任务取消的WKURLSchemeHandler NSInternalInconsistencyException

Question

我在WKURLSchemeHandler和任务取消方面有问题，并在下面提供了一个示例实现。

问题是，有时在调用webView(_:stop:)之后(以及“停止任务.”)) try Task.checkCancellation()没有抛出，或者已经被调用了(我不确定)，所以urlSchemeTask.didReceive或didFinish中的一个可以像这样让应用程序崩溃：

Stopping task <WKURLSchemeTaskImpl: 0x7fd445c209c0>
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'This task has already been stopped'

有注释的示例实现：

import WebKit

class AsyncURLSchemeHandler: NSObject, WKURLSchemeHandler {
    private var pendingTasks = [ObjectIdentifier: TaskItem]()
    
    func webView(_ webView: WKWebView, stop urlSchemeTask: WKURLSchemeTask) {
        guard let task = pendingTasks.removeValue(forKey: urlSchemeTask.id) else { return }
        print("Stopping task \(urlSchemeTask)")
        task.stop()
    }

    func webView(_ webView: WKWebView, start urlSchemeTask: WKURLSchemeTask) {
        let task = Task { [weak self] in
            var request = urlSchemeTask.request
        
            // Do some mutation on the request
            
            do {
                try Task.checkCancellation()
                
                 // Conditionally get a URLSession 
                let session: URLSession 
                
                // Fire off the request
                let (data, response) = try await session.data(for: request)
                
                await Task.yield()
                try Task.checkCancellation()

                // Report back to the scheme task
                // Either of these !! may crash in this implementation
                urlSchemeTask.didReceive(response) // !!
                urlSchemeTask.didReceive(data) // !!
                urlSchemeTask.didFinish() // !!
                
            } catch is CancellationError {
                // Do not call didFailWithError, didFinish, or didReceive in this case
                print("Task for WKURLSchemeTask \(urlSchemeTask) has been cancelled")
            } catch {
                if !Task.isCancelled {
                    // !! This can crash, too
                    urlSchemeTask.didFailWithError(error)
                }
            }
            
            self?.pendingTasks.removeValue(forKey: urlSchemeTask.id)
        }
        
        pendingTasks[urlSchemeTask.id] = .init(urlSchemeTask: urlSchemeTask, task: task)
    }
}

private extension WKURLSchemeTask {
    var id: ObjectIdentifier {
        ObjectIdentifier(self)
    }
}

private struct TaskItem {
    enum Error: Swift.Error {
        case manualCancellation
    }
    
    let urlSchemeTask: WKURLSchemeTask
    let task: Task<Void, Never>
    
    /// Should be called when urlSchemeTask has been stopped by the system
    /// Calling anything on the urlSchemeTask afterwards would result in an exception
    func stop() {
        task.cancel()
    }
    
    /// Should be called when the urlSchemeTask should be stopped manually
    func cancel() {
        task.cancel()
        urlSchemeTask.didFailWithError(Error.manualCancellation)
    }
}

有人能帮我避免这些车祸吗？

这是一个交叉的：https://developer.apple.com/forums/thread/712430

Answer 1

要解决这个问题，我执行以下操作：

我将挂起的任务状态封装在一个参与者cancellation.

• I中，我在该参与者中使用了一个Set<ObjectIdentifier>，并检查了contains，而不是使用任务

• ，使用这样的方法(https://stackoverflow.com/a/35003095/5771177)捕获objc异常并忽略它--

最重要的是：

• 主要问题超出了这个问题的范围，我重构了围绕WebView生命周期的东西.