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Fix memory leak in lock-mutex' (aka. scm_lock_mutex'.)

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The memory leak is trivially reproducible with:

  (define m (make-mutex))
  (let loop () (lock-mutex m) (unlock-mutex m) (loop))

or similarly with:

  (define p (delay (+ 1 2)))
  (let loop () (force p) (loop))

since `force' acquires P's mutex.

It could also lead to premature release of a thread waiting in
`fat_mutex_lock' when a former owner's `do_thread_exit' is run.

* libguile/threads.c (fat_mutex_unlock): When `m->level' becomes 0,
  remove MUTEX from `t->mutexes'.
  (fat_mutex_lock): Update comment above the `t->mutexes' assignment.
  (do_thread_exit): Add an assertion making sure that each mutex in
  `t->mutexes' is owned by T.
This commit is contained in:
Ludovic Courtès 2010-09-02 14:42:14 +02:00
parent d31ae2c363
commit f57fdf07d6
1 changed files with 21 additions and 6 deletions
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23
libguile/threads.c
View file

@ -38,6 +38,8 @@
#include <sys/time.h>
#endif
#include <assert.h>
#include "libguile/validate.h"
#include "libguile/root.h"
#include "libguile/eval.h"
@ -466,7 +468,12 @@ do_thread_exit (void *v)
fat_mutex *m = SCM_MUTEX_DATA (mutex);
scm_i_pthread_mutex_lock (&m->lock);
/* Since MUTEX is in `t->mutexes', T must be its owner. */
assert (scm_is_eq (m->owner, t->handle));
unblock_from_queue (m->waiting);
scm_i_pthread_mutex_unlock (&m->lock);
}
@ -1234,10 +1241,10 @@ fat_mutex_lock (SCM mutex, scm_t_timespec *timeout, SCM owner, int *ret)
scm_i_pthread_mutex_lock (&t->admin_mutex);
/* Only keep a weak reference to MUTEX so that it's not
retained when not referenced elsewhere (bug #27450). Note
that the weak pair itself it still retained, but it's better
than retaining MUTEX and the threads referred to by its
associated queue. */
retained when not referenced elsewhere (bug #27450).
The weak pair itself is eventually removed when MUTEX
is unlocked. Note that `t->mutexes' lists mutexes
currently held by T, so it should be small. */
t->mutexes = scm_weak_car_pair (mutex, t->mutexes);
scm_i_pthread_mutex_unlock (&t->admin_mutex);
@ -1409,7 +1416,11 @@ fat_mutex_unlock (SCM mutex, SCM cond,
if (m->level > 0)
m->level--;
if (m->level == 0)
{
/* Change the owner of MUTEX. */
t->mutexes = scm_delq_x (mutex, t->mutexes);
m->owner = unblock_from_queue (m->waiting);
}
t->block_asyncs++;
@ -1453,7 +1464,11 @@ fat_mutex_unlock (SCM mutex, SCM cond,
if (m->level > 0)
m->level--;
if (m->level == 0)
{
/* Change the owner of MUTEX. */
t->mutexes = scm_delq_x (mutex, t->mutexes);
m->owner = unblock_from_queue (m->waiting);
}
scm_i_pthread_mutex_unlock (&m->lock);
ret = 1;