我们知道遍历数组是一个相对耗时的操作,而同时手机的核是越来越多,所以我们需要充分利用iOS多核的作用.
特别是在遍历操作中还有其他耗时操作.像我们平时直接遍历数组的操作
for (NSInteger i= 0,i< 100,i++){
//do something
}
这样的代码不会随着手机的不断升级而提高效率.
但是利用GCD可以实现充分利用多核.并且随着手机不断升级,同样的代码,执行效率会自动提高,十分OK.下面提供两种常用方法.
NSArray* arr =@[@"1",@"2",@"3",@"4",@"5"];
dispatch_queue_tqueue =dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT,0);
dispatch_group_tgroup =dispatch_group_create();
for(NSIntegeri =0; i < arr.count; i++) {
NSLog(@"%ld",(long)i);
dispatch_group_async(group, queue, ^{
sleep(5);
NSLog(@"%ld -- %@",(long)i,[NSThreadcurrentThread]);
});
}
//dispatch_group_wait(group, DISPATCH_TIME_FOREVER);//等待queue任务执行完,才往下走;
dispatch_group_notify(group, queue, ^{//往下走,回调block
NSLog(@"group end");
});
NSLog(@"end”);
2016-07-26 15:59:09.566学习之路[4448:1770686] 0
2016-07-26 15:59:09.566学习之路[4448:1770686] 1
2016-07-26 15:59:09.566学习之路[4448:1770686] 2
2016-07-26 15:59:09.567学习之路[4448:1770686] 3
2016-07-26 15:59:09.567学习之路[4448:1770686] 4
2016-07-26 15:59:09.567学习之路[4448:1770686] end
2016-07-26 15:59:14.569学习之路[4448:1772333] 4 -- {number = 6, name = (null)}
2016-07-26 15:59:14.569学习之路[4448:1772330] 1 -- {number = 2, name = (null)}
2016-07-26 15:59:14.569学习之路[4448:1771326] 0 -- {number = 3, name = (null)}
2016-07-26 15:59:14.569学习之路[4448:1772332] 3 -- {number = 5, name = (null)}
2016-07-26 15:59:14.569学习之路[4448:1772331] 2 -- {number = 4, name = (null)}
2016-07-26 15:59:14.570学习之路[4448:1772331] group end
dispatch group 只能异步,并且不会在主线程走任务
NSArray* arr =@[@"1",@"2",@"3",@"4",@"5"];
dispatch_apply([arrcount],dispatch_get_global_queue(0,0), ^(size_tindex) {
sleep(1);
NSLog(@"%@ %@",arr[index],[NSThreadcurrentThread]);
});
NSLog(@"end”);
dispatch_apply它以指定的次数将指定的Block加入到指定的队列中,并等待队列中操作全部完成,NSLog(@"end”)在上面任务执行完才会执行
2016-07-26 16:00:58.106学习之路[4463:1787375] 2 {number = 4, name = (null)}
2016-07-26 16:00:58.106学习之路[4463:1787363] 3 {number = 2, name = (null)}
2016-07-26 16:00:58.106学习之路[4463:1787587] 4 {number = 3, name = (null)}
2016-07-26 16:00:58.106学习之路[4463:1787047] 1 {number = 1, name = main}
2016-07-26 16:00:59.110学习之路[4463:1787375] 5 {number = 4, name = (null)}
2016-07-26 16:00:59.110学习之路[4463:1787047] end
dispatch apply 是同步的,可以在主线程走任务,如果想异步可以在外面包一层
NSArray* arr =@[@"1",@"2",@"3",@"4",@"5"];
dispatch_async(dispatch_get_global_queue(0,0), ^{
dispatch_apply([arrcount],dispatch_get_global_queue(0,0), ^(size_tindex) {
sleep(1);
NSLog(@"%@ %@",arr[index],[NSThreadcurrentThread]);
});
});
NSLog(@"end");
}
但是这样效果就和dispatch group一样了,不会在主线程走任务
