Perform disk cache out operations asynchronousely in order to prevent from blocking the main runloop when a lot of cache queries are performed at the same time

Author: Olivier Poitrey

SDImageCache.h

@@ -7,12 +7,13 @@
  */
 
 #import <Foundation/Foundation.h>
+#import "SDImageCacheDelegate.h"
 
 @interface SDImageCache : NSObject
 {
     NSMutableDictionary *memCache, *storeDataQueue;
     NSString *diskCachePath;
-    NSOperationQueue *cacheInQueue;
+    NSOperationQueue *cacheInQueue, *cacheOutQueue;
 }
 
 + (SDImageCache *)sharedImageCache;
@@ -21,6 +22,8 @@
 - (void)storeImage:(UIImage *)image imageData:(NSData *)data forKey:(NSString *)key toDisk:(BOOL)toDisk;
 - (UIImage *)imageFromKey:(NSString *)key;
 - (UIImage *)imageFromKey:(NSString *)key fromDisk:(BOOL)fromDisk;
+- (void)queryDiskCacheForKey:(NSString *)key delegate:(id <SDImageCacheDelegate>)delegate userInfo:(NSDictionary *)info;
+
 - (void)removeImageForKey:(NSString *)key;
 - (void)clearMemory;
 - (void)clearDisk;

SDImageCache.m

@@ -39,7 +39,9 @@ - (id)init
 
         // Init the operation queue
         cacheInQueue = [[NSOperationQueue alloc] init];
-        cacheInQueue.maxConcurrentOperationCount = 2;
+        cacheInQueue.maxConcurrentOperationCount = 1;
+        cacheOutQueue = [[NSOperationQueue alloc] init];
+        cacheOutQueue.maxConcurrentOperationCount = 1;
 
         // Subscribe to app events
         [[NSNotificationCenter defaultCenter] addObserver:self
@@ -134,6 +136,45 @@ - (void)storeKeyToDisk:(NSString *)key
     [fileManager release];
 }
 
+- (void)notifyDelegate:(NSDictionary *)arguments
+{
+    NSString *key = [arguments objectForKey:@"key"];
+    id <SDImageCacheDelegate> delegate = [arguments objectForKey:@"delegate"];
+    NSDictionary *info = [arguments objectForKey:@"userInfo"];
+    UIImage *image = [arguments objectForKey:@"image"];
+
+    if (image)
+    {
+        [memCache setObject:image forKey:key];
+
+        if ([delegate respondsToSelector:@selector(imageCache:didFindImage:forKey:userInfo:)])
+        {
+            [delegate imageCache:self didFindImage:image forKey:key userInfo:info];
+        }
+    }
+    else
+    {
+        if ([delegate respondsToSelector:@selector(imageCache:didNotFindImageForKey:userInfo:)])
+        {
+            [delegate imageCache:self didNotFindImageForKey:key userInfo:info];
+        }
+    }
+}
+
+- (void)queryDiskCacheOperation:(NSDictionary *)arguments
+{
+    NSString *key = [arguments objectForKey:@"key"];
+    NSMutableDictionary *mutableArguments = [[arguments mutableCopy] autorelease];
+
+    UIImage *image = [[[UIImage alloc] initWithContentsOfFile:[self cachePathForKey:key]] autorelease];
+    if (image)
+    {
+        [mutableArguments setObject:image forKey:@"image"];
+    }
+
+    [self performSelectorOnMainThread:@selector(notifyDelegate:) withObject:mutableArguments waitUntilDone:NO];
+}
+
 #pragma mark ImageCache
 
 - (void)storeImage:(UIImage *)image imageData:(NSData *)data forKey:(NSString *)key toDisk:(BOOL)toDisk
@@ -154,7 +195,6 @@ - (void)storeImage:(UIImage *)image imageData:(NSData *)data forKey:(NSString *)
     {
         [storeDataQueue setObject:data forKey:key];
         [cacheInQueue addOperation:[[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(storeKeyToDisk:) object:key] autorelease]];
-
     }
 }
 
@@ -185,17 +225,54 @@ - (UIImage *)imageFromKey:(NSString *)key fromDisk:(BOOL)fromDisk
 
     if (!image && fromDisk)
     {
-        image = [[UIImage alloc] initWithContentsOfFile:[self cachePathForKey:key]];
-        if (image != nil)
+        image = [[[UIImage alloc] initWithContentsOfFile:[self cachePathForKey:key]] autorelease];
+        if (image)
         {
             [memCache setObject:image forKey:key];
-            [image autorelease];
         }
     }
 
     return image;
 }
 
+- (void)queryDiskCacheForKey:(NSString *)key delegate:(id <SDImageCacheDelegate>)delegate userInfo:(NSDictionary *)info
+{
+    if (!delegate)
+    {
+        return;
+    }
+
+    if (!key)
+    {
+        if ([delegate respondsToSelector:@selector(imageCache:didNotFindImageForKey:userInfo:)])
+        {
+            [delegate imageCache:self didNotFindImageForKey:key userInfo:info];
+        }
+        return;
+    }
+
+    // First check the in-memory cache...
+    UIImage *image = [memCache objectForKey:key];
+    if (image)
+    {
+        // ...notify delegate immediately, no need to go async
+        if ([delegate respondsToSelector:@selector(imageCache:didFindImage:forKey:userInfo:)])
+        {
+            [delegate imageCache:self didFindImage:image forKey:key userInfo:info];
+        }
+        return;
+    }
+
+    NSMutableDictionary *arguments = [NSMutableDictionary dictionaryWithCapacity:3];
+    [arguments setObject:key forKey:@"key"];
+    [arguments setObject:delegate forKey:@"delegate"];
+    if (info)
+    {
+        [arguments setObject:info forKey:@"userInfo"];
+    }
+    [cacheOutQueue addOperation:[[[NSInvocationOperation alloc] initWithTarget:self selector:@selector(queryDiskCacheOperation:) object:arguments] autorelease]];
+}
+
 - (void)removeImageForKey:(NSString *)key
 {
     if (key == nil)

SDImageCacheDelegate.h

@@ -0,0 +1,19 @@
+//
+//  SDImageCacheDelegate.h
+//  Dailymotion
+//
+//  Created by Olivier Poitrey on 16/09/10.
+//  Copyright 2010 Dailymotion. All rights reserved.
+//
+
+#import <UIKit/UIKit.h>
+
+@class SDImageCache;
+
+@protocol SDImageCacheDelegate <NSObject>
+
+@optional
+- (void)imageCache:(SDImageCache *)imageCache didFindImage:(UIImage *)image forKey:(NSString *)key userInfo:(NSDictionary *)info;
+- (void)imageCache:(SDImageCache *)imageCache didNotFindImageForKey:(NSString *)key userInfo:(NSDictionary *)info;
+
+@end

SDWebImageManager.h

@@ -9,8 +9,9 @@
 #import <UIKit/UIKit.h>
 #import "SDWebImageDownloaderDelegate.h"
 #import "SDWebImageManagerDelegate.h"
+#import "SDImageCacheDelegate.h"
 
-@interface SDWebImageManager : NSObject <SDWebImageDownloaderDelegate>
+@interface SDWebImageManager : NSObject <SDWebImageDownloaderDelegate, SDImageCacheDelegate>
 {
     NSMutableArray *delegates;
     NSMutableArray *downloaders;

SDWebImageManager.m

@@ -46,29 +46,24 @@ + (id)sharedManager
     return instance;
 }
 
+/**
+ * @deprecated
+ */
 - (UIImage *)imageWithURL:(NSURL *)url
 {
     return [[SDImageCache sharedImageCache] imageFromKey:[url absoluteString]];
 }
 
 - (void)downloadWithURL:(NSURL *)url delegate:(id<SDWebImageManagerDelegate>)delegate
 {
-    if (url == nil || [failedURLs containsObject:url])
+    if (!url || !delegate || [failedURLs containsObject:url])
     {
         return;
     }
 
-    // Share the same downloader for identical URLs so we don't download the same URL several times
-    SDWebImageDownloader *downloader = [downloaderForURL objectForKey:url];
-
-    if (!downloader)
-    {
-        downloader = [SDWebImageDownloader downloaderWithURL:url delegate:self];
-        [downloaderForURL setObject:downloader forKey:url];
-    }
-
-    [delegates addObject:delegate];
-    [downloaders addObject:downloader];
+    // Check the on-disk cache async so we don't block the main thread
+    NSDictionary *info = [NSDictionary dictionaryWithObjectsAndKeys:delegate, @"delegate", url, @"url", nil];
+    [[SDImageCache sharedImageCache] queryDiskCacheForKey:[url absoluteString] delegate:self userInfo:info];
 }
 
 - (void)cancelForDelegate:(id<SDWebImageManagerDelegate>)delegate
@@ -95,6 +90,37 @@ - (void)cancelForDelegate:(id<SDWebImageManagerDelegate>)delegate
     [downloader release];
 }
 
+#pragma mark SDImageCacheDelegate
+
+- (void)imageCache:(SDImageCache *)imageCache didFindImage:(UIImage *)image forKey:(NSString *)key userInfo:(NSDictionary *)info
+{
+    id<SDWebImageManagerDelegate> delegate = [info objectForKey:@"delegate"];
+    if ([delegate respondsToSelector:@selector(webImageManager:didFinishWithImage:)])
+    {
+        [delegate performSelector:@selector(webImageManager:didFinishWithImage:) withObject:self withObject:image];
+    }
+}
+
+- (void)imageCache:(SDImageCache *)imageCache didNotFindImageForKey:(NSString *)key userInfo:(NSDictionary *)info
+{
+    NSURL *url = [info objectForKey:@"url"];
+    id<SDWebImageManagerDelegate> delegate = [info objectForKey:@"delegate"];
+
+    // Share the same downloader for identical URLs so we don't download the same URL several times
+    SDWebImageDownloader *downloader = [downloaderForURL objectForKey:url];
+
+    if (!downloader)
+    {
+        downloader = [SDWebImageDownloader downloaderWithURL:url delegate:self];
+        [downloaderForURL setObject:downloader forKey:url];
+    }
+
+    [delegates addObject:delegate];
+    [downloaders addObject:downloader];
+}
+
+#pragma mark SDWebImageDownloaderDelegate
+
 - (void)imageDownloader:(SDWebImageDownloader *)downloader didFinishWithImage:(UIImage *)image
 {
     [downloader retain];

UIImageView+WebCache.m

@@ -23,31 +23,11 @@ - (void)setImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder
     // Remove in progress downloader from queue
     [manager cancelForDelegate:self];
 
-    UIImage *cachedImage = nil;
-    if (url)
-    {
-        cachedImage = [manager imageWithURL:url];
-    }
-    else
-    {
-        self.image = placeholder;
-    }
+    self.image = placeholder;
 
-    if (cachedImage)
-    {
-        self.image = cachedImage;
-    }
-    else
+    if (url)
     {
-        if (placeholder)
-        {
-            self.image = placeholder;
-        }
-
-        if (url)
-        {
-            [manager downloadWithURL:url delegate:self];
-        }
+        [manager downloadWithURL:url delegate:self];
     }
 }