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

@@ -98,12 +98,14 @@ extern int ff_isom_write_av1c(AVIOContext *pb, const uint8_t *buf, int size,
         _formatDescImageBuffer = nil;
     }
 
-    if (_decompressionSession != nil){
+    @synchronized(self) {
-        VTDecompressionSessionWaitForAsynchronousFrames(_decompressionSession);
+        if (_decompressionSession != nil){
+            VTDecompressionSessionWaitForAsynchronousFrames(_decompressionSession);
 
-        VTDecompressionSessionInvalidate(_decompressionSession);
+            VTDecompressionSessionInvalidate(_decompressionSession);
-        CFRelease(_decompressionSession);
+            CFRelease(_decompressionSession);
-        _decompressionSession = nil;
+            _decompressionSession = nil;
+        }
     }
 }
 
@@ -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);
@@ -367,10 +370,12 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
         [_displayLink invalidate];
     }
 
-    if (_decompressionSession != NULL) {
+    @synchronized(self) {
-        VTDecompressionSessionInvalidate(_decompressionSession);
+        if (_decompressionSession != NULL) {
-        CFRelease(_decompressionSession);
+            VTDecompressionSessionInvalidate(_decompressionSession);
-        _decompressionSession = nil;
+            CFRelease(_decompressionSession);
+            _decompressionSession = nil;
+        }
     }
 }
 
@@ -845,28 +850,30 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
                             frameNumber:(int)frameNumber
                               frameType:(int)frameType
                         decodeStartTime:(CFTimeInterval)decodeStartTime {
-  // Check if we need to create/recreate the decompression session
+  // Synchronize access to decompression session to prevent race conditions during background/foreground transitions
-  BOOL needsNewSession = (frameType == FRAME_TYPE_IDR || _decompressionSession == nil);
+  @synchronized(self) {
+    // Check if we need to create/recreate the decompression session
+    BOOL needsNewSession = (frameType == FRAME_TYPE_IDR || _decompressionSession == nil);
 
-  // Also check if the session might have been invalidated by iOS during background
+    // Also check if the session might have been invalidated by iOS during background
-  if (!needsNewSession && _decompressionSession != nil) {
+    if (!needsNewSession && _decompressionSession != nil) {
-    Boolean isValid = VTDecompressionSessionCanAcceptFormatDescription(_decompressionSession, _formatDesc);
+      Boolean isValid = VTDecompressionSessionCanAcceptFormatDescription(_decompressionSession, _formatDesc);
-    if (!isValid) {
+      if (!isValid) {
-      Log(LOG_W, @"Decompression session is invalid, needs recreation");
+        Log(LOG_W, @"Decompression session is invalid, needs recreation");
-      needsNewSession = YES;
+        needsNewSession = YES;
+      }
     }
-  }
 
-  if (needsNewSession) {
+    if (needsNewSession) {
-    [self setupDecompressionSession];
+      [self setupDecompressionSession];
-  }
+    }
 
-  if (_decompressionSession == nil) {
+    if (_decompressionSession == nil) {
-    Log(LOG_E, @"Failed to create decompression session");
+      Log(LOG_E, @"Failed to create decompression session");
-    return kVTInvalidSessionErr;
+      return kVTInvalidSessionErr;
-  }
+    }
 
-  OSStatus status = VTDecompressionSessionDecodeFrameWithOutputHandler(
+    OSStatus status = VTDecompressionSessionDecodeFrameWithOutputHandler(
       _decompressionSession,
       sampleBuffer,
       0,
@@ -878,10 +885,12 @@ 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.
-                if (self->_decompressionSession) {
+                @synchronized(self) {
-                    VTDecompressionSessionInvalidate(self->_decompressionSession);
+                    if (self->_decompressionSession) {
-                    CFRelease(self->_decompressionSession);
+                        VTDecompressionSessionInvalidate(self->_decompressionSession);
-                    self->_decompressionSession = nil;
+                        CFRelease(self->_decompressionSession);
+                        self->_decompressionSession = nil;
+                    }
                 }
             }
             LiRequestIdrFrame(); // Request an IDR to restart the stream
@@ -948,7 +957,8 @@ int DrSubmitDecodeUnit(PDECODE_UNIT decodeUnit);
           });
       });
 
-  return status;
+    return status;
+  }
 }
 
 - (void)setHdrMode:(BOOL)enabled {