Bug report and patch: race condition for setting thread ID in unix implementation [pj_thread_create]

[p.lukac@xxxxxxxxx (Peter Lukac)]

hello all,

I think i'm found little problem when is creating new thread with function
pj_thread_create() with implementation in os_core_unix.c throught
pthread.

when you look at line 587 in  os_core_unix.c :

rc = pthread_create( &rec->thread, &thread_attr, &thread_main, rec);

This method create thread and run it with function:
 static void *thread_main(void *param)
and set pthread_t structure.

Problem occured when thread is running  before function pthread_create() set 
new thread ID to pthread_t structure (rec->thread) which is passed like 
argument to thread function.  In my situation in ALSA sound driver in thread 
for microphone is setting thread priority by tread ID :

alsa_dev.c
line: 430

thid = (pthread_t*) pj_thread_get_os_handle (pj_thread_this());

this command return invalid threadID because function pthread_create() still 
don't set new thread ID... (OS scheduler don't switch to thread from which was 
pthread_create() called )

This problem can occur on all threads in which on beginning is calling some 
function with "this thread ID".

Solution should be using  "suspended_mutex" from structure pj_thread_t or add 
new wait mutex...

i made little patch which should works. If somebody have better solution 
please send me... 

thanks

here is patch:

*** pjproject-1.8.5/pjlib/src/pj/os_core_unix.c 2010-09-24 09:49:32.000000000 
+0200
--- pjproject-1.8.5_alsa_test/pjlib/src/pj/os_core_unix.c       2011-02-16 
17:41:19.000000000 +0100
***************
*** 58,64 ****
      pj_uint32_t           signature1;
      pj_uint32_t           signature2;
  
!     pj_mutex_t           *suspended_mutex;
  
  #if defined(PJ_OS_HAS_CHECK_STACK) && PJ_OS_HAS_CHECK_STACK!=0
      pj_uint32_t           stk_size;
--- 58,65 ----
      pj_uint32_t           signature1;
      pj_uint32_t           signature2;
  
!     pj_mutex_t     *suspended_mutex;
!     pj_mutex_t     *wait_mutex;
  
  #if defined(PJ_OS_HAS_CHECK_STACK) && PJ_OS_HAS_CHECK_STACK!=0
      pj_uint32_t           stk_size;
***************
*** 480,485 ****
--- 482,491 ----
        pj_assert(!"Thread TLS ID is not set (pj_init() error?)");
      }
  
+     /* Wait while function pthread_create() finish */
+     pj_mutex_lock(rec->wait_mutex);
+     pj_mutex_unlock(rec->wait_mutex);
+ 
      /* Check if suspension is required. */
      if (rec->suspended_mutex) {
        pj_mutex_lock(rec->suspended_mutex);
***************
*** 556,561 ****
--- 562,578 ----
        pj_assert(rec->suspended_mutex == NULL);
      }
      
+     /* 
+        Create wait mutex because thread can be run before as
+        pthread_create() set thread ID
+     */
+     rc = pj_mutex_create_simple(pool, NULL, &rec->wait_mutex);
+     if (rc != PJ_SUCCESS) {
+         return rc;
+     }
+ 
+     /* lock wait mutex..new thread will be wait while pthread_create() end*/
+     pj_mutex_lock(rec->wait_mutex);
  
      /* Init thread attributes */
      pthread_attr_init(&thread_attr);
***************
*** 587,592 ****
--- 604,612 ----
        return PJ_RETURN_OS_ERROR(rc);
      }
  
+     /* unlock new thread... now thread ID is set*/
+     pj_mutex_unlock(rec->wait_mutex);
+ 
      *ptr_thread = rec;
  
      PJ_LOG(6, (rec->obj_name, "Thread created"));
***************
*** 700,705 ****
--- 720,731 ----
        p->suspended_mutex = NULL;
      }
  
+     /* Destroy mutex used to wait thread */
+     if (p->wait_mutex) {
+         pj_mutex_destroy(p->wait_mutex);
+         p->wait_mutex = NULL;
+     }
+ 
      return PJ_SUCCESS;
  }