-( void ) setSafeObject:( id ) object forKey:( NSString *) bindingKey @synchronized ( self .dic) { if (bindingKey && object){ [ self .dic setObject:object forKey:bindingKey]; -( void ) testSyncizedDictionary for ( int i = 0 ; i < 1000000 ; i++) { dispatch_async (dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0 ), ^{ //多线程写 [ self setSafeObject:[ NSString stringWithFormat: @"86+111111111 %i" , i] forKey:KEY]; //主线程读 NSString *result = [ self getSafeObjectForKey:KEY]; NSLog ( @"get string: %@, length : %lu" , result, result.length);

原因分析:程序还没执行到 NSLog 那一行的时候， get 出来的一个值,在多线程中执行了 set 方法执行导致 key 对应的 result 对释放掉了。此时执行到 NSLog ,导致了崩溃.

修改方案:

	//主线程读
	NSString *result = [[self getSafeObjectForKey:KEY] retain];
	NSLog(@"get string: %@, length : %lu", result, result.length);
	[result release];
在读取的时候retain一下，后续在release,还是会崩溃。因为在retain之前很可能野掉了，此时retain也只是对野掉的的指针
二. 最终修改方案
#pragma mark- 用GCD的方式去实现
-(id) getRightObjectForKey:(NSString *) bindingKey
    if (!bindingKey) {
        return nil;
    __block id result = nil;
    dispatch_sync(self.ioQueue, ^{
        result = [[_dic objectForKey:bindingKey] retain]; //关键点1
    return [result autorelease]; //关键点2
-(void) setRightObject:(id) object forKey:(NSString*) bindingKey
    bindingKey = [bindingKey copy];
    dispatch_barrier_async(self.ioQueue, ^{
        if(bindingKey && object){
            [_dic setObject:object forKey:bindingKey];
-(void) testSyncizedDictionaryRight
    for (int i = 0; i < 1000000; i++) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //多线程写
            [self setRightObject:[NSString stringWithFormat:@"86+111111111   %i", i] forKey:KEY];
        //主线程读
        NSString *result = [[self getRightObjectForKey:KEY] retain];
        NSLog(@"get string: %@, length : %lu", result, result.length);
        [result release];
请看关键点1和关键点2，如果没有retain和autorelease,还是会崩溃。原因同上。
ARC下:
怎么操作都不崩溃。不过还是建议写法
@property(nonatomic,strong) NSMutableDictionary *dic;  
@property(nonatomic,strong) dispatch_queue_t ioQueue;
self.ioQueue = dispatch_queue_create("ioQueue", DISPATCH_QUEUE_CONCURRENT);  
self.dic = [NSMutableDictionary dictionaryWithCapacity:1];
#pragma mark- 用GCD的方式去实现
-(id) getRightObjectForKey:(NSString *) bindingKey
    if (!bindingKey) {
        return nil;
    __block id result = nil;
    dispatch_sync(self.ioQueue, ^{
        result = [_dic objectForKey:bindingKey];     	    });
    return result;
-(void) setRightObject:(id) object forKey:(NSString*) bindingKey
    bindingKey = [bindingKey copy];
    dispatch_barrier_async(self.ioQueue, ^{
        if(bindingKey && object){
            [_dic setObject:object forKey:bindingKey];
-(void) testSyncizedDictionaryRight
    for (int i = 0; i < 1000000; i++) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //多线程写
            [self setRightObject:[NSString stringWithFormat:@"86+111111111   %i", i] forKey:KEY];
        //主线程读
        NSString *result = [self getRightObjectForKey:KEY];
        NSLog(@"get string: %@, length : %lu", result, result.length);
三. 异步读写
创建一个串行队列。然后gcd结合锁去执行
@property(nonatomic,strong) dispatch_queue_t asynModelQueue;
self.asynModelQueue = dispatch_queue_create("AsynModelQueue", DISPATCH_QUEUE_SERIAL);
#pragma mark- 用GCD去异步读写
-(void) getAsyncRightObjectForKey:(NSString *) bindingKey block:(void(^)(NSMutableDictionary* modelDicCache)) modelCallBack
    if (!bindingKey && modelCallBack) {
        modelCallBack(nil);
        return;
    __block id result = nil;
    dispatch_async(self.asynModelQueue, ^{
        @synchronized(self) {//@synchronized是为了多一层保护
            result = [_dic objectForKey:bindingKey];     //由于self.bindingInfo重写过，此处不能用self.bindingInfo，否则造成死锁
            modelCallBack(result);
-(void) setAsyncRightObject:(id) object forKey:(NSString*) bindingKey
    bindingKey = [bindingKey copy];
    dispatch_barrier_async(self.asynModelQueue, ^{
        @synchronized(self) {//@synchronized是为了多一层保护
            if(bindingKey && object){
                [_dic setObject:object forKey:bindingKey];
-(void) testAsyncSyncizedDictionaryRight
    for (int i = 0; i < 1000000; i++) {
        dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
            //多线程写
            [self setRightObject:[NSString stringWithFormat:@"86+111111111   %i", i] forKey:KEY];
        //主线程读
        NSString *result = [self getRightObjectForKey:KEY];
        NSLog(@"get string: %@, length : %lu", result, result.length);
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