Author: mdounin
Date: 2011-11-23 13:55:38 +0000 (Wed, 23 Nov 2011)
New Revision: 4310

Log:
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().


Modified:
trunk/src/core/ngx_cycle.c
trunk/src/core/ngx_shmtx.c
trunk/src/core/ngx_shmtx.h
trunk/src/core/ngx_slab.h
trunk/src/event/ngx_event.c
trunk/src/os/unix/ngx_process.c

Modified: trunk/src/core/ngx_cycle.c
===================================================================
--- trunk/src/core/ngx_cycle.c 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/core/ngx_cycle.c 2011-11-23 13:55:38 UTC (rev 4310)
@@ -952,7 +952,7 @@

#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;
}


Modified: trunk/src/core/ngx_shmtx.c
===================================================================
--- trunk/src/core/ngx_shmtx.c 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/core/ngx_shmtx.c 2011-11-23 13:55:38 UTC (rev 4310)
@@ -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 @@

#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_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 @@
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_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 @@
#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 +134,56 @@
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");
}

- for ( ;; ) {
+ if (ngx_atomic_cmp_set(mtx->lock, ngx_pid, 0)) {
+ ngx_shmtx_wakeup(mtx);
+ }
+}

- old = *mtx->lock;
- wait = old & 0x7fffffff;
- val = wait ? wait - 1 : 0;

- if (ngx_atomic_cmp_set(mtx->lock, old, val)) {
- break;
- }
+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)) {
+ ngx_shmtx_wakeup(mtx);
+ return 1;
}

+ return 0;
+}
+
+
+static void
+ngx_shmtx_wakeup(ngx_shmtx_t *mtx)
+{
#if (NGX_HAVE_POSIX_SEM)
+ ngx_atomic_uint_t wait;

- if (wait == 0 || !mtx->semaphore) {
+ if (!mtx->semaphore) {
return;
}

+ for ( ;; ) {
+
+ wait = *mtx->wait;
+
+ if (wait == 0) {
+ return;
+ }
+
+ if (ngx_atomic_cmp_set(mtx->wait, wait, wait - 1)) {
+ break;
+ }
+ }
+
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 +198,7 @@


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 +298,11 @@
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

Modified: trunk/src/core/ngx_shmtx.h
===================================================================
--- trunk/src/core/ngx_shmtx.h 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/core/ngx_shmtx.h 2011-11-23 13:55:38 UTC (rev 4310)
@@ -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 @@
} 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_ */

Modified: trunk/src/core/ngx_slab.h
===================================================================
--- trunk/src/core/ngx_slab.h 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/core/ngx_slab.h 2011-11-23 13:55:38 UTC (rev 4310)
@@ -22,7 +22,7 @@


typedef struct {
- ngx_atomic_t lock;
+ ngx_shmtx_sh_t lock;

size_t min_size;
size_t min_shift;

Modified: trunk/src/event/ngx_event.c
===================================================================
--- trunk/src/event/ngx_event.c 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/event/ngx_event.c 2011-11-23 13:55:38 UTC (rev 4310)
@@ -521,7 +521,8 @@
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;

Modified: trunk/src/os/unix/ngx_process.c
===================================================================
--- trunk/src/os/unix/ngx_process.c 2011-11-23 10:22:44 UTC (rev 4309)
+++ trunk/src/os/unix/ngx_process.c 2011-11-23 13:55:38 UTC (rev 4310)
@@ -504,7 +504,7 @@
* held it
*/

- ngx_atomic_cmp_set(ngx_accept_mutex_ptr, pid, 0);
+ ngx_shmtx_force_unlock(&ngx_accept_mutex, pid);
}



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