GCD多线程—串行、并行、同步、异步线程数目

一、串行队列

1、同步运行

dispatch_queue_t queue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_sync(queue, ^{
    NSLog(@"当前线程---%@",[NSThread currentThread]);
});
//结果打印
当前线程---<NSThread: 0x600000441480>{number = 1, name = main}

结论：串行队列-同步运行，不会开启新的线程，线程函数会在创建队列所在的线程中执行（如上，在主线程中创建串行队列，同步线程函数在主线程中执行）

2、异步运行

dispatch_queue_t queue = dispatch_queue_create("serialQueue", DISPATCH_QUEUE_SERIAL);
dispatch_async(queue, ^{
    NSLog(@"当前线程1---%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"当前线程2---%@",[NSThread currentThread]);
});
//结果打印
当前线程1---<NSThread: 0x600002f3e380>{number = 3, name = (null)}
当前线程2---<NSThread: 0x600002f3e380>{number = 3, name = (null)}

结论：串行队列-异步运行，会开启新的线程，但无论有几个异步函数(dispatch_async)，都只开启一个线程

二、并行队列

1、同步运行

dispatch_queue_t queue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_sync(queue, ^{
    NSLog(@"当前线程---%@",[NSThread currentThread]);
});
//结果打印
当前线程---<NSThread: 0x600000b11480>{number = 1, name = main}

结论：并行队列-同步运行，不会开启新的线程

2、异步运行

dispatch_queue_t queue = dispatch_queue_create("concurrentQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^{
    NSLog(@"当前线程1---%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
    NSLog(@"当前线程2---%@",[NSThread currentThread]);
});
//结果打印
当前线程1---<NSThread: 0x600001d0c500>{number = 3, name = (null)}
当前线程2---<NSThread: 0x600001df2540>{number = 4, name = (null)}

结论：并行队列-异步执行：会开启新的线程，且有几个异步函数(dispatch_async)，就开启几个线程

结论.png