vibed_test2/vtest2/source/test4.d

// https://dlang.org/phobos/std_parallelism.html

alias uint8  = ubyte;
alias uint64 = ulong;


import std.stdio;
import std.concurrency : spawn;
import std.parallelism : parallel, defaultPoolThreads;
import core.time : Duration, dur;
import core.thread : Thread;



uint64 fact(uint64 n){
  return fact(n, 1);
}

uint64 fact(uint64 n, uint64 a){
  if(n == 0){
    return a;
  }else{
    return fact(n - 1, n * a);
  }
}


//void test4_worker(uint8 n){
void test4_worker(int n){
  writeln("started worker = ", n);
  
  while(true){
    //Thread.sleep(dur!"seconds"(120));
    
    //Thread.sleep(dur!"seconds"(3));
    
    auto v20 = fact(20);
    //writeln("worker = ", n, " fact 20 = ", v20); // this is sync lock ((
  }
  
  Thread.sleep(dur!"seconds"(3));
  
  writeln("stopped worker = ", n);
}


void test4_spawner(){
  //uint8 i = 10; // 10 = 1.8 Mb RAM // 255 = 2.9 Mb RAM // 1000 = 6.1 Mb RAM // 10_000 = 47.9 Mb RAM // 100_000 = 180.3 -> 434.4 Mb RAM ,, 161.8 -> 607.7 Mb RAM
  //int i = 100_000; // fails
  //int i = 30_000;
  //int i = 35_000; // fails
  
  /*
  while(i > 0){
    spawn(&test1_worker, i);
    
    i--;
  }
  */
  
  writeln("defaultPoolThreads = ", defaultPoolThreads()); // 19
  defaultPoolThreads(5);
  writeln("defaultPoolThreads = ", defaultPoolThreads()); // 5
  
  //int[] ints = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
  int[] ints = [1, 2, 3, 4, 5];
  
  foreach(i, ref num; parallel(ints)){
    test4_worker(num);
  }
  
}


/*

> make run
./vtest2
// 21 threads for 10 elems
// 21 threads for 5 elems too
// 7 threadf for 5 elems
// writeln locking

*/