fix: occasional crashes when put in foreground

VoidLink/Stream/VideoDecoderRenderer.h

@@ -43,4 +43,6 @@
                               frameType:(int)frameType
                         decodeStartTime:(CFTimeInterval)decodeStartTime;
 
+- (void)invalidateDecompressionSession;
+
 @end

VoidLink/Stream/VideoDecoderRenderer.m

@@ -98,6 +98,7 @@ extern int ff_isom_write_av1c(AVIOContext *pb, const uint8_t *buf, int size,
         _formatDescImageBuffer = nil;
     }
 
+    @synchronized(self) {
         if (_decompressionSession != nil){
             VTDecompressionSessionWaitForAsynchronousFrames(_decompressionSession);
 
@@ -105,6 +106,7 @@ extern int ff_isom_write_av1c(AVIOContext *pb, const uint8_t *buf, int size,
             CFRelease(_decompressionSession);
             _decompressionSession = nil;
         }
+    }
 }
 
 - (id)initWithView:(UIView* )view callbacks:(id<ConnectionCallbacks>)callbacks streamAspectRatio:(float)aspectRatio
@@ -174,6 +176,7 @@ extern int ff_isom_write_av1c(AVIOContext *pb, const uint8_t *buf, int size,
 
 
 - (void)setupDecompressionSessionWithAttributes:(NSDictionary *)destinationPixelBufferAttributes {
+    // This method is called from within synchronized block, so no additional sync needed here
     if (_decompressionSession != NULL) {
         VTDecompressionSessionInvalidate(_decompressionSession);
         CFRelease(_decompressionSession);
@@ -367,11 +370,13 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
         [_displayLink invalidate];
     }
 
+    @synchronized(self) {
         if (_decompressionSession != NULL) {
             VTDecompressionSessionInvalidate(_decompressionSession);
             CFRelease(_decompressionSession);
             _decompressionSession = nil;
         }
+    }
 }
 
 #define NALU_START_PREFIX_SIZE 3
@@ -845,6 +850,8 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
                             frameNumber:(int)frameNumber
                               frameType:(int)frameType
                         decodeStartTime:(CFTimeInterval)decodeStartTime {
+  // Synchronize access to decompression session to prevent race conditions during background/foreground transitions
+  @synchronized(self) {
     // Check if we need to create/recreate the decompression session
     BOOL needsNewSession = (frameType == FRAME_TYPE_IDR || _decompressionSession == nil);
 
@@ -878,12 +885,14 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
             if (status == kVTInvalidSessionErr) {
                 // The session was invalidated by the OS. Destroy our reference
                 // so it gets recreated on the next IDR frame.
+                @synchronized(self) {
                     if (self->_decompressionSession) {
                         VTDecompressionSessionInvalidate(self->_decompressionSession);
                         CFRelease(self->_decompressionSession);
                         self->_decompressionSession = nil;
                     }
                 }
+            }
             LiRequestIdrFrame(); // Request an IDR to restart the stream
             return;
           }
@@ -949,6 +958,7 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
       });
 
     return status;
+  }
 }
 
 - (void)setHdrMode:(BOOL)enabled {