[PATCH 1 of 2] Added shmtx interface to forcibly unlock mutexes
Maxim Dounin
mdounin at mdounin.ru
Wed Nov 23 13:02:20 UTC 2011
# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1321467405 -10800
# Node ID 7bedc6b7d2f34da90c6f564b7e6118c584cd826e
# Parent db820db0915f6df3f8950664d544d3f45b7b968c
Added shmtx interface to forcibly unlock mutexes.
It is currently used from master process on abnormal worker termination to
unlock accept mutex (unlocking of accept mutex was broken in 1.0.2). It is
expected to be used in the future to unlock other mutexes as well.
Shared mutex code was rewritten to make this possible in a safe way, i.e.
with a check if lock was actually held by the exited process. We again use
pid to lock mutex, and use separate atomic variable for a count of processes
waiting in sem_wait().
diff --git a/src/core/ngx_cycle.c b/src/core/ngx_cycle.c
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -952,7 +952,7 @@ ngx_init_zone_pool(ngx_cycle_t *cycle, n
#endif
- if (ngx_shmtx_create(&sp->mutex, (void *) &sp->lock, file) != NGX_OK) {
+ if (ngx_shmtx_create(&sp->mutex, &sp->lock, file) != NGX_OK) {
return NGX_ERROR;
}
diff --git a/src/core/ngx_shmtx.c b/src/core/ngx_shmtx.c
--- a/src/core/ngx_shmtx.c
+++ b/src/core/ngx_shmtx.c
@@ -11,10 +11,13 @@
#if (NGX_HAVE_ATOMIC_OPS)
+static void ngx_shmtx_wakeup(ngx_shmtx_t *mtx);
+
+
ngx_int_t
-ngx_shmtx_create(ngx_shmtx_t *mtx, void *addr, u_char *name)
+ngx_shmtx_create(ngx_shmtx_t *mtx, ngx_shmtx_sh_t *addr, u_char *name)
{
- mtx->lock = addr;
+ mtx->lock = &addr->lock;
if (mtx->spin == (ngx_uint_t) -1) {
return NGX_OK;
@@ -24,6 +27,8 @@ ngx_shmtx_create(ngx_shmtx_t *mtx, void
#if (NGX_HAVE_POSIX_SEM)
+ mtx->wait = &addr->wait;
+
if (sem_init(&mtx->sem, 1, 0) == -1) {
ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
"sem_init() failed");
@@ -56,12 +61,7 @@ ngx_shmtx_destory(ngx_shmtx_t *mtx)
ngx_uint_t
ngx_shmtx_trylock(ngx_shmtx_t *mtx)
{
- ngx_atomic_uint_t val;
-
- val = *mtx->lock;
-
- return ((val & 0x80000000) == 0
- && ngx_atomic_cmp_set(mtx->lock, val, val | 0x80000000));
+ return (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid));
}
@@ -69,17 +69,12 @@ void
ngx_shmtx_lock(ngx_shmtx_t *mtx)
{
ngx_uint_t i, n;
- ngx_atomic_uint_t val;
ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0, "shmtx lock");
for ( ;; ) {
- val = *mtx->lock;
-
- if ((val & 0x80000000) == 0
- && ngx_atomic_cmp_set(mtx->lock, val, val | 0x80000000))
- {
+ if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) {
return;
}
@@ -91,10 +86,8 @@ ngx_shmtx_lock(ngx_shmtx_t *mtx)
ngx_cpu_pause();
}
- val = *mtx->lock;
-
- if ((val & 0x80000000) == 0
- && ngx_atomic_cmp_set(mtx->lock, val, val | 0x80000000))
+ if (*mtx->lock == 0
+ && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid))
{
return;
}
@@ -104,24 +97,24 @@ ngx_shmtx_lock(ngx_shmtx_t *mtx)
#if (NGX_HAVE_POSIX_SEM)
if (mtx->semaphore) {
- val = *mtx->lock;
+ ngx_atomic_fetch_add(mtx->wait, 1);
- if ((val & 0x80000000)
- && ngx_atomic_cmp_set(mtx->lock, val, val + 1))
- {
- ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
- "shmtx wait %XA", val);
+ if (*mtx->lock == 0 && ngx_atomic_cmp_set(mtx->lock, 0, ngx_pid)) {
+ return;
+ }
- while (sem_wait(&mtx->sem) == -1) {
- ngx_err_t err;
+ ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
+ "shmtx wait %uA", *mtx->wait);
- err = ngx_errno;
+ while (sem_wait(&mtx->sem) == -1) {
+ ngx_err_t err;
- if (err != NGX_EINTR) {
- ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, err,
- "sem_wait() failed while waiting on shmtx");
- break;
- }
+ err = ngx_errno;
+
+ if (err != NGX_EINTR) {
+ ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, err,
+ "sem_wait() failed while waiting on shmtx");
+ break;
}
ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
@@ -141,31 +134,59 @@ ngx_shmtx_lock(ngx_shmtx_t *mtx)
void
ngx_shmtx_unlock(ngx_shmtx_t *mtx)
{
- ngx_atomic_uint_t val, old, wait;
-
if (mtx->spin != (ngx_uint_t) -1) {
ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0, "shmtx unlock");
}
+ if (!ngx_atomic_cmp_set(mtx->lock, ngx_pid, 0)) {
+ return;
+ }
+
+ ngx_shmtx_wakeup(mtx);
+}
+
+
+ngx_uint_t
+ngx_shmtx_force_unlock(ngx_shmtx_t *mtx, ngx_pid_t pid)
+{
+ ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
+ "shmtx forced unlock");
+
+ if (!ngx_atomic_cmp_set(mtx->lock, pid, 0)) {
+ return 0;
+ }
+
+ ngx_shmtx_wakeup(mtx);
+
+ return 1;
+}
+
+
+static void
+ngx_shmtx_wakeup(ngx_shmtx_t *mtx)
+{
+#if (NGX_HAVE_POSIX_SEM)
+ ngx_atomic_uint_t wait;
+
+ if (!mtx->semaphore) {
+ return;
+ }
+
for ( ;; ) {
- old = *mtx->lock;
- wait = old & 0x7fffffff;
- val = wait ? wait - 1 : 0;
+ wait = *mtx->wait;
- if (ngx_atomic_cmp_set(mtx->lock, old, val)) {
+ if (wait == 0) {
+ return;
+ }
+
+ if (ngx_atomic_cmp_set(mtx->wait, wait, wait - 1)) {
break;
}
}
-#if (NGX_HAVE_POSIX_SEM)
-
- if (wait == 0 || !mtx->semaphore) {
- return;
- }
-
ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
- "shmtx wake %XA", old);
+ "shmtx wake %uA", wait);
if (sem_post(&mtx->sem) == -1) {
ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, ngx_errno,
@@ -180,7 +201,7 @@ ngx_shmtx_unlock(ngx_shmtx_t *mtx)
ngx_int_t
-ngx_shmtx_create(ngx_shmtx_t *mtx, void *addr, u_char *name)
+ngx_shmtx_create(ngx_shmtx_t *mtx, ngx_shmtx_sh_t *addr, u_char *name)
{
if (mtx->name) {
@@ -280,4 +301,11 @@ ngx_shmtx_unlock(ngx_shmtx_t *mtx)
ngx_log_abort(err, ngx_unlock_fd_n " %s failed", mtx->name);
}
+
+void
+ngx_shmtx_force_unlock(ngx_shmtx_t *mtx, ngx_pid_t pid)
+{
+ /* void */
+}
+
#endif
diff --git a/src/core/ngx_shmtx.h b/src/core/ngx_shmtx.h
--- a/src/core/ngx_shmtx.h
+++ b/src/core/ngx_shmtx.h
@@ -13,9 +13,18 @@
typedef struct {
+ ngx_atomic_t lock;
+#if (NGX_HAVE_POSIX_SEM)
+ ngx_atomic_t wait;
+#endif
+} ngx_shmtx_sh_t;
+
+
+typedef struct {
#if (NGX_HAVE_ATOMIC_OPS)
ngx_atomic_t *lock;
#if (NGX_HAVE_POSIX_SEM)
+ ngx_atomic_t *wait;
ngx_uint_t semaphore;
sem_t sem;
#endif
@@ -27,11 +36,13 @@ typedef struct {
} ngx_shmtx_t;
-ngx_int_t ngx_shmtx_create(ngx_shmtx_t *mtx, void *addr, u_char *name);
+ngx_int_t ngx_shmtx_create(ngx_shmtx_t *mtx, ngx_shmtx_sh_t *addr,
+ u_char *name);
void ngx_shmtx_destory(ngx_shmtx_t *mtx);
ngx_uint_t ngx_shmtx_trylock(ngx_shmtx_t *mtx);
void ngx_shmtx_lock(ngx_shmtx_t *mtx);
void ngx_shmtx_unlock(ngx_shmtx_t *mtx);
+ngx_uint_t ngx_shmtx_force_unlock(ngx_shmtx_t *mtx, ngx_pid_t pid);
#endif /* _NGX_SHMTX_H_INCLUDED_ */
diff --git a/src/core/ngx_slab.h b/src/core/ngx_slab.h
--- a/src/core/ngx_slab.h
+++ b/src/core/ngx_slab.h
@@ -22,7 +22,7 @@ struct ngx_slab_page_s {
typedef struct {
- ngx_atomic_t lock;
+ ngx_shmtx_sh_t lock;
size_t min_size;
size_t min_shift;
diff --git a/src/event/ngx_event.c b/src/event/ngx_event.c
--- a/src/event/ngx_event.c
+++ b/src/event/ngx_event.c
@@ -521,7 +521,8 @@ ngx_event_module_init(ngx_cycle_t *cycle
ngx_accept_mutex_ptr = (ngx_atomic_t *) shared;
ngx_accept_mutex.spin = (ngx_uint_t) -1;
- if (ngx_shmtx_create(&ngx_accept_mutex, shared, cycle->lock_file.data)
+ if (ngx_shmtx_create(&ngx_accept_mutex, (ngx_shmtx_sh_t *) shared,
+ cycle->lock_file.data)
!= NGX_OK)
{
return NGX_ERROR;
diff --git a/src/os/unix/ngx_process.c b/src/os/unix/ngx_process.c
--- a/src/os/unix/ngx_process.c
+++ b/src/os/unix/ngx_process.c
@@ -504,7 +504,7 @@ ngx_process_get_status(void)
* held it
*/
- ngx_atomic_cmp_set(ngx_accept_mutex_ptr, pid, 0);
+ ngx_shmtx_force_unlock(&ngx_accept_mutex, pid);
}
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