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avcodec/utils: av_lockmgr_register defines behavior 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: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Manfred Georg 2014-10-02 11:54:31 -07:00 committed by Michael Niedermayer
parent cdd6f059a6
commit a950edb472
2 changed files with 41 additions and 21 deletions
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28
libavcodec/avcodec.h
View File

@ -5121,16 +5121,26 @@ 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: FFmpeg 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));

34
libavcodec/utils.c
View File

@ -3474,22 +3474,32 @@ 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;
codec_mutex = NULL;
// 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;
}
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;
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_EXTERNAL : 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_EXTERNAL : err;
}
lockmgr_cb = cb;
codec_mutex = new_codec_mutex;
avformat_mutex = new_avformat_mutex;
}
return 0;
}