1.

//不延时,可能会导致界面黑屏并卡住一会

[self performSelector:@selector(startScan) withObject:nil afterDelay:0.3];

- (void)viewWillDisappear:(BOOL)animated

{

[super viewWillDisappear:animated];

[NSObject cancelPreviousPerformRequestsWithTarget:self];

[self stopScan];

2.ZXCapture

_captureQueue = dispatch_queue_create("com.zxing.captureQueue", NULL);

[_output setSampleBufferDelegate:self queue:_captureQueue];

3.gcd 生产者 消费者

http://blog.csdn.net/jeffasd/article/details/50495977

//
// ViewController.m
// tick01
//
// Created by temp on 2018/1/5.
// Copyright © 2018年 temp. All rights reserved.
// #import "ViewController.h" #define WS(weakSelf) __weak __typeof(&*self)weakSelf = self; @interface ViewController ()
{
dispatch_queue_t _dispatchQueue; dispatch_semaphore_t sem; } @property (readwrite) BOOL playing;
@property (weak, nonatomic) IBOutlet UIButton *playBtn; @end @implementation ViewController - (void)dealloc
{
_dispatchQueue = nil; NSLog(@"111--- ViewController dealloc");
} - (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib. _dispatchQueue = dispatch_queue_create("KxMovie", DISPATCH_QUEUE_SERIAL);
sem = dispatch_semaphore_create(); } - (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
} - (void)viewWillDisappear
{
[self pause];
} #pragma mark - 播放与暂停
- (IBAction)playAndpauseAction:(id)sender
{
if (self.playing){
[self state];
}
else{
//[_activityIndicatorView startAnimating];
[self play];
[_playBtn setImage:[UIImage imageNamed:@"playback_pause"] forState:UIControlStateNormal];
}
} - (void)state
{
if (self.playing){
[_playBtn setImage:[UIImage imageNamed:@"playback_play"] forState:UIControlStateNormal];
// [_activityIndicatorView stopAnimating];
[self pause];
}
} - (void) pause
{
if (!self.playing)
return;
self.playing = NO;
// [self enableAudio:NO];
// [self updatePlayButton];
} #pragma mark - play
-(void) play
{
if (self.playing)
return; self.playing = YES; [self asyncDecodeFrames];
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 0.1 * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ [self tick]; }); WS(weakSelf);
dispatch_async(dispatch_get_global_queue(, ), ^{ while () {
__strong ViewController *strongSelf = weakSelf;
{
if (!strongSelf.playing)
return;
} NSLog(@"111--- dispatch_semaphore_wait");
if (dispatch_semaphore_wait(sem, dispatch_time(DISPATCH_TIME_NOW, *NSEC_PER_SEC))) {
continue;
}
[strongSelf tick];
} });
} - (void) tick
{
CGFloat interval = ; if (self.playing) {
[self asyncDecodeFrames]; NSLog(@"111--- tick"); }
} - (void) asyncDecodeFrames
{ WS(weakSelf); dispatch_async(_dispatchQueue, ^{
__strong ViewController *strongSelf = weakSelf;
{
if (!strongSelf.playing)
return;
} NSLog(@"111---do some thing...");
[NSThread sleepForTimeInterval:]; if (!dispatch_semaphore_signal(sem))
{
//       sleep(1); //wait for a while
//       continue;
NSLog(@"111--- signal fail");
} //通知成功 });
} @end

gpuimage

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
if (!self.captureSession.isRunning)
{
return;
}
else if (captureOutput == audioOutput)
{
[self processAudioSampleBuffer:sampleBuffer];
}
else
{
if (dispatch_semaphore_wait(frameRenderingSemaphore, DISPATCH_TIME_NOW) != )
{
return;
} CFRetain(sampleBuffer);
runAsynchronouslyOnVideoProcessingQueue(^{
//Feature Detection Hook.
if (self.delegate)
{
[self.delegate willOutputSampleBuffer:sampleBuffer];
} [self processVideoSampleBuffer:sampleBuffer]; CFRelease(sampleBuffer);
dispatch_semaphore_signal(frameRenderingSemaphore);
});
}
}

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