ios - DispatchSourceTimer 在 deinit/dealloc 中崩溃

Question

我正在尝试使用 DispatchSourceTimer 在另一个线程上运行重复计时器。这段代码在 Playground 上运行良好，但在我的 iOS 应用程序中，它总是在 deinit 方法上崩溃(或者如果我删除 deinit，它会在运行线程的 dealloc 上崩溃)，我不知道为什么。有没有更好的方法来使用 DispatchSourceTimer？

import UIKit

class DispatchTest {
    var timer: DispatchSourceTimer
    var count: Int = 0
    init(timeInterval: TimeInterval) {
        timer = DispatchSource.makeTimerSource(flags: .strict, queue: DispatchQueue.global(qos: .default))
        timer.schedule(deadline: .now() + timeInterval, repeating: timeInterval, leeway: .milliseconds(100))
    }

    func startTimer() {
        timer.setEventHandler(handler: {[weak self] in
            self?.count += 1
            if let count = self?.count {
                print(count)
            }
            
        })
        timer.resume()
    }
    
    deinit {
        timer.setEventHandler {}
        timer.cancel()
    }
    
    func stopTimer() {
        self.timer.cancel()
    }
}

let dispatch = DispatchTest(timeInterval: 1)
dispatch.startTimer()

Answer 1

我遇到了同样的问题。仔细研究后，我在 Apple 的 Dispatch 文档中找到了答案。

https://developer.apple.com/documentation/dispatch/1452801-dispatch_suspend :

It is a programmer error to release an object that is currently suspended, because suspension implies that there is still work to be done. Therefore, always balance calls to this method with a corresponding call to dispatch_resume before disposing of the object. The behavior when releasing the last reference to a dispatch object while it is in a suspended state is undefined.

https://developer.apple.com/documentation/dispatch/1452929-dispatch_resume :

New dispatch event source objects returned by dispatch_source_create have a suspension count of 1

我从中推断出所有新的 DispatchSource 对象都开始挂起，因此如果您在释放之前没有恢复计时器，就会发生崩溃。

解决方案是确保定时器在释放前处于恢复状态。