From 87231c34a1832cd6cb57d8ce555b1c65e1f0ac6a Mon Sep 17 00:00:00 2001
From: "Kevin P. Fleming" <kpfleming@digium.com>
Date: Sun, 10 Jul 2005 13:06:54 +0000
Subject: [PATCH] simplify locking (use a single lock, no deadlock possible)
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@6070 65c4cc65-6c06-0410-ace0-fbb531ad65f3
---
devicestate.c | 31 +++++++++++++------------------
1 file changed, 13 insertions(+), 18 deletions(-)
diff --git a/devicestate.c b/devicestate.c
index 621e8f1fd0..0474f5de1c 100755
--- a/devicestate.c
+++ b/devicestate.c
@@ -44,7 +44,6 @@ struct state_change {
static AST_LIST_HEAD_STATIC(state_changes, state_change);
static pthread_t change_thread = AST_PTHREADT_NULL;
-AST_MUTEX_DEFINE_STATIC(change_pending_lock);
static pthread_cond_t change_pending;
int ast_parse_device_state(const char *device)
@@ -138,6 +137,7 @@ void ast_devstate_del(ast_devstate_cb_type callback, void *data)
AST_LIST_UNLOCK(&devstate_cbs);
}
+/*--- do_state_change: Notify callback watchers of change, and notify PBX core for hint updates */
static void do_state_change(const char *device)
{
int state;
@@ -155,7 +155,6 @@ static void do_state_change(const char *device)
ast_hint_state_changed(device);
}
-/*--- ast_device_state_changed: Notify callback watchers of change, and notify PBX core for hint updates */
int ast_device_state_changed(const char *fmt, ...)
{
char buf[AST_MAX_EXTENSION];
@@ -183,15 +182,10 @@ int ast_device_state_changed(const char *fmt, ...)
strcpy(change->device, device);
AST_LIST_LOCK(&state_changes);
AST_LIST_INSERT_TAIL(&state_changes, change, list);
- if (AST_LIST_FIRST(&state_changes) == change) {
- AST_LIST_UNLOCK(&state_changes);
+ if (AST_LIST_FIRST(&state_changes) == change)
/* the list was empty, signal the thread */
- ast_mutex_lock(&change_pending_lock);
pthread_cond_signal(&change_pending);
- ast_mutex_unlock(&change_pending_lock);
- } else {
- AST_LIST_UNLOCK(&state_changes);
- }
+ AST_LIST_UNLOCK(&state_changes);
}
return 1;
@@ -201,20 +195,21 @@ static void *do_changes(void *data)
{
struct state_change *cur;
+ AST_LIST_LOCK(&state_changes);
for(;;) {
- ast_mutex_lock(&change_pending_lock);
- pthread_cond_wait(&change_pending, &change_pending_lock);
- for (;;) {
- AST_LIST_LOCK(&state_changes);
- cur = AST_LIST_REMOVE_HEAD(&state_changes, list);
+ /* the list lock will _always_ be held at this point in the loop */
+ cur = AST_LIST_REMOVE_HEAD(&state_changes, list);
+ if (cur) {
+ /* we got an entry, so unlock the list while we process it */
AST_LIST_UNLOCK(&state_changes);
- if (!cur)
- break;
-
do_state_change(cur->device);
free(cur);
+ AST_LIST_LOCK(&state_changes);
+ } else {
+ /* there was no entry, so atomically unlock the list and wait for
+ the condition to be signalled (returns with the lock held) */
+ pthread_cond_wait(&change_pending, &state_changes.lock);
}
- ast_mutex_unlock(&change_pending_lock);
}
return NULL;
--
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