Merge pull request SDWebImage#3460 from dreampiggy/feat/ioqueue_concurrent_config

Added `ioQueueAttributes` to use concurrent or control QoS for image cache internal IO Queue

Author: dreampiggy

SDWebImage/Core/SDImageCache.m

@@ -109,14 +109,16 @@ - (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
     if ((self = [super init])) {
         NSAssert(ns, @"Cache namespace should not be nil");
 
-        // Create IO serial queue
-        _ioQueue = dispatch_queue_create("com.hackemist.SDImageCache", DISPATCH_QUEUE_SERIAL);
-        
         if (!config) {
             config = SDImageCacheConfig.defaultCacheConfig;
         }
         _config = [config copy];
 
+        // Create IO queue
+        dispatch_queue_attr_t ioQueueAttributes = _config.ioQueueAttributes;
+        _ioQueue = dispatch_queue_create("com.hackemist.SDImageCache", ioQueueAttributes);
+        NSAssert(_ioQueue, @"The IO queue should not be nil. Your configured `ioQueueAttributes` may be wrong");
+        
         // Init the memory cache
         NSAssert([config.memoryCacheClass conformsToProtocol:@protocol(SDMemoryCache)], @"Custom memory cache class must conform to `SDMemoryCache` protocol");
         _memoryCache = [[config.memoryCacheClass alloc] initWithConfig:_config];

SDWebImage/Core/SDImageCacheConfig.h

@@ -127,6 +127,15 @@ typedef NS_ENUM(NSUInteger, SDImageCacheConfigExpireType) {
  */
 @property (strong, nonatomic, nullable) NSFileManager *fileManager;
 
+/**
+ * The dispatch queue attr for ioQueue. You can config the QoS and concurrent/serial to internal IO queue. The ioQueue is used by SDImageCache to access read/write for disk data.
+ * Defaults we use `DISPATCH_QUEUE_SERIAL`(NULL), to use serial dispatch queue to ensure single access for disk data. It's safe but may be slow.
+ * @note You can override this to use `DISPATCH_QUEUE_CONCURRENT`, use concurrent queue.
+ * @warning **MAKE SURE** to keep `diskCacheWritingOptions` to use `NSDataWritingAtomic`, or concurrent queue may cause corrupted disk data (because multiple threads read/write same file without atomic is not IO-safe).
+ * @note This value does not support dynamic changes. Which means further modification on this value after cache initialized has no effect.
+ */
+@property (strong, nonatomic, nullable) dispatch_queue_attr_t ioQueueAttributes;
+
 /**
  * The custom memory cache class. Provided class instance must conform to `SDMemoryCache` protocol to allow usage.
  * Defaults to built-in `SDMemoryCache` class.

SDWebImage/Core/SDImageCacheConfig.m

@@ -35,6 +35,8 @@ - (instancetype)init {
         _maxDiskAge = kDefaultCacheMaxDiskAge;
         _maxDiskSize = 0;
         _diskCacheExpireType = SDImageCacheConfigExpireTypeModificationDate;
+        _fileManager = nil;
+        _ioQueueAttributes = DISPATCH_QUEUE_SERIAL; // NULL
         _memoryCacheClass = [SDMemoryCache class];
         _diskCacheClass = [SDDiskCache class];
     }
@@ -56,6 +58,7 @@ - (id)copyWithZone:(NSZone *)zone {
     config.maxMemoryCount = self.maxMemoryCount;
     config.diskCacheExpireType = self.diskCacheExpireType;
     config.fileManager = self.fileManager; // NSFileManager does not conform to NSCopying, just pass the reference
+    config.ioQueueAttributes = self.ioQueueAttributes; // Pass the reference
     config.memoryCacheClass = self.memoryCacheClass;
     config.diskCacheClass = self.diskCacheClass;
 

Tests/Tests/SDImageCacheTests.m

@@ -650,6 +650,27 @@ - (void)test47DiskCacheExtendedData {
     [self waitForExpectationsWithCommonTimeout];
 }
 
+- (void)test48CacheUseConcurrentIOQueue {
+    XCTestExpectation *expectation = [self expectationWithDescription:@"SDImageCache concurrent ioQueue"];
+    expectation.expectedFulfillmentCount = 2;
+    
+    SDImageCacheConfig *config = [SDImageCacheConfig new];
+    dispatch_queue_attr_t attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_CONCURRENT, QOS_CLASS_BACKGROUND, 0);
+    config.ioQueueAttributes = attr;
+    
+    SDImageCache *cache = [[SDImageCache alloc] initWithNamespace:@"Concurrent" diskCacheDirectory:@"/" config:config];
+    NSData *pngData = [NSData dataWithContentsOfFile:[self testPNGPath]];
+    [cache queryCacheOperationForKey:@"Key1" done:^(UIImage * _Nullable image, NSData * _Nullable data, SDImageCacheType cacheType) {
+        expect(data).beNil();
+        [expectation fulfill];
+    }];
+    [cache storeImageData:pngData forKey:@"Key1" completion:^{
+        [expectation fulfill];
+    }];
+    
+    [self waitForExpectationsWithCommonTimeout];
+}
+
 #pragma mark - SDImageCache & SDImageCachesManager
 - (void)test49SDImageCacheQueryOp {
     XCTestExpectation *expectation = [self expectationWithDescription:@"SDImageCache query op works"];