我們知道遍歷數組是一個相對耗時的操作,而同時手機的核是越來越多,所以我們需要充分利用iOS多核的作用.
特別是在遍歷操作中還有其他耗時操作.像我們平時直接遍歷數組的操作
for (NSInteger i= 0,i< 100,i++){
//do something
}
這樣的代碼不會隨著手機的不斷升級而提高效率.
但是利用GCD可以實現充分利用多核.并且隨著手機不斷升級,同樣的代碼,執行效率會自動提高,十分OK.下面提供兩種常用方法.
NSArray * arr = @[@"1",@"2",@"3",@"4",@"5"];
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_group_t group = dispatch_group_create();
for (NSInteger i = 0; i < arr.count; i++) {
NSLog(@"%ld",(long)i);
dispatch_group_async(group, queue, ^{
sleep(5);
NSLog(@"%ld -- %@",(long)i,[NSThread currentThread]);
});
}
//dispatch_group_wait(group, DISPATCH_TIME_FOREVER);// 等待queue任務執行完,才往下走;
dispatch_group_notify(group, queue, ^{ // 往下走,回調block
NSLog(@"group end");
});
NSLog(@"end”);
2016-07-26 15:59:09.566 ****學習之路****[4448:1770686] 0
2016-07-26 15:59:09.566 ****學習之路****[4448:1770686] 1
2016-07-26 15:59:09.566 ****學習之路****[4448:1770686] 2
2016-07-26 15:59:09.567 ****學習之路****[4448:1770686] 3
2016-07-26 15:59:09.567 ****學習之路****[4448:1770686] 4
2016-07-26 15:59:09.567 ****學習之路****[4448:1770686] end
2016-07-26 15:59:14.569 ****學習之路****[4448:1772333] 4 -- <NSThread: 0x7fc412631120>{number = 6, name = (null)}
2016-07-26 15:59:14.569 ****學習之路****[4448:1772330] 1 -- <NSThread: 0x7fc4124bf8e0>{number = 2, name = (null)}
2016-07-26 15:59:14.569 ****學習之路****[4448:1771326] 0 -- <NSThread: 0x7fc4126255e0>{number = 3, name = (null)}
2016-07-26 15:59:14.569 ****學習之路****[4448:1772332] 3 -- <NSThread: 0x7fc41261d900>{number = 5, name = (null)}
2016-07-26 15:59:14.569 ****學習之路****[4448:1772331] 2 -- <NSThread: 0x7fc4124bb230>{number = 4, name = (null)}
2016-07-26 15:59:14.570 ****學習之路****[4448:1772331] group end
dispatch group 只能異步,并且不會在主線程走任務
NSArray * arr = @[@"1",@"2",@"3",@"4",@"5"];
dispatch_apply([arr count], dispatch_get_global_queue(0, 0), ^(size_t index) {
sleep(1);
NSLog(@"%@ %@",arr[index],[NSThread currentThread]);
});
NSLog(@"end”);
dispatch_apply它以指定的次數將指定的Block加入到指定的隊列中,并等待隊列中操作全部完成,NSLog(@"end”)在上面任務執行完才會執行
2016-07-26 16:00:58.106 ****學習之路****[4463:1787375] 2 <NSThread: 0x7f98fa61aff0>{number = 4, name = (null)}
2016-07-26 16:00:58.106 ****學習之路****[4463:1787363] 3 <NSThread: 0x7f98fa61e680>{number = 2, name = (null)}
2016-07-26 16:00:58.106 ****學習之路****[4463:1787587] 4 <NSThread: 0x7f98fa747a00>{number = 3, name = (null)}
2016-07-26 16:00:58.106 ****學習之路****[4463:1787047] 1 <NSThread: 0x7f98fa402c30>{number = 1, name = main}
2016-07-26 16:00:59.110 ****學習之路****[4463:1787375] 5 <NSThread: 0x7f98fa61aff0>{number = 4, name = (null)}
2016-07-26 16:00:59.110 ****學習之路****[4463:1787047] end
dispatch apply 是同步的,可以在主線程走任務,如果想異步可以在外面包一層
NSArray * arr = @[@"1",@"2",@"3",@"4",@"5"];
dispatch_async(dispatch_get_global_queue(0, 0), ^{
dispatch_apply([arr count], dispatch_get_global_queue(0, 0), ^(size_t index) {
sleep(1);
NSLog(@"%@ %@",arr[index],[NSThread currentThread]);
});
});
NSLog(@"end");
}
但是這樣效果就和dispatch group一樣了,不會在主線程走任務
