Question

我正在使用Xcode 4.6.3和iOS 5.5 / 6.1.6。

我正在使用后台线程从服务器向iOS设备加载大量的jpg。

dispatch_async(kBgQueue, ^
               {
                   // get the array of filenames to download
                   NSURL* url = [NSURL URLWithString:webPath];
                   NSArray* theArray = [NSArray arrayWithContentsOfURL:url];
                   if( theArray )
                   {
                       dispatch_async(dispatch_get_main_queue(), ^{
                           // disable screen buttons
                           [self setButtons:false];
                       });

                       [self loadImagesFromList:theArray sourceBundle:bundlePath destBundle:localBundlePath manager:manager];

                       if (!stopFlag) {
                           // if no memory error has occurred
                           NSLog(@"calling refresh after load_images");
                           dispatch_async(dispatch_get_main_queue(), ^{
                               [self refresh];
                           });
                       }
                       theArray = nil;
                   }
                   else
                   {
                       NSLog(@"Error loading bundle");
                   }
               });

背景方法：

-(void)loadImagesFromList:(NSArray *)theArray
             sourceBundle:(NSString *)bundlePath
               destBundle:(NSString *)localBundlePath
                  manager:(NSFileManager *)manager {

    // initialize the progress and activity indicator
    dispatch_async(dispatch_get_main_queue(), ^{
        [self.activityIndictor startAnimating];
        [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
        [self.progressIndictor setProgress:0 animated:NO];
    });

    NSURL *url;
    NSString *srcFile;
    NSString *destFile;
    NSError *error = nil;

    int counter = 0;
    float prog = 0;
    float increment = 1.0 / [theArray count];
    float stepSize = [theArray count] / 10;

    for (NSString *file in theArray)
    {
        if (stopFlag) {
            NSLog(@"I see stopFlag = true, counter = %d, prog = %f", counter, prog);
            return;
        }
        srcFile = [bundlePath stringByAppendingPathComponent:file];
        destFile = [localBundlePath stringByAppendingPathComponent:file];

        counter += 1;
        prog += increment;
        if (counter == stepSize) {
            dispatch_async(dispatch_get_main_queue(), ^{
                self.progressIndictor.progress = prog;
            });
            counter = 0;
        }

        // only download if file isn't already here
        BOOL fileExists = [manager fileExistsAtPath:destFile]; // check if we already have it
        if (!fileExists) {
            // jpg or folder check
            if ([[destFile pathExtension] isEqualToString:@"jpg"]) {
                url = [NSURL URLWithString:srcFile];
                data = [NSData dataWithContentsOfURL:url
                                             options:0
                                               error:&error];

                [data writeToFile:destFile options:NSDataWritingAtomic error:&error];
                data = nil;
            } else {
                [manager createDirectoryAtPath:destFile withIntermediateDirectories:YES attributes:nil error:&error];
            }
        }
    }
}

如果文件存在，循环将拉开数组并退回到主线程ok。如果缺少任何文件，下载/写入部分似乎会咀嚼RAM并导致低内存警告触发。这需要几千个文件。

我尝试在循环外声明变量，甚至在主线程中执行整个操作以测试是否导致泄漏。我尝试使用备用dataWithContentsOfURL：options：错误调用。我试过了仪器，但它确实很慢并经常崩溃。在崩溃之前，它确实显示分配上升，上升，缓慢上升。

经过几天的努力，我很难过。

Answer 1

我建议的第一件事就是使用@autoreleasepool来控制消耗的峰值内存量。现在，您将内容作为自动释放对象下载到NSData中，完成后，您将nil - 变量loadImagesFromList - 该变量简单标记为一次解除分配排出自动释放池（在for完成之前不会发生这种情况）。通过（a）在@autoreleasepool循环内移动变量声明; （b）将其包装在-(void)loadImagesFromList:(NSArray *)theArray sourceBundle:(NSString *)bundlePath destBundle:(NSString *)localBundlePath manager:(NSFileManager *)manager { // initialize the progress and activity indicator dispatch_async(dispatch_get_main_queue(), ^{ // your UI update here }); int counter = 0; float prog = 0; float increment = 1.0 / [theArray count]; float stepSize = [theArray count] / 10; for (NSString *file in theArray) { @autoreleasepool { if (stopFlag) { NSLog(@"I see stopFlag = true, counter = %d, prog = %f", counter, prog); return; } NSString *srcFile = [bundlePath stringByAppendingPathComponent:file]; NSString *destFile = [localBundlePath stringByAppendingPathComponent:file]; counter += 1; prog += increment; if (counter == stepSize) { dispatch_async(dispatch_get_main_queue(), ^{ self.progressIndictor.progress = prog; }); counter = 0; } // only download if file isn't already here BOOL fileExists = [manager fileExistsAtPath:destFile]; // check if we already have it if (!fileExists) { NSError *error = nil; // jpg or folder check if ([[destFile pathExtension] isEqualToString:@"jpg"]) { NSURL *url = [NSURL URLWithString:srcFile]; NSData *data = [NSData dataWithContentsOfURL:url options:0 error:&error]; [data writeToFile:destFile options:NSDataWritingAtomic error:&error]; } else { [manager createDirectoryAtPath:destFile withIntermediateDirectories:YES attributes:nil error:&error]; } } } } }中，当个人下载完成后，您的记忆将被解除分配。

{{1}}

Answer 2

您可能希望重构此代码以使用NSOperationQueue。这解决了峰值内存问题，但也让您享受一定程度的并发性。因为iOS无论如何只允许4-5个并发请求，所以您希望将最大并发操作数限制为合理的数量，如果尝试运行过多的并发请求，这可以减轻网络超时风险。（此maxConcurrentOperationCount功能是我建议使用操作队列的主要原因。）

无论如何，这可能看起来像：

-(void)loadImagesFromList:(NSArray *)theArray
             sourceBundle:(NSString *)bundlePath
               destBundle:(NSString *)localBundlePath
                  manager:(NSFileManager *)manager {

    // initialize the progress and activity indicator
    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        // your UI update here
    }];

    int   __block counter = 0;
    float __block prog = 0;
    float increment = 1.0 / [theArray count];
    float stepSize = [theArray count] / 10;

    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    queue.maxConcurrentOperationCount = 4;

    for (NSString *file in theArray)
    {
        [queue addOperationWithBlock:^{
            if (stopFlag) {
                NSLog(@"I see stopFlag = true, counter = %d, prog = %f", counter, prog);
                return;
            }

            NSString *srcFile = [bundlePath stringByAppendingPathComponent:file];
            NSString *destFile = [localBundlePath stringByAppendingPathComponent:file];

            [[NSOperationQueue mainQueue] addOperationWithBlock:^{
                counter += 1;
                prog += increment;
                if (counter == stepSize) {
                    self.progressIndictor.progress = prog;
                    counter = 0;
                }
            }];

            // only download if file isn't already here
            BOOL fileExists = [manager fileExistsAtPath:destFile]; // check if we already have it
            if (!fileExists) {
                NSError *error = nil;

                // jpg or folder check
                if ([[destFile pathExtension] isEqualToString:@"jpg"]) {
                    NSURL *url = [NSURL URLWithString:srcFile];
                    NSData *data = [NSData dataWithContentsOfURL:url
                                                         options:0
                                                           error:&error];

                    [data writeToFile:destFile options:NSDataWritingAtomic error:&error];
                } else {
                    [manager createDirectoryAtPath:destFile withIntermediateDirectories:YES attributes:nil error:&error];
                }
            }
        }];
    }
}

我可能会建议其他一些改进（例如，实现取消逻辑而不是查看stopFlag），但我试图最小化代码更改。我只是利用了一个可以轻松替换dispatch_async的事实：

dispatch_async(dispatchQueue, ^{ ... });

使用NSOperationQueue方法addOperationWithBlock：

[operationQueue addOperationWithBlock:^{ ... }];

但是现在我们可以使用并发NSOperationQueue和maxConcurrentOperationCount的4或5，你会突然享受一个很好的，受限制的并发度。您可能会发现这比按顺序下载文件要快得多。

内存泄漏在循环中使用dataWithContentsOfURL

2 个答案: