[Guile-commits] 10/24: Remove thread-local weak mutex set

[Andy Wingo]

wingo pushed a commit to branch master
in repository guile.

commit 857aa581a245f49946baa9b5ce25ab3fdb2f15af
Author: Andy Wingo <address@hidden>
Date:   Sat Nov 5 00:20:39 2016 +0100

    Remove thread-local weak mutex set
    
    * libguile/threads.h (scm_i_thread):
    * libguile/threads.c (guilify_self_1, do_thread_exit, fat_mutex_lock):
      Remove thread-local weak mutex set.
---
 libguile/threads.c |   76 +++-------------------------------------------------
 libguile/threads.h |    1 -
 2 files changed, 4 insertions(+), 73 deletions(-)

diff --git a/libguile/threads.c b/libguile/threads.c
index 79d0f81..76abe35 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -411,7 +411,6 @@ guilify_self_1 (struct GC_stack_base *base)
   t.pthread = scm_i_pthread_self ();
   t.handle = SCM_BOOL_F;
   t.result = SCM_BOOL_F;
-  t.mutexes = SCM_EOL;
   t.held_mutex = NULL;
   t.join_queue = SCM_EOL;
   t.freelists = NULL;
@@ -543,28 +542,6 @@ do_thread_exit (void *v)
   while (scm_is_true (unblock_from_queue (t->join_queue)))
     ;
 
-  while (!scm_is_null (t->mutexes))
-    {
-      SCM mutex = scm_c_weak_vector_ref (scm_car (t->mutexes), 0);
-
-      if (scm_is_true (mutex))
-       {
-         fat_mutex *m  = SCM_MUTEX_DATA (mutex);
-
-         scm_i_pthread_mutex_lock (&m->lock);
-
-         /* Check whether T owns MUTEX.  This is usually the case, unless
-            T abandoned MUTEX; in that case, T is no longer its owner (see
-            `fat_mutex_lock') but MUTEX is still in `t->mutexes'.  */
-         if (scm_is_eq (m->owner, t->handle))
-           unblock_from_queue (m->waiting);
-
-         scm_i_pthread_mutex_unlock (&m->lock);
-       }
-
-      t->mutexes = scm_cdr (t->mutexes);
-    }
-
   scm_i_pthread_mutex_unlock (&t->admin_mutex);
 
   return NULL;
@@ -1183,26 +1160,6 @@ fat_mutex_lock (SCM mutex, scm_t_timespec *timeout, int 
*ret)
        {
          m->owner = new_owner;
          m->level++;
-
-         if (SCM_I_IS_THREAD (new_owner))
-           {
-             scm_i_thread *t = SCM_I_THREAD_DATA (new_owner);
-
-             /* FIXME: The order in which `t->admin_mutex' and
-                `m->lock' are taken differs from that in
-                `on_thread_exit', potentially leading to deadlocks.  */
-             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).
-                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_cons (scm_make_weak_vector (SCM_INUM1, mutex),
-                                     t->mutexes);
-
-             scm_i_pthread_mutex_unlock (&t->admin_mutex);
-           }
          *ret = 1;
          break;
        }
@@ -1330,25 +1287,6 @@ typedef struct {
 #define SCM_CONDVARP(x)       SCM_SMOB_PREDICATE (scm_tc16_condvar, x)
 #define SCM_CONDVAR_DATA(x)   ((fat_cond *) SCM_SMOB_DATA (x))
 
-static void
-remove_mutex_from_thread (SCM mutex, scm_i_thread *t)
-{
-  SCM walk, prev;
-  
-  for (prev = SCM_BOOL_F, walk = t->mutexes; scm_is_pair (walk);
-       walk = SCM_CDR (walk))
-    {
-      if (scm_is_eq (mutex, scm_c_weak_vector_ref (SCM_CAR (walk), 0)))
-        {
-          if (scm_is_pair (prev))
-            SCM_SETCDR (prev, SCM_CDR (walk));
-          else
-            t->mutexes = SCM_CDR (walk);
-          break;
-        }
-    }
-}
-
 static int
 fat_mutex_unlock (SCM mutex, SCM cond,
                  const scm_t_timespec *waittime, int relock)
@@ -1391,11 +1329,8 @@ fat_mutex_unlock (SCM mutex, SCM cond,
          if (m->level > 0)
            m->level--;
          if (m->level == 0)
-           {
-             /* Change the owner of MUTEX.  */
-             remove_mutex_from_thread (mutex, t);
-             m->owner = unblock_from_queue (m->waiting);
-           }
+            /* Change the owner of MUTEX.  */
+            m->owner = unblock_from_queue (m->waiting);
 
          t->block_asyncs++;
 
@@ -1439,11 +1374,8 @@ fat_mutex_unlock (SCM mutex, SCM cond,
       if (m->level > 0)
        m->level--;
       if (m->level == 0)
-       {
-         /* Change the owner of MUTEX.  */
-         remove_mutex_from_thread (mutex, t);
-         m->owner = unblock_from_queue (m->waiting);
-       }
+        /* Change the owner of MUTEX.  */
+        m->owner = unblock_from_queue (m->waiting);
 
       scm_i_pthread_mutex_unlock (&m->lock);
       ret = 1;
diff --git a/libguile/threads.h b/libguile/threads.h
index f6165a5..e88a7e5 100644
--- a/libguile/threads.h
+++ b/libguile/threads.h
@@ -63,7 +63,6 @@ typedef struct scm_i_thread {
   SCM join_queue;
 
   scm_i_pthread_mutex_t admin_mutex;
-  SCM mutexes;
   scm_i_pthread_mutex_t *held_mutex;
 
   SCM result;