preface

Last time we ran the use of GCD functions and saw deadlocks through the understanding of serial queues and concurrent queues. This time we look at the relationship between GCD functions and queues

I. Main queue analysis

Queues are divided into serial queues and parallel queues

Serial queue:dispatch_queue_t serial = dispatch_queue_create("test", DISPATCH_QUEUE_SERIAL);
Concurrent queue:dispatch_queue_t conque = dispatch_queue_create("test", DISPATCH_QUEUE_CONCURRENT);
The home side columns:dispatch_queue_t mainQueue = dispatch_get_main_queue();
Global queue:dispatch_queue_t globQueue =dispatch_get_global_queue(0, 0);

Find libDispatch-1271.120.2 through BT print source analysis GCD

Search dispatch_get_main_queue through the libDispatch source code

_dispatch_main_q

Find the name by printing the main queue

Search globally for com.apple.main-thread

Dq_atomic_flags = DQF_WIDTH(1),.dq_serialNum = 1, so it is a serial queue

Serial and concurrent underlying source identification

Both serial and parallel queues are created using dispatch_queue_CREATE. Let’s examine the source code below

Enter the _dispatch_lane_create_with_target

Dqai_concurrent? Is passed through the _dispatch_queue_init function. DISPATCH_QUEUE_WIDTH_MAX: 1 Go to dispatch_queue_init and let’s see

So DQF_WIDTH =1 is a serial queue and it has nothing to do with dq_serialNum =1

dq_serialnum =os_atomic_inc_orig(&_dispatch_queue_serial_numbers, relaxed)

So what’s dispatch_queue_serial_numbers

What’s DISPATCH_QUEUE_SERIAL_NUMBER_INIT

The following method does the prioritization

Serial queuingNULLThe reason is whendqaiforNULLDirectly return whendqai

Three.GCD underlying source inheritance chain

Print com.apple.root.default-qos through BT

Search com.apple.root.default-qos through libDispatch source code

Dispatch_queue_t and I’ll go in

DISPATCH_DECL corresponds in the source code

#define DISPATCH_DECL(name) \
typedef struct name##_s : public dispatch_object_s {} *name##_t
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DISPATCH_DECL(dispatch_queue);

typedef struct dispatch_queue_s : public dispatch_object_s {} *dispatch_queue_t

Equivalent to dispatch_queue_t-> dispatch_queue_S ->dispatch_object_s-> _OS_OBJect_s ->dispatch_object_t class->objc_object

All of themdispatch_object_tThis type of

Four.MT and KS interview questions

- (void)MTDemo{

    while(self.num < 5) {

        dispatch_async(dispatch_get_global_queue(0.0), ^{

            self.num++;

        });

    }
    NSLog(@"end : %d",self.num); / / > = 5 results
}
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- (void)KSDemo{

   

    for(int i= 0; i<10000; i++) {

        dispatch_async(dispatch_get_global_queue(0.0), ^{

            self.num++;

        });

    }

    NSLog(@"end : %d",self.num); / / < = 10000

}
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