一 初識(shí) dispatch_semaphore_t signal
//傳遞的參數(shù)是信號(hào)量最初值,下面例子的信號(hào)量最初值是1
dispatch_semaphore_t signal = dispatch_semaphore_create(1);
dispatch_time_t overTime = dispatch_time(DISPATCH_TIME_NOW, 5 * NSEC_PER_SEC);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// 當(dāng)信號(hào)量是0的時(shí)候,dispatch_semaphore_wait(signal, overTime);這句代碼會(huì)一直等待直到overTime超時(shí).
//這里信號(hào)量是1 所以不會(huì)在這里發(fā)生等待.
dispatch_semaphore_wait(signal, overTime);
NSLog(@"需要線程同步的操作1 開始");
sleep(2);
NSLog(@"需要線程同步的操作1 結(jié)束");
long signalValue = dispatch_semaphore_signal(signal);//這句代碼會(huì)使信號(hào)值 增加1
//并且會(huì)喚醒一個(gè)線程去開始繼續(xù)工作,如果喚醒成功,那么返回一個(gè)非零的數(shù),如果沒有喚醒,那么返回 0
NSLog(@"%ld",signalValue);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(1);
dispatch_semaphore_wait(signal, overTime);
NSLog(@"需要線程同步的操作2");
dispatch_semaphore_signal(signal);
long signalValue = dispatch_semaphore_signal(signal);
NSLog(@"%ld",signalValue);
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
sleep(1);
dispatch_semaphore_wait(signal, overTime);
NSLog(@"需要線程同步的操作3");
dispatch_semaphore_signal(signal);
long signalValue = dispatch_semaphore_signal(signal);
NSLog(@"%ld",signalValue);
});
二 實(shí)戰(zhàn):利用 dispatch_semaphore_t signal 組織一個(gè)并發(fā)數(shù)是10 的一個(gè)多線程工作隊(duì)列.
dispatch_group_t group = dispatch_group_create();
dispatch_semaphore_t semaphore = dispatch_semaphore_create(10);
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
for (int i = 0; i < 100; i++)
{
dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER);
//注意這里信號(hào)量從10開始遞減,并不會(huì)阻塞循環(huán).循環(huán)10次,遞減到0的時(shí)候,開始阻塞.
NSLog(@"-------");
dispatch_group_async(group, queue, ^{
NSLog(@"%i",i);
sleep(1);
dispatch_semaphore_signal(semaphore);
});//創(chuàng)建一個(gè)新線程,并在線程結(jié)束后,發(fā)送信號(hào)量,通知阻塞的循環(huán)繼續(xù)創(chuàng)建新線程.
}
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
如此循環(huán)就形成了對(duì)并發(fā)的控制，如上就是一個(gè)并發(fā)數(shù)為10的一個(gè)線程隊(duì)列。
三 實(shí)戰(zhàn):利用 dispatch_semaphore_t signal 組織一個(gè)生產(chǎn)消費(fèi)模式
__block int product = 0;
dispatch_semaphore_t sem = dispatch_semaphore_create(0);
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //消費(fèi)者隊(duì)列
while (1) {
if(!dispatch_semaphore_wait(sem, dispatch_time(DISPATCH_TIME_NOW, DISPATCH_TIME_FOREVER))){
////非 0的時(shí)候,就是成功的timeout了,這里判斷就是沒有timeout 成功的時(shí)候是 0
NSLog(@"消費(fèi)%d產(chǎn)品",product);
product--;
};
}
});
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ //生產(chǎn)者隊(duì)列
while (1) {
sleep(1); //wait for a while
product++;
NSLog(@"生產(chǎn)%d產(chǎn)品",product);
dispatch_semaphore_signal(sem);
}
});
打印如下:
2016-07-08 11:31:58.266 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:31:58.267 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:31:59.269 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:31:59.270 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:00.270 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:00.270 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:01.270 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:01.271 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:02.276 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:02.276 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:03.280 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:03.281 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:04.286 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:04.286 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:05.290 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:05.291 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:06.295 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:06.295 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:07.298 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:07.298 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:08.300 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:08.301 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:09.306 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:09.306 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:10.311 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:10.311 TestS[481:129600] 消費(fèi)1產(chǎn)品
2016-07-08 11:32:11.316 TestS[481:129603] 生產(chǎn)1產(chǎn)品
2016-07-08 11:32:11.316 TestS[481:129600] 消費(fèi)1產(chǎn)品
