个人感觉Task 的WaitAny和WhenAny以及TaskFactory 的ContinueWhenAny有相似的地方，而WaitAll和WhenAll以及TaskFactory 的ContinueWhenAll也是相同，但是WaitAny和WhenAny的返回值有所不同。我们首先来看看Task WhenAny和WhenAll 的实现吧，
public class Task : IThreadPoolWorkItem, IAsyncResult, IDisposable
{
//Creates a task that will complete when any of the supplied tasks have completed.
public static Task<Task> WhenAny(IEnumerable<Task> tasks)
{
if (tasks == null) throw new ArgumentNullException("tasks");
Contract.EndContractBlock();
List<Task> taskList = new List<Task>();
foreach (Task task in tasks)
{
if (task == null) throw new ArgumentException(Environment.GetResourceString("Task_MultiTaskContinuation_NullTask"), "tasks");
taskList.Add(task);
}
if (taskList.Count == )
{
throw new ArgumentException(Environment.GetResourceString("Task_MultiTaskContinuation_EmptyTaskList"), "tasks");
}
// Previously implemented CommonCWAnyLogic() can handle the rest
return TaskFactory.CommonCWAnyLogic(taskList);
} //Creates a task that will complete when all of the supplied tasks have completed.
public static Task<TResult[]> WhenAll<TResult>(params Task<TResult>[] tasks)
{
if (tasks == null) throw new ArgumentNullException("tasks");
Contract.EndContractBlock(); int taskCount = tasks.Length;
if (taskCount == ) return InternalWhenAll<TResult>(tasks); // small optimization in the case of an empty task array Task<TResult>[] tasksCopy = new Task<TResult>[taskCount];
for (int i = ; i < taskCount; i++)
{
Task<TResult> task = tasks[i];
if (task == null) throw new ArgumentException(Environment.GetResourceString("Task_MultiTaskContinuation_NullTask"), "tasks");
tasksCopy[i] = task;
}
return InternalWhenAll<TResult>(tasksCopy);
} private static Task<TResult[]> InternalWhenAll<TResult>(Task<TResult>[] tasks)
{
Contract.Requires(tasks != null, "Expected a non-null tasks array");
return (tasks.Length == ) ? new Task<TResult[]>(false, new TResult[], TaskCreationOptions.None, default(CancellationToken)) : new WhenAllPromise<TResult>(tasks);
} private sealed class WhenAllPromise<T> : Task<T[]>, ITaskCompletionAction
{
private readonly Task<T>[] m_tasks;
private int m_count; internal WhenAllPromise(Task<T>[] tasks) :base()
{
Contract.Requires(tasks != null, "Expected a non-null task array");
Contract.Requires(tasks.Length > , "Expected a non-zero length task array");
m_tasks = tasks;
m_count = tasks.Length;
if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationCreation(CausalityTraceLevel.Required, this.Id, "Task.WhenAll", ); if (s_asyncDebuggingEnabled)
{
AddToActiveTasks(this);
}
foreach (var task in tasks)
{
if (task.IsCompleted) this.Invoke(task); // short-circuit the completion action, if possible
else task.AddCompletionAction(this); // simple completion action
}
} public void Invoke(Task ignored)
{
if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationRelation(CausalityTraceLevel.Important, this.Id, CausalityRelation.Join); // Decrement the count, and only continue to complete the promise if we're the last one.
if (Interlocked.Decrement(ref m_count) == 0)
{
T[] results = new T[m_tasks.Length];
List<ExceptionDispatchInfo> observedExceptions = null;
Task canceledTask = null; for (int i = ; i < m_tasks.Length; i++)
{
Task<T> task = m_tasks[i];
Contract.Assert(task != null, "Constituent task in WhenAll should never be null"); if (task.IsFaulted)
{
if (observedExceptions == null) observedExceptions = new List<ExceptionDispatchInfo>();
observedExceptions.AddRange(task.GetExceptionDispatchInfos());
}
else if (task.IsCanceled)
{
if (canceledTask == null) canceledTask = task; // use the first task that's canceled
}
else
{
Contract.Assert(task.Status == TaskStatus.RanToCompletion);
results[i] = task.GetResultCore(waitCompletionNotification: false); // avoid Result, which would triggering debug notification
}
if (task.IsWaitNotificationEnabled) this.SetNotificationForWaitCompletion(enabled: true);
else m_tasks[i] = null; // avoid holding onto tasks unnecessarily
} if (observedExceptions != null)
{
Contract.Assert(observedExceptions.Count > , "Expected at least one exception");
TrySetException(observedExceptions);
}
else if (canceledTask != null)
{
TrySetCanceled(canceledTask.CancellationToken, canceledTask.GetCancellationExceptionDispatchInfo());
}
else
{
if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationCompletion(CausalityTraceLevel.Required, this.Id, AsyncCausalityStatus.Completed); if (Task.s_asyncDebuggingEnabled)
{
RemoveFromActiveTasks(this.Id);
}
TrySetResult(results);
}
}
Contract.Assert(m_count >= , "Count should never go below 0");
} internal override bool ShouldNotifyDebuggerOfWaitCompletion
{
get
{
return base.ShouldNotifyDebuggerOfWaitCompletion && Task.AnyTaskRequiresNotifyDebuggerOfWaitCompletion(m_tasks);
}
}
}
}
首先我们来看看Task的WhenAny的实现，非常简单调用TaskFactory.CommonCWAnyLogic方法，直接返回Task，而WaitAny【也调用TaskFactory.CommonCWAnyLogic】则需要等待这个Task完成。接下来我们来看看WhenAll的实现，WhenAll核心方法是InternalWhenAll，在InternalWhenAll里面返回了一个WhenAllPromise的Task，WhenAllPromise里面有一个计数器m_count，每当Task完成一个，就调用WhenAllPromise的Invoke方法，实现计数器m_count减1，当计数器m_count为0时表示所有的Task有已经完成。【在Task的WaitAll里面用的是SetOnCountdownMres，和这里的WhenAllPromise相似，都有一个计数器】。
那么我们现在来看看TaskFactory的ContinueWhenAny和ContinueWhenAll的实现
public class TaskFactory
{
public Task ContinueWhenAny<TAntecedentResult>(Task<TAntecedentResult>[] tasks, Action<Task<TAntecedentResult>> continuationAction,
CancellationToken cancellationToken, TaskContinuationOptions continuationOptions, TaskScheduler scheduler)
{
if (continuationAction == null) throw new ArgumentNullException("continuationAction");
Contract.EndContractBlock(); StackCrawlMark stackMark = StackCrawlMark.LookForMyCaller;
return TaskFactory<VoidTaskResult>.ContinueWhenAnyImpl<TAntecedentResult>(tasks, null, continuationAction, continuationOptions, cancellationToken, scheduler, ref stackMark);
}
// Creates a continuation Task<TResult> ,that will be started upon the completion of a set of provided Tasks.
public Task<TResult> ContinueWhenAll<TAntecedentResult>(Task<TAntecedentResult>[] tasks, Func<Task<TAntecedentResult>[], TResult> continuationFunction,
CancellationToken cancellationToken)
{
if (continuationFunction == null) throw new ArgumentNullException("continuationFunction");
Contract.EndContractBlock(); StackCrawlMark stackMark = StackCrawlMark.LookForMyCaller;
return ContinueWhenAllImpl<TAntecedentResult>(tasks, continuationFunction, null, m_defaultContinuationOptions, cancellationToken, DefaultScheduler, ref stackMark);
} internal static Task<TResult> ContinueWhenAnyImpl<TAntecedentResult>(Task<TAntecedentResult>[] tasks,
Func<Task<TAntecedentResult>, TResult> continuationFunction, Action<Task<TAntecedentResult>> continuationAction,
TaskContinuationOptions continuationOptions, CancellationToken cancellationToken, TaskScheduler scheduler, ref StackCrawlMark stackMark)
{ TaskFactory.CheckMultiTaskContinuationOptions(continuationOptions);
if (tasks == null) throw new ArgumentNullException("tasks");
if (tasks.Length == ) throw new ArgumentException(Environment.GetResourceString("Task_MultiTaskContinuation_EmptyTaskList"), "tasks");
Contract.Requires((continuationFunction != null) != (continuationAction != null), "Expected exactly one of endFunction/endAction to be non-null");
if (scheduler == null) throw new ArgumentNullException("scheduler");
Contract.EndContractBlock(); var starter = TaskFactory.CommonCWAnyLogic(tasks); // Bail early if cancellation has been requested.
if (cancellationToken.IsCancellationRequested
&& ((continuationOptions & TaskContinuationOptions.LazyCancellation) == )
)
{
return CreateCanceledTask(continuationOptions, cancellationToken);
} // returned continuation task, off of starter
if (continuationFunction != null)
{
return starter.ContinueWith<TResult>(
GenericDelegateCache<TAntecedentResult, TResult>.CWAnyFuncDelegate,
continuationFunction, scheduler, cancellationToken, continuationOptions, ref stackMark);
}
else
{
Contract.Assert(continuationAction != null);
return starter.ContinueWith<TResult>(
// Use a cached delegate
GenericDelegateCache<TAntecedentResult,TResult>.CWAnyActionDelegate,
continuationAction, scheduler, cancellationToken, continuationOptions, ref stackMark);
}
}
internal static Task<TResult> ContinueWhenAllImpl<TAntecedentResult>(Task<TAntecedentResult>[] tasks,
Func<Task<TAntecedentResult>[], TResult> continuationFunction, Action<Task<TAntecedentResult>[]> continuationAction,
TaskContinuationOptions continuationOptions, CancellationToken cancellationToken, TaskScheduler scheduler, ref StackCrawlMark stackMark)
{ TaskFactory.CheckMultiTaskContinuationOptions(continuationOptions);
if (tasks == null) throw new ArgumentNullException("tasks"); Contract.Requires((continuationFunction != null) != (continuationAction != null), "Expected exactly one of endFunction/endAction to be non-null");
if (scheduler == null) throw new ArgumentNullException("scheduler");
Contract.EndContractBlock(); Task<TAntecedentResult>[] tasksCopy = TaskFactory.CheckMultiContinuationTasksAndCopy<TAntecedentResult>(tasks); if (cancellationToken.IsCancellationRequested
&& ((continuationOptions & TaskContinuationOptions.LazyCancellation) == )
)
{
return CreateCanceledTask(continuationOptions, cancellationToken);
} var starter = TaskFactory.CommonCWAllLogic(tasksCopy);
if (continuationFunction != null)
{
return starter.ContinueWith<TResult>(
// use a cached delegate
GenericDelegateCache<TAntecedentResult, TResult>.CWAllFuncDelegate,
continuationFunction, scheduler, cancellationToken, continuationOptions, ref stackMark);
}
else
{
Contract.Assert(continuationAction != null); return starter.ContinueWith<TResult>(
// use a cached delegate
GenericDelegateCache<TAntecedentResult, TResult>.CWAllActionDelegate,
continuationAction, scheduler, cancellationToken, continuationOptions, ref stackMark);
}
}
internal static Task<Task<T>[]> CommonCWAllLogic<T>(Task<T>[] tasksCopy)
{
Contract.Requires(tasksCopy != null); // Create a promise task to be returned to the user
CompleteOnCountdownPromise<T> promise = new CompleteOnCountdownPromise<T>(tasksCopy); for (int i = ; i < tasksCopy.Length; i++)
{
if (tasksCopy[i].IsCompleted) promise.Invoke(tasksCopy[i]); // Short-circuit the completion action, if possible
else tasksCopy[i].AddCompletionAction(promise); // simple completion action
} return promise;
}
private sealed class CompleteOnCountdownPromise<T> : Task<Task<T>[]>, ITaskCompletionAction
{
private readonly Task<T>[] _tasks;
private int _count; internal CompleteOnCountdownPromise(Task<T>[] tasksCopy) : base()
{
Contract.Requires((tasksCopy != null) && (tasksCopy.Length > ), "Expected non-null task array with at least one element in it");
_tasks = tasksCopy;
_count = tasksCopy.Length; if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationCreation(CausalityTraceLevel.Required, this.Id, "TaskFactory.ContinueWhenAll<>", ); if (Task.s_asyncDebuggingEnabled)
{
AddToActiveTasks(this);
}
} public void Invoke(Task completingTask)
{
if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationRelation(CausalityTraceLevel.Important, this.Id, CausalityRelation.Join); if (completingTask.IsWaitNotificationEnabled) this.SetNotificationForWaitCompletion(enabled: true);
if (Interlocked.Decrement(ref _count) == 0)
{
if (AsyncCausalityTracer.LoggingOn)
AsyncCausalityTracer.TraceOperationCompletion(CausalityTraceLevel.Required, this.Id, AsyncCausalityStatus.Completed); if (Task.s_asyncDebuggingEnabled)
{
RemoveFromActiveTasks(this.Id);
} TrySetResult(_tasks);
}
Contract.Assert(_count >= , "Count should never go below 0");
} internal override bool ShouldNotifyDebuggerOfWaitCompletion
{
get
{
return base.ShouldNotifyDebuggerOfWaitCompletion && Task.AnyTaskRequiresNotifyDebuggerOfWaitCompletion(_tasks);
}
}
} }
首先我们来看看TaskFactory的ContinueWhenAny方法，ContinueWhenAny方法主要调用的是ContinueWhenAnyImpl，在ContinueWhenAnyImpl里面主要调用的是TaskFactory.CommonCWAnyLogic(tasks)方法，这个方法方返回的是一个CompleteOnInvokePromise Task，在Task的WhenAny方法中直接返回这个CompleteOnInvokePromise task,而Task的WaitAny则需要等待这个CompleteOnInvokePromise task的完成；而TaskFactory的ContinueWhenAny则是返回这个CompleteOnInvokePromise task的ContinueWith方法。
接下来我们在看看TaskFactory的ContinueWhenAll方法，ContinueWhenAll方法主要调用的是ContinueWhenAllImpl方法，ContinueWhenAllImpl方法主要是调用TaskFactory.CommonCWAnyLogic(tasks)方法，TaskFactory.CommonCWAnyLogic(tasks)方法返回一个CompleteOnCountdownPromise<T> 的task，然后ContinueWhenAllImpl最后返回这个task的ContinueWith方法，这里的CompleteOnCountdownPromise和Task的WhenAllPromise相似，里面都有一个计数器来标记里面的task是否执行完毕。