Utilisation d'async / en attente de tâches multiples
j'utilise un client API qui est complètement asynchrone, c'est-à-dire que chaque opération renvoie Task ou Task<T> , E. g:
static async Task DoSomething(int siteId, int postId, IBlogClient client)
{
await client.DeletePost(siteId, postId); // call API client
Console.WriteLine("Deleted post {0}.", siteId);
}
en utilisant les opérateurs C# 5 async/wait, Quelle est la manière correcte/la plus efficace de démarrer plusieurs tâches et d'attendre qu'elles soient toutes terminées:
int[] ids = new[] { 1, 2, 3, 4, 5 };
Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());
ou:
int[] ids = new[] { 1, 2, 3, 4, 5 };
Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());
étant donné que le client API utilise HttpClient en interne, Je m'attends à ce que ce numéro 5 HTTP demande immédiatement, en écrivant sur la console au fur et à mesure que chacun d'eux est terminé.
310
demandé sur
tugberk
2012-09-09 12:40:04
5 réponses
int[] ids = new[] { 1, 2, 3, 4, 5 };
Parallel.ForEach(ids, i => DoSomething(1, i, blogClient).Wait());
bien que vous exécutiez les opérations en parallèle avec le code ci-dessus, ce code bloque chaque thread sur lequel chaque opération s'exécute. Par exemple, si l'appel réseau prend 2 secondes, chaque thread est suspendu pendant 2 secondes sans rien faire d'autre que d'attendre.
int[] ids = new[] { 1, 2, 3, 4, 5 };
Task.WaitAll(ids.Select(i => DoSomething(1, i, blogClient)).ToArray());
d'autre part, le code ci-dessus avec WaitAll bloque également les fils et vos fils ne seront pas libres de traiter tout autre travail jusqu'à la fin de l'opération.
Approche Recommandée
je préférerais WhenAll qui effectuera vos opérations en parallèle de façon asynchrone.
public async Task DoWork() {
int[] ids = new[] { 1, 2, 3, 4, 5 };
await Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient)));
}
en fait, dans le cas ci-dessus, vous n'avez même pas besoin de
await, vous pouvez simplement revenir directement de la méthode car vous n'avez pas de continuations:public Task DoWork() { int[] ids = new[] { 1, 2, 3, 4, 5 }; return Task.WhenAll(ids.Select(i => DoSomething(1, i, blogClient))); }
pour étayer cela, Voici un billet de blog détaillé passant par tous les les alternatives et leur Avantages/ Désavantages: comment et où les E/S asynchrones concurrentes avec ASP.NET API Web
452
répondu
tugberk
2016-07-07 10:41:40
j'étais curieux de voir les résultats des méthodes fournies dans la question ainsi que l'on a accepté la réponse, donc je l'ai mis à l'épreuve.
voici le code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
namespace AsyncTest
{
class Program
{
class Worker
{
public int Id;
public int SleepTimeout;
public async Task DoWork(DateTime testStart)
{
var workerStart = DateTime.Now;
Console.WriteLine("Worker {0} started on thread {1}, beginning {2} seconds after test start.",
Id, Thread.CurrentThread.ManagedThreadId, (workerStart-testStart).TotalSeconds.ToString("F2"));
await Task.Run(() => Thread.Sleep(SleepTimeout));
var workerEnd = DateTime.Now;
Console.WriteLine("Worker {0} stopped; the worker took {1} seconds, and it finished {2} seconds after the test start.",
Id, (workerEnd-workerStart).TotalSeconds.ToString("F2"), (workerEnd-testStart).TotalSeconds.ToString("F2"));
}
}
static void Main(string[] args)
{
var workers = new List<Worker>
{
new Worker { Id = 1, SleepTimeout = 1000 },
new Worker { Id = 2, SleepTimeout = 2000 },
new Worker { Id = 3, SleepTimeout = 3000 },
new Worker { Id = 4, SleepTimeout = 4000 },
new Worker { Id = 5, SleepTimeout = 5000 },
};
var startTime = DateTime.Now;
Console.WriteLine("Starting test: Parallel.ForEach...");
PerformTest_ParallelForEach(workers, startTime);
var endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
startTime = DateTime.Now;
Console.WriteLine("Starting test: Task.WaitAll...");
PerformTest_TaskWaitAll(workers, startTime);
endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
startTime = DateTime.Now;
Console.WriteLine("Starting test: Task.WhenAll...");
var task = PerformTest_TaskWhenAll(workers, startTime);
task.Wait();
endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
Console.ReadKey();
}
static void PerformTest_ParallelForEach(List<Worker> workers, DateTime testStart)
{
Parallel.ForEach(workers, worker => worker.DoWork(testStart).Wait());
}
static void PerformTest_TaskWaitAll(List<Worker> workers, DateTime testStart)
{
Task.WaitAll(workers.Select(worker => worker.DoWork(testStart)).ToArray());
}
static Task PerformTest_TaskWhenAll(List<Worker> workers, DateTime testStart)
{
return Task.WhenAll(workers.Select(worker => worker.DoWork(testStart)));
}
}
}
et la sortie résultante:
Starting test: Parallel.ForEach...
Worker 1 started on thread 1, beginning 0.21 seconds after test start.
Worker 4 started on thread 5, beginning 0.21 seconds after test start.
Worker 2 started on thread 3, beginning 0.21 seconds after test start.
Worker 5 started on thread 6, beginning 0.21 seconds after test start.
Worker 3 started on thread 4, beginning 0.21 seconds after test start.
Worker 1 stopped; the worker took 1.90 seconds, and it finished 2.11 seconds after the test start.
Worker 2 stopped; the worker took 3.89 seconds, and it finished 4.10 seconds after the test start.
Worker 3 stopped; the worker took 5.89 seconds, and it finished 6.10 seconds after the test start.
Worker 4 stopped; the worker took 5.90 seconds, and it finished 6.11 seconds after the test start.
Worker 5 stopped; the worker took 8.89 seconds, and it finished 9.10 seconds after the test start.
Test finished after 9.10 seconds.
Starting test: Task.WaitAll...
Worker 1 started on thread 1, beginning 0.01 seconds after test start.
Worker 2 started on thread 1, beginning 0.01 seconds after test start.
Worker 3 started on thread 1, beginning 0.01 seconds after test start.
Worker 4 started on thread 1, beginning 0.01 seconds after test start.
Worker 5 started on thread 1, beginning 0.01 seconds after test start.
Worker 1 stopped; the worker took 1.00 seconds, and it finished 1.01 seconds after the test start.
Worker 2 stopped; the worker took 2.00 seconds, and it finished 2.01 seconds after the test start.
Worker 3 stopped; the worker took 3.00 seconds, and it finished 3.01 seconds after the test start.
Worker 4 stopped; the worker took 4.00 seconds, and it finished 4.01 seconds after the test start.
Worker 5 stopped; the worker took 5.00 seconds, and it finished 5.01 seconds after the test start.
Test finished after 5.01 seconds.
Starting test: Task.WhenAll...
Worker 1 started on thread 1, beginning 0.00 seconds after test start.
Worker 2 started on thread 1, beginning 0.00 seconds after test start.
Worker 3 started on thread 1, beginning 0.00 seconds after test start.
Worker 4 started on thread 1, beginning 0.00 seconds after test start.
Worker 5 started on thread 1, beginning 0.00 seconds after test start.
Worker 1 stopped; the worker took 1.00 seconds, and it finished 1.00 seconds after the test start.
Worker 2 stopped; the worker took 2.00 seconds, and it finished 2.00 seconds after the test start.
Worker 3 stopped; the worker took 3.00 seconds, and it finished 3.00 seconds after the test start.
Worker 4 stopped; the worker took 4.00 seconds, and it finished 4.00 seconds after the test start.
Worker 5 stopped; the worker took 5.00 seconds, and it finished 5.00 seconds after the test start.
Test finished after 5.00 seconds.
31
répondu
RiaanDP
2018-08-04 12:09:41
puisque l'API que vous appelez est async, la version Parallel.ForEach n'a pas beaucoup de sens. Vous ne devez pas utiliser .Wait dans la version WaitAll car cela perdrait le parallélisme une autre alternative si l'appelant est async utilise Task.WhenAll après avoir fait Select et ToArray pour générer le tableau des tâches. Une deuxième alternative est D'utiliser RX 2.0
18
répondu
James Manning
2016-10-13 16:25:33
Parallel.ForEach exige une liste de définis par l'utilisateur travailleurs et un non-async Action pour effectuer avec chaque travailleur.
Task.WaitAll et Task.WhenAll besoin d'un List<Task> , qui sont, par définition, asynchrone.
j'ai trouvé RiaanDP 's réponse très utile pour comprendre la différence, mais il a besoin d'une correction pour Parallel.ForEach . Pas assez de réputation pour répondre à son commentaire, donc ma propre réponse.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
namespace AsyncTest
{
class Program
{
class Worker
{
public int Id;
public int SleepTimeout;
public void DoWork(DateTime testStart)
{
var workerStart = DateTime.Now;
Console.WriteLine("Worker {0} started on thread {1}, beginning {2} seconds after test start.",
Id, Thread.CurrentThread.ManagedThreadId, (workerStart - testStart).TotalSeconds.ToString("F2"));
Thread.Sleep(SleepTimeout);
var workerEnd = DateTime.Now;
Console.WriteLine("Worker {0} stopped; the worker took {1} seconds, and it finished {2} seconds after the test start.",
Id, (workerEnd - workerStart).TotalSeconds.ToString("F2"), (workerEnd - testStart).TotalSeconds.ToString("F2"));
}
public async Task DoWorkAsync(DateTime testStart)
{
var workerStart = DateTime.Now;
Console.WriteLine("Worker {0} started on thread {1}, beginning {2} seconds after test start.",
Id, Thread.CurrentThread.ManagedThreadId, (workerStart - testStart).TotalSeconds.ToString("F2"));
await Task.Run(() => Thread.Sleep(SleepTimeout));
var workerEnd = DateTime.Now;
Console.WriteLine("Worker {0} stopped; the worker took {1} seconds, and it finished {2} seconds after the test start.",
Id, (workerEnd - workerStart).TotalSeconds.ToString("F2"), (workerEnd - testStart).TotalSeconds.ToString("F2"));
}
}
static void Main(string[] args)
{
var workers = new List<Worker>
{
new Worker { Id = 1, SleepTimeout = 1000 },
new Worker { Id = 2, SleepTimeout = 2000 },
new Worker { Id = 3, SleepTimeout = 3000 },
new Worker { Id = 4, SleepTimeout = 4000 },
new Worker { Id = 5, SleepTimeout = 5000 },
};
var startTime = DateTime.Now;
Console.WriteLine("Starting test: Parallel.ForEach...");
PerformTest_ParallelForEach(workers, startTime);
var endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
startTime = DateTime.Now;
Console.WriteLine("Starting test: Task.WaitAll...");
PerformTest_TaskWaitAll(workers, startTime);
endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
startTime = DateTime.Now;
Console.WriteLine("Starting test: Task.WhenAll...");
var task = PerformTest_TaskWhenAll(workers, startTime);
task.Wait();
endTime = DateTime.Now;
Console.WriteLine("Test finished after {0} seconds.\n",
(endTime - startTime).TotalSeconds.ToString("F2"));
Console.ReadKey();
}
static void PerformTest_ParallelForEach(List<Worker> workers, DateTime testStart)
{
Parallel.ForEach(workers, worker => worker.DoWork(testStart));
}
static void PerformTest_TaskWaitAll(List<Worker> workers, DateTime testStart)
{
Task.WaitAll(workers.Select(worker => worker.DoWorkAsync(testStart)).ToArray());
}
static Task PerformTest_TaskWhenAll(List<Worker> workers, DateTime testStart)
{
return Task.WhenAll(workers.Select(worker => worker.DoWorkAsync(testStart)));
}
}
}
la sortie résultante est ci-dessous. Les temps d'exécution sont comparables. J'ai fait ce test pendant que mon ordinateur faisait le balayage anti-virus hebdomadaire. Changer l'ordre des tests a changé les temps d'exécution.
Starting test: Parallel.ForEach...
Worker 1 started on thread 9, beginning 0.02 seconds after test start.
Worker 2 started on thread 10, beginning 0.02 seconds after test start.
Worker 3 started on thread 11, beginning 0.02 seconds after test start.
Worker 4 started on thread 13, beginning 0.03 seconds after test start.
Worker 5 started on thread 14, beginning 0.03 seconds after test start.
Worker 1 stopped; the worker took 1.00 seconds, and it finished 1.02 seconds after the test start.
Worker 2 stopped; the worker took 2.00 seconds, and it finished 2.02 seconds after the test start.
Worker 3 stopped; the worker took 3.00 seconds, and it finished 3.03 seconds after the test start.
Worker 4 stopped; the worker took 4.00 seconds, and it finished 4.03 seconds after the test start.
Worker 5 stopped; the worker took 5.00 seconds, and it finished 5.03 seconds after the test start.
Test finished after 5.03 seconds.
Starting test: Task.WaitAll...
Worker 1 started on thread 9, beginning 0.00 seconds after test start.
Worker 2 started on thread 9, beginning 0.00 seconds after test start.
Worker 3 started on thread 9, beginning 0.00 seconds after test start.
Worker 4 started on thread 9, beginning 0.00 seconds after test start.
Worker 5 started on thread 9, beginning 0.01 seconds after test start.
Worker 1 stopped; the worker took 1.00 seconds, and it finished 1.01 seconds after the test start.
Worker 2 stopped; the worker took 2.00 seconds, and it finished 2.01 seconds after the test start.
Worker 3 stopped; the worker took 3.00 seconds, and it finished 3.01 seconds after the test start.
Worker 4 stopped; the worker took 4.00 seconds, and it finished 4.01 seconds after the test start.
Worker 5 stopped; the worker took 5.00 seconds, and it finished 5.01 seconds after the test start.
Test finished after 5.01 seconds.
Starting test: Task.WhenAll...
Worker 1 started on thread 9, beginning 0.00 seconds after test start.
Worker 2 started on thread 9, beginning 0.00 seconds after test start.
Worker 3 started on thread 9, beginning 0.00 seconds after test start.
Worker 4 started on thread 9, beginning 0.00 seconds after test start.
Worker 5 started on thread 9, beginning 0.00 seconds after test start.
Worker 1 stopped; the worker took 1.00 seconds, and it finished 1.00 seconds after the test start.
Worker 2 stopped; the worker took 2.00 seconds, and it finished 2.00 seconds after the test start.
Worker 3 stopped; the worker took 3.00 seconds, and it finished 3.00 seconds after the test start.
Worker 4 stopped; the worker took 4.00 seconds, and it finished 4.00 seconds after the test start.
Worker 5 stopped; the worker took 5.00 seconds, and it finished 5.01 seconds after the test start.
Test finished after 5.01 seconds.
3
répondu
JPortillo
2018-09-14 19:28:28
vous pouvez utiliser Task.WhenAll fonction que vous pouvez passer n tâches; Task.WhenAll retournera une tâche qui se termine lorsque toutes les tâches que vous avez passées à Task.WhenAll terminé. Vous devez attendre de façon asynchrone sur Task.WhenAll pour ne pas bloquer votre fil D'interface utilisateur:
public async Task DoSomeThing() {
var Task[] tasks = new Task[numTasks];
for(int i = 0; i < numTask; i++)
{
tasks[i] = CallSomeAsync();
}
await Task.WhenAll(tasks);
// code that'll execute on UI thread
}
2
répondu
Ahmed Wasim
2018-01-08 16:33:31