调用 -[NSRunLoop runUntilDate:] 是个好主意吗? [英] Is calling -[NSRunLoop runUntilDate:] a good idea?

问题描述

通常调用 -[NSRunLoop runUntilDate:] 是个好主意吗?它似乎没有任何问题地工作，但是告诉运行循环从运行循环内运行让我感到紧张.

Is it generally a good idea to call -[NSRunLoop runUntilDate:]? It seems to work without any issues, but it makes me nervous to tell the run loop to run from within the run loop.

更多信息:

我现在有一个从 REST 服务获取数据的项目.需要获取的一项关键信息是具有有效数据的日期范围.这是一个非常小的数据，只需要获取一次，所以我决定处理它的最佳方法是如果局部变量为 nil，则让属性下载数据.我正在使用 ASIHTTPRequest 和一个 ASINetworkQueue，所以默认情况下一切都是异步的，为了让它工作，这个属性在数据下载之前不能返回并处理.这是我的代码大纲，为了保护无辜，变量的名称已更改:

I have a project right now that is fetching data from a REST service. One critical piece of information that needs to be obtained is the range of dates with valid data. It's a very small bit of data that only needs to be gotten once, so I decided that the best way to handle it is to have the property download the data if the local variable is nil. I'm using ASIHTTPRequest and an ASINetworkQueue, so everything is asynchronous by default, and in order for this to work, this property can't return until the data has been downloaded and processed. Here's an outline of my code, the names of variables have been changed to protect the innocent:

__block BOOL isWorking = YES;
__block ASIHTTPRequest *request = [[[ASIHTTPRequest alloc] initWithURL:/*actual URL*/] autorelease];
[request setCompletionBlock:^{
    // set local variable
    isWorking = NO;
}];
[request setFailedBlock:^{
    // show alert to user
    isWorking = NO;
}];
[queue addOperation:request];

while (isWorking) {
    [[NSRunLoop currentRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
}

同样，这似乎工作正常.使用这种方法有什么潜在问题吗?

Again, this seems to be working fine. Are there any potential issues with using this approach?

推荐答案

您必须确保不要从您正在调用的运行循环可能调用的任何方法中执行此操作，除非重叠调用树完全重新参赛者.

You have to make sure not to do this from any method that could be called by the run loop you are invoking, unless the overlapping call tree is completely re-entrant.

Cocoa Touch UI 代码没有记录为可重入(事实上，Apple DTS 有警告/提示表明它不是)，因此如果您的提取数据处理程序可以通过 UI 方法以任何方式调用(或其他可在 UI 运行循环中调用的不可重入代码)，不推荐从其内部调用 UI 运行循环.

The Cocoa Touch UI code is not documented as re-entrant (in fact, there are warnings/hints from Apple DTS that it is not), so if your fetch data handler can in any way be called by a UI method (or other non-reentrant code that could be called in the UI run loop), calling the UI run loop from inside it is not recommended.

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