lavc: specify the behavior of av_lockmgr_register on failure.

The register function now specifies that the user callback should
leave things in the same state that it found them on failure but
that failure to destroy is ignored by the library.  The register
function is now explicit about its behavior on failure
(it unregisters the previous callback and destroys all mutex).

Signed-off-by: Manfred Georg <mgeorg@google.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index dfbab9b60fec36bbabd807bfa6c62fbb7b5804f0..f0fa7a959f76d17d231fbb9834a23fe09eeac458 100644 (file)
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -4393,16 +4393,26 @@ enum AVLockOp {
 
 /**
  * Register a user provided lock manager supporting the operations
- * specified by AVLockOp. mutex points to a (void *) where the
- * lockmgr should store/get a pointer to a user allocated mutex. It's
- * NULL upon AV_LOCK_CREATE and != NULL for all other ops.
+ * specified by AVLockOp. The "mutex" argument to the function points
+ * to a (void *) where the lockmgr should store/get a pointer to a user
+ * allocated mutex. It is NULL upon AV_LOCK_CREATE and equal to the
+ * value left by the last call for all other ops. If the lock manager is
+ * unable to perform the op then it should leave the mutex in the same
+ * state as when it was called and return a non-zero value. However,
+ * when called with AV_LOCK_DESTROY the mutex will always be assumed to
+ * have been successfully destroyed. If av_lockmgr_register succeeds
+ * it will return a non-negative value, if it fails it will return a
+ * negative value and destroy all mutex and unregister all callbacks.
+ * av_lockmgr_register is not thread-safe, it must be called from a
+ * single thread before any calls which make use of locking are used.
  *
- * @param cb User defined callback. Note: Libav may invoke calls to this
- *           callback during the call to av_lockmgr_register().
- *           Thus, the application must be prepared to handle that.
- *           If cb is set to NULL the lockmgr will be unregistered.
- *           Also note that during unregistration the previously registered
- *           lockmgr callback may also be invoked.
+ * @param cb User defined callback. av_lockmgr_register invokes calls
+ *           to this callback and the previously registered callback.
+ *           The callback will be used to create more than one mutex
+ *           each of which must be backed by its own underlying locking
+ *           mechanism (i.e. do not use a single static object to
+ *           implement your lock manager). If cb is set to NULL the
+ *           lockmgr will be unregistered.
  */
 int av_lockmgr_register(int (*cb)(void **mutex, enum AVLockOp op));
 

diff --git a/libavcodec/utils.c b/libavcodec/utils.c
index a47207610d8ff948354f9c2be7357901b1ee9777..94eca9bd11e1f5022355b27282e0a772e8c37b73 100644 (file)
--- a/libavcodec/utils.c
+++ b/libavcodec/utils.c
@@ -2318,20 +2318,32 @@ AVHWAccel *av_hwaccel_next(const AVHWAccel *hwaccel)
 int av_lockmgr_register(int (*cb)(void **mutex, enum AVLockOp op))
 {
     if (lockmgr_cb) {
-        if (lockmgr_cb(&codec_mutex, AV_LOCK_DESTROY))
-            return -1;
-        if (lockmgr_cb(&avformat_mutex, AV_LOCK_DESTROY))
-            return -1;
+        // There is no good way to rollback a failure to destroy the
+        // mutex, so we ignore failures.
+        lockmgr_cb(&codec_mutex,    AV_LOCK_DESTROY);
+        lockmgr_cb(&avformat_mutex, AV_LOCK_DESTROY);
+        lockmgr_cb     = NULL;
+        codec_mutex    = NULL;
+        avformat_mutex = NULL;
+    }
+
+    if (cb) {
+        void *new_codec_mutex    = NULL;
+        void *new_avformat_mutex = NULL;
+        int err;
+        if (err = cb(&new_codec_mutex, AV_LOCK_CREATE)) {
+            return err > 0 ? AVERROR_UNKNOWN : err;
+        }
+        if (err = cb(&new_avformat_mutex, AV_LOCK_CREATE)) {
+            // Ignore failures to destroy the newly created mutex.
+            cb(&new_codec_mutex, AV_LOCK_DESTROY);
+            return err > 0 ? AVERROR_UNKNOWN : err;
+        }
+        lockmgr_cb     = cb;
+        codec_mutex    = new_codec_mutex;
+        avformat_mutex = new_avformat_mutex;
     }
 
-    lockmgr_cb = cb;
-
-    if (lockmgr_cb) {
-        if (lockmgr_cb(&codec_mutex, AV_LOCK_CREATE))
-            return -1;
-        if (lockmgr_cb(&avformat_mutex, AV_LOCK_CREATE))
-            return -1;
-    }
     return 0;
 }
 

diff --git a/libavcodec/version.h b/libavcodec/version.h
index 849c4b2dadaab22e92f36ecbabde6a9aaad7be6c..773d21e355ceed1f3dddd18d19a1aaa71cf25402 100644 (file)
--- a/libavcodec/version.h
+++ b/libavcodec/version.h
@@ -30,7 +30,7 @@
 
 #define LIBAVCODEC_VERSION_MAJOR 56
 #define LIBAVCODEC_VERSION_MINOR  2
-#define LIBAVCODEC_VERSION_MICRO  0
+#define LIBAVCODEC_VERSION_MICRO  1
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
                                                LIBAVCODEC_VERSION_MINOR, \