我能想到的最好的方法是ContinueWith
为 each指定 a Task
,检查结果,以及是否true
取消其他任务。对于取消任务,您可能需要使用CancellationToken。
var tasks = servers
.Select(s => Task.Run(...)
.ContinueWith(t =>
if (t.Result) {
// cancel other threads
}
)
).ToArray();
更新:另一种解决方案是WaitAny
直到正确的任务完成(但它有一些缺点,例如从列表中删除已完成的任务并从剩余的任务中创建一个新数组是相当繁重的操作):
List<Task<bool>> tasks = servers.Select(s => Task<bool>.Factory.StartNew(server => CallServer((string)server), s)).ToList();
bool result;
do {
int idx = Task.WaitAny(tasks.ToArray());
result = tasks[idx].Result;
tasks.RemoveAt(idx);
} while (!result && tasks.Count > 0);
// cancel other tasks
更新 2:现在我会用 Rx 来做:
[Fact]
public async Task AwaitFirst()
{
var servers = new[] { "server1", "server2", "server3", "server4" };
var server = await servers
.Select(s => Observable
.FromAsync(ct => CallServer(s, ct))
.Where(p => p)
.Select(_ => s)
)
.Merge()
.FirstAsync();
output.WriteLine($"Got result from {server}");
}
private async Task<bool> CallServer(string server, CancellationToken ct)
{
try
{
if (server == "server1")
{
await Task.Delay(TimeSpan.FromSeconds(1), ct);
output.WriteLine($"{server} finished");
return false;
}
if (server == "server2")
{
await Task.Delay(TimeSpan.FromSeconds(2), ct);
output.WriteLine($"{server} finished");
return false;
}
if (server == "server3")
{
await Task.Delay(TimeSpan.FromSeconds(3), ct);
output.WriteLine($"{server} finished");
return true;
}
if (server == "server4")
{
await Task.Delay(TimeSpan.FromSeconds(4), ct);
output.WriteLine($"{server} finished");
return true;
}
}
catch(OperationCanceledException)
{
output.WriteLine($"{server} Cancelled");
throw;
}
throw new ArgumentOutOfRangeException(nameof(server));
}
在我的机器上测试需要 3.32 秒(这意味着它没有等待第四台服务器),我得到以下输出:
server1 finished
server2 finished
server3 finished
server4 Cancelled
Got result from server3