mirror/guile
mirror/guile
1
Fork 0
mirror of https://git.savannah.gnu.org/git/guile.git synced 2025-04-30 03:40:34 +02:00
Code Activity

Fix two wait-condition-variable race conditions

Browse source 
* libguile/threads.c (timed_wait): When looping to reacquire mutex,
  check if mutex owner after dropping mutex to run asyncs when the
  reacquire is interrupted.

  Also for asyncs that interrupted the initial wait, just return #t
  directly, and allow the caller to loop.  Fixes a deadlock in which a
  thread could have pending asyncs after dropping a mutex and which
  prevent it from going to wait on a cond, but then the broadcast comes
  while nobody is waiting and the mutex is dropped, then after
  reacquiring the mutex when we go to wait again, we wait forever.

  The correct thing to do is after reacquiring the mutex, to allow the
  application to check if waiting is appropriate.
This commit is contained in:
Andy Wingo 2016-11-30 22:56:54 +01:00
parent 8bd5dae8c3
commit a9dc553893
1 changed files with 10 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

20
libguile/threads.c
View file

@ -1316,12 +1316,7 @@ timed_wait (enum scm_mutex_kind kind, struct scm_mutex *m, struct scm_cond *c,
/* We woke up for some reason. Reacquire the mutex before doing
anything else. */
if (scm_is_eq (m->owner, SCM_BOOL_F))
{
m->owner = current_thread->handle;
scm_i_pthread_mutex_unlock (&m->lock);
}
else if (kind == SCM_MUTEX_RECURSIVE &&
if (kind == SCM_MUTEX_RECURSIVE &&
scm_is_eq (m->owner, current_thread->handle))
{
m->level++;
@ -1330,6 +1325,12 @@ timed_wait (enum scm_mutex_kind kind, struct scm_mutex *m, struct scm_cond *c,
else
while (1)
{
if (scm_is_eq (m->owner, SCM_BOOL_F))
{
m->owner = current_thread->handle;
scm_i_pthread_mutex_unlock (&m->lock);
break;
}
block_self (m->waiting, &m->lock, waittime);
if (scm_is_eq (m->owner, SCM_BOOL_F))
{
@ -1348,11 +1349,8 @@ timed_wait (enum scm_mutex_kind kind, struct scm_mutex *m, struct scm_cond *c,
else if (err == ETIMEDOUT)
return SCM_BOOL_F;
else if (err == EINTR)
{
scm_async_tick ();
scm_i_scm_pthread_mutex_lock (&m->lock);
continue;
}
/* Let caller run scm_async_tick() and loop. */
return SCM_BOOL_T;
else
{
/* Shouldn't happen. */