不要等待正在等待的异步方法中的异步调用

Question

I am seeing some odd behavior from my async methods. I recently discovered that unzipping my entire zip archive was not performant on all Windows devices. So much so that I've resorted to extracting a single file I need, using it while I wait for the rest of the archive to extract. However, currently the code to extract the single file and the code to extract the entire archive is being called from the same method. This method is async and ultimately originally called on the UI thread by code in App.xaml.cs. When I call this method, I am using the await keyword to wait for it to complete as there is one file in the zip archive I need for the loading of the app.

App.xaml looks like this:

SharedContext.ChangeUniverse("1234");

SharedContext looks like this:

public static void ChangeUniverse(string universe) {
    await DownloadArchive(universe);
}

public async Task DownloadArchive(string universe) {
    ZipArchive archive = magic; // get it somehow
    var someLocalFilePath = magic; // the exact location I need to extract data.json
    var someLocalPath = magic; // the exact location I need to extract the zip
    archive.GetEntry("data.json").ExtractToFile(someLocalFilePath);
    // notice I do NOT await
    ExtractFullArchive(archive, someLocalPath);
}

public async Task ExtractFullArchive(ZipArchive archive, string path) {
    archive.ExtractToDirectory(path, true); // extracting using an override nice extension method I found on SO.com
}

The problem is that DownloadArchive doesn't return until ExtractFullArchive completes and ExtractFullArchive is what is taking a LONG time. I need ExtractFullArchive to execute asynchronously while DownloadArchive completes. I really don't care when it finishes.

Answer 1

Dont return Task if you don't want to wait instead return void like this

public async void ExtractFullArchive(ZipArchive archive, string path) {
    archive.ExtractToDirectory(path, true); // extracting using an override nice extension method I found on SO.com
}

Answer 2

When you don't care when ExtractFullArchive finishes, you can start a new Task to execute the method on another thread. With this approach, the DownloadArchive method finishes, although the ExtractFullArchive has not finished yet. This could look like this for example.

public async Task DownloadArchive(string universe) {
    ZipArchive archive = magic; // get it somehow
    var someLocalFilePath = magic; // the exact location I need to extract data.json
    var someLocalPath = magic; // the exact location I need to extract the zip
    archive.GetEntry("data.json").ExtractToFile(someLocalFilePath);
    Task.Run(() => ExtractFullArchive(archive, someLocalPath));
}