why spawn crash?

[mzfhhhh via Digitalmars-d-learn]

i wrote a test code:

void worker(int firstNumber)
{
      Thread.sleep(1.msecs);
}

void main()
{
     foreach (i; 1 .. 1000) {
         spawn(&worker, i );
         writeln(i);
     }
     thread_joinAll();
     writeln("ok");
}


sometimes it's ok,sometimes it's crashed ! why ?
here is one of times callstack message:

  	test.exe!_free()	
  	test.exe!_fwide()	
  	test.exe!_fwide()	
  	test.exe!__ReleaseSemaphore()	
  	test.exe!_fwide()	
>	test.exe!main at __modctor() 行 3
  
	test.exe!rt at minfo@__T14runModuleFuncsS482rt5minfo11ModuleGroup11runTlsCtorsMFZ9__lambda1Z at runModuleFuncs()
  	test.exe!___threadstartex at 4()