大牛们是如何构建一个线程安全的字典的！

/**
 线程安全的字典
 */
@interface OSSSyncMutableDictionary : NSObject
@property (nonatomic, strong) NSMutableDictionary *dictionary;
@property (nonatomic, strong) dispatch_queue_t dispatchQueue;

- (id)objectForKey:(id)aKey;
- (NSArray *)allKeys;
- (void)setObject:(id)anObject forKey:(id )aKey;
- (void)removeObjectForKey:(id)aKey;
@end

@implementation OSSSyncMutableDictionary

- (instancetype)init {
    if (self = [super init]) {
        _dictionary = [NSMutableDictionary new];
        _dispatchQueue = dispatch_queue_create("com.aliyun.aliyunsycmutabledictionary", DISPATCH_QUEUE_SERIAL);
    }

    return self;
}

- (NSArray *)allKeys {
    __block NSArray *allKeys = nil;
    dispatch_sync(self.dispatchQueue, ^{
        allKeys = [self.dictionary allKeys];
    });
    return allKeys;
}

- (id)objectForKey:(id)aKey {
    __block id returnObject = nil;

    dispatch_sync(self.dispatchQueue, ^{
        returnObject = [self.dictionary objectForKey:aKey];
    });

    return returnObject;
}

- (void)setObject:(id)anObject forKey:(id )aKey {
    dispatch_sync(self.dispatchQueue, ^{
        [self.dictionary setObject:anObject forKey:aKey];
    });
}

- (void)removeObjectForKey:(id)aKey {
    dispatch_sync(self.dispatchQueue, ^{
        [self.dictionary removeObjectForKey:aKey];
    });
}

@end

看不懂的话，请留言我！！！