Fra*_*Nel 5 .net c# priority-queue task-parallel-library async-await
我很难找到一个任务调度程序,我可以在其上安排优先级任务,但也可以处理"包装"任务.它类似于Task.Run尝试解决的问题,但您无法指定任务调度程序Task.Run.我一直在使用一个QueuedTaskScheduler从并行扩展额外的样品,解决了任务优先级要求(也被这个建议后).
这是我的例子:
class Program
{
private static QueuedTaskScheduler queueScheduler = new QueuedTaskScheduler(targetScheduler: TaskScheduler.Default, maxConcurrencyLevel: 1);
private static TaskScheduler ts_priority1;
private static TaskScheduler ts_priority2;
static void Main(string[] args)
{
ts_priority1 = queueScheduler.ActivateNewQueue(1);
ts_priority2 = queueScheduler.ActivateNewQueue(2);
QueueValue(1, ts_priority2);
QueueValue(2, ts_priority2);
QueueValue(3, ts_priority2);
QueueValue(4, ts_priority1);
QueueValue(5, ts_priority1);
QueueValue(6, ts_priority1);
Console.ReadLine();
}
private static Task QueueTask(Func<Task> f, TaskScheduler ts)
{
return Task.Factory.StartNew(f, CancellationToken.None, TaskCreationOptions.HideScheduler | TaskCreationOptions.DenyChildAttach, ts);
}
private static Task QueueValue(int i, TaskScheduler ts)
{
return QueueTask(async () =>
{
Console.WriteLine("Start {0}", i);
await Task.Delay(1000);
Console.WriteLine("End {0}", i);
}, ts);
}
}
上面例子的典型输出是:
Start 4
Start 5
Start 6
Start 1
Start 2
Start 3
End 4
End 3
End 5
End 2
End 1
End 6
我想要的是:
Start 4
End 4
Start 5
End 5
Start 6
End 6
Start 1
End 1
Start 2
End 2
Start 3
End 3
编辑:
我想我正在寻找一个QueuedTaskScheduler可以解决这个问题的任务调度程序.但欢迎任何其他建议.
我能找到的最好的解决方案是制作我自己的版本（原始版本在Parallel Extensions Extras SamplesQueuedTaskScheduler源代码中找到）。
我bool awaitWrappedTasks向 的构造函数添加了一个参数QueuedTaskScheduler。
public QueuedTaskScheduler(
TaskScheduler targetScheduler,
int maxConcurrencyLevel,
bool awaitWrappedTasks = false)
{
...
_awaitWrappedTasks = awaitWrappedTasks;
...
}
public QueuedTaskScheduler(
int threadCount,
string threadName = "",
bool useForegroundThreads = false,
ThreadPriority threadPriority = ThreadPriority.Normal,
ApartmentState threadApartmentState = ApartmentState.MTA,
int threadMaxStackSize = 0,
Action threadInit = null,
Action threadFinally = null,
bool awaitWrappedTasks = false)
{
...
_awaitWrappedTasks = awaitWrappedTasks;
// code starting threads (removed here in example)
...
}
然后我将ProcessPrioritizedAndBatchedTasks()方法修改为async
private async void ProcessPrioritizedAndBatchedTasks()
然后我修改了执行计划任务部分之后的代码：
private async void ProcessPrioritizedAndBatchedTasks()
{
bool continueProcessing = true;
while (!_disposeCancellation.IsCancellationRequested && continueProcessing)
{
try
{
// Note that we're processing tasks on this thread
_taskProcessingThread.Value = true;
// Until there are no more tasks to process
while (!_disposeCancellation.IsCancellationRequested)
{
// Try to get the next task. If there aren't any more, we're done.
Task targetTask;
lock (_nonthreadsafeTaskQueue)
{
if (_nonthreadsafeTaskQueue.Count == 0) break;
targetTask = _nonthreadsafeTaskQueue.Dequeue();
}
// If the task is null, it's a placeholder for a task in the round-robin queues.
// Find the next one that should be processed.
QueuedTaskSchedulerQueue queueForTargetTask = null;
if (targetTask == null)
{
lock (_queueGroups) FindNextTask_NeedsLock(out targetTask, out queueForTargetTask);
}
// Now if we finally have a task, run it. If the task
// was associated with one of the round-robin schedulers, we need to use it
// as a thunk to execute its task.
if (targetTask != null)
{
if (queueForTargetTask != null) queueForTargetTask.ExecuteTask(targetTask);
else TryExecuteTask(targetTask);
// ***** MODIFIED CODE START ****
if (_awaitWrappedTasks)
{
var targetTaskType = targetTask.GetType();
if (targetTaskType.IsConstructedGenericType && typeof(Task).IsAssignableFrom(targetTaskType.GetGenericArguments()[0]))
{
dynamic targetTaskDynamic = targetTask;
// Here we await the completion of the proxy task.
// We do not await the proxy task directly, because that would result in that await will throw the exception of the wrapped task (if one existed)
// In the continuation we then simply return the value of the exception object so that the exception (stored in the proxy task) does not go totally unobserved (that could cause the process to crash)
await TaskExtensions.Unwrap(targetTaskDynamic).ContinueWith((Func<Task, Exception>)(t => t.Exception), TaskContinuationOptions.ExecuteSynchronously);
}
}
// ***** MODIFIED CODE END ****
}
}
}
finally
{
// Now that we think we're done, verify that there really is
// no more work to do. If there's not, highlight
// that we're now less parallel than we were a moment ago.
lock (_nonthreadsafeTaskQueue)
{
if (_nonthreadsafeTaskQueue.Count == 0)
{
_delegatesQueuedOrRunning--;
continueProcessing = false;
_taskProcessingThread.Value = false;
}
}
}
}
}
方法的改变ThreadBasedDispatchLoop有点不同，因为我们不能使用async关键字，否则我们将破坏在专用线程中执行计划任务的功能。所以这是修改后的版本ThreadBasedDispatchLoop
private void ThreadBasedDispatchLoop(Action threadInit, Action threadFinally)
{
_taskProcessingThread.Value = true;
if (threadInit != null) threadInit();
try
{
// If the scheduler is disposed, the cancellation token will be set and
// we'll receive an OperationCanceledException. That OCE should not crash the process.
try
{
// If a thread abort occurs, we'll try to reset it and continue running.
while (true)
{
try
{
// For each task queued to the scheduler, try to execute it.
foreach (var task in _blockingTaskQueue.GetConsumingEnumerable(_disposeCancellation.Token))
{
Task targetTask = task;
// If the task is not null, that means it was queued to this scheduler directly.
// Run it.
if (targetTask != null)
{
TryExecuteTask(targetTask);
}
// If the task is null, that means it's just a placeholder for a task
// queued to one of the subschedulers. Find the next task based on
// priority and fairness and run it.
else
{
// Find the next task based on our ordering rules...
QueuedTaskSchedulerQueue queueForTargetTask;
lock (_queueGroups) FindNextTask_NeedsLock(out targetTask, out queueForTargetTask);
// ... and if we found one, run it
if (targetTask != null) queueForTargetTask.ExecuteTask(targetTask);
}
if (_awaitWrappedTasks)
{
var targetTaskType = targetTask.GetType();
if (targetTaskType.IsConstructedGenericType && typeof(Task).IsAssignableFrom(targetTaskType.GetGenericArguments()[0]))
{
dynamic targetTaskDynamic = targetTask;
// Here we wait for the completion of the proxy task.
// We do not wait for the proxy task directly, because that would result in that Wait() will throw the exception of the wrapped task (if one existed)
// In the continuation we then simply return the value of the exception object so that the exception (stored in the proxy task) does not go totally unobserved (that could cause the process to crash)
TaskExtensions.Unwrap(targetTaskDynamic).ContinueWith((Func<Task, Exception>)(t => t.Exception), TaskContinuationOptions.ExecuteSynchronously).Wait();
}
}
}
}
catch (ThreadAbortException)
{
// If we received a thread abort, and that thread abort was due to shutting down
// or unloading, let it pass through. Otherwise, reset the abort so we can
// continue processing work items.
if (!Environment.HasShutdownStarted && !AppDomain.CurrentDomain.IsFinalizingForUnload())
{
Thread.ResetAbort();
}
}
}
}
catch (OperationCanceledException) { }
}
finally
{
// Run a cleanup routine if there was one
if (threadFinally != null) threadFinally();
_taskProcessingThread.Value = false;
}
}
我已经对此进行了测试，它给出了所需的输出。该技术也可用于任何其他调度程序。例如LimitedConcurrencyLevelTaskScheduler和OrderedTaskScheduler