Swiftgram/SSignalKit/SQueue.m

#import "SQueue.h"

static const void *SQueueSpecificKey = &SQueueSpecificKey;

@interface SQueue ()
{
    dispatch_queue_t _queue;
    void *_queueSpecific;
    bool _specialIsMainQueue;
}

@end

@implementation SQueue

+ (SQueue *)mainQueue
{
    static SQueue *queue = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
    {
        queue = [[SQueue alloc] initWithNativeQueue:dispatch_get_main_queue() queueSpecific:NULL];
        queue->_specialIsMainQueue = true;
    });
    
    return queue;
}

+ (SQueue *)concurrentDefaultQueue
{
    static SQueue *queue = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
    {
        queue = [[SQueue alloc] initWithNativeQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) queueSpecific:NULL];
    });
    
    return queue;
}

+ (SQueue *)concurrentBackgroundQueue
{
    static SQueue *queue = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^
    {
        queue = [[SQueue alloc] initWithNativeQueue:dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0) queueSpecific:NULL];
    });
    
    return queue;
}

- (instancetype)init
{
    dispatch_queue_t queue = dispatch_queue_create(NULL, NULL);
    dispatch_queue_set_specific(queue, SQueueSpecificKey, (__bridge void *)self, NULL);
    return [self initWithNativeQueue:queue queueSpecific:(__bridge void *)self];
}

- (instancetype)initWithNativeQueue:(dispatch_queue_t)queue queueSpecific:(void *)queueSpecific
{
    self = [super init];
    if (self != nil)
    {
        _queue = queue;
        _queueSpecific = queueSpecific;
    }
    return self;
}

- (dispatch_queue_t)_dispatch_queue
{
    return _queue;
}

- (void)dispatch:(dispatch_block_t)block
{
    dispatch_async(_queue, block);
}

- (void)dispatchSync:(dispatch_block_t)block
{
    if (_queueSpecific != NULL && dispatch_get_specific(SQueueSpecificKey) == _queueSpecific)
        block();
    else if (_specialIsMainQueue && [NSThread isMainThread])
        block();
    else
        dispatch_sync(_queue, block);
}

@end