Memleak when emptying session history and using session-based execute callbacks.

[crouchingtiger]

When calling [FFmpegKitConfig clearSessions], only the sessionHistoryList is emptied, leaving sessionHistoryMap to leak and retain a reference to the FFmpegSession.

Sessions history list and map are added at https://github.com/tanersener/ffmpeg-kit/blob/5d11e79fc2734a7c61b741f3a729409a17b212e1/apple/src/FFmpegKitConfig.m#L115

Notably, if you are using session execute callbacks , ffmpeg-kit will continue to leak FFmpegSession objects, even if you set [FFmpegKitConfig setSessionHistorySize:0]. I've noticed this behaviour in previous versions but didn't investigate further at the time and was happy enough to use the global callbacks. My use-case has shifted and I have concurrent ffmpeg sessions running for my application, so I took a further look. This affects asynchronous commands issued on another queue. lldb will not be able to point out any obvious leaks here.

As a test, I issued a sample command to + (FFmpegSession*)executeAsync:(NSString*)command withExecuteCallback:(ExecuteCallback)executeCallback withLogCallback:(LogCallback)logCallback withStatisticsCallback:(StatisticsCallback)statisticsCallback onDispatchQueue:(dispatch_queue_t)queue with non-null, empty blocks. I monitored and waited for the autoreleasepool and took some samples after successful return.

Here's the situation without calling the newly added [FFmpegKitConfig clearSessions]:

and if you do decide to clear the session list:

Only if ([sessionHistoryList count] > sessionHistorySize) are entries removed when adding a new session. This means at least 1 session will always linger and leak, replacing the previous reference.

Based off this commit, I added a method call to clear out sessionHistoryMap. I can confirm that in my use-case, my leaks disappear once I call [FFmpegKitConfig clearSessions].

Environment

Platform: [macOS]
Architecture: [x86_64]
Version [v4.5]
Source branch [master, v4.5]
Xcode version [13.0]

[tanersener]

Good catch! Thanks for reporting this. It looks like we need to patch clearSessions method. This affects Android too.

[tanersener]

Fixed in the development branch.

[crouchingtiger]

@tanersener Thanks for the quick response and fix (and project)!

[tanersener]

The fix is released in v4.5.1.