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Merge pull request #29359 from zcinclude:fix/avfoundation-videowriter-destructor-sigsegv

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videoio(avfoundation): fix SIGSEGV crash when releasing VideoWriter on iOS #29359

Replace deprecated synchronous finishWriting with
finishWritingWithCompletionHandler + dispatch_semaphore
to properly wait for the async completion handler.

The synchronous finishWriting method is deprecated since iOS 6
and, despite blocking until writing status completes, does NOT
wait for internal NSOperation KVO observer blocks that are
dispatched asynchronously to GCD worker threads. When the
destructor returns and drains the autorelease pool, these
blocks may access already-released objects, causing SIGSEGV.

This fix uses a semaphore to block until the
finishWritingWithCompletionHandler callback has fully completed,
eliminating the race condition between the async block and
autorelease pool drain.

Fixes #28165
This commit is contained in:
ZC
2026-06-29 20:22:16 +08:00
committed by GitHub
parent 2a47e2c1a5
commit a16c4a9fe2
1 changed files with 15 additions and 1 deletions
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modules/videoio/src/cap_avfoundation_mac.mm
+15 -1
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@@ -1211,7 +1211,21 @@ CvVideoWriter_AVFoundation::~CvVideoWriter_AVFoundation() {
if (mMovieWriterInput && mMovieWriter && mMovieWriterAdaptor)
{
[mMovieWriterInput markAsFinished];
[mMovieWriter finishWriting];
// Use finishWritingWithCompletionHandler + semaphore to synchronously
// wait for the async completion block to finish, avoiding a race
// condition where NSOperation KVO observer blocks are dispatched
// asynchronously to GCD worker threads and may access already-released
// objects after the autorelease pool is drained.
// Replaces deprecated finishWriting (sync) which falsely appears safe
// but does NOT wait for internal NSOperation KVO callbacks to complete.
dispatch_semaphore_t sem = dispatch_semaphore_create(0);
[mMovieWriter finishWritingWithCompletionHandler:^{
dispatch_semaphore_signal(sem);
}];
dispatch_semaphore_wait(sem, DISPATCH_TIME_FOREVER);
dispatch_release(sem);
[mMovieWriter release];
[mMovieWriterInput release];
[mMovieWriterAdaptor release];