问类方法中的@sychronized

EN

@implementation MyObject {

}

@synthesize data = _data;


- (instancetype)init
{
    self = [super init];
    if (self) {
    }
    return self;
}

// these methods are the only ones to be used for managing the MyObject life cycle

+ (NSMutableDictionary *)objectsDict
{
    static NSMutableDictionary *map = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        map = [NSMutableDictionary new];
    });
    return map;
}

+ (MyObject *)getRefrenceForId:(NSString *)identifier
{
    return [[MyObject objectsDict] objectForKey:identifier];
}

+ (MyObject *)newRefrenceWithId:(NSString *)identifier
{
    MyObject *obj;
    @synchronized (self) {
        obj = [[MyObject objectsDict] objectForKey:identifier];

        if (obj == nil) {
            obj = [[MyObject alloc] init];
            obj.identifier = identifier;
            [[MyObject objectsDict] setObject:obj forKey:identifier];
            NSLog(@"new instance of MyObject created with id:%@",identifier);  
        }

    }
    return  obj;
}

+ (MyObject *)newRefrenceWithId:(NSString *)identifier andClassType:(Class)classType
{
    MyObject *obj;
    @synchronized (self) {
        obj = [[MyObject objectsDict] objectForKey:identifier];

        if (obj == nil) {
            obj = [[MyObject alloc] initWithClassType:classType andId:identifier];
            [[MyObject objectsDict] setObject:obj forKey:identifier];
            NSLog(@"new instance of MyObject created with id:%@ of ClassType :%@",identifier,NSStringFromClass(classType));
        }
    }
    return obj;
}

+ (void)deleteInstance:(NSString *)identifier
{
    @synchronized (self) {
        [[MyObject objectsDict] removeObjectForKey:identifier];
    }
}

+ (void)clearAllMyObjectsFromMap
{
    @synchronized (self) {
        [[MyObject objectsDict] removeAllObjects];
    }
}