retrieveImage not callback

[openman1992]

version 8.3.2

Hello, I am using ImagePrefetcher to preload images while simultaneously using retrieveImage. Both addresses are the same. In a multi-threaded environment, this may result in two sessionTasks being added via addDownloadTask. However, since the same downloader's sessionDelegate maintains a map of URLs to tasks, one task will eventually be overwritten, causing external callbacks to be lost. How should I use this library to avoid this issue? If I use two downloaders, it would lead to downloading the same image twice even under normal circumstances, which is not what I want. What should I do?

[openman1992]

sure this code

private func addDownloadTask(
        context: DownloadingContext,
        callback: SessionDataTask.TaskCallback
    ) -> DownloadTask
    {
        // Ready to start download. Add it to session task manager (`sessionHandler`)
        let downloadTask: DownloadTask
        if let existingTask = sessionDelegate.task(for: context.url) {
            downloadTask = sessionDelegate.append(existingTask, callback: callback)
        } else {
            let sessionDataTask = session.dataTask(with: context.request)
            sessionDataTask.priority = context.options.downloadPriority
            downloadTask = sessionDelegate.add(sessionDataTask, url: context.url, callback: callback)
        }
        return downloadTask
    }

The sessionDelegate externally adds a session data task, while internally checking whether the task already exists.

[openman1992]

func add(
_ dataTask: URLSessionDataTask,
url: URL,
callback: SessionDataTask.TaskCallback) -> DownloadTask
{
lock.lock()
defer { lock.unlock() }
if let exsitTask = tasks[url] {
return append(exsitTask, callback: callback)
}
// Create a new task if necessary.
let task = SessionDataTask(task: dataTask)
task.onCallbackCancelled.delegate(on: self) { [weak task] (self, value) in
guard let task = task else { return }

        let (token, callback) = value

        let error = KingfisherError.requestError(reason: .taskCancelled(task: task, token: token))
        task.onTaskDone.call((.failure(error), [callback]))
        // No other callbacks waiting, we can clear the task now.
        if !task.containsCallbacks {
            let dataTask = task.task

            self.cancelTask(dataTask)
            self.remove(task)
        }
    }
    let token = task.addCallback(callback)
    tasks[url] = task
    return DownloadTask(sessionTask: task, cancelToken: token)
}

Can it be modified and fixed like this?

[darkbrewx]

Yes, I think adding a check here and falling back to the append handling is an effective solution.

[darkbrewx]

Assuming it’s the same kind of issue.
#2231
#2342
#2314