使用 GCD 在块内赋值

发布于 2024-11-09 14:04:57 字数 785 浏览 0 评论 0原文

我正在执行一个不断从网站寻找更新的线程。应该可以在某些视图中设置刷新率。

更新线程不断检查更新间隔。但我想避免竞争条件。（我什至需要担心 GCD 的这个问题吗？）

//This variable is used to avoid race conditions, refreshRate is a instance variable
int threadRefreshRate = refreshRate;
BOOL autoRefresh = YES;


dispatch_async(autoUpdateQueue, ^ { 
    while(YES){
        NSLog(@"Runs autoupdate thread");
        dispatch_async(dispatch_get_main_queue(), ^{

            if(autoRefresh){
                [self checkForUpdate];
                //Trying to set thread variable to avoid race condition
                threadRefreshRate = refreshRate;
            }
            else
                NSLog(@"Should not auto refresh");
        });
        sleep(threadRefreshRate);
    }

});

我尝试实现这段代码。但是，它无法在块内分配“线程”变量。

原文

Im executing a thread that keeps looking for updates from a web site. It should be possible to set the refresh rate in some view.

The update thread keeps checking for a updated interval. But I would like to avoid race conditions. (Do I even have to worry for this with GCD?)

//This variable is used to avoid race conditions, refreshRate is a instance variable
int threadRefreshRate = refreshRate;
BOOL autoRefresh = YES;


dispatch_async(autoUpdateQueue, ^ { 
    while(YES){
        NSLog(@"Runs autoupdate thread");
        dispatch_async(dispatch_get_main_queue(), ^{

            if(autoRefresh){
                [self checkForUpdate];
                //Trying to set thread variable to avoid race condition
                threadRefreshRate = refreshRate;
            }
            else
                NSLog(@"Should not auto refresh");
        });
        sleep(threadRefreshRate);
    }

});

I tried to implement this code. However it doesn't work to assing the 'thread'-variable within a block.

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暗地喜欢 2024-11-16 14:04:57

对于您给出的代码类型，我将使用队列上引发的计时器事件，而不是在代码中进行显式睡眠。这样你就不必担心竞争条件等。

queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
if (!timer) return;
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), refreshRate * NSEC_PER_SEC, 5 * NSEC_PER_SEC);
dispatch_source_t timer = self.timer;
//initialize self to blockSelf with __block
self.timerAction = ^{
[blockSelf checkForUpdate];
};

dispatch_source_set_event_handler(timer, timerAction);
dispatch_resume(timer);

当 autoRefresh 设置为 NO 时，你可以通过以下方式取消它：

dispatch_source_cancel(timer);

For the kind of code you have given, i would use the timer events raised on the queue instead doing explicit sleep in the code. This way you dont have to worry about the race conditions etc..

queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0);
self.timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
if (!timer) return;
dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), refreshRate * NSEC_PER_SEC, 5 * NSEC_PER_SEC);
dispatch_source_t timer = self.timer;
//initialize self to blockSelf with __block
self.timerAction = ^{
[blockSelf checkForUpdate];
};

dispatch_source_set_event_handler(timer, timerAction);
dispatch_resume(timer);

When the autoRefresh is set to NO, you can cancel it by