href="#audit_process-1">audit_process/1</a></td><td></td></tr><tr><td valign="top"><a href="#await-1">await/1</a></td><td>Equivalent to <a href="#await-2"><tt>await(Key, infinity)</tt></a>.</td></tr><tr><td valign="top"><a href="#await-2">await/2</a></td><td>Wait for a local name to be registered.</td></tr><tr><td valign="top"><a href="#cancel_wait-2">cancel_wait/2</a></td><td>Cancels a previous call to nb_wait/1.</td></tr><tr><td valign="top"><a href="#cancel_wait_or_monitor-1">cancel_wait_or_monitor/1</a></td><td></td></tr><tr><td valign="top"><a href="#default-1">default/1</a></td><td></td></tr><tr><td valign="top"><a href="#demonitor-2">demonitor/2</a></td><td>Remove a monitor on a registered name
+This function is the reverse of monitor/1.</td></tr><tr><td valign="top"><a href="#first-1">first/1</a></td><td>Behaves as ets:first(Tab) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#get_env-3">get_env/3</a></td><td>Equivalent to <a href="#get_env-4"><tt>get_env(Scope, App, Key, [app_env])</tt></a>.</td></tr><tr><td valign="top"><a href="#get_env-4">get_env/4</a></td><td>Read an environment value, potentially cached as a <code>gproc_env</code> property.</td></tr><tr><td valign="top"><a href="#get_set_env-3">get_set_env/3</a></td><td>Equivalent to <a href="#get_set_env-4"><tt>get_set_env(Scope, App, Key, [app_env])</tt></a>.</td></tr><tr><td valign="top"><a href="#get_set_env-4">get_set_env/4</a></td><td>Fetch and cache an environment value, if not already cached.</td></tr><tr><td valign="top"><a href="#get_value-1">get_value/1</a></td><td>Reads the value stored with a key registered to the current process.</td></tr><tr><td valign="top"><a href="#get_value-2">get_value/2</a></td><td>Reads the value stored with a key registered to the process Pid.</td></tr><tr><td valign="top"><a href="#give_away-2">give_away/2</a></td><td>Atomically transfers the key <code>From</code> to the process identified by <code>To</code>.</td></tr><tr><td valign="top"><a href="#goodbye-0">goodbye/0</a></td><td>Unregister all items of the calling process and inform gproc  
 to forget about the calling process.</td></tr><tr><td valign="top"><a href="#i-0">i/0</a></td><td>Similar to the built-in shell command <code>i()</code> but inserts information
-about names and properties registered in Gproc, where applicable.</td></tr><tr><td valign="top"><a href="#info-1">info/1</a></td><td>Similar to <code>process_info(Pid)</code> but with additional gproc info.</td></tr><tr><td valign="top"><a href="#info-2">info/2</a></td><td>Similar to process_info(Pid, Item), but with additional gproc info.</td></tr><tr><td valign="top"><a href="#last-1">last/1</a></td><td>Behaves as ets:last(Tab) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#lookup_global_aggr_counter-1">lookup_global_aggr_counter/1</a></td><td>Lookup a global (unique) aggregated counter and returns its value.</td></tr><tr><td valign="top"><a href="#lookup_global_counters-1">lookup_global_counters/1</a></td><td>Look up all global (non-unique) instances of a given Counter.</td></tr><tr><td valign="top"><a href="#lookup_global_name-1">lookup_global_name/1</a></td><td>Lookup a global unique name.</td></tr><tr><td valign="top"><a href="#lookup_global_properties-1">lookup_global_properties/1</a></td><td>Look up all global (non-unique) instances of a given Property.</td></tr><tr><td valign="top"><a href="#lookup_local_aggr_counter-1">lookup_local_aggr_counter/1</a></td><td>Lookup a local (unique) aggregated counter and returns its value.</td></tr><tr><td valign="top"><a href="#lookup_local_counters-1">lookup_local_counters/1</a></td><td>Look up all local (non-unique) instances of a given Counter.</td></tr><tr><td valign="top"><a href="#lookup_local_name-1">lookup_local_name/1</a></td><td>Lookup a local unique name.</td></tr><tr><td valign="top"><a href="#lookup_local_properties-1">lookup_local_properties/1</a></td><td>Look up all local (non-unique) instances of a given Property.</td></tr><tr><td valign="top"><a href="#lookup_pid-1">lookup_pid/1</a></td><td>Lookup the Pid stored with a key.</td></tr><tr><td valign="top"><a href="#lookup_pids-1">lookup_pids/1</a></td><td>Returns a list of pids with the published key Key.</td></tr><tr><td valign="top"><a href="#lookup_value-1">lookup_value/1</a></td><td>Lookup the value stored with a key.</td></tr><tr><td valign="top"><a href="#lookup_values-1">lookup_values/1</a></td><td>Retrieve the <code>{Pid,Value}</code> pairs corresponding to Key.</td></tr><tr><td valign="top"><a href="#mreg-3">mreg/3</a></td><td>Register multiple {Key,Value} pairs of a given type and scope.</td></tr><tr><td valign="top"><a href="#munreg-3">munreg/3</a></td><td>Unregister multiple Key items of a given type and scope.</td></tr><tr><td valign="top"><a href="#nb_wait-1">nb_wait/1</a></td><td>Wait for a local name to be registered.</td></tr><tr><td valign="top"><a href="#next-2">next/2</a></td><td>Behaves as ets:next(Tab,Key) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#prev-2">prev/2</a></td><td>Behaves as ets:prev(Tab,Key) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#reg-1">reg/1</a></td><td>Equivalent to <a href="#reg-2"><tt>reg(Key, default(Key))</tt></a>.</td></tr><tr><td valign="top"><a href="#reg-2">reg/2</a></td><td>Register a name or property for the current process.</td></tr><tr><td valign="top"><a href="#reg_shared-1">reg_shared/1</a></td><td>Register a resource, but don't tie it to a particular process.</td></tr><tr><td valign="top"><a href="#reg_shared-2">reg_shared/2</a></td><td>Register a resource, but don't tie it to a particular process.</td></tr><tr><td valign="top"><a href="#reset_counter-1">reset_counter/1</a></td><td>Reads and resets a counter in a "thread-safe" way.</td></tr><tr><td valign="top"><a href="#select-1">select/1</a></td><td>
+about names and properties registered in Gproc, where applicable.</td></tr><tr><td valign="top"><a href="#info-1">info/1</a></td><td>Similar to <code>process_info(Pid)</code> but with additional gproc info.</td></tr><tr><td valign="top"><a href="#info-2">info/2</a></td><td>Similar to process_info(Pid, Item), but with additional gproc info.</td></tr><tr><td valign="top"><a href="#last-1">last/1</a></td><td>Behaves as ets:last(Tab) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#lookup_global_aggr_counter-1">lookup_global_aggr_counter/1</a></td><td>Lookup a global (unique) aggregated counter and returns its value.</td></tr><tr><td valign="top"><a href="#lookup_global_counters-1">lookup_global_counters/1</a></td><td>Look up all global (non-unique) instances of a given Counter.</td></tr><tr><td valign="top"><a href="#lookup_global_name-1">lookup_global_name/1</a></td><td>Lookup a global unique name.</td></tr><tr><td valign="top"><a href="#lookup_global_properties-1">lookup_global_properties/1</a></td><td>Look up all global (non-unique) instances of a given Property.</td></tr><tr><td valign="top"><a href="#lookup_local_aggr_counter-1">lookup_local_aggr_counter/1</a></td><td>Lookup a local (unique) aggregated counter and returns its value.</td></tr><tr><td valign="top"><a href="#lookup_local_counters-1">lookup_local_counters/1</a></td><td>Look up all local (non-unique) instances of a given Counter.</td></tr><tr><td valign="top"><a href="#lookup_local_name-1">lookup_local_name/1</a></td><td>Lookup a local unique name.</td></tr><tr><td valign="top"><a href="#lookup_local_properties-1">lookup_local_properties/1</a></td><td>Look up all local (non-unique) instances of a given Property.</td></tr><tr><td valign="top"><a href="#lookup_pid-1">lookup_pid/1</a></td><td>Lookup the Pid stored with a key.</td></tr><tr><td valign="top"><a href="#lookup_pids-1">lookup_pids/1</a></td><td>Returns a list of pids with the published key Key.</td></tr><tr><td valign="top"><a href="#lookup_value-1">lookup_value/1</a></td><td>Lookup the value stored with a key.</td></tr><tr><td valign="top"><a href="#lookup_values-1">lookup_values/1</a></td><td>Retrieve the <code>{Pid,Value}</code> pairs corresponding to Key.</td></tr><tr><td valign="top"><a href="#monitor-1">monitor/1</a></td><td>monitor a registered name
+This function works much like erlang:monitor(process, Pid), but monitors
+a unique name registered via gproc.</td></tr><tr><td valign="top"><a href="#mreg-3">mreg/3</a></td><td>Register multiple {Key,Value} pairs of a given type and scope.</td></tr><tr><td valign="top"><a href="#munreg-3">munreg/3</a></td><td>Unregister multiple Key items of a given type and scope.</td></tr><tr><td valign="top"><a href="#nb_wait-1">nb_wait/1</a></td><td>Wait for a local name to be registered.</td></tr><tr><td valign="top"><a href="#next-2">next/2</a></td><td>Behaves as ets:next(Tab,Key) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#prev-2">prev/2</a></td><td>Behaves as ets:prev(Tab,Key) for a given type of registration object.</td></tr><tr><td valign="top"><a href="#reg-1">reg/1</a></td><td>Equivalent to <a href="#reg-2"><tt>reg(Key, default(Key))</tt></a>.</td></tr><tr><td valign="top"><a href="#reg-2">reg/2</a></td><td>Register a name or property for the current process.</td></tr><tr><td valign="top"><a href="#reg_shared-1">reg_shared/1</a></td><td>Register a resource, but don't tie it to a particular process.</td></tr><tr><td valign="top"><a href="#reg_shared-2">reg_shared/2</a></td><td>Register a resource, but don't tie it to a particular process.</td></tr><tr><td valign="top"><a href="#register_name-2">register_name/2</a></td><td>Behaviour support callback.</td></tr><tr><td valign="top"><a href="#reset_counter-1">reset_counter/1</a></td><td>Reads and resets a counter in a "thread-safe" way.</td></tr><tr><td valign="top"><a href="#select-1">select/1</a></td><td>
 see http://www.erlang.org/doc/man/ets.html#select-1.</td></tr><tr><td valign="top"><a href="#select-2">select/2</a></td><td>Perform a select operation on the process registry.</td></tr><tr><td valign="top"><a href="#select-3">select/3</a></td><td>Like <a href="#select-2"><code>select/2</code></a> but returns Limit objects at a time.</td></tr><tr><td valign="top"><a href="#select_count-1">select_count/1</a></td><td>Equivalent to <a href="#select_count-2"><tt>select_count(all, Pat)</tt></a>.</td></tr><tr><td valign="top"><a href="#select_count-2">select_count/2</a></td><td>Perform a select_count operation on the process registry.</td></tr><tr><td valign="top"><a href="#send-2">send/2</a></td><td>Sends a message to the process, or processes, corresponding to Key.</td></tr><tr><td valign="top"><a href="#set_env-5">set_env/5</a></td><td>Updates the cached value as well as underlying environment.</td></tr><tr><td valign="top"><a href="#set_value-2">set_value/2</a></td><td>Sets the value of the registeration entry given by Key.</td></tr><tr><td valign="top"><a href="#start_link-0">start_link/0</a></td><td>Starts the gproc server.</td></tr><tr><td valign="top"><a href="#table-0">table/0</a></td><td>Equivalent to <a href="#table-1"><tt>table({all, all})</tt></a>.</td></tr><tr><td valign="top"><a href="#table-1">table/1</a></td><td>Equivalent to <a href="#table-2"><tt>table(Context, [])</tt></a>.</td></tr><tr><td valign="top"><a href="#table-2">table/2</a></td><td>QLC table generator for the gproc registry.</td></tr><tr><td valign="top"><a href="#unreg-1">unreg/1</a></td><td>Unregister a name or property.</td></tr><tr><td valign="top"><a href="#unreg_shared-1">unreg_shared/1</a></td><td>Unregister a shared resource.</td></tr><tr><td valign="top"><a href="#unregister_name-1">unregister_name/1</a></td><td>Equivalent to <tt>unreg / 1</tt>.</td></tr><tr><td valign="top"><a href="#update_counter-2">update_counter/2</a></td><td>Updates the counter registered as Key for the current process.</td></tr><tr><td valign="top"><a href="#update_shared_counter-2">update_shared_counter/2</a></td><td></td></tr><tr><td valign="top"><a href="#where-1">where/1</a></td><td>Returns the pid registered as Key.</td></tr><tr><td valign="top"><a href="#whereis_name-1">whereis_name/1</a></td><td>Equivalent to <tt>where / 1</tt>.</td></tr></table>
 
 
@@ -358,7 +361,25 @@ registered (the difference: await/2 also returns the value).<a name="cancel_wait
 
 
 
-`cancel_wait(Key, Ref) -> any()`
+<pre>cancel_wait(Key::<a href="#type-key">key()</a>, Ref) -> ok</pre>
+<ul class="definitions"><li><pre>Ref = all | reference()</pre></li></ul>
+
+
+
+
+
+Cancels a previous call to nb_wait/1
+
+If `Ref = all`, all wait requests on `Key` from the calling process
+are canceled.<a name="cancel_wait_or_monitor-1"></a>
+
+<h3>cancel_wait_or_monitor/1</h3>
+
+
+
+
+
+`cancel_wait_or_monitor(Key) -> any()`
 
 <a name="default-1"></a>
 
@@ -370,7 +391,23 @@ registered (the difference: await/2 also returns the value).<a name="cancel_wait
 
 `default(X1) -> any()`
 
-<a name="first-1"></a>
+<a name="demonitor-2"></a>
+
+<h3>demonitor/2</h3>
+
+
+
+
+
+<pre>demonitor(Key::<a href="#type-key">key()</a>, Ref::reference()) -> ok</pre>
+<br></br>
+
+
+
+
+Remove a monitor on a registered name
+This function is the reverse of monitor/1. It removes a monitor previously
+set on a unique name. This function always succeeds given legal input.<a name="first-1"></a>
 
 <h3>first/1</h3>
 
@@ -871,7 +908,29 @@ Retrieve the `{Pid,Value}` pairs corresponding to Key.
 
 Key refer to any type of registry object. If it refers to a unique
 object, the list will be of length 0 or 1. If it refers to a non-unique
-object, the return value can be a list of any length.<a name="mreg-3"></a>
+object, the return value can be a list of any length.<a name="monitor-1"></a>
+
+<h3>monitor/1</h3>
+
+
+
+
+
+<pre>monitor(Key::<a href="#type-key">key()</a>) -> reference()</pre>
+<br></br>
+
+
+
+
+
+
+monitor a registered name
+This function works much like erlang:monitor(process, Pid), but monitors
+a unique name registered via gproc. A message, `{gproc, unreg, Ref, Key}`  
+will be sent to the requesting process, if the name is unregistered or  
+the registered process dies.
+
+If the name is not yet registered, the same message is sent immediately.<a name="mreg-3"></a>
 
 <h3>mreg/3</h3>
 
@@ -1043,7 +1102,21 @@ results, shared resources appear as other similar resources, except that
 increment the shared counter `myCounter` with 1, provided it exists.
 
 A shared aggregated counter will track updates in exactly the same way as
-an aggregated counter which is owned by a process.<a name="reset_counter-1"></a>
+an aggregated counter which is owned by a process.<a name="register_name-2"></a>
+
+<h3>register_name/2</h3>
+
+
+
+
+
+<pre>register_name(Name::<a href="#type-key">key()</a>, Pid::pid()) -> yes | no</pre>
+<br></br>
+
+
+
+
+Behaviour support callback<a name="reset_counter-1"></a>
 
 <h3>reset_counter/1</h3>
 

doc/gproc_lib.md

@@ -28,7 +28,7 @@ For a detailed description, see gproc/doc/erlang07-wiger.pdf.
 
 
 
-<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#await-3">await/3</a></td><td></td></tr><tr><td valign="top"><a href="#do_set_counter_value-3">do_set_counter_value/3</a></td><td></td></tr><tr><td valign="top"><a href="#do_set_value-3">do_set_value/3</a></td><td></td></tr><tr><td valign="top"><a href="#ensure_monitor-2">ensure_monitor/2</a></td><td></td></tr><tr><td valign="top"><a href="#insert_many-4">insert_many/4</a></td><td></td></tr><tr><td valign="top"><a href="#insert_reg-4">insert_reg/4</a></td><td></td></tr><tr><td valign="top"><a href="#remove_many-4">remove_many/4</a></td><td></td></tr><tr><td valign="top"><a href="#remove_reg-2">remove_reg/2</a></td><td></td></tr><tr><td valign="top"><a href="#update_aggr_counter-3">update_aggr_counter/3</a></td><td></td></tr><tr><td valign="top"><a href="#update_counter-3">update_counter/3</a></td><td></td></tr><tr><td valign="top"><a href="#valid_opts-2">valid_opts/2</a></td><td></td></tr></table>
+<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#add_monitor-3">add_monitor/3</a></td><td></td></tr><tr><td valign="top"><a href="#await-3">await/3</a></td><td></td></tr><tr><td valign="top"><a href="#do_set_counter_value-3">do_set_counter_value/3</a></td><td></td></tr><tr><td valign="top"><a href="#do_set_value-3">do_set_value/3</a></td><td></td></tr><tr><td valign="top"><a href="#ensure_monitor-2">ensure_monitor/2</a></td><td></td></tr><tr><td valign="top"><a href="#insert_many-4">insert_many/4</a></td><td></td></tr><tr><td valign="top"><a href="#insert_reg-4">insert_reg/4</a></td><td></td></tr><tr><td valign="top"><a href="#notify-2">notify/2</a></td><td></td></tr><tr><td valign="top"><a href="#notify-3">notify/3</a></td><td></td></tr><tr><td valign="top"><a href="#remove_many-4">remove_many/4</a></td><td></td></tr><tr><td valign="top"><a href="#remove_monitor-3">remove_monitor/3</a></td><td></td></tr><tr><td valign="top"><a href="#remove_monitors-3">remove_monitors/3</a></td><td></td></tr><tr><td valign="top"><a href="#remove_reg-3">remove_reg/3</a></td><td></td></tr><tr><td valign="top"><a href="#remove_reg-4">remove_reg/4</a></td><td></td></tr><tr><td valign="top"><a href="#remove_reverse_mapping-3">remove_reverse_mapping/3</a></td><td></td></tr><tr><td valign="top"><a href="#remove_wait-4">remove_wait/4</a></td><td></td></tr><tr><td valign="top"><a href="#update_aggr_counter-3">update_aggr_counter/3</a></td><td></td></tr><tr><td valign="top"><a href="#update_counter-3">update_counter/3</a></td><td></td></tr><tr><td valign="top"><a href="#valid_opts-2">valid_opts/2</a></td><td></td></tr></table>
 
 
 
@@ -36,6 +36,16 @@ For a detailed description, see gproc/doc/erlang07-wiger.pdf.
 <h2><a name="functions">Function Details</a></h2>
 
 
+<a name="add_monitor-3"></a>
+
+<h3>add_monitor/3</h3>
+
+
+
+
+
+`add_monitor(T, Pid, Ref) -> any()`
+
 <a name="await-3"></a>
 
 <h3>await/3</h3>
@@ -100,6 +110,26 @@ For a detailed description, see gproc/doc/erlang07-wiger.pdf.
 <br></br>
 
 
+<a name="notify-2"></a>
+
+<h3>notify/2</h3>
+
+
+
+
+
+`notify(Key, Opts) -> any()`
+
+<a name="notify-3"></a>
+
+<h3>notify/3</h3>
+
+
+
+
+
+`notify(Event, Key, Opts) -> any()`
+
 <a name="remove_many-4"></a>
 
 <h3>remove_many/4</h3>
@@ -110,15 +140,65 @@ For a detailed description, see gproc/doc/erlang07-wiger.pdf.
 
 `remove_many(T, Scope, L, Pid) -> any()`
 
-<a name="remove_reg-2"></a>
+<a name="remove_monitor-3"></a>
+
+<h3>remove_monitor/3</h3>
+
+
+
+
+
+`remove_monitor(T, Pid, Ref) -> any()`
+
+<a name="remove_monitors-3"></a>
+
+<h3>remove_monitors/3</h3>
+
+
+
+
+
+`remove_monitors(Key, Pid, MPid) -> any()`
+
+<a name="remove_reg-3"></a>
+
+<h3>remove_reg/3</h3>
+
+
+
+
+
+`remove_reg(Key, Pid, Event) -> any()`
+
+<a name="remove_reg-4"></a>
+
+<h3>remove_reg/4</h3>
+
+
+
+
+
+`remove_reg(Key, Pid, Event, Opts) -> any()`
+
+<a name="remove_reverse_mapping-3"></a>
+
+<h3>remove_reverse_mapping/3</h3>
+
+
+
+
+
+`remove_reverse_mapping(Event, Pid, Key) -> any()`
+
+<a name="remove_wait-4"></a>
 
-<h3>remove_reg/2</h3>
+<h3>remove_wait/4</h3>
 
 
 
 
 
-`remove_reg(Key, Pid) -> any()`
+`remove_wait(Key, Pid, Ref, Waiters) -> any()`
 
 <a name="update_aggr_counter-3"></a>
 

doc/gproc_monitor.md

@@ -0,0 +1,100 @@
+Module gproc_monitor
+====================
+
+
+<h1>Module gproc_monitor</h1>
+
+* [Description](#description)
+* [Function Index](#index)
+* [Function Details](#functions)
+
+
+
+This module implements a notification system for gproc names
+When a process subscribes to notifications for a given name, a message
+will be sent each time that name is registered.
+
+
+
+__Behaviours:__ [`gen_server`](gen_server.md).
+
+__Authors:__ Ulf Wiger ([`ulf.wiger@feuerlabs.com`](mailto:ulf.wiger@feuerlabs.com)).
+
+<h2><a name="index">Function Index</a></h2>
+
+
+
+<table width="100%" border="1" cellspacing="0" cellpadding="2" summary="function index"><tr><td valign="top"><a href="#start_link-0">start_link/0</a></td><td>
+Starts the server.</td></tr><tr><td valign="top"><a href="#subscribe-1">subscribe/1</a></td><td>  
+Subscribe to registration events for a certain name.</td></tr><tr><td valign="top"><a href="#unsubscribe-1">unsubscribe/1</a></td><td>  
+Unsubscribe from registration events for a certain name.</td></tr></table>
+
+
+
+
+<h2><a name="functions">Function Details</a></h2>
+
+
+<a name="start_link-0"></a>
+
+<h3>start_link/0</h3>
+
+
+
+
+
+<pre>start_link() -> {ok, Pid} | ignore | {error, Error}</pre>
+<br></br>
+
+
+
+
+
+Starts the server
+<a name="subscribe-1"></a>
+
+<h3>subscribe/1</h3>
+
+
+
+
+
+<pre>subscribe(Key::<a href="#type-key">key()</a>) -> ok</pre>
+<br></br>
+
+
+
+
+
+
+  
+Subscribe to registration events for a certain name
+
+
+
+The subscribing process will receive a `{gproc_monitor, Name, Pid}` message
+whenever a process registers under the given name, and a
+`{gproc_monitor, Name, undefined}` message when the name is unregistered,  
+either explicitly, or because the registered process dies.
+
+When the subscription is first ordered, one of the above messages will be
+sent immediately, indicating the current status of the name.<a name="unsubscribe-1"></a>
+
+<h3>unsubscribe/1</h3>
+
+
+
+
+
+<pre>unsubscribe(Key::<a href="#type-key">key()</a>) -> ok</pre>
+<br></br>
+
+
+
+
+
+
+  
+Unsubscribe from registration events for a certain name
+
+This function is the reverse of subscribe/1. It removes the subscription.

src/gproc.erl

@@ -73,6 +73,9 @@
          await/1, await/2,
          nb_wait/1,
          cancel_wait/2,
+	 cancel_wait_or_monitor/1,
+	 monitor/1,
+	 demonitor/2,
          lookup_pid/1,
          lookup_pids/1,
          lookup_value/1,
@@ -119,6 +122,7 @@
 
 %% Callbacks for behaviour support
 -export([whereis_name/1,
+	 register_name/2,
          unregister_name/1]).
 
 -export([default/1]).
@@ -656,6 +660,15 @@ nb_wait({n,l,_} = Key) ->
 nb_wait(Key) ->
     erlang:error(badarg, [Key]).
 
+%% @spec cancel_wait(Key::key(), Ref) -> ok
+%%    Ref = all | reference()
+%%
+%% @doc Cancels a previous call to nb_wait/1
+%%
+%% If `Ref = all', all wait requests on `Key' from the calling process
+%% are canceled.
+%% @end
+%%
 cancel_wait({_,g,_} = Key, Ref) ->
     ?CHK_DIST,
     cast({cancel_wait, self(), Key, Ref}, g),
@@ -664,6 +677,46 @@ cancel_wait({_,l,_} = Key, Ref) ->
     cast({cancel_wait, self(), Key, Ref}, l),
     ok.
 
+cancel_wait_or_monitor({_,g,_} = Key) ->
+    ?CHK_DIST,
+    cast({cancel_wait_or_monitor, self(), Key}, g),
+    ok;
+cancel_wait_or_monitor({_,l,_} = Key) ->
+    cast({cancel_wait_or_monitor, self(), Key}, l),
+    ok.
+
+
+%% @spec monitor(key()) -> reference()
+%%
+%% @doc monitor a registered name
+%% This function works much like erlang:monitor(process, Pid), but monitors
+%% a unique name registered via gproc. A message, `{gproc, unreg, Ref, Key}'
+%% will be sent to the requesting process, if the name is unregistered or
+%% the registered process dies.
+%%
+%% If the name is not yet registered, the same message is sent immediately.
+%% @end
+monitor({T,g,_} = Key) when T==n; T==a ->
+    ?CHK_DIST,
+    call({monitor, Key, self()}, g);
+monitor({T,l,_} = Key) when T==n; T==a ->
+    call({monitor, Key, self()}, l);
+monitor(Key) ->
+    erlang:error(badarg, [Key]).
+
+%% @spec demonitor(key(), reference()) -> ok
+%%
+%% @doc Remove a monitor on a registered name
+%% This function is the reverse of monitor/1. It removes a monitor previously
+%% set on a unique name. This function always succeeds given legal input.
+%% @end
+demonitor({T,g,_} = Key, Ref) when T==n; T==a ->
+    ?CHK_DIST,
+    call({demonitor, Key, Ref, self()}, g);
+demonitor({T,l,_} = Key, Ref) when T==n; T==a ->
+    call({demonitor, Key, Ref, self()}, l);
+demonitor(Key, Ref) ->
+    erlang:error(badarg, [Key, Ref]).
 
 %% @spec reg(Key::key(), Value) -> true
 %%
@@ -795,7 +848,7 @@ unreg(Key) ->
         {_, l, _} ->
             case ets:member(?TAB, {Key,self()}) of
                 true ->
-                    _ = gproc_lib:remove_reg(Key, self()),
+                    _ = gproc_lib:remove_reg(Key, self(), unreg),
                     true;
                 false ->
                     erlang:error(badarg)
@@ -817,6 +870,17 @@ unreg_shared(Key) ->
 	    erlang:error(badarg)
     end.
 
+%% @spec (key(), pid()) -> yes | no
+%%
+%% @doc Behaviour support callback
+%% @end
+register_name({n,_,_} = Name, Pid) when Pid == self() ->
+    try reg(Name), yes
+    catch
+	error:_ ->
+	    no
+    end.
+
 %% @equiv unreg/1
 unregister_name(Key) ->
     unreg(Key).
@@ -890,7 +954,7 @@ local_mreg(T, [_|_] = KVL) ->
     end.
 
 local_munreg(T, L) when T==p; T==c ->
-    _ = [gproc_lib:remove_reg({T,l,K}, self()) || K <- L],
+    _ = [gproc_lib:remove_reg({T,l,K}, self(), unreg) || K <- L],
     true.
 
 %% @spec (Key :: key(), Value) -> true
@@ -1342,27 +1406,22 @@ handle_cast({monitor_me, Pid}, S) ->
     erlang:monitor(process, Pid),
     {noreply, S};
 handle_cast({cancel_wait, Pid, {T,_,_} = Key, Ref}, S) ->
-    Rev = {Pid,Key},
     case ets:lookup(?TAB, {Key,T}) of
-        [{K, Waiters}] ->
-            case Waiters -- [{Pid,Ref}] of
-                [] ->
-                    ets:delete(?TAB, K),
-                    ets:delete(?TAB, Rev);
-                NewWaiters ->
-                    ets:insert(?TAB, {K, NewWaiters}),
-                    case lists:keymember(Pid, 1, NewWaiters) of
-                        true ->
-                            %% should be extremely unlikely
-                            ok;
-                        false ->
-                            %% delete the reverse entry
-                            ets:delete(?TAB, Rev)
-                    end
-            end;
+        [{_, Waiters}] ->
+	    gproc_lib:remove_wait(Key, Pid, Ref, Waiters);
         _ ->
             ignore
     end,
+    {noreply, S};
+handle_cast({cancel_wait_or_monitor, Pid, {T,_,_} = Key}, S) ->
+    case ets:lookup(?TAB, {Key, T}) of
+	[{_, Waiters}] ->
+	    gproc_lib:remove_wait(Key, Pid, all, Waiters);
+	[{_, OtherPid, _}] ->
+	    gproc_lib:remove_monitors(Key, OtherPid, Pid);
+	_ ->
+	    ok
+    end,
     {noreply, S}.
 
 %% @hidden
@@ -1374,6 +1433,36 @@ handle_call({reg, {_T,l,_} = Key, Val}, {Pid,_}, S) ->
         false ->
             {reply, badarg, S}
     end;
+handle_call({monitor, {T,l,_} = Key, Pid}, _From, S)
+  when T==n; T==a ->
+    Ref = make_ref(),
+    case where(Key) of
+	undefined ->
+	    Pid ! {gproc, unreg, Ref, Key};
+	RegPid ->
+	    case ets:lookup(?TAB, {RegPid, Key}) of
+		[{K,r}] ->
+		    ets:insert(?TAB, {K, [{monitor, [{Pid,Ref}]}]});
+		[{K, Opts}] ->
+		    ets:insert(?TAB, {K, gproc_lib:add_monitor(Opts, Pid, Ref)})
+	    end
+    end,
+    {reply, Ref, S};
+handle_call({demonitor, {T,l,_} = Key, Ref, Pid}, _From, S)
+  when T==n; T==a ->
+    case where(Key) of
+	undefined ->
+	    ok;  % be nice
+	RegPid ->
+	    case ets:lookup(?TAB, {RegPid, Key}) of
+		[{_K,r}] ->
+		    ok;   % be nice
+		[{K, Opts}] ->
+		    ets:insert(?TAB, {K, gproc_lib:remove_monitor(
+					   Opts, Pid, Ref)})
+	    end
+    end,
+    {reply, ok, S};
 handle_call({reg_shared, {_T,l,_} = Key, Val}, _From, S) ->
     case try_insert_reg(Key, Val, shared) of
     %% case try_insert_shared(Key, Val) of
@@ -1383,15 +1472,26 @@ handle_call({reg_shared, {_T,l,_} = Key, Val}, _From, S) ->
 	    {reply, badarg, S}
     end;
 handle_call({unreg, {_,l,_} = Key}, {Pid,_}, S) ->
-    case ets:member(?TAB, {Pid,Key}) of
-        true ->
-            _ = gproc_lib:remove_reg(Key, Pid),
+    case ets:lookup(?TAB, {Pid,Key}) of
+        [{_, r}] ->
+            _ = gproc_lib:remove_reg(Key, Pid, unreg),
             {reply, true, S};
-        false ->
+        [{_, Opts}] when is_list(Opts) ->
+            _ = gproc_lib:remove_reg(Key, Pid, unreg, Opts),
+            {reply, true, S};
+        [] ->
             {reply, badarg, S}
     end;
 handle_call({unreg_shared, {_,l,_} = Key}, _, S) ->
-    _ = gproc_lib:remove_reg(Key, shared),
+    case ets:lookup(?TAB, {shared, Key}) of
+	[{_, r}] ->
+	    _ = gproc_lib:remove_reg(Key, shared, unreg);
+	[{_, Opts}] ->
+	    _ = gproc_lib:remove_reg(Key, shared, unreg, Opts);
+	[] ->
+	    %% don't crash if shared key already unregged.
+	    ok
+    end,
     {reply, true, S};
 handle_call({await, {_,l,_} = Key, Pid}, From, S) ->
     %% Passing the pid explicitly is needed when leader_call is used,
@@ -1504,6 +1604,7 @@ try_insert_reg({T,l,_} = Key, Val, Pid) ->
             true
     end.
 
+
 %% try_insert_shared({c,l,_} = Key, Val) ->
 %%     ets:insert_new(?TAB, [{{Key,shared}, shared, Val}, {{shared, Key}, []}]);
 %% try_insert_shared({a,l,_} = Key, Val) ->
@@ -1525,14 +1626,16 @@ process_is_down(Pid) when is_pid(Pid) ->
         false ->
             ok;
         true ->
-            Revs = ets:select(?TAB, [{{{Pid,'$1'}, '_'},
-                                      [{'==',{element,2,'$1'},l}], ['$1']}]),
+            Revs = ets:select(?TAB, [{{{Pid,'$1'}, '$2'},
+                                      [{'==',{element,2,'$1'},l}],
+				      [{{'$1','$2'}}]}]),
             lists:foreach(
-              fun({n,l,_}=K) ->
+              fun({{n,l,_}=K, R}) ->
                       Key = {K,n},
                       case ets:lookup(?TAB, Key) of
                           [{_, Pid, _}] ->
-                              ets:delete(?TAB, Key);
+                              ets:delete(?TAB, Key),
+			      opt_notify(R, K);
                           [{_, Waiters}] ->
                               case [W || {P,_} = W <- Waiters,
                                          P =/= Pid] of
@@ -1544,14 +1647,15 @@ process_is_down(Pid) when is_pid(Pid) ->
                           [] ->
                               true
                       end;
-                 ({c,l,C} = K) ->
+                 ({{c,l,C} = K, _}) ->
                       Key = {K, Pid},
                       [{_, _, Value}] = ets:lookup(?TAB, Key),
                       ets:delete(?TAB, Key),
                       gproc_lib:update_aggr_counter(l, C, -Value);
-                 ({a,l,_} = K) ->
-                      ets:delete(?TAB, {K,a});
-                 ({p,_,_} = K) ->
+                 ({{a,l,_} = K, R}) ->
+                      ets:delete(?TAB, {K,a}),
+		      opt_notify(R, K);
+                 ({{p,_,_} = K, _}) ->
                       ets:delete(?TAB, {K, Pid})
               end, Revs),
             ets:select_delete(?TAB, [{{{Pid,{'_',l,'_'}},'_'}, [], [true]}]),
@@ -1559,6 +1663,12 @@ process_is_down(Pid) when is_pid(Pid) ->
             ok
     end.
 
+opt_notify(r, _) ->
+    ok;
+opt_notify(Opts, Key) ->
+    gproc_lib:notify(Key, Opts).
+
+
 do_give_away({T,l,_} = K, To, Pid) when T==n; T==a ->
     Key = {K, T},
     case ets:lookup(?TAB, Key) of
@@ -1572,11 +1682,11 @@ do_give_away({T,l,_} = K, To, Pid) when T==n; T==a ->
                 ToPid when is_pid(ToPid) ->
                     ets:insert(?TAB, [{Key, ToPid, Value},
                                       {{ToPid, K}, []}]),
-                    ets:delete(?TAB, {Pid, K}),
+		    gproc_lib:remove_reverse_mapping({migrated,ToPid}, Pid, K),
                     _ = gproc_lib:ensure_monitor(ToPid, l),
                     ToPid;
                 undefined ->
-                    _ = gproc_lib:remove_reg(K, Pid),
+                    _ = gproc_lib:remove_reg(K, Pid, unreg),
                     undefined
             end;
         _ ->
@@ -1601,7 +1711,7 @@ do_give_away({T,l,_} = K, To, Pid) when T==c; T==p ->
                             ToPid
                     end;
                 undefined ->
-                    _ = gproc_lib:remove_reg(K, Pid),
+                    _ = gproc_lib:remove_reg(K, Pid, migrated),
                     undefined
             end;
         _ ->
@@ -1645,8 +1755,6 @@ set_monitors({Pids, Cont}) ->
     _ = [erlang:monitor(process,Pid) || Pid <- Pids],
     set_monitors(ets:select(Cont)).
 
-
-
 monitor_me() ->
     case ets:insert_new(?TAB, {{self(),l}}) of
         false -> true;

src/gproc_dist.erl

@@ -279,6 +279,39 @@ handle_leader_call({reg, {C,g,Name} = K, Value, Pid}, _From, S, _E) ->
                 end,
             {reply, true, [{insert, Vals}], S}
     end;
+handle_leader_call({monitor, {T,g,_} = Key, Pid}, _From, S, _E)
+  when T==n; T==a ->
+    Ref = make_ref(),
+    case gproc:where(Key) of
+	undefined ->
+	    Pid ! {gproc, unreg, Ref, Key},
+	    {reply, Ref, [], S};
+	RegPid ->
+	    NewRev =
+		case ets:lookup_element(?TAB, K = {RegPid, Key}, 2) of
+		    r ->
+			{K, [{monitor, [{Pid,Ref}]}]};
+		    Opts ->
+			{K, gproc_lib:add_monitor(Opts, Pid, Ref)}
+		end,
+	    ets:insert(?TAB, NewRev),
+	    {reply, Ref, [{insert, [NewRev]}], S}
+    end;
+handle_leader_call({demonitor, {T,g,_} = Key, Ref, Pid}, _From, S, _E)
+  when T==n; T==a ->
+    case gproc:where(Key) of
+	undefined ->
+	    {reply, ok, [], S};
+	RegPid ->
+	    case ets:lookup_element(?TAB, K = {RegPid, Key}, 2) of
+		r ->
+		    {reply, ok, [], S};
+		Opts ->
+		    NewRev = {K, gproc_lib:remove_monitor(Opts, Pid, Ref)},
+		    ets:insert(?TAB, NewRev),
+		    {reply, Ref, [{insert, [NewRev]}], S}
+	    end
+    end;
 handle_leader_call({update_counter, {c,g,_Ctr} = Key, Incr, Pid}, _From, S, _E)
   when is_integer(Incr) ->
     try New = ets:update_counter(?TAB, {Key, Pid}, {3,Incr}),
@@ -310,18 +343,18 @@ handle_leader_call({unreg, {T,g,Name} = K, Pid}, _From, S, _E) ->
           end,
     case ets:member(?TAB, Key) of
         true ->
-            _ = gproc_lib:remove_reg(K, Pid),
+            _ = gproc_lib:remove_reg(K, Pid, unreg),
             if T == c ->
                     case ets:lookup(?TAB, {{a,g,Name},a}) of
                         [Aggr] ->
-                            %% updated by remove_reg/2
-                            {reply, true, [{delete,[Key, {Pid,K}]},
+                            %% updated by remove_reg/3
+                            {reply, true, [{delete,[Key, {Pid,K}], unreg},
                                            {insert, [Aggr]}], S};
                         [] ->
-                            {reply, true, [{delete, [Key, {Pid,K}]}], S}
+                            {reply, true, [{delete, [Key, {Pid,K}], unreg}], S}
                     end;
                true ->
-                    {reply, true, [{delete, [Key]}], S}
+                    {reply, true, [{delete, [Key, {Pid,K}], unreg}], S}
             end;
         false ->
             {reply, badarg, S}
@@ -338,12 +371,12 @@ handle_leader_call({give_away, {T,g,_} = K, To, Pid}, _From, S, _E)
                     ets:insert(?TAB, [{Key, ToPid, Value},
                                       {{ToPid,K}, []}]),
                     _ = gproc_lib:ensure_monitor(ToPid, g),
-                    {reply, ToPid, [{delete, [Key, {Pid,K}]},
-                                   {insert, [{Key, ToPid, Value}]}], S};
+                    {reply, ToPid, [{delete, [Key, {Pid,K}], {migrated,ToPid}},
+				    {insert, [{Key, ToPid, Value}]}], S};
                 undefined ->
                     ets:delete(?TAB, Key),
-                    ets:delete(?TAB, {Pid, K}),
-                    {reply, undefined, [{delete, [Key, {Pid,K}]}], S}
+		    Rev = gproc_lib:remove_reverse_mapping(unreg, Pid, K),
+                    {reply, undefined, [{delete, [Key, Rev], unreg}], S}
             end;
         _ ->
             {reply, badarg, S}
@@ -363,7 +396,7 @@ handle_leader_call({munreg, T, g, L, Pid}, _From, S, _E) ->
         [] ->
             {reply, true, S};
         Objs ->
-            {reply, true, [{delete, Objs}], S}
+            {reply, true, [{delete, Objs, unreg}], S}
     catch
         error:_ -> {reply, badarg, S}
     end;
@@ -434,8 +467,25 @@ handle_leader_cast({add_globals, Missing}, S, _E) ->
     ets:insert(?TAB, Missing),
     {ok, [{insert, Missing}], S};
 handle_leader_cast({remove_globals, Globals}, S, _E) ->
-    delete_globals(Globals),
+    delete_globals(Globals, []),
     {ok, S};
+handle_leader_cast({cancel_wait, Pid, {T,_,_} = Key, Ref}, S, _E) ->
+    case ets:lookup(?TAB, {Key, T}) of
+	[{_, Waiters}] ->
+	    Ops = gproc_lib:remove_wait(Key, Pid, Ref, Waiters),
+	    {ok, Ops, S};
+	_ ->
+	    {ok, [], S}
+    end;
+handle_leader_cast({cancel_wait_or_monitor, Pid, {T,_,_} = Key}, S, _E) ->
+    case ets:lookup(?TAB, {Key, T}) of
+	[{_, Waiters}] ->
+	    Ops = gproc_lib:remove_wait(Key, Pid, all, Waiters),
+	    {ok, Ops, S};
+	[{_, OtherPid, _}] ->
+	    Ops = gproc_lib:remove_monitors(Key, OtherPid, Pid),
+	    {ok, Ops, S}
+    end;
 handle_leader_cast({pid_is_DOWN, Pid}, S, _E) ->
     Globals = ets:select(?TAB, [{{{Pid,'$1'}, '_'},
                                  [{'==',{element,2,'$1'},g}],[{{'$1',Pid}}]}]),
@@ -460,11 +510,24 @@ process_globals(Globals) ->
                        end,
                   K = ets_key(Key, Pid),
                   ets:delete(?TAB, K),
-                  ets:delete(?TAB, {Pid,Key}),
+                  remove_rev_entry(Pid, Key, unreg),
                   A1
           end, [], Globals),
-    [{Op,Objs} || {Op,Objs} <- [{insert,Modified},
-                                {delete,Globals}], Objs =/= []].
+    [{insert, Modified} || Modified =/= []] ++
+	[{delete, Globals, unreg} || Globals =/= []].
+
+remove_rev_entry(Pid, {T,g,_} = K, Event) when T==n; T==a ->
+    Key = {Pid, K},
+    case ets:lookup(?TAB, Key) of
+	[]       -> ok;
+	[{_, r}] -> ok;
+	[{_, Opts}] when is_list(Opts) ->
+	    gproc_lib:notify(Event, K, Opts)
+    end,
+    ets:delete(?TAB, Key);
+remove_rev_entry(Pid, K, _Event) ->
+    ets:delete(?TAB, {Pid, K}).
+
 
 code_change(_FromVsn, S, _Extra, _E) ->
     {ok, S}.
@@ -477,15 +540,16 @@ from_leader({sync, Ref}, S, _E) ->
     {ok, S};
 from_leader(Ops, S, _E) ->
     lists:foreach(
-      fun({delete, Globals}) ->
-              delete_globals(Globals);
+      fun({delete, Globals, Event}) ->
+              delete_globals(Globals, Event);
          ({insert, Globals}) ->
               ets:insert(?TAB, Globals),
               lists:foreach(
                 fun({{{_,g,_}=Key,_}, P, _}) ->
-                        ets:insert(?TAB, {{P,Key}, []}),
+                        ets:insert_new(?TAB, {{P,Key}, []}),
                         gproc_lib:ensure_monitor(P,g);
-                   ({{P,_K}, _}) when is_pid(P) ->
+                   ({{P,_K}, _Opts} = Obj) when is_pid(P) ->
+			ets:insert(?TAB, Obj),
                         gproc_lib:ensure_monitor(P,g);
                    (_) ->
                         skip
@@ -493,16 +557,18 @@ from_leader(Ops, S, _E) ->
       end, Ops),
     {ok, S}.
 
-delete_globals(Globals) ->
+delete_globals(Globals, Event) ->
     lists:foreach(
       fun({{_,g,_},T} = K) when is_atom(T) ->
               ets:delete(?TAB, K);
          ({Key, Pid}) when is_pid(Pid); Pid==shared ->
               K = ets_key(Key,Pid),
               ets:delete(?TAB, K),
-              ets:delete(?TAB, {Pid, Key});
-         ({Pid, K}) when is_pid(Pid); Pid==shared ->
-              ets:delete(?TAB, {Pid, K})
+	      remove_rev_entry(Pid, Key, Event);
+         ({Pid, Key}) when is_pid(Pid); Pid==shared ->
+	      K = ets_key(Key, Pid),
+	      ets:delete(?TAB, K),
+	      remove_rev_entry(Pid, Key, Event)
       end, Globals).
 
 ets_key({T,_,_} = K, _) when T==n; T==a ->
@@ -539,13 +605,18 @@ surrendered_1(Globs) ->
     Ldr_local_globs =
         lists:foldl(
           fun({{Key,_}=K, Pid, V}, Acc) when node(Pid) =/= node() ->
-                  ets:insert(?TAB, [{K, Pid, V}, {{Pid,Key}}]),
+                  ets:insert(?TAB, {K, Pid, V}),
+		  ets:insert_new(?TAB, {{Pid,Key}, r}),
                   Acc;
+	     ({{Pid,_}=K, Opts}, Acc) when node(Pid) =/= node() ->
+		     ets:insert(?TAB, {K, Opts}),
+		     Acc;
              ({_, Pid, _} = Obj, Acc) when node(Pid) == node() ->
                   [Obj|Acc]
           end, [], Globs),
     case [{K,P,V} || {K,P,V} <- My_local_globs,
-                   not(lists:keymember(K, 1, Ldr_local_globs))] of
+		     is_pid(P) andalso
+			 not(lists:keymember(K, 1, Ldr_local_globs))] of
         [] ->
             %% phew! We have the same picture
             ok;
@@ -554,7 +625,8 @@ surrendered_1(Globs) ->
             leader_cast({add_globals, Missing})
     end,
     case [{K,P} || {K,P,_} <- Ldr_local_globs,
-                   not(lists:keymember(K, 1, My_local_globs))] of
+		   is_pid(P) andalso
+		       not(lists:keymember(K, 1, My_local_globs))] of
         [] ->
             ok;
         [_|_] = Remove ->

src/gproc_lib.erl

@@ -28,7 +28,13 @@
          insert_many/4,
          insert_reg/4,
          remove_many/4,
-         remove_reg/2,
+         remove_reg/3, remove_reg/4,
+	 add_monitor/3,
+	 remove_monitor/3,
+	 remove_monitors/3,
+	 remove_reverse_mapping/3,
+	 notify/2, notify/3,
+	 remove_wait/4,
          update_aggr_counter/3,
          update_counter/3,
 	 valid_opts/2]).
@@ -181,6 +187,51 @@ notify_waiters(Waiters, K, Pid, V) ->
          end || {P, Ref} <- Waiters],
     ok.
 
+remove_wait({T,_,_} = Key, Pid, Ref, Waiters) ->
+    Rev = {Pid,Key},
+    case remove_from_waiters(Waiters, Pid, Ref) of
+	[] ->
+	    ets:delete(?TAB, {Key,T}),
+	    ets:delete(?TAB, Rev),
+	    [{delete, [{Key,T}, Rev], []}];
+	NewWaiters ->
+	    ets:insert(?TAB, {Key, NewWaiters}),
+	    case lists:keymember(Pid, 1, NewWaiters) of
+		true ->
+		    %% should be extremely unlikely
+		    [{insert, [{Key, NewWaiters}]}];
+		false ->
+		    %% delete the reverse entry
+		    ets:delete(?TAB, Rev),
+		    [{insert, [{Key, NewWaiters}]},
+		     {delete, [Rev], []}]
+	    end
+    end.
+
+remove_from_waiters(Waiters, Pid, all) ->
+    [{P,R} || {P,R} <- Waiters,
+	      P =/= Pid];
+remove_from_waiters(Waiters, Pid, Ref) ->
+    Waiters -- [{Pid, Ref}].
+
+remove_monitors(Key, Pid, MPid) ->
+    case ets:lookup(?TAB, {Pid, Key}) of
+	[{_, r}] ->
+	    [];
+	[{K, Opts}] when is_list(Opts) ->
+	    case lists:keyfind(monitors, 1, Opts) of
+		false ->
+		    [];
+		{_, Ms} ->
+		    Ms1 = [{P,R} || {P,R} <- Ms,
+				    P =/= MPid],
+		    NewMs = lists:keyreplace(monitors, 1, {monitors,Ms1}),
+		    ets:insert(?TAB, {K, NewMs}),
+		    [{insert, [{{Pid,Key}, NewMs}]}]
+	    end;
+	_ ->
+	    []
+    end.
 
 
 mk_reg_objs(T, Scope, Pid, L) when T==n; T==a ->
@@ -208,17 +259,74 @@ ensure_monitor(Pid, Scope) when Scope==g; Scope==l ->
         true  -> erlang:monitor(process, Pid)
     end.
 
-remove_reg(Key, Pid) ->
+remove_reg(Key, Pid, Event) ->
+    remove_reg(Key, Pid, Event, []).
+
+remove_reg(Key, Pid, Event, Opts) ->
     Reg = remove_reg_1(Key, Pid),
-    ets:delete(?TAB, Rev = {Pid,Key}),
+    Rev = remove_reverse_mapping(Event, Pid, Key, Opts),
     [Reg, Rev].
 
+remove_reverse_mapping(Event, Pid, Key) ->
+    Opts = case ets:lookup(?TAB, {Pid, Key}) of
+	       [] ->       [];
+	       [{_, r}] -> [];
+	       [{_, L}] when is_list(L) ->
+		   L
+	   end,
+    remove_reverse_mapping(Event, Pid, Key, Opts).
+
+remove_reverse_mapping(Event, Pid, Key, Opts) when Event==unreg;
+						   element(1,Event)==migrated ->
+    Rev = {Pid, Key},
+    notify(Event, Key, Opts),
+    ets:delete(?TAB, Rev),
+    Rev.
+
+notify(Key, Opts) ->
+    notify(unreg, Key, Opts).
+
+notify([], _, _) ->
+    [];
+notify(Event, Key, Opts) ->
+    case lists:keyfind(monitor, 1, Opts) of
+	false ->
+	    [];
+	{_, Mons} ->
+	    [begin P ! {gproc, Event, Ref, Key}, P end || {P, Ref} <- Mons,
+							  node(P) == node()]
+    end.
+
+add_monitor([{monitor, Mons}|T], Pid, Ref) ->
+    [{monitor, [{Pid,Ref}|Mons]}|T];
+add_monitor([H|T], Pid, Ref) ->
+    [H|add_monitor(T, Pid, Ref)];
+add_monitor([], Pid, Ref) ->
+    [{monitor, [{Pid, Ref}]}].
+
+remove_monitor([{monitor, Mons}|T], Pid, Ref) ->
+    [{monitor, Mons -- [{Pid, Ref}]}|T];
+remove_monitor([H|T], Pid, Ref) ->
+    [H|remove_monitor(T, Pid, Ref)];
+remove_monitor([], _Pid, _Ref) ->
+    [].
+
 remove_many(T, Scope, L, Pid) ->
     lists:flatmap(fun(K) ->
                           Key = {T, Scope, K},
-                          remove_reg(Key, Pid)
+                          remove_reg(Key, Pid, unreg, unreg_opts(Key, Pid))
                   end, L).
 
+unreg_opts(Key, Pid) ->
+    case ets:lookup(?TAB, {Pid, Key}) of
+	[] ->
+	    [];
+	[{_,r}] ->
+	    [];
+	[{_,Opts}] ->
+	    Opts
+    end.
+
 remove_reg_1({c,_,_} = Key, Pid) ->
     remove_counter_1(Key, ets:lookup_element(?TAB, Reg = {Key,Pid}, 3), Pid),
     Reg;

src/gproc_monitor.erl

@@ -0,0 +1,282 @@
+%% ``The contents of this file are subject to the Erlang Public License,
+%% Version 1.1, (the "License"); you may not use this file except in
+%% compliance with the License. You should have received a copy of the
+%% Erlang Public License along with this software. If not, it can be
+%% retrieved via the world wide web at http://www.erlang.org/.
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and limitations
+%% under the License.
+%%
+%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
+%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
+%% AB. All Rights Reserved.''
+%%
+%% @author Ulf Wiger <ulf.wiger@feuerlabs.com>
+%%
+%% @doc
+%% This module implements a notification system for gproc names
+%% When a process subscribes to notifications for a given name, a message
+%% will be sent each time that name is registered
+-module(gproc_monitor).
+
+-behaviour(gen_server).
+
+%% API
+-export([subscribe/1,
+	 unsubscribe/1]).
+
+%% Process start function
+-export([start_link/0]).
+
+%% gen_server callbacks
+-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
+	 terminate/2, code_change/3]).
+
+-define(SERVER, ?MODULE).
+-define(TAB, ?MODULE).
+
+-record(state, {}).
+
+%%%===================================================================
+%%% API
+%%%===================================================================
+
+%%--------------------------------------------------------------------
+%% @spec subscribe(key()) -> ok
+%%
+%% @doc
+%% Subscribe to registration events for a certain name
+%%
+%% The subscribing process will receive a `{gproc_monitor, Name, Pid}' message
+%% whenever a process registers under the given name, and a
+%% `{gproc_monitor, Name, undefined}' message when the name is unregistered,
+%% either explicitly, or because the registered process dies.
+%%
+%% When the subscription is first ordered, one of the above messages will be
+%% sent immediately, indicating the current status of the name.
+%% @end
+%%--------------------------------------------------------------------
+subscribe({T,S,_} = Key) when (T==n orelse T==a)
+			      andalso (S==g orelse S==l) ->
+    try gproc:reg({p,l,{?MODULE,Key}})
+    catch
+	error:badarg -> ok
+    end,
+    gen_server:cast(?SERVER, {subscribe, self(), Key}).
+
+
+%%--------------------------------------------------------------------
+%% @spec unsubscribe(key()) -> ok
+%%
+%% @doc
+%% Unsubscribe from registration events for a certain name
+%%
+%% This function is the reverse of subscribe/1. It removes the subscription.
+%% @end
+%%--------------------------------------------------------------------
+unsubscribe({T,S,_} = Key) when (T==n orelse T==a)
+				andalso (S==g orelse S==l) ->
+    try gproc:unreg({p, l, {?MODULE,Key}})
+    catch
+	error:badarg -> ok
+    end,
+    gen_server:cast(?SERVER, {unsubscribe, self(), Key}).
+
+%%--------------------------------------------------------------------
+%% @doc
+%% Starts the server
+%%
+%% @spec start_link() -> {ok, Pid} | ignore | {error, Error}
+%% @end
+%%--------------------------------------------------------------------
+start_link() ->
+    Me = self(),
+    case ets:info(?TAB, owner) of
+	undefined ->
+	    ets:new(?TAB, [ordered_set, protected, named_table,
+			      {heir, self(), []}]);
+	Me ->
+	    ok
+    end,
+    {ok, Pid} = proc_lib:start_link(?MODULE, init, [Me]),
+    ets:give_away(?TAB, Pid, []),
+    {ok, Pid}.
+
+%%%===================================================================
+%%% gen_server callbacks
+%%%===================================================================
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% Initializes the server
+%%
+%% @spec init(Args) -> {ok, State} |
+%%                     {ok, State, Timeout} |
+%%                     ignore |
+%%                     {stop, Reason}
+%% @end
+%%--------------------------------------------------------------------
+init(Parent) ->
+    process_flag(priority, high),
+    register(?SERVER, self()),
+    proc_lib:init_ack(Parent, {ok, self()}),
+    receive {'ETS-TRANSFER',?TAB,_,_} -> ok end,
+    gen_server:enter_loop(?MODULE, [], #state{}).
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% Handling call messages
+%%
+%% @spec handle_call(Request, From, State) ->
+%%                                   {reply, Reply, State} |
+%%                                   {reply, Reply, State, Timeout} |
+%%                                   {noreply, State} |
+%%                                   {noreply, State, Timeout} |
+%%                                   {stop, Reason, Reply, State} |
+%%                                   {stop, Reason, State}
+%% @end
+%%--------------------------------------------------------------------
+handle_call(_Request, _From, State) ->
+    Reply = ok,
+    {reply, Reply, State}.
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% Handling cast messages
+%%
+%% @spec handle_cast(Msg, State) -> {noreply, State} |
+%%                                  {noreply, State, Timeout} |
+%%                                  {stop, Reason, State}
+%% @end
+%%--------------------------------------------------------------------
+handle_cast({subscribe, Pid, Key}, State) ->
+    Status = gproc:where(Key),
+    add_subscription(Pid, Key),
+    do_monitor(Key, Status),
+    Pid ! {?MODULE, Key, Status},
+    monitor_pid(Pid),
+    {noreply, State};
+handle_cast({unsubscribe, Pid, Key}, State) ->
+    del_subscription(Pid, Key),
+    {noreply, State}.
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% Handling all non call/cast messages
+%%
+%% @spec handle_info(Info, State) -> {noreply, State} |
+%%                                   {noreply, State, Timeout} |
+%%                                   {stop, Reason, State}
+%% @end
+%%--------------------------------------------------------------------
+handle_info({gproc, unreg, _Ref, Name}, State) ->
+    ets:delete(?TAB, {m, Name}),
+    notify(Name, undefined),
+    do_monitor(Name, undefined),
+    {noreply, State};
+handle_info({gproc, {migrated,ToPid}, _Ref, Name}, State) ->
+    ets:delete(?TAB, {m, Name}),
+    notify(Name, {migrated, ToPid}),
+    do_monitor(Name, ToPid),
+    {noreply, State};
+handle_info({gproc, _, registered, {{T,_,_} = Name, Pid, _}}, State)
+  when T==n; T==a ->
+    ets:delete(?TAB, {w, Name}),
+    notify(Name, Pid),
+    do_monitor(Name, Pid),
+    {noreply, State};
+handle_info({'DOWN', _, process, Pid, _}, State) ->
+    pid_is_down(Pid),
+    {noreply, State};
+handle_info(_Msg, State) ->
+    {noreply, State}.
+
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% This function is called by a gen_server when it is about to
+%% terminate. It should be the opposite of Module:init/1 and do any
+%% necessary cleaning up. When it returns, the gen_server terminates
+%% with Reason. The return value is ignored.
+%%
+%% @spec terminate(Reason, State) -> void()
+%% @end
+%%--------------------------------------------------------------------
+terminate(_Reason, _State) ->
+    ok.
+
+%%--------------------------------------------------------------------
+%% @private
+%% @doc
+%% Convert process state when code is changed
+%%
+%% @spec code_change(OldVsn, State, Extra) -> {ok, NewState}
+%% @end
+%%--------------------------------------------------------------------
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.
+
+%%%===================================================================
+%%% Internal functions
+%%%===================================================================
+
+add_subscription(Pid, {_,_,_} = Key) when is_pid(Pid) ->
+    ets:insert(?TAB, [{{s, Key, Pid}}, {{r, Pid, Key}}]).
+
+del_subscription(Pid, Key) ->
+    ets:delete(?TAB, {{s, Key, Pid}}),
+    ets:delete(?TAB, {{r, Pid, Key}}),
+    maybe_cancel_wait(Key).
+
+do_monitor(Name, undefined) ->
+    case ets:member(?TAB, {w, Name}) of
+	false ->
+	    Ref = gproc:nb_wait(Name),
+	    ets:insert(?TAB, {{w, Name}, Ref})
+    end;
+do_monitor(Name, Pid) when is_pid(Pid) ->
+    case ets:member(?TAB, {m, Name}) of
+	true ->
+	    ok;
+	_ ->
+	    Ref = gproc:monitor(Name),
+	    ets:insert(?TAB, {{m, Name}, Ref})
+    end.
+
+monitor_pid(Pid) when is_pid(Pid) ->
+    case ets:member(?TAB, {p,Pid}) of
+	false ->
+	    Ref = erlang:monitor(process, Pid),
+	    ets:insert(?TAB, {{p,Pid}, Ref});
+	true ->
+	    ok
+    end.
+
+pid_is_down(Pid) ->
+    Keys = ets:select(?TAB, [{ {{r, Pid, '$1'}}, [], ['$1'] }]),
+    ets:select_delete(?TAB, [{ {{r, Pid, '$1'}}, [], [true] }]),
+    lists:foreach(fun(K) ->
+			  ets:delete(?TAB, {s,K,Pid}),
+			  maybe_cancel_wait(K)
+		  end, Keys),
+    ets:delete(?TAB, {p, Pid}).
+
+maybe_cancel_wait(K) ->
+    case ets:next(?TAB, {s,K}) of
+	{s,K,P} when is_pid(P) ->
+	    ok;
+	_ ->
+	    gproc:cancel_wait_or_monitor(K),
+	    ets:delete(?TAB, {m, K}),
+	    ets:delete(?TAB, {w, K})
+    end.
+
+notify(Name, Where) ->
+    gproc:send({p, l, {?MODULE, Name}}, {?MODULE, Name, Where}).

src/gproc_sup.erl

@@ -48,7 +48,9 @@ init(_Args) ->
                    [{gproc_dist, {gproc_dist, start_link, [Env]},
                      permanent, 2000, worker, [gproc_dist]}]
            end,
-    {ok,{{one_for_one, 15, 60}, [GProc | Dist]}}.
+    Mon = {gproc_monitor, {gproc_monitor, start_link, []},
+	   permanent, 2000, worker, [gproc_monitor]},
+    {ok,{{one_for_one, 15, 60}, [GProc| Dist] ++ [Mon]}}.
 
 
 %%%----------------------------------------------------------------------

test/gproc_dist_tests.erl

@@ -69,6 +69,12 @@ dist_test_() ->
 			       end,
 			       fun() ->
 				       ?debugVal(t_sync(Ns))
+			       end,
+			       fun() ->
+				       ?debugVal(t_monitor(Ns))
+			       end,
+			       fun() ->
+				       ?debugVal(t_subscribe(Ns))
 			       end
 			      ]
 		 },
@@ -164,7 +170,7 @@ t_await_reg([A,B|_]) ->
 
 t_await_self([A|_]) ->
     Name = ?T_NAME,
-    P = t_spawn(A, false),  % buffer unknowns
+    P = t_spawn(A, false),  % don't buffer unknowns
     Ref = t_call(P, {apply, gproc, nb_wait, [Name]}),
     ?assertMatch(ok, t_call(P, {selective, true})),
     ?assertMatch(true, t_call(P, {apply, gproc, reg, [Name, some_value]})),
@@ -216,6 +222,45 @@ t_sync(Ns) ->
     [?assertMatch(true, rpc:call(N, gproc_dist, sync, []))
      || N <- Ns].
 
+t_monitor([A,B|_]) ->
+    Na = ?T_NAME,
+    Pa = t_spawn_reg(A, Na),
+    Pb = t_spawn(B, _Selective = true),
+    Ref = t_call(Pb, {apply, gproc, monitor, [Na]}),
+    ?assert(is_reference(Ref)),
+    ?assertMatch(ok, t_call(Pa, die)),
+    ?assertMatch({gproc,unreg,Ref,Na}, got_msg(Pb, gproc)),
+    Pc = t_spawn_reg(A, Na),
+    Ref1 = t_call(Pb, {apply, gproc, monitor, [Na]}),
+    ?assertMatch(true, t_call(Pc, {apply, gproc, unreg, [Na]})),
+    ?assertMatch({gproc,unreg,Ref1,Na}, got_msg(Pb, gproc)).
+
+t_subscribe([A,B|_] = Ns) ->
+    Na = ?T_NAME,
+    Pb = t_spawn(B, _Selective = true),
+    ?assertEqual(ok, t_call(Pb, {apply, gproc_monitor, subscribe, [Na]})),
+    ?assertMatch({gproc_monitor, Na, undefined}, got_msg(Pb, gproc_monitor)),
+    Pa = t_spawn_reg(A, Na),
+    ?assertMatch({gproc_monitor, Na, Pa}, got_msg(Pb, gproc_monitor)),
+    Pc = t_spawn(A),
+    t_call(Pa, {apply, gproc, give_away, [Na, Pc]}),
+    ?assertMatch(ok, t_lookup_everywhere(Na, Ns, Pc)),
+    ?assertEqual({gproc_monitor,Na,{migrated,Pc}}, got_msg(Pb, gproc_monitor)),
+    ?assertEqual(ok, t_call(Pc, die)),
+    ?assertEqual({gproc_monitor,Na,undefined}, got_msg(Pb, gproc_monitor)).
+
+got_msg(Pb, Tag) ->
+    t_call(Pb,
+	   {apply_fun,
+	    fun() ->
+		    receive
+			M when element(1, M) == Tag ->
+			    M
+		    after 1000 ->
+			    timeout
+		    end
+	    end}).
+
 %% Verify that the gproc_dist:sync() call returns true even if a candidate dies
 %% while the sync is underway. This test makes use of sys:suspend() to ensure that
 %% the other candidate doesn't respond too quickly.

test/gproc_tests.erl

@@ -69,49 +69,55 @@ reg_test_() ->
 	     application:stop(mnesia)
      end,
      [
-      {spawn, ?_test(t_simple_reg())}
+      {spawn, ?_test(?debugVal(t_simple_reg()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_simple_counter())}
+      , {spawn, ?_test(?debugVal(t_simple_counter()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_simple_aggr_counter())}
+      , {spawn, ?_test(?debugVal(t_simple_aggr_counter()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_simple_prop())}
+      , {spawn, ?_test(?debugVal(t_simple_prop()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_await())}
+      , {spawn, ?_test(?debugVal(t_await()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_await_self())}
+      , {spawn, ?_test(?debugVal(t_await_self()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_simple_mreg())}
+      , {spawn, ?_test(?debugVal(t_simple_mreg()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_gproc_crash())}
+      , {spawn, ?_test(?debugVal(t_gproc_crash()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_cancel_wait_and_register())}
+      , {spawn, ?_test(?debugVal(t_cancel_wait_and_register()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_give_away_to_pid())}
+      , {spawn, ?_test(?debugVal(t_give_away_to_pid()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_give_away_to_self())}
+      , {spawn, ?_test(?debugVal(t_give_away_to_self()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_give_away_badarg())}
+      , {spawn, ?_test(?debugVal(t_give_away_badarg()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_give_away_to_unknown())}
+      , {spawn, ?_test(?debugVal(t_give_away_to_unknown()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_give_away_and_back())}
+      , {spawn, ?_test(?debugVal(t_give_away_and_back()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_select())}
+      , {spawn, ?_test(?debugVal(t_select()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_select_count())}
+      , {spawn, ?_test(?debugVal(t_select_count()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_qlc())}
+      , {spawn, ?_test(?debugVal(t_qlc()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_get_env())}
+      , {spawn, ?_test(?debugVal(t_get_env()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_get_set_env())}
+      , {spawn, ?_test(?debugVal(t_get_set_env()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_set_env())}
+      , {spawn, ?_test(?debugVal(t_set_env()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_get_env_inherit())}
+      , {spawn, ?_test(?debugVal(t_get_env_inherit()))}
       , ?_test(t_is_clean())
-      , {spawn, ?_test(t_gproc_info())}
+      , {spawn, ?_test(?debugVal(t_monitor()))}
+      , ?_test(t_is_clean())
+      , {spawn, ?_test(?debugVal(t_monitor_give_away()))}
+      , ?_test(t_is_clean())
+      , {spawn, ?_test(?debugVal(t_subscribe()))}
+      , ?_test(t_is_clean())
+      , {spawn, ?_test(?debugVal(t_gproc_info()))}
       , ?_test(t_is_clean())
      ]}.
 
@@ -197,8 +203,11 @@ t_await_self() ->
 
 t_is_clean() ->
     sys:get_status(gproc), % in order to synch
+    sys:get_status(gproc_monitor),
     T = ets:tab2list(gproc),
-    ?assertMatch([], T).
+    Tm = ets:tab2list(gproc_monitor),
+    ?assertMatch([], Tm),
+    ?assertMatch([], T -- [{{whereis(gproc_monitor), l}}]).
 
 t_simple_mreg() ->
     P = self(),
@@ -453,7 +462,8 @@ t_get_env_inherit() ->
 		   end),
     ?assertEqual({P,undefined}, gproc:await({n,l,get_env_p},1000)),
     ?assertEqual(bar, gproc:get_env(l, gproc, foo, [{inherit, P}])),
-    ?assertEqual(bar, gproc:get_env(l, gproc, foo, [{inherit, {n,l,get_env_p}}])),
+    ?assertEqual(bar, gproc:get_env(l, gproc, foo,
+				    [{inherit, {n,l,get_env_p}}])),
     ?assertEqual(ok, t_call(P, die)).
 
 %% What we test here is that we return the same current_function as the
@@ -490,6 +500,64 @@ t4() ->
     {_, I} = gproc:info(self(), current_function),
     {I0, I}.
 
+t_monitor() ->
+    Me = self(),
+    P = spawn_link(fun() ->
+			   gproc:reg({n,l,a}),
+			   Me ! continue,
+			   t_loop()
+		   end),
+    receive continue ->
+	    ok
+    end,
+    Ref = gproc:monitor({n,l,a}),
+    ?assertEqual(ok, t_call(P, die)),
+    receive
+	M ->
+	    ?assertEqual({gproc,unreg,Ref,{n,l,a}}, M)
+    end.
+
+t_monitor_give_away() ->
+    Me = self(),
+    P = spawn_link(fun() ->
+			   gproc:reg({n,l,a}),
+			   Me ! continue,
+			   t_loop()
+		   end),
+    receive continue ->
+	    ok
+    end,
+    Ref = gproc:monitor({n,l,a}),
+    ?assertEqual(ok, t_call(P, {give_away, {n,l,a}})),
+    receive
+	M ->
+	    ?assertEqual({gproc,{migrated,Me},Ref,{n,l,a}}, M)
+    end,
+    ?assertEqual(ok, t_call(P, die)).
+
+t_subscribe() ->
+    Key = {n,l,a},
+    ?assertEqual(ok, gproc_monitor:subscribe(Key)),
+    ?assertEqual({gproc_monitor, Key, undefined}, get_msg()),
+    P = spawn_link(fun() ->
+			   gproc:reg({n,l,a}),
+			   t_loop()
+		   end),
+    ?assertEqual({gproc_monitor, Key, P}, get_msg()),
+    ?assertEqual(ok, t_call(P, {give_away, Key})),
+    ?assertEqual({gproc_monitor, Key, {migrated,self()}}, get_msg()),
+    gproc:give_away(Key, P),
+    ?assertEqual({gproc_monitor, Key, {migrated,P}}, get_msg()),
+    ?assertEqual(ok, t_call(P, die)),
+    ?assertEqual({gproc_monitor, Key, undefined}, get_msg()),
+    ?assertEqual(ok, gproc_monitor:unsubscribe(Key)).
+
+get_msg() ->
+    receive M ->
+	    M
+    after 1000 ->
+	    timeout
+    end.
 
 t_loop() ->
     receive