線程安全的NSMutableArray

NSMutableArray本身是線程不安全的生均。多線程訪問(wèn)NSMutableArray 會(huì)出現(xiàn)異常和Crash

一、不能使用atomic 修飾屬性

原因：atomic 的內(nèi)存管理語(yǔ)義是原子性的，僅保證了屬性的setter和getter方法是原子性的感昼，是線程安全的赡矢，但是屬性的其他方法，不能保證線程安全饱须。同時(shí)atomic 效率低域醇，編程時(shí)慎用。

二蓉媳、打造線程安全的NSMutableArray

1譬挚、讀寫(xiě)數(shù)組時(shí)加鎖
2、讀寫(xiě)數(shù)組放到串行隊(duì)列中酪呻。
3减宣、使用并發(fā)隊(duì)列，結(jié)合GCD的攔珊塊(barrier)來(lái)實(shí)現(xiàn)線程同步玩荠。

第三種實(shí)現(xiàn)方式：

@interface QSThreadSafeMutableArray : NSMutableArray

@end

//QSThreadSafeMutableArray.m
#import "QSThreadSafeMutableArray.h"
@interface QSThreadSafeMutableArray()

@property (nonatomic, strong) dispatch_queue_t syncQueue;
@property (nonatomic, strong) NSMutableArray* array;

@end

@implementation QSThreadSafeMutableArray

#pragma mark - init 方法
- (instancetype)initCommon{

    self = [super init];
    if (self) {
        //%p 以16進(jìn)制的形式輸出內(nèi)存地址漆腌，附加前綴0x
        NSString* uuid = [NSString stringWithFormat:@"com.jzp.array_%p", self];
        //注意：_syncQueue是并行隊(duì)列
        _syncQueue = dispatch_queue_create([uuid UTF8String], DISPATCH_QUEUE_CONCURRENT);
    }
    return self;
}

- (instancetype)init{

    self = [self initCommon];
    if (self) {
        _array = [NSMutableArray array];
    }
    return self;
}

//其他init方法略

#pragma mark - 數(shù)據(jù)操作方法 (凡涉及更改數(shù)組中元素的操作，使用異步派發(fā)+柵欄塊阶冈；讀取數(shù)據(jù)使用 同步派發(fā)+并行隊(duì)列)
- (NSUInteger)count{

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

- (id)objectAtIndex:(NSUInteger)index{

    __block id obj;
    dispatch_sync(_syncQueue, ^{
        if (index < [_array count]) {
            obj = _array[index];
        }
    });
    return obj;
}

- (NSEnumerator *)objectEnumerator{

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

- (void)insertObject:(id)anObject atIndex:(NSUInteger)index{

    dispatch_barrier_async(_syncQueue, ^{
        if (anObject && index < [_array count]) {
            [_array insertObject:anObject atIndex:index];
        }
    });
}

- (void)addObject:(id)anObject{

    dispatch_barrier_async(_syncQueue, ^{
        if(anObject){
           [_array addObject:anObject];
        }
    });
}

- (void)removeObjectAtIndex:(NSUInteger)index{

    dispatch_barrier_async(_syncQueue, ^{

        if (index < [_array count]) {
            [_array removeObjectAtIndex:index];
        }
    });
}

- (void)removeLastObject{

    dispatch_barrier_async(_syncQueue, ^{
        [_array removeLastObject];
    });
}

- (void)replaceObjectAtIndex:(NSUInteger)index withObject:(id)anObject{

    dispatch_barrier_async(_syncQueue, ^{
        if (anObject && index < [_array count]) {
            [_array replaceObjectAtIndex:index withObject:anObject];
        }
    });
}

- (NSUInteger)indexOfObject:(id)anObject{

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

- (void)dealloc{

    if (_syncQueue) {
        _syncQueue = NULL;
    }
}
@end

參考：
NSMutableArray使用中忽視的問(wèn)題
dispatch_async與dispatch_sync區(qū)別
GCD有關(guān)問(wèn)題:dispatch_sync(dispatch_get_main_queue(), ^{NSLog(@"Hello ?");}); 死鎖的原因
dispatch_barrier_sync 和dispatch_barrier_async的區(qū)別
iOS多線程-GCD之串行隊(duì)列和并行隊(duì)列