internal void RemoveDependency(JoinableTask joinChild)
{
Requires.NotNull(joinChild, nameof(joinChild));
using (this.Factory.Context.NoMessagePumpSynchronizationContext.Apply())
{
lock (this.owner.Context.SyncContextLock)
{
int refCount;
if (this.childOrJoinedJobs != null && this.childOrJoinedJobs.TryGetValue(joinChild, out refCount))
{
if (refCount == 1)
{
this.childOrJoinedJobs.Remove(joinChild);
this.RemoveDependingSynchronousTaskFromChild(joinChild);
}
else
{
this.childOrJoinedJobs[joinChild] = --refCount;
}
}
}
}
}
/// <summary>Runs a loop to process all queued work items, returning only when the task is completed.</summary>
internal void CompleteOnCurrentThread()
{
Assumes.NotNull(this.wrappedTask);
// "Push" this task onto the TLS field's virtual stack so that on hang reports we know which task to 'blame'.
JoinableTask priorCompletingTask = CompletingTask.Value;
CompletingTask.Value = this;
try
{
bool onMainThread = false;
var additionalFlags = JoinableTaskFlags.CompletingSynchronously;
if (this.owner.Context.IsOnMainThread)
{
additionalFlags |= JoinableTaskFlags.SynchronouslyBlockingMainThread;
onMainThread = true;
}
this.AddStateFlags(additionalFlags);
if (!this.IsCompleteRequested)
{
if (ThreadingEventSource.Instance.IsEnabled())
{
ThreadingEventSource.Instance.CompleteOnCurrentThreadStart(this.GetHashCode(), onMainThread);
}
using (this.Factory.Context.NoMessagePumpSynchronizationContext.Apply())
{
lock (this.owner.Context.SyncContextLock)
{
this.pendingEventCount = 0;
// Add the task to the depending tracking list of itself, so it will monitor the event queue.
this.pendingEventSource = this.AddDependingSynchronousTask(this, ref this.pendingEventCount)?.WeakSelf;
}
}
if (onMainThread)
{
this.owner.Context.OnSynchronousJoinableTaskToCompleteOnMainThread(this);
}
try
{
// Don't use IsCompleted as the condition because that
// includes queues of posted work that don't have to complete for the
// JoinableTask to be ready to return from the JTF.Run method.
HashSet <JoinableTask> visited = null;
while (!this.IsCompleteRequested)
{
if (this.TryDequeueSelfOrDependencies(onMainThread, ref visited, out SingleExecuteProtector work, out Task tryAgainAfter))
{
work.TryExecute();
}
else if (tryAgainAfter != null)
{
ThreadingEventSource.Instance.WaitSynchronouslyStart();
this.owner.WaitSynchronously(tryAgainAfter);
ThreadingEventSource.Instance.WaitSynchronouslyStop();
Assumes.True(tryAgainAfter.IsCompleted);
}
}
}
public Task <T> GetValueAsync(CancellationToken cancellationToken)
{
if (!((this.value != null && this.value.IsCompleted) || this.recursiveFactoryCheck.Value == null))
{
// PERF: we check the condition and *then* retrieve the string resource only on failure
// because the string retrieval has shown up as significant on ETL traces.
Verify.FailOperation(Strings.ValueFactoryReentrancy);
}
if (this.value == null)
{
if (Monitor.IsEntered(this.syncObject))
{
// PERF: we check the condition and *then* retrieve the string resource only on failure
// because the string retrieval has shown up as significant on ETL traces.
Verify.FailOperation(Strings.ValueFactoryReentrancy);
}
InlineResumable resumableAwaiter = null;
lock (this.syncObject)
{
// Note that if multiple threads hit GetValueAsync() before
// the valueFactory has completed its synchronous execution,
// then only one thread will execute the valueFactory while the
// other threads synchronously block till the synchronous portion
// has completed.
if (this.value == null)
{
cancellationToken.ThrowIfCancellationRequested();
resumableAwaiter = new InlineResumable();
Func <Task <T> > originalValueFactory = this.valueFactory;
this.valueFactory = null;
Func <Task <T> > valueFactory = async delegate
{
try
{
await resumableAwaiter;
return(await originalValueFactory().ConfigureAwaitRunInline());
}
finally
{
this.jobFactory = null;
this.joinableTask = null;
}
};
this.recursiveFactoryCheck.Value = RecursiveCheckSentinel;
try
{
if (this.jobFactory != null)
{
// Wrapping with RunAsync allows a future caller
// to synchronously block the Main thread waiting for the result
// without leading to deadlocks.
this.joinableTask = this.jobFactory.RunAsync(valueFactory);
this.value = this.joinableTask.Task;
}
else
{
this.value = valueFactory();
}
}
finally
{
this.recursiveFactoryCheck.Value = null;
}
}
}
// Allow the original value factory to actually run.
resumableAwaiter?.Resume();
}
if (!this.value.IsCompleted)
{
this.joinableTask?.JoinAsync(cancellationToken).Forget();
}
return(this.value.WithCancellation(cancellationToken));
}
/// <summary>
/// Check whether a task is being tracked in our tracking list.
/// </summary>
internal static bool IsDependingSynchronousTask(IJoinableTaskDependent taskItem, JoinableTask syncTask)
{
Requires.NotNull(taskItem, nameof(taskItem));
return(taskItem.GetJoinableTaskDependentData().IsDependingSynchronousTask(syncTask));
}
/// <summary>
/// When the current dependent node is a synchronous task, this method is called after the synchronous is completed, and the thread is no longer blocked.
/// This removes the current task from the dependingSynchronousTaskTracking list of the task itself (and propergate through its dependencies.)
/// It reverts the data structure change done in the <see cref="OnSynchronousTaskStartToBlockWaiting"/>.
/// </summary>
internal static void OnSynchronousTaskEndToBlockWaiting(JoinableTask taskItem)
{
Requires.NotNull(taskItem, nameof(taskItem));
JoinableTaskDependentData.OnSynchronousTaskEndToBlockWaiting(taskItem);
}
/// <summary>
/// When the current dependent node is a synchronous task, this method is called before the thread is blocked to wait it to complete.
/// This adds the current task to the dependingSynchronousTaskTracking list of the task itself (which will propergate through its dependencies.)
/// After the task is finished, <see cref="OnSynchronousTaskEndToBlockWaiting"/> is called to revert this change.
/// This method is expected to be used with the JTF lock.
/// </summary>
/// <param name="taskItem">The current joinableTask or collection.</param>
/// <param name="taskHasPendingRequests">Return the JoinableTask which has already had pending requests to be handled.</param>
/// <param name="pendingRequestsCount">The number of pending requests.</param>
internal static void OnSynchronousTaskStartToBlockWaiting(JoinableTask taskItem, out JoinableTask?taskHasPendingRequests, out int pendingRequestsCount)
{
Requires.NotNull(taskItem, nameof(taskItem));
Assumes.True(Monitor.IsEntered(taskItem.Factory.Context.SyncContextLock));
JoinableTaskDependentData.OnSynchronousTaskStartToBlockWaiting(taskItem, out taskHasPendingRequests, out pendingRequestsCount);
}
/// <summary>
/// Initializes a new instance of the <see cref="JoinableTaskSynchronizationContext"/> class.
/// </summary>
/// <param name="joinableTask">The <see cref="JoinableTask"/> that owns this instance.</param>
/// <param name="mainThreadAffinitized">A value indicating whether messages posted to this instance should execute on the main thread.</param>
internal JoinableTaskSynchronizationContext(JoinableTask joinableTask, bool mainThreadAffinitized)
: this(Requires.NotNull(joinableTask, "joinableTask").Factory)
{
this.job = joinableTask;
this.mainThreadAffinitized = mainThreadAffinitized;
}
internal ExecutionQueue(JoinableTask owningJob)
{
Requires.NotNull(owningJob, nameof(owningJob));
this.owningJob = owningJob;
}
public DependentSynchronousTask(JoinableTask task)
{
this.SynchronousTask = task;
this.ReferenceCount = 1;
}
/// <summary>
/// Remove a synchronous task from the tracking list of this task.
/// </summary>
/// <param name="task">The synchronous task need be removed</param>
/// <param name="reachableTasks">
/// If it is not null, it will contain all task which can track the synchronous task. We will ignore reference count in that case.
/// </param>
/// <param name="remainingDependentTasks">This will retain the tasks which still tracks the synchronous task.</param>
private void RemoveDependingSynchronousTask(JoinableTask task, HashSet <JoinableTask> reachableTasks, ref HashSet <JoinableTask> remainingDependentTasks)
{
Requires.NotNull(task, nameof(task));
DependentSynchronousTask previousTaskTracking = null;
DependentSynchronousTask currentTaskTracking = this.dependingSynchronousTaskTracking;
bool removed = false;
while (currentTaskTracking != null)
{
if (currentTaskTracking.SynchronousTask == task)
{
if (--currentTaskTracking.ReferenceCount > 0)
{
if (reachableTasks != null)
{
if (!reachableTasks.Contains(this))
{
currentTaskTracking.ReferenceCount = 0;
}
}
}
if (currentTaskTracking.ReferenceCount == 0)
{
removed = true;
if (previousTaskTracking != null)
{
previousTaskTracking.Next = currentTaskTracking.Next;
}
else
{
this.dependingSynchronousTaskTracking = currentTaskTracking.Next;
}
}
if (reachableTasks == null)
{
if (removed)
{
if (remainingDependentTasks != null)
{
remainingDependentTasks.Remove(this);
}
}
else
{
if (remainingDependentTasks == null)
{
remainingDependentTasks = new HashSet <JoinableTask>();
}
remainingDependentTasks.Add(this);
}
}
break;
}
previousTaskTracking = currentTaskTracking;
currentTaskTracking = currentTaskTracking.Next;
}
if (removed && this.childOrJoinedJobs != null)
{
foreach (var item in this.childOrJoinedJobs)
{
item.Key.RemoveDependingSynchronousTask(task, reachableTasks, ref remainingDependentTasks);
}
}
}
/// <summary>
/// Remove a synchronous task from the tracking list of a list of tasks.
/// </summary>
/// <param name="tasks">A list of tasks we need update the tracking list.</param>
/// <param name="syncTask">The synchronous task we want to remove</param>
/// <param name="force">We always remove it from the tracking list if it is true. Otherwise, we keep tracking the reference count.</param>
private static void RemoveDependingSynchronousTaskFrom(IReadOnlyList <JoinableTask> tasks, JoinableTask syncTask, bool force)
{
Requires.NotNull(tasks, nameof(tasks));
Requires.NotNull(syncTask, nameof(syncTask));
HashSet <JoinableTask> reachableTasks = null;
HashSet <JoinableTask> remainTasks = null;
if (force)
{
reachableTasks = new HashSet <JoinableTask>();
}
foreach (var task in tasks)
{
task.RemoveDependingSynchronousTask(syncTask, reachableTasks, ref remainTasks);
}
if (!force && remainTasks != null && remainTasks.Count > 0)
{
// a set of tasks may form a dependent loop, so it will make the reference count system
// not to work correctly when we try to remove the synchronous task.
// To get rid of those loops, if a task still tracks the synchronous task after reducing
// the reference count, we will calculate the entire reachable tree from the root. That will
// tell us the exactly tasks which need track the synchronous task, and we will clean up the rest.
reachableTasks = new HashSet <JoinableTask>();
syncTask.ComputeSelfAndDescendentOrJoinedJobsAndRemainTasks(reachableTasks, remainTasks);
// force to remove all invalid items
HashSet <JoinableTask> remainPlaceHold = null;
foreach (var remainTask in remainTasks)
{
remainTask.RemoveDependingSynchronousTask(syncTask, reachableTasks, ref remainPlaceHold);
}
}
}
/// <summary>
/// Tracks a new synchronous task for this task.
/// A synchronous task is a task blocking a thread and waits it to be completed. We may want the blocking thread
/// to process events from this task.
/// </summary>
/// <param name="task">The synchronous task</param>
/// <param name="totalEventsPending">The total events need be processed</param>
/// <returns>The task causes us to trigger the event of the synchronous task, so it can process new events. Null means we don't need trigger any event</returns>
private JoinableTask AddDependingSynchronousTask(JoinableTask task, ref int totalEventsPending)
{
Requires.NotNull(task, nameof(task));
Assumes.True(Monitor.IsEntered(this.owner.Context.SyncContextLock));
if (this.IsCompleted)
{
return(null);
}
if (this.IsCompleteRequested)
{
// A completed task might still have pending items in the queue.
int pendingCount = this.GetPendingEventCountForTask(task);
if (pendingCount > 0)
{
totalEventsPending += pendingCount;
return(this);
}
return(null);
}
DependentSynchronousTask existingTaskTracking = this.dependingSynchronousTaskTracking;
while (existingTaskTracking != null)
{
if (existingTaskTracking.SynchronousTask == task)
{
existingTaskTracking.ReferenceCount++;
return(null);
}
existingTaskTracking = existingTaskTracking.Next;
}
int pendingItemCount = this.GetPendingEventCountForTask(task);
JoinableTask eventTriggeringTask = null;
if (pendingItemCount > 0)
{
totalEventsPending += pendingItemCount;
eventTriggeringTask = this;
}
// For a new synchronous task, we need apply it to our child tasks.
DependentSynchronousTask newTaskTracking = new DependentSynchronousTask(task)
{
Next = this.dependingSynchronousTaskTracking,
};
this.dependingSynchronousTaskTracking = newTaskTracking;
if (this.childOrJoinedJobs != null)
{
foreach (var item in this.childOrJoinedJobs)
{
var childTiggeringTask = item.Key.AddDependingSynchronousTask(task, ref totalEventsPending);
if (eventTriggeringTask == null)
{
eventTriggeringTask = childTiggeringTask;
}
}
}
return(eventTriggeringTask);
}
/// <summary>Runs a loop to process all queued work items, returning only when the task is completed.</summary>
internal void CompleteOnCurrentThread()
{
Assumes.NotNull(this.wrappedTask);
// "Push" this task onto the TLS field's virtual stack so that on hang reports we know which task to 'blame'.
JoinableTask priorCompletingTask = CompletingTask.Value;
CompletingTask.Value = this;
try
{
bool onMainThread = false;
var additionalFlags = JoinableTaskFlags.CompletingSynchronously;
if (this.owner.Context.IsOnMainThread)
{
additionalFlags |= JoinableTaskFlags.SynchronouslyBlockingMainThread;
onMainThread = true;
}
this.AddStateFlags(additionalFlags);
if (!this.IsCompleteRequested)
{
if (ThreadingEventSource.Instance.IsEnabled())
{
ThreadingEventSource.Instance.CompleteOnCurrentThreadStart(this.GetHashCode(), onMainThread);
}
using (this.Factory.Context.NoMessagePumpSynchronizationContext.Apply())
{
lock (this.owner.Context.SyncContextLock)
{
this.pendingEventCount = 0;
// Add the task to the depending tracking list of itself, so it will monitor the event queue.
this.pendingEventSource = new WeakReference <JoinableTask>(this.AddDependingSynchronousTask(this, ref this.pendingEventCount));
}
}
if (onMainThread)
{
this.owner.Context.OnSynchronousJoinableTaskToCompleteOnMainThread(this);
}
try
{
// Don't use IsCompleted as the condition because that
// includes queues of posted work that don't have to complete for the
// JoinableTask to be ready to return from the JTF.Run method.
HashSet <JoinableTask> visited = null;
while (!this.IsCompleteRequested)
{
SingleExecuteProtector work;
Task tryAgainAfter;
if (this.TryDequeueSelfOrDependencies(onMainThread, ref visited, out work, out tryAgainAfter))
{
work.TryExecute();
}
else if (tryAgainAfter != null)
{
ThreadingEventSource.Instance.WaitSynchronouslyStart();
this.owner.WaitSynchronously(tryAgainAfter);
ThreadingEventSource.Instance.WaitSynchronouslyStop();
Assumes.True(tryAgainAfter.IsCompleted);
}
}
}
finally
{
using (this.Factory.Context.NoMessagePumpSynchronizationContext.Apply())
{
lock (this.owner.Context.SyncContextLock)
{
// Remove itself from the tracking list, after the task is completed.
this.RemoveDependingSynchronousTask(this, true);
}
}
}
if (ThreadingEventSource.Instance.IsEnabled())
{
ThreadingEventSource.Instance.CompleteOnCurrentThreadStop(this.GetHashCode());
}
}
else
{
if (onMainThread)
{
this.owner.Context.OnSynchronousJoinableTaskToCompleteOnMainThread(this);
}
}
// Now that we're about to stop blocking a thread, transfer any work
// that was queued but evidently not required to complete this task
// back to the threadpool so it still gets done.
if (this.threadPoolQueue?.Count > 0)
{
SingleExecuteProtector executor;
while (this.threadPoolQueue.TryDequeue(out executor))
{
ThreadPool.QueueUserWorkItem(SingleExecuteProtector.ExecuteOnceWaitCallback, executor);
}
}
Assumes.True(this.Task.IsCompleted);
this.Task.GetAwaiter().GetResult(); // rethrow any exceptions
}
finally
{
CompletingTask.Value = priorCompletingTask;
}
}
/// <summary>
/// Raised whenever a joinable task has completed a transition to the main thread.
/// </summary>
/// <param name="joinableTask">The task whose request to transition to the main thread has completed.</param>
/// <param name="canceled">A value indicating whether the transition was cancelled before it was fulfilled.</param>
/// <remarks>
/// This event is usually raised on the main thread, but can be on another thread when <paramref name="canceled"/> is <c>true</c>.
/// </remarks>
protected internal override void OnTransitionedToMainThread(JoinableTask joinableTask, bool canceled)
{
this.innerFactory.OnTransitionedToMainThread(joinableTask, canceled);
}
/// <summary>
/// Raised when a joinable task has requested a transition to the main thread.
/// </summary>
/// <param name="joinableTask">The task requesting the transition to the main thread.</param>
/// <remarks>
/// This event may be raised on any thread, including the main thread.
/// </remarks>
protected internal override void OnTransitioningToMainThread(JoinableTask joinableTask)
{
this.innerFactory.OnTransitioningToMainThread(joinableTask);
}
