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@__modctor() 行 3
 
	test.exe!rt@minfo@__T14runModuleFuncsS482rt5minfo11ModuleGroup11runTlsCtorsMFZ9__lambda1Z@runModuleFuncs()
        test.exe!___threadstartex@4()