Fix the thread-safe issue for coders manager. Use lock and immutable object to k…

…eep `addCoder`, `removeCoder` thread-safe.

@@ -39,7 +39,7 @@
 /**
  All coders in coders manager. The coders array is a priority queue, which means the later added coder will have the highest priority
  */
-@property (nonatomic, strong, readwrite, nullable) NSArray<id<SDWebImageCoder>> *coders;
+@property (nonatomic, copy, readwrite, nullable) NSArray<id<SDWebImageCoder>> *coders;
 
 /**
  Add a new coder to the end of coders array. Which has the highest priority.

@@ -13,10 +13,12 @@
 #import "SDWebImageWebPCoder.h"
 #endif
 
+#define LOCK(lock) dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
+#define UNLOCK(lock) dispatch_semaphore_signal(lock);
+
 @interface SDWebImageCodersManager ()
 
-@property (strong, nonatomic, nonnull) NSMutableArray<SDWebImageCoder>* mutableCoders;
-@property (strong, nonatomic, nullable) dispatch_queue_t mutableCodersAccessQueue;
+@property (nonatomic, strong, nonnull) dispatch_semaphore_t codersLock;
 
 @end
 
@@ -34,11 +36,12 @@
 - (instancetype)init {
     if (self = [super init]) {
         // initialize with default coders
-        _mutableCoders = [@[[SDWebImageImageIOCoder sharedCoder]] mutableCopy];
+        NSMutableArray<id<SDWebImageCoder>> *mutableCoders = [@[[SDWebImageImageIOCoder sharedCoder]] mutableCopy];
 #ifdef SD_WEBP
-        [_mutableCoders addObject:[SDWebImageWebPCoder sharedCoder]];
+        [mutableCoders addObject:[SDWebImageWebPCoder sharedCoder]];
 #endif
-        _mutableCodersAccessQueue = dispatch_queue_create("com.hackemist.SDWebImageCodersManager", DISPATCH_QUEUE_CONCURRENT);
+        _coders = [mutableCoders copy];
+        _codersLock = dispatch_semaphore_create(1);
     }
     return self;
 }
@@ -46,36 +49,36 @@
 #pragma mark - Coder IO operations
 
 - (void)addCoder:(nonnull id<SDWebImageCoder>)coder {
-    if ([coder conformsToProtocol:@protocol(SDWebImageCoder)]) {
-        dispatch_barrier_sync(self.mutableCodersAccessQueue, ^{
-            [self.mutableCoders addObject:coder];
-        });
+    if (![coder conformsToProtocol:@protocol(SDWebImageCoder)]) {
+        return;
     }
+    LOCK(self.codersLock);
+    NSMutableArray<id<SDWebImageCoder>> *mutableCoders = [self.coders mutableCopy];
+    if (!mutableCoders) {
+        mutableCoders = [NSMutableArray array];
+    }
+    [mutableCoders addObject:coder];
+    self.coders = [mutableCoders copy];
+    UNLOCK(self.codersLock);
 }
 
 - (void)removeCoder:(nonnull id<SDWebImageCoder>)coder {
-    dispatch_barrier_sync(self.mutableCodersAccessQueue, ^{
-        [self.mutableCoders removeObject:coder];
-    });
-}
-
-- (NSArray<id<SDWebImageCoder>> *)coders {
-    __block NSArray<id<SDWebImageCoder>> *sortedCoders = nil;
-    dispatch_sync(self.mutableCodersAccessQueue, ^{
-        sortedCoders = (NSArray<id<SDWebImageCoder>> *)[[[self.mutableCoders copy] reverseObjectEnumerator] allObjects];
-    });
-    return sortedCoders;
-}
-
-- (void)setCoders:(NSArray<id<SDWebImageCoder>> *)coders {
-    dispatch_barrier_sync(self.mutableCodersAccessQueue, ^{
-        self.mutableCoders = [coders mutableCopy];
-    });
+    if (![coder conformsToProtocol:@protocol(SDWebImageCoder)]) {
+        return;
+    }
+    LOCK(self.codersLock);
+    NSMutableArray<id<SDWebImageCoder>> *mutableCoders = [self.coders mutableCopy];
+    [mutableCoders removeObject:coder];
+    self.coders = [mutableCoders copy];
+    UNLOCK(self.codersLock);
 }
 
 #pragma mark - SDWebImageCoder
 - (BOOL)canDecodeFromData:(NSData *)data {
-    for (id<SDWebImageCoder> coder in self.coders) {
+    LOCK(self.codersLock);
+    NSArray<id<SDWebImageCoder>> *coders = self.coders;
+    UNLOCK(self.codersLock);
+    for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canDecodeFromData:data]) {
             return YES;
         }
@@ -84,7 +87,10 @@
 }
 
 - (BOOL)canEncodeToFormat:(SDImageFormat)format {
-    for (id<SDWebImageCoder> coder in self.coders) {
+    LOCK(self.codersLock);
+    NSArray<id<SDWebImageCoder>> *coders = self.coders;
+    UNLOCK(self.codersLock);
+    for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canEncodeToFormat:format]) {
             return YES;
         }
@@ -93,10 +99,10 @@
 }
 
 - (UIImage *)decodedImageWithData:(NSData *)data {
-    if (!data) {
-        return nil;
-    }
-    for (id<SDWebImageCoder> coder in self.coders) {
+    LOCK(self.codersLock);
+    NSArray<id<SDWebImageCoder>> *coders = self.coders;
+    UNLOCK(self.codersLock);
+    for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canDecodeFromData:data]) {
             return [coder decodedImageWithData:data];
         }
@@ -110,7 +116,10 @@
     if (!image) {
         return nil;
     }
-    for (id<SDWebImageCoder> coder in self.coders) {
+    LOCK(self.codersLock);
+    NSArray<id<SDWebImageCoder>> *coders = self.coders;
+    UNLOCK(self.codersLock);
+    for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canDecodeFromData:*data]) {
             return [coder decompressedImageWithImage:image data:data options:optionsDict];
         }
@@ -122,7 +131,10 @@
     if (!image) {
         return nil;
     }
-    for (id<SDWebImageCoder> coder in self.coders) {
+    LOCK(self.codersLock);
+    NSArray<id<SDWebImageCoder>> *coders = self.coders;
+    UNLOCK(self.codersLock);
+    for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canEncodeToFormat:format]) {
             return [coder encodedDataWithImage:image format:format];
         }