BUG likely：Create thread using libpthread failed in HHVM extesion

[zhangmuhua]

1. i want create a thread in HHVM extension but failed.
   code as follows:
   59 int stacksize = 1048576;
   60 int guardsize = 4096;
   61
   62 pthread_t thread1;
   63 void *thread_result;
   64 pthread_attr_t attr;
   65 int res_init = pthread_attr_init(&attr);
   66 int res_detach = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
   67 int res_sstack = pthread_attr_setstacksize(&attr, stacksize);
   68 int res_sguard = pthread_attr_setguardsize(&attr, guardsize);
   69 int res = pthread_create(&thread1, &attr, pfunc, NULL);
   70 sleep(1);
   71 pthread_join(thread1, &thread_result)

However, create failed and core dumped in pthread_create.

2. we just to adjust pthread_attr_t attr,
   if we set attr = NULL, work ok!!!!
   if we set attr.stacksize=1MB, work failed!!!!!.
   if we set attr.stacksize=2B, work ok!!!!

Is there anything different in HHVM to create a thread using libpthread?? this errors strongly confused me for 3 weeks. And we just read HHVM code involved MemoryManager and some functions involved Initing some params of thread, such as hphp_process_init(), init_thread_locals(), InitAllocatorThreadLocal(), init_stringdata_allocator(). But we couldnot fix this problem. is there anybody to give us some useful idea??
Thanks.

[zhangmuhua]

if we set attr.stacksize=2B, work ok!!!! --> if we set attr.stacksize=2MB, work ok!!!!

[scannell]

Dupe of #1015.