Question

使用Pthreads在C中为学校项目工作，将一维数组分解为tRows和tCols的子矩阵。整个数组的大小为wRows和wCols。让我们说wCols = 4，wRows = 4，tCols = 2，tRows = 2.如果数组的输入是整数1-16，我们将得到以下网格：

1  2  3  4
5  6  7  8
9 10 11 12
1314 15 17

Thus Thread 0 would process the subgrid
1 2 
5 6

Thread 1
3 4
7 8 

Thread 2 
9  10
13 14

Thread 3
11 12
15 17

如何使用两个for循环迭代一维数组以获取基于使用哪个Thread的值？我觉得我需要计算两个线程的开始和结束，但我完全坚持这个。

任何帮助将不胜感激。

Answer 1

pthread_create()的第四个参数被转发给线程启动函数作为其参数。这样做的目的是将任何必要的特定于线程的数据传递给线程，例如，矩阵补丁的起始行和列。

在这种情况下，向每个线程传递指向其矩阵补丁的最顶部，最左边元素的指针会特别干净。假设每个线程都知道补丁的大小和矩阵中的列数，这足以确定行号和列号。

Answer 2

这就是我做的方式（它确实利用了第四个参数，如第一个答案中所述）：

- (void)main {
    for (NSInteger index = 0; index < AppDelegate.sharedAppDelegate.getAssetCount; index++) {
        dispatch_queue_t threadQueue = dispatch_queue_create([[NSString stringWithFormat:@"threadQueue %ld", index] UTF8String], DISPATCH_QUEUE_CONCURRENT);
        dispatch_async(threadQueue, ^{
            pthread_t thread_tid;
            pthread_attr_t attr;
            int            returnVal;

            // init and check if init a new thread successful
            returnVal = pthread_attr_init(&attr);
            assert(!returnVal);

            // set attribute detach state for new thread
            returnVal = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
            assert(!returnVal);

            // create and run the new thread
            int threadError = pthread_create_from_mach_thread(&thread_tid, &attr, &ThreadMethod, (void*)index);
            returnVal = pthread_attr_destroy(&attr);
            assert(!returnVal);
            if (threadError != 0)
            {
                NSLog(@"Thread error: %i", threadError);
                // Report an error.
            }
        });
        //NSLog(@"index: %ld", index);
        index = index + 4;
    }
}

void* ThreadMethod(void *arg)
{
    for (NSInteger loop = 0; loop < 4. ; loop++) {
        NSInteger index = (NSInteger)arg + loop;
        NSLog(@"index: %ld", index);

        [AppDelegate.sharedAppDelegate.imageManager requestAVAssetForVideo:AppDelegate.sharedAppDelegate.assetsFetchResults[(NSInteger)index] options:AppDelegate.sharedAppDelegate.videoOptions resultHandler:^(AVAsset * _Nullable asset, AVAudioMix * _Nullable audioMix, NSDictionary * _Nullable info) {
            if(![[info objectForKey:PHImageResultIsInCloudKey] boolValue]) {
                if (asset) {
                    NSError __autoreleasing *error = nil;
                    AVAssetReader *reader;
                    [reader = [AVAssetReader assetReaderWithAsset:asset error:&error] addOutput:[AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] outputSettings:@{(id)kCVPixelBufferPixelFormatTypeKey: @(kCVPixelFormatType_32BGRA), (id)kCVPixelBufferWidthKey  : @([[UIScreen mainScreen] bounds].size.width / (int)floor(sqrt([AppDelegate.sharedAppDelegate getAssetCount]))), (id)kCVPixelBufferHeightKey : @(([[UIScreen mainScreen] bounds].size.width / (int)floor(sqrt([AppDelegate.sharedAppDelegate getAssetCount]))) * (9.0/16.0))}]];
                    [reader startReading];


                    while ([reader status] != AVAssetReaderStatusReading) { }
                    if ([reader status] == AVAssetReaderStatusReading) { NSLog(@"reader %ld reading", index); }
                    else { NSLog(@"reader %ld NOT reading", index); }
                    DisplayLayer *displayLayer = (DisplayLayer *)[[AppDelegate.sharedAppDelegate consumers] objectForKey:[NSString stringWithFormat:@"%ld", (NSInteger)index]];
                    dispatch_queue_t readerQueue = dispatch_queue_create([[NSString stringWithFormat:@"readerQueue %ld", (NSInteger)index] UTF8String], DISPATCH_QUEUE_SERIAL);

                    [displayLayer requestMediaDataWhenReadyOnQueue:readerQueue usingBlock:^{
                        @autoreleasepool {
                            if ([reader status] == AVAssetReaderStatusReading) {
                                CMSampleBufferRef sampleBuffer = [[[reader outputs] firstObject] copyNextSampleBuffer];
                                if (sampleBuffer) {
                                    [displayLayer enqueueSampleBuffer:sampleBuffer];
                                    /*OSStatus err = CMSimpleQueueEnqueue(displayLayer.simpleBuffer, sampleBuffer);
                                     if (err) {
                                     NSLog(@"Producer %ld buffer error: %d", index, (int)err);
                                     CMSimpleQueueReset(displayLayer.simpleBuffer);
                                     }*/
                                    CFRelease(sampleBuffer);
                                    sampleBuffer = nil;
                                }
                            }
                        }
                    }];
                }
            }
        }];
    }
    return NULL;
}

Pthreads数组块分发

2 个答案: