取消异步并行代码

Question

给出以下示例：

private async Task<List<string>> SearchStrings(string text, ImmutableList<string> words, CancellationToken token) {
        var foundWords = new List<string>(words.Count);
        var result = await Task.Run(() =>
            Parallel.ForEach(words, (s) => {
                if (s.ToLower().Contains(text)) {
                    foundWords.Add(s);
                }
            }));
        return foundWords;
    }

我的令牌取消了什么？是任务，并行执行还是两者兼而有之？我在哪里可以捕获哪个例外？

Answer 1

将CancellationToken传递给任务和循环，如下所示：

private async Task<List<string>> SearchStrings(string text, ImmutableList<string> words, CancellationToken token) {
    var foundWords = new List<string>( words.Count );
    var result = await Task.Run( () =>
         Parallel.ForEach( words, new ParallelOptions { CancellationToken = token, }, ( s ) => {
             if ( s.ToLower().Contains( text ) )
             {
                 foundWords.Add( s );
             }
         } ), token );
    return foundWords;
}

• Task.Run( Action action, CancellationToken token )

    

  如果在任务开始执行之前请求取消，则该任务不会执行。相反，它被设置为Canceled状态并抛出TaskCanceledException例外。

• Parallel.ForEach<TSource>( IEnumerable<TSource> source, ParallelOptions parallelOptions, Action<TSource> body )

  OperationCanceledException参数中的CancellationToken被取消时抛出parallelOptions

PS 您应该为foundWords使用线程安全列表/集合