Need to download 50,000 images or more - ios

Question

Currently, i am downloading multiple images with below code. In My app need to download 50,000 images or more.
When memory consumption reaches to 600 MB application crash due to memory pressure.
When I download 10K images its working fine.But when I want to download 20K images from a server then after downloading 9-10K images application crash due to memory pressure.
I also try to Instrument to find memory leak but there is no memory leak.
In Debug Session (When download 20K images) :
Memory Consumption : 500-600 MB and After that its crash.
CPU Usage : 130 -160%
Can you please help me what I did wrong in my code?
- (void)Downloadimages:(NSMutableArray *)aMutArray
{
//newchange
SDImageCache *imageCache = [SDImageCache sharedImageCache];
[imageCache clearMemory];
[imageCache clearDisk];
// NSLog(#"DocumentsDirectory Path : %#", DocumentsDirectory);
NSMutableURLRequest *urlRequest = [[NSMutableURLRequest alloc] init];
static AFURLSessionManager *sessionManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
sessionManager = [[AFURLSessionManager alloc] initWithSessionConfiguration:sessionConfiguration];
});
__block int iCounter = 0;
for (NSInteger aIndex = 0; aIndex < aMutArray.count; aIndex++)
{
NSURLRequest *req = [NSURLRequest requestWithURL:[NSURL URLWithString:aMutArray[aIndex]] cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:(aMutArray.count * 120)];
// urlRequest = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:aMutArray[aIndex]] cachePolicy:NSURLRequestReloadIgnoringLocalAndRemoteCacheData timeoutInterval:100];
//NSLog(#"%#",urlRequest);
// [urlRequest setTimeoutInterval:(aMutArray.count * 120)];
NSURLSessionDownloadTask *downloadTask = [sessionManager downloadTaskWithRequest:req progress:nil destination:^NSURL *(NSURL *targetPath, NSURLResponse *response)
{
return [NSURL fileURLWithPath:[DocumentsDirectory stringByAppendingPathComponent:urlRequest.URL.lastPathComponent]];
}
completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error)
{
iCounter ++;
if (!error){
// NSLog(#"(%ld) SUCCESS : %#",(long)aIndex, aMutArray[aIndex]);
}
else
{
NSLog(#"(%ld) ERROR : %#",(long)aIndex, aMutArray[aIndex]);
// [CommonMethod DeleteImageWithName:filePath.lastPathComponent];
}
[labelSyncProducts setText:[NSString stringWithFormat:#"Syncing Images %d of %lu", iCounter, (unsigned long)aMutArray.count]];
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantPast]];
if (aMutArray.count == iCounter)
{
[self controlsEnableDisable:true];
}
}];
[downloadTask resume];
}
}

Answer 1

I will suggest you not to download this many images in the app, this will increase your app size on device.
Even though you want to do, then this is the solution.
As you know, every image you download will store temporary in RAM. As number of images increases RAM occupation increases. At one point RAM will full and app terminates.
For solving this, Download some images and save them. After saving, remove this images from RAM and start downloading some more images and save them.
Continue this process until you are done with all images.
This may solve your problem.

Answer 2

The problem is not in the amount of images to download, Download task does not use memory to hold images, but rather just save the image directly to sandbox which is fine. But the problem here lies in the concurrent NSURLSession that you run. Imagine you have 50,000 NSURLSession tasks in memory. That is what make the app crash.
for (NSInteger aIndex = 0; aIndex < 50000; aIndex++)
{
// NSURLSESSION BLOCK
}
What you need to do is a queued downloads. You need to handle this by yourself. For example, at one time, download 10 images first, then after 10 is done, then download next 10 and so on. But... it is crazy really. Who would want to wait for 50,000 images to be downloaded???