3.9 自定义任务调度
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
class Example
{
static void Main()
{
// Create a scheduler that uses two threads.
LimitedConcurrencyLevelTaskScheduler lcts = new LimitedConcurrencyLevelTaskScheduler(2);
List<Task> tasks = new List<Task>();
// Create a TaskFactory and pass it our custom scheduler.
TaskFactory factory = new TaskFactory(lcts);
CancellationTokenSource cts = new CancellationTokenSource();
// Use our factory to run a set of tasks.
Object lockObj = new Object();
int outputItem = 0;
for (int tCtr = 0; tCtr <= 4; tCtr++)
{
int iteration = tCtr;
Task t = factory.StartNew(() => {
for (int i = 0; i < 1000; i++)
{
lock (lockObj)
{
Console.Write("{0} in task t-{1} on thread {2} ",
i, iteration, Thread.CurrentThread.ManagedThreadId);
outputItem++;
if (outputItem % 3 == 0)
Console.WriteLine();
}
}
}, cts.Token);
tasks.Add(t);
}
// Use it to run a second set of tasks.
for (int tCtr = 0; tCtr <= 4; tCtr++)
{
int iteration = tCtr;
Task t1 = factory.StartNew(() => {
for (int outer = 0; outer <= 10; outer++)
{
for (int i = 0x21; i <= 0x7E; i++)
{
lock (lockObj)
{
Console.Write("'{0}' in task t1-{1} on thread {2} ",
Convert.ToChar(i), iteration, Thread.CurrentThread.ManagedThreadId);
outputItem++;
if (outputItem % 3 == 0)
Console.WriteLine();
}
}
}
}, cts.Token);
tasks.Add(t1);
}
// Wait for the tasks to complete before displaying a completion message.
Task.WaitAll(tasks.ToArray());
cts.Dispose();
Console.WriteLine("\n\nSuccessful completion.");
}
}
// Provides a task scheduler that ensures a maximum concurrency level while
// running on top of the thread pool.
public class LimitedConcurrencyLevelTaskScheduler : TaskScheduler
{
// Indicates whether the current thread is processing work items.
[ThreadStatic]
private static bool _currentThreadIsProcessingItems;
// The list of tasks to be executed
private readonly LinkedList<Task> _tasks = new LinkedList<Task>(); // protected by lock(_tasks)
// The maximum concurrency level allowed by this scheduler.
private readonly int _maxDegreeOfParallelism;
// Indicates whether the scheduler is currently processing work items.
private int _delegatesQueuedOrRunning = 0;
// Creates a new instance with the specified degree of parallelism.
public LimitedConcurrencyLevelTaskScheduler(int maxDegreeOfParallelism)
{
if (maxDegreeOfParallelism < 1) throw new ArgumentOutOfRangeException("maxDegreeOfParallelism");
_maxDegreeOfParallelism = maxDegreeOfParallelism;
}
// Queues a task to the scheduler.
protected sealed override void QueueTask(Task task)
{
// Add the task to the list of tasks to be processed. If there aren't enough
// delegates currently queued or running to process tasks, schedule another.
lock (_tasks)
{
_tasks.AddLast(task);
if (_delegatesQueuedOrRunning < _maxDegreeOfParallelism)
{
++_delegatesQueuedOrRunning;
NotifyThreadPoolOfPendingWork();
}
}
}
// Inform the ThreadPool that there's work to be executed for this scheduler.
private void NotifyThreadPoolOfPendingWork()
{
ThreadPool.UnsafeQueueUserWorkItem(_ =>
{
// Note that the current thread is now processing work items.
// This is necessary to enable inlining of tasks into this thread.
_currentThreadIsProcessingItems = true;
try
{
// Process all available items in the queue.
while (true)
{
Task item;
lock (_tasks)
{
// When there are no more items to be processed,
// note that we're done processing, and get out.
if (_tasks.Count == 0)
{
--_delegatesQueuedOrRunning;
break;
}
// Get the next item from the queue
item = _tasks.First.Value;
_tasks.RemoveFirst();
}
// Execute the task we pulled out of the queue
base.TryExecuteTask(item);
}
}
// We're done processing items on the current thread
finally { _currentThreadIsProcessingItems = false; }
}, null);
}
// Attempts to execute the specified task on the current thread.
protected sealed override bool TryExecuteTaskInline(Task task, bool taskWasPreviouslyQueued)
{
// If this thread isn't already processing a task, we don't support inlining
if (!_currentThreadIsProcessingItems) return false;
// If the task was previously queued, remove it from the queue
if (taskWasPreviouslyQueued)
// Try to run the task.
if (TryDequeue(task))
return base.TryExecuteTask(task);
else
return false;
else
return base.TryExecuteTask(task);
}
// Attempt to remove a previously scheduled task from the scheduler.
protected sealed override bool TryDequeue(Task task)
{
lock (_tasks) return _tasks.Remove(task);
}
// Gets the maximum concurrency level supported by this scheduler.
public sealed override int MaximumConcurrencyLevel { get { return _maxDegreeOfParallelism; } }
// Gets an enumerable of the tasks currently scheduled on this scheduler.
protected sealed override IEnumerable<Task> GetScheduledTasks()
{
bool lockTaken = false;
try
{
Monitor.TryEnter(_tasks, ref lockTaken);
if (lockTaken) return _tasks;
else throw new NotSupportedException();
}
finally
{
if (lockTaken) Monitor.Exit(_tasks);
}
}
}
// The following is a portion of the output from a single run of the example:
// 'T' in task t1-4 on thread 3 'U' in task t1-4 on thread 3 'V' in task t1-4 on thread 3
// 'W' in task t1-4 on thread 3 'X' in task t1-4 on thread 3 'Y' in task t1-4 on thread 3
// 'Z' in task t1-4 on thread 3 '[' in task t1-4 on thread 3 '\' in task t1-4 on thread 3
// ']' in task t1-4 on thread 3 '^' in task t1-4 on thread 3 '_' in task t1-4 on thread 3
// '`' in task t1-4 on thread 3 'a' in task t1-4 on thread 3 'b' in task t1-4 on thread 3
// 'c' in task t1-4 on thread 3 'd' in task t1-4 on thread 3 'e' in task t1-4 on thread 3
// 'f' in task t1-4 on thread 3 'g' in task t1-4 on thread 3 'h' in task t1-4 on thread 3
// 'i' in task t1-4 on thread 3 'j' in task t1-4 on thread 3 'k' in task t1-4 on thread 3
// 'l' in task t1-4 on thread 3 'm' in task t1-4 on thread 3 'n' in task t1-4 on thread 3
// 'o' in task t1-4 on thread 3 'p' in task t1-4 on thread 3 ']' in task t1-2 on thread 4
// '^' in task t1-2 on thread 4 '_' in task t1-2 on thread 4 '`' in task t1-2 on thread 4
// 'a' in task t1-2 on thread 4 'b' in task t1-2 on thread 4 'c' in task t1-2 on thread 4
// 'd' in task t1-2 on thread 4 'e' in task t1-2 on thread 4 'f' in task t1-2 on thread 4
// 'g' in task t1-2 on thread 4 'h' in task t1-2 on thread 4 'i' in task t1-2 on thread 4
// 'j' in task t1-2 on thread 4 'k' in task t1-2 on thread 4 'l' in task t1-2 on thread 4
// 'm' in task t1-2 on thread 4 'n' in task t1-2 on thread 4 'o' in task t1-2 on thread 4
// 'p' in task t1-2 on thread 4 'q' in task t1-2 on thread 4 'r' in task t1-2 on thread 4
// 's' in task t1-2 on thread 4 't' in task t1-2 on thread 4 'u' in task t1-2 on thread 4
// 'v' in task t1-2 on thread 4 'w' in task t1-2 on thread 4 'x' in task t1-2 on thread 4
// 'y' in task t1-2 on thread 4 'z' in task t1-2 on thread 4 '{' in task t1-2 on thread 4
// '|' in task t1-2 on thread 4 '}' in task t1-2 on thread 4 '~' in task t1-2 on thread 4
// 'q' in task t1-4 on thread 3 'r' in task t1-4 on thread 3 's' in task t1-4 on thread 3
// 't' in task t1-4 on thread 3 'u' in task t1-4 on thread 3 'v' in task t1-4 on thread 3
// 'w' in task t1-4 on thread 3 'x' in task t1-4 on thread 3 'y' in task t1-4 on thread 3
// 'z' in task t1-4 on thread 3 '{' in task t1-4 on thread 3 '|' in task t1-4 on thread 3
