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
index db473571f6e9a501b1cfedd7dce6830e790a243b..525ef41d79a0ea2037f5dd9df1a1debafc665213 100644 (file)
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -952,7 +952,7 @@ ngx_init_zone_pool(ngx_cycle_t *cycle, ngx_shm_zone_t *zn)
 
 #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
index 3b429c4f979ecf99a8a455c1805c685d8c14aead..5a9242dfe879187eb31a7b917d848b37b455deb6 100644 (file)
--- 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 *addr, u_char *name)
 
 #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 +134,56 @@ 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");
     }
 
-    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_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 +298,11 @@ 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
index 714f73aa624fcba51ffd9f0501152d911042e40d..3ee7d3a7933bb85026102e5ba7a920fc90202189 100644 (file)
--- a/src/core/ngx_shmtx.h
+++ b/src/core/ngx_shmtx.h
@@ -12,10 +12,19 @@
 #include <ngx_core.h>
 
 
+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
index 291e1b51e13ddcb9d4a6e1fc030c28f29e7a3190..202fd938011c3ec5711fd1b1038231d0073ffeda 100644 (file)
--- 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
index 8a472ffe80d3bac9420b1d090624327234500c66..7d297d96ba55153f967d4f01d00f58641cdf0962 100644 (file)
--- 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
index 08069c4b698d2b8280f6379fa89ab1d24a8af3d9..cbdae8be1614e374a1aa6e03ff081c61e8756942 100644 (file)
--- 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);
         }