当有一个或两个任务时，它可以正常工作，但当我们列出多个任务时，会抛出错误“任务已取消”。
List<Task> allTasks = new List<Task>();
allTasks.Add(....);
allTasks.Add(....);
Task.WaitAll(allTasks.ToArray(), configuration.CancellationToken);
private static Task<T> HttpClientSendAsync<T>(string url, object data, HttpMethod method, string contentType, CancellationToken token)
{
HttpRequestMessage httpRequestMessage = new HttpRequestMessage(method, url);
HttpClient httpClient = new HttpClient();
httpClient.Timeout = new TimeSpan(Constants.TimeOut);
if (data != null)
{
byte[] byteArray = Encoding.ASCII.GetBytes(Helper.ToJSON(data));
MemoryStream memoryStream = new MemoryStream(byteArray);
httpRequestMessage.Content = new StringContent(new StreamReader(memoryStream).ReadToEnd(), Encoding.UTF8, contentType);
}
return httpClient.SendAsync(httpRequestMessage).ContinueWith(task =>
{
var response = task.Result;
return response.Content.ReadAsStringAsync().ContinueWith(stringTask =>
{
var json = stringTask.Result;
return Helper.FromJSON<T>(json);
});
}).Unwrap();
}
推广@JobaDiniz的评论来回答:
不要做显而易见的事情，释放HttpClient实例，即使代码“看起来是正确的”:
async Task<HttpResponseMessage> Method() {
using (var client = new HttpClient())
return client.GetAsync(request);
}
丢弃HttpClient实例会导致其他HttpClient实例启动的HTTP请求被取消!
c#的新RIAA语法也是如此;稍微不那么明显:
async Task<HttpResponseMessage> Method() {
using var client = new HttpClient();
return client.GetAsync(request);
}
相反，正确的方法是为你的应用程序或库缓存一个静态HttpClient实例，并重用它:
static HttpClient client = new HttpClient();
async Task<HttpResponseMessage> Method() {
return client.GetAsync(request);
}
Async()请求方法都是线程安全的。
推广@JobaDiniz的评论来回答:
不要做显而易见的事情，释放HttpClient实例，即使代码“看起来是正确的”:
async Task<HttpResponseMessage> Method() {
using (var client = new HttpClient())
return client.GetAsync(request);
}
丢弃HttpClient实例会导致其他HttpClient实例启动的HTTP请求被取消!
c#的新RIAA语法也是如此;稍微不那么明显:
async Task<HttpResponseMessage> Method() {
using var client = new HttpClient();
return client.GetAsync(request);
}
相反，正确的方法是为你的应用程序或库缓存一个静态HttpClient实例，并重用它:
static HttpClient client = new HttpClient();
async Task<HttpResponseMessage> Method() {
return client.GetAsync(request);
}
Async()请求方法都是线程安全的。
我使用了一个简单的调用，而不是异步。当我添加等待和使方法异步开始工作良好。
public async Task<T> ExecuteScalarAsync<T>(string query, object parameter = null, CommandType commandType = CommandType.Text) where T : IConvertible
{
using (IDbConnection db = new SqlConnection(_con))
{
return await db.ExecuteScalarAsync<T>(query, parameter, null, null, commandType);
}
}
抛出TaskCanceledException有2个可能的原因:
在任务完成之前，与取消令牌关联的CancellationTokenSource上的Cancel()。
请求超时，即没有在您在HttpClient.Timeout中指定的时间范围内完成。
我猜是暂停了。(如果它是一个明确的消去，你可能已经知道了。)你可以通过检查异常来确定:
try
{
var response = task.Result;
}
catch (TaskCanceledException ex)
{
// Check ex.CancellationToken.IsCancellationRequested here.
// If false, it's pretty safe to assume it was a timeout.
}
