//问题效率低，传入对象必须等待之前的锁执行完成之后才能执行，无法达到异步的效果
-(void) synchronizedMethod{
    NSObject *obj = [[NSObject alloc]init];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        @synchronized (self) { //锁self
            NSLog(@"同步操作开始！");
            sleep(3);
            NSLog(@"同步操作结束！");
       }
    });
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 1), ^{
        sleep(2);
        @synchronized (obj) {//锁obj
            NSLog(@"同步操作2");
        }
    });
}

//.h
#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@interface GCDAccessor : NSObject
-(id)readWithGCD:(id(^)(void))readBlock;
-(void)writeWithGCD:(void(^)(void))writeBlock;
@end

NS_ASSUME_NONNULL_END


//.m

#import "GCDAccessor.h"

@interface GCDAccessor ()
@property(nonatomic,strong) dispatch_queue_t syncQueue;
@end


@implementation GCDAccessor
//串行同步队列
-(instancetype)init{
    self = [super init];
    if (self != nil) {
        _syncQueue = dispatch_queue_create("accessor", DISPATCH_QUEUE_CONCURRENT);
    }
    return self;
}

-(id)readWithGCD:(id(^)(void))readBlock{
    __block id readValue = nil;
    dispatch_sync(_syncQueue, ^{
        readValue = readBlock();
    });
    return readValue;
}

-(void)writeWithGCD:(void(^)(void))writeBlock{
    dispatch_barrier_async(_syncQueue, writeBlock);
}

@interface ViewController ()<WKNavigationDelegate>
@property (nonatomic,readonly) GCDAccessor *testDataAccessor;
@property (nonatomic) NSMutableDictionary <NSString *,NSString *>* testDic;

@end

- (void)initData{
    _testDataAccessor = [[GCDAccessor alloc]init];
    self.testDic = [NSMutableDictionary<NSString*,NSString*> dictionary];
}

-(void)settestDicWithString:(NSString *)str andKey:(NSString*)key{
    [_testDataAccessor writeWithGCD:^{
        self.testDic = [NSMutableDictionary dictionaryWithObject:str forKey:key];
    }];
}
-(NSString *)gettestDicWithString:(NSString *)str{
    return [_testDataAccessor readWithGCD:^id _Nonnull{
        return self.testDic[str];
    }];
}