同步和異步：
同步：囂張跋扈漩勤，立刻馬上執(zhí)行笙以，如果我沒執(zhí)行完淌实，大家都別執(zhí)行
異步：謙虛禮讓，我沒有執(zhí)行猖腕，其他人可以執(zhí)行
1）同步 + 并發(fā):不開線程拆祈，串行執(zhí)行（同步函數(shù)霸道，執(zhí)行完start倘感，必須把同步函數(shù)的任務(wù)執(zhí)行完放坏，再執(zhí)行end）。
NSLog(@"----%@",[NSThread currentThread] );
//1,創(chuàng)建隊(duì)列
/*參數(shù)1老玛，C語(yǔ)言的字符串淤年，標(biāo)簽
參數(shù)2，隊(duì)列類型
DISPATCH_QUEUE_CONCURRENT 并發(fā)
DISPATCH_QUEUE_SERIAL 串行
*/
// dispatch_queue_t queue = dispatch_queue_create("fff", DISPATCH_QUEUE_CONCURRENT);
//獲得全局并發(fā)隊(duì)列逻炊，參數(shù)1互亮，優(yōu)先級(jí)
//1,獲取并發(fā)隊(duì)列，
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
NSLog(@"start");
//2,同步函數(shù)把任務(wù)添加到隊(duì)列
dispatch_sync(queue, ^{
NSLog(@"download1---%@",[NSThread currentThread]);
});
dispatch_sync(queue, ^{
NSLog(@"download2---%@",[NSThread currentThread]);
});
dispatch_sync(queue, ^{
NSLog(@"download3---%@",[NSThread currentThread]);
});
NSLog(@"end");
Snip20170327_7.png
2）異步 + 并發(fā) ：開多條線程余素，隊(duì)列任務(wù)并發(fā)執(zhí)行(異步函數(shù)謙讓，執(zhí)行完start炊昆，可以先執(zhí)行end桨吊，再執(zhí)行異步函數(shù)的任務(wù)）
NSLog(@"----%@",[NSThread currentThread] );
//1,獲取并發(fā)隊(duì)列，
dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
NSLog(@"start");
//2,異步函數(shù)把任務(wù)添加到隊(duì)列
dispatch_async(queue, ^{
NSLog(@"download1---%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"download2---%@",[NSThread currentThread]);
});
dispatch_async(queue, ^{
NSLog(@"download3---%@",[NSThread currentThread]);
});
NSLog(@"end");
Snip20170327_8.png
