我正在尝试使用信号量
但是如果我使用dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
AVVideoComposition *videoComposition = [AVVideoComposition videoCompositionWithAsset:self.selectedVideo applyingCIFiltersWithHandler:^(AVAsynchronousCIImageFilteringRequest * _Nonnull request) {
CIImage *filteredImage = [CIImage CIFilterCustomLUTFilter:request.sourceImage CustomLUTFilter:self.filterArray[indexPath.row]];
[request finishWithImage:filteredImage context:nil];
NSLog(@"signal here %@", [NSThread currentThread]);
dispatch_semaphore_signal(semaphore);
}];
NSLog(@"wait here %@", [NSThread currentThread]);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
self.playerLayer.player.currentItem.videoComposition = videoComposition;
AVAssetExportSession *export = [AVAssetExportSession exportSessionWithAsset:self.selectedVideo presetName:AVAssetExportPresetHighestQuality];
export.outputFileType = AVFileTypeQuickTimeMovie;
export.videoComposition = videoComposition;
NSString *savingPath = [NSString stringWithFormat:@"%@/video.mov", NSTemporaryDirectory()];
export.outputURL = [NSURL fileURLWithPath:savingPath];
[export exportAsynchronouslyWithCompletionHandler:^{
UISaveVideoAtPathToSavedPhotosAlbum(savingPath, nil, nil, nil);
}];
});
，则永远不会执行
我检查了线程，绝对等待线程和信令线程是不同的线程。
首先，我尝试了以下代码。
applyCIFilterWithHandler我在这里尝试做的是在导出视频之前等待dispatch_semaphore_wait()的结果。
但通过这种方式，主线程被阻止，App陷入死锁状态。
第一个问题。我不能在主线程上使用dispatch_semaphore_t semaphore = dispatch_semaphore_create(0);
AVVideoComposition *videoComposition = [AVVideoComposition videoCompositionWithAsset:self.selectedVideo applyingCIFiltersWithHandler:^(AVAsynchronousCIImageFilteringRequest * _Nonnull request) {
CIImage *filteredImage = [CIImage CIFilterCustomLUTFilter:request.sourceImage CustomLUTFilter:self.filterArray[indexPath.row]];
[request finishWithImage:filteredImage context:nil];
NSLog(@"signal here %@", [NSThread currentThread]);
dispatch_semaphore_signal(semaphore);
}];
dispatch_queue_t myQueue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(myQueue, ^{
NSLog(@"wait here %@", [NSThread currentThread]);
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
self.playerLayer.player.currentItem.videoComposition = videoComposition;
AVAssetExportSession *export = [AVAssetExportSession exportSessionWithAsset:self.selectedVideo presetName:AVAssetExportPresetHighestQuality];
export.outputFileType = AVFileTypeQuickTimeMovie;
export.videoComposition = videoComposition;
NSString *savingPath = [NSString stringWithFormat:@"%@/video.mov", NSTemporaryDirectory()];
export.outputURL = [NSURL fileURLWithPath:savingPath];
[export exportAsynchronouslyWithCompletionHandler:^{
UISaveVideoAtPathToSavedPhotosAlbum(savingPath, nil, nil, nil);
}];
});
吗？即使等待的线程和信令线程彼此不同呢？
我尝试了以下代码后
dispatch_group一切都是一样但我让我的自定义线程等待信号。但这一次，块永远不会被执行。虽然我的应用程序没有陷入僵局......（当然，这次我没有阻止主线程）
第二个问题。如何在这里正确实现信号量？
如果你不只是说'只使用dispatch_group来代替！，我将非常感激。当然，提供另一种选择来实现相同的东西是非常好的。那么，请给我两种方式来实现信号量和dispatch_group。
非常感谢！
另一次尝试
我尝试使用dispatch_group_notify和applyCIFilterWithHandler实现此功能，但仍然永远不会调用and块。（当没有像dispatch_group，semaphore这样的东西时，它会被调用。
这是由1dispatch_group dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
AVVideoComposition *videoComposition = [AVVideoComposition videoCompositionWithAsset:self.selectedVideo applyingCIFiltersWithHandler:^(AVAsynchronousCIImageFilteringRequest * _Nonnull request) {
CIImage *filteredImage = [CIImage CIFilterCustomLUTFilter:request.sourceImage CustomLUTFilter:self.filterArray[indexPath.row]];
[request finishWithImage:filteredImage context:nil];
NSLog(@"block done here %@", [NSThread currentThread]);
dispatch_group_leave(group);
}];
dispatch_group_notify(group, dispatch_get_main_queue(), ^{
NSLog(@"start saving here %@", [NSThread currentThread]);
self.playerLayer.player.currentItem.videoComposition = videoComposition;
AVAssetExportSession *export = [AVAssetExportSession exportSessionWithAsset:self.selectedVideo presetName:AVAssetExportPresetHighestQuality];
export.outputFileType = AVFileTypeQuickTimeMovie;
export.videoComposition = videoComposition;
NSString *savingPath = [NSString stringWithFormat:@"%@/video.mov", NSTemporaryDirectory()];
export.outputURL = [NSURL fileURLWithPath:savingPath];
[export exportAsynchronouslyWithCompletionHandler:^{
UISaveVideoAtPathToSavedPhotosAlbum(savingPath, nil, nil, nil);
}];
});
dispatch_group_notify`实现的代码
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