是UIGraphicsBeginImageContext线程安全吗？

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所以我一直觉得UIGraphicsBeginImageContext是线程安全的，可以从任何线程调用来创建一个新的CGContextRef，可以用来绘制。

So I've been under the impression that UIGraphicsBeginImageContext is thread safe, and can be called from any thread to create a new CGContextRef that can be used to draw.

但是，目前的文档说明

您应该从您的主线程调用此函数应用程序。

但是，在WWDC 2012会话视频构建并发用户界面背景，并在后台调用该方法：

However, in the WWDC 2012 session video "Building Concurrent User Interfaces", the speaker shows that you can actually draw in the background, and call that method in the background:

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你可以看到，他向一个 _queue （在BG线程上运行）添加一个操作，它调用 renderedGraphOfSize ，它调用 UIGraphicsBeginImageContext 。那么什么交易？我在我的应用程序中遇到一些崩溃，当它涉及到在后台绘制，所以我不知道为什么有困惑的例子从苹果。

So as you can see, he adds an operation to a _queue (which runs on a BG thread), which calls renderedGraphOfSize, which calls UIGraphicsBeginImageContext. So what's the deal? I am getting some crashes in my app when it comes to drawing in the background, so I don't know why there are confused examples from Apple.

推荐答案

UIGraphicsBeginImageContext绝对是线程安全的iOS 4及更高版本。 WWDC 2012会话视频涉及iOS 6，所以也许你应该涉及到iOS 6文档：）

UIGraphicsBeginImageContext definitely is thread safe in iOS 4 and later. WWDC 2012 session videos relate to iOS 6, so maybe you should relate to iOS 6 documentation as well :)