iOS中有一些类在多线程下操作是不安全的，比如我们常使用的可变类型：NSMutableArray，NSMutableDictnory,NSMutableString...，我们可以通过CGD对这些类进行构建，使这些类在多线程下的操作达到安全的目的。

使用同步串行队列构建

@interface LockArray : NSObject
@property (nonatomic,readonly,assign) NSUInteger count;
- (id)objectAtIndex:(NSUInteger)index;
- (NSEnumerator *)objectEnumerator;

- (void)addObject:(id)anObject;
- (void)insertObject:(id)anObject atIndex:(NSUInteger)index;

- (void)removeObjectAtIndex:(NSUInteger)index;
- (void)removeLastObject;

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject;
- (NSUInteger)indexOfObject:(id)anObject;
@end

#import "LockArray.h"

@interface LockArray ()
@property (nonatomic, strong) NSMutableArray *array;

@property (nonatomic, strong) dispatch_queue_t dispatchQueue;

@end
@implementation LockArray
- (instancetype)init{
    if (self) {
        NSString* queueid = [NSString stringWithFormat:@"com.lock.array_%p", self];
        _dispatchQueue = dispatch_queue_create([queueid UTF8String], DISPATCH_QUEUE_SERIAL);
        _array = [NSMutableArray array];
    }
    return self;
}

-(NSUInteger)count
{
    __block NSUInteger count;
    dispatch_sync(_dispatchQueue, ^{
        count = _array.count;
    });
    return count;
}

- (id)objectAtIndex:(NSUInteger)index{
    __block id obj;
    dispatch_sync(_dispatchQueue, ^{
        if (index < [_array count]) {
            obj = _array[index];
        }
    });
    return obj;
}

- (NSEnumerator *)objectEnumerator{
    __block NSEnumerator *enu;
    dispatch_sync(_dispatchQueue, ^{
        enu = [_array objectEnumerator];
    });
    return enu;
}

- (void)insertObject:(id)anObject atIndex:(NSUInteger)index{
    dispatch_sync(_dispatchQueue, ^{
        if (anObject && index < [_array count]) {
            [_array insertObject:anObject atIndex:index];
        }
    });
    
}

- (void)addObject:(id)anObject{
    dispatch_sync(_dispatchQueue, ^{
        if(anObject){
            [_array addObject:anObject];
        }
    });
}

- (void)removeObjectAtIndex:(NSUInteger)index{
    dispatch_sync(_dispatchQueue, ^{
        if (index < [_array count]) {
            [_array removeObjectAtIndex:index];
        }
    });
}

- (void)removeLastObject{
    dispatch_sync(_dispatchQueue, ^{
        [_array removeLastObject];

    });
}

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject{
    dispatch_sync(_dispatchQueue, ^{
        if (anObject && index < [_array count]) {
            [_array replaceObjectAtIndex:index withObject:anObject];
        }
    });
}

- (NSUInteger)indexOfObject:(id)anObject{
    
    __block NSUInteger index = NSNotFound;
    dispatch_sync(_dispatchQueue, ^{
        for (int i = 0; i < [_array count]; i ++) {
            if ([_array objectAtIndex:i] == anObject) {
                index = i;
                break;
            }
        }
    });
    
    return index;
}

- (void)dealloc{
    if (_dispatchQueue) {
        _dispatchQueue = NULL;
    }
}
@end

同步串行队列虽然可以达到线程安全的目的，但效率没那么高，如果能将同步与异步派发结合起来，实现与普通加锁机制一样的同步行为，又不会阻塞执行异步派发的线程，效率会比单纯的同步要好

并发队列结合栅栏块

当我们进行读的操作时使用同步执行，当进行写的操作时使用异步栅栏

@interface HLockArray : NSObject
@property (nonatomic,readonly,assign) NSUInteger count;
- (id)objectAtIndex:(NSUInteger)index;
- (NSEnumerator *)objectEnumerator;

- (void)addObject:(id)anObject;
- (void)insertObject:(id)anObject atIndex:(NSUInteger)index;

- (void)removeObjectAtIndex:(NSUInteger)index;
- (void)removeLastObject;

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject;
- (NSUInteger)indexOfObject:(id)anObject;
@end

@interface HLockArray ()
@property (nonatomic, strong) NSMutableArray *array;

@property (nonatomic, strong) dispatch_queue_t dispatchQueue;
@end
@implementation HLockArray
- (instancetype)init{
    if (self) {
        NSString* queueid = [NSString stringWithFormat:@"com.lock.array_%p", self];
        _dispatchQueue = dispatch_queue_create([queueid UTF8String], DISPATCH_QUEUE_SERIAL);
        _array = [NSMutableArray array];
    }
    return self;
}

- (NSUInteger)count{
    __block NSUInteger count;
    dispatch_sync(_dispatchQueue, ^{
        count = _array.count;
    });
    return count;
}

- (id)objectAtIndex:(NSUInteger)index{
    __block id obj;
    dispatch_sync(_dispatchQueue, ^{
        if (index < [_array count]) {
            obj = _array[index];
        }
    });
    return obj;
}

- (NSEnumerator *)objectEnumerator{
    __block NSEnumerator *enu;
    dispatch_sync(_dispatchQueue, ^{
        enu = [_array objectEnumerator];
    });
    return enu;
}

- (void)insertObject:(id)anObject atIndex:(NSUInteger)index{
    dispatch_barrier_async(_dispatchQueue, ^{
        if (anObject && index < [_array count]) {
            [_array insertObject:anObject atIndex:index];
        }
    });
}

- (void)addObject:(id)anObject{
    dispatch_barrier_async(_dispatchQueue, ^{
        if(anObject){
            [_array addObject:anObject];
        }
    });
}

- (void)removeObjectAtIndex:(NSUInteger)index{
    dispatch_barrier_async(_dispatchQueue, ^{
        
        if (index < [_array count]) {
            [_array removeObjectAtIndex:index];
        }
    });
}

- (void)removeLastObject{
    dispatch_barrier_async(_dispatchQueue, ^{
        [_array removeLastObject];
    });
}

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject{
    dispatch_barrier_async(_dispatchQueue, ^{
        if (anObject && index < [_array count]) {
            [_array replaceObjectAtIndex:index withObject:anObject];
        }
    });
}

- (NSUInteger)indexOfObject:(id)anObject{
    __block NSUInteger index = NSNotFound;
    dispatch_sync(_dispatchQueue, ^{
        for (int i = 0; i < [_array count]; i ++) {
            if ([_array objectAtIndex:i] == anObject) {
                index = i;
                break;
            }
        }
    });
    return index;
}

- (void)dealloc{
    if (_dispatchQueue) {
        _dispatchQueue = NULL;
    }
}

参考文章：
Cocoa线程安全／非线程安全的类和函数汇总
大牛们是如何构建一个线程安全的字典的!
关于NSMutableArray线程安全的思考和实现