跨线程拆分工作
本文关键字：工作 拆分 线程 | 更新日期: 2023-09-27 18:16:32
目前，我是一个一个地处理从视频中读取的帧，然后将它们写入文件。这似乎效率低下，速度慢，所以我想把工作分成多个线程。
我当前的代码可以总结如下:
for(long n = 0; n < totalframes; n++) {
using(Bitmap frame = vreader.ReadVideoFrame()) {
Process(frame); //awfully slow
WriteToFile(frame);
}
}
我如何加载，比如说，四个帧，在四个线程中处理它们，等待它们全部完成，然后将它们写入文件?重要的是，这些帧的写入顺序与视频中的顺序完全相同。
您可以使用例如Parallel.ForEach()来处理帧。然后用迭代器块(IEnumerable<>)读取它们。
但是写作需要更多的注意。确保你附加一个数字到每一帧，并在处理结束时，转储他们在一个BlockingCollection<T>。启动一个单独的线程(Task)来处理队列并按顺序写入帧。这是一个典型的n-生产者/1-消费者解决方案。
这就是你想要一个Pipeline的地方。我几乎直接从并行编程模式中复制了代码，并在步骤2中引入了额外的并行性(我包含了使用并行任务和PLINQ的示例)。它不是太复杂，而且很好用，在我的机器上，它的运行速度比顺序版本快很多倍。您可能看不到代码中相同程度的改进(因为我猜您的Process比Thread.Sleep更复杂)，但它仍然会运行得更快。
显然，由于额外的并行性和我试图匹配你的对象模型，有很多混乱。参考《并行编程模式》第55页的原始、简单的示例代码。这是一件美丽的事情，所以一定要去看看(http://www.microsoft.com/en-au/download/details.aspx?id=19222)。
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
namespace PipelineExample
{
/// <summary>
/// Stack Overflow question 16882318.
/// </summary>
public class Program
{
/// <summary>
/// This is our simulated "file". In essense it will contain the
/// ID of each Frame which has been processed and written to file.
/// </summary>
private static readonly List<long> FrameFile = new List<long>();
/// <summary>
/// This is a modification of Stephen Toub's Pipelines
/// example from Patterns Of Parallel Programming.
/// </summary>
private static void RunPipeline(VReader vreader, long totalframes)
{
var rawFrames = new BlockingCollection<Bitmap>();
var processedFrames = new BlockingCollection<Bitmap>();
// Stage 1: read raw frames.
var readTask = Task.Run(() =>
{
try
{
for (long n = 0; n < totalframes; n++)
{
rawFrames.Add(vreader.ReadVideoFrame());
}
}
finally { rawFrames.CompleteAdding(); }
});
// Stage 2: process frames in parallel.
var processTask = Task.Run(() =>
{
try
{
// Try both - see which performs better in your scenario.
Step2WithParallelTasks(rawFrames, processedFrames);
//Step2WithPLinq(rawFrames, processedFrames);
}
finally { processedFrames.CompleteAdding(); }
});
// Stage 3: write results to file and dispose of the frame.
var writeTask = Task.Run(() =>
{
foreach (var processedFrame in processedFrames.GetConsumingEnumerable())
{
WriteToFile(processedFrame);
processedFrame.Dispose();
}
});
Task.WaitAll(readTask, processTask, writeTask);
}
/// <summary>
/// Processes frames in rawFrames and adds them to
/// processedFrames preserving the original frame order.
/// </summary>
private static void Step2WithPLinq(BlockingCollection<Bitmap> rawFrames, BlockingCollection<Bitmap> processedFrames)
{
Console.WriteLine("Executing Step 2 via PLinq.");
var processed = rawFrames.GetConsumingEnumerable()
.AsParallel()
.AsOrdered()
.Select(frame =>
{
Process(frame);
return frame;
});
foreach (var frame in processed)
{
processedFrames.Add(frame);
}
}
/// <summary>
/// Processes frames in rawFrames and adds them to
/// processedFrames preserving the original frame order.
/// </summary>
private static void Step2WithParallelTasks(BlockingCollection<Bitmap> rawFrames, BlockingCollection<Bitmap> processedFrames)
{
Console.WriteLine("Executing Step 2 via parallel tasks.");
var degreesOfParallellism = Environment.ProcessorCount;
var inbox = rawFrames.GetConsumingEnumerable();
// Start our parallel tasks.
while (true)
{
var tasks = inbox
.Take(degreesOfParallellism)
.Select(frame => Task.Run(() =>
{
Process(frame);
return frame;
}))
.ToArray();
if (tasks.Length == 0)
{
break;
}
Task.WaitAll(tasks);
foreach (var t in tasks)
{
processedFrames.Add(t.Result);
}
}
}
/// <summary>
/// Sequential implementation - as is (for comparison).
/// </summary>
private static void RunSequential(VReader vreader, long totalframes)
{
for (long n = 0; n < totalframes; n++)
{
using (var frame = vreader.ReadVideoFrame())
{
Process(frame);
WriteToFile(frame);
}
}
}
/// <summary>
/// Main entry point.
/// </summary>
private static void Main(string[] args)
{
// Arguments.
long totalframes = 1000;
var vreader = new VReader();
// We'll time our run.
var sw = Stopwatch.StartNew();
// Try both for comparison.
//RunSequential(vreader, totalframes);
RunPipeline(vreader, totalframes);
sw.Stop();
Console.WriteLine("Elapsed ms: {0}.", sw.ElapsedMilliseconds);
// Validation: count, order and contents.
if (Range(1, totalframes).SequenceEqual(FrameFile))
{
Console.WriteLine("Frame count and order of frames in the file are CORRECT.");
}
else
{
Console.WriteLine("Frame count and order of frames in the file are INCORRECT.");
}
Console.ReadLine();
}
/// <summary>
/// Simulate CPU work.
/// </summary>
private static void Process(Bitmap frame)
{
Thread.Sleep(10);
}
/// <summary>
/// Simulate IO pressure.
/// </summary>
private static void WriteToFile(Bitmap frame)
{
Thread.Sleep(5);
FrameFile.Add(frame.ID);
}
/// <summary>
/// Naive implementation of Enumerable.Range(int, int) for long.
/// </summary>
private static IEnumerable<long> Range(long start, long count)
{
for (long i = start; i < start + count; i++)
{
yield return i;
}
}
private class VReader
{
public Bitmap ReadVideoFrame()
{
return new Bitmap();
}
}
private class Bitmap : IDisposable
{
private static int MaxID;
public readonly long ID;
public Bitmap()
{
this.ID = Interlocked.Increment(ref MaxID);
}
public void Dispose()
{
// Dummy method.
}
}
}
}
要并行操作元素，请使用System.Linq的并行方法，如ParallelEnumerable.Range()。为了保持元素的顺序，可以使用.AsOrdered() .
ParallelEnumerable.Range(0, totalframes)
.AsOrdered()
.Select(x => vreader.ReadVideoFrame())
.Select(Process)
.Select(WriteToFile);
是的-你需要一个线程池，一些线程，一个输入图像数据的类+一个'序列号'或'帧号'来识别顺序和一个线程安全的'ReSerializer'类，它有一个容器来缓存所有收到的'乱序'帧，直到更早的帧进来。
可能是4个BackgroundWorker的。从1-4传递一个数字到每个除了数据本身-并在他们的RunWorkerCompleted事件处理程序-检查是否所有其他3已经完成…(您可以使用bool[4])
据我所知-你不必担心2 RunWorkerCompleted 's同时被调用，因为它们都在同一个线程上运行。
我有一个类似的问题，我问在这个线程。
我确实想出了一个解决方案，似乎还可以，但对于你的目的来说似乎太复杂了。
它围绕着您能够提供3个委托:一个用于检索工作项(在您的情况下，它将返回Bitmap)，一个用于处理该工作项，最后一个用于输出该工作项。它还允许您指定将要运行的并发线程的最大数量——您可以使用它来限制内存使用。参见下面ParallelBlockProcessor构造函数中的numTasks参数。
只有处理委托可以被多个线程调用。
和您一样，我需要确保最终输出与原始输入的顺序相同。我使用了一个优先级队列。
使用。net 4.5的TPL可能有更好的解决方案，但我仅限于。net 4。
这是我想出的代码，我想你可以把它适应你的问题:
ParallelBlockProcessor类:using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.Threading.Tasks;
using ConsoleApplication1;
namespace Demo
{
public sealed class ParallelBlockProcessor<T> where T: class
{
public delegate T Read(); // Called by only one thread.
public delegate T Process(T block); // Called simultaneously by multiple threads.
public delegate void Write(T block); // Called by only one thread.
public ParallelBlockProcessor(Read read, Process process, Write write, int numTasks = 0)
{
Contract.Requires(read != null);
Contract.Requires(process != null);
Contract.Requires(write != null);
Contract.Requires((0 <= numTasks) && (numTasks <= 64));
_read = read;
_process = process;
_write = write;
numTasks = (numTasks > 0) ? numTasks : Environment.ProcessorCount;
_workPool = new BlockingCollection<WorkItem>(numTasks*2);
_inputQueue = new BlockingCollection<WorkItem>(numTasks);
_outputQueue = new ConcurrentPriorityQueue<int, T>();
_processors = new Task[numTasks];
initWorkItems();
startProcessors();
Task.Factory.StartNew(enqueueBlocks);
_dequeuer = Task.Factory.StartNew(dequeueBlocks);
}
private void startProcessors()
{
for (int i = 0; i < _processors.Length; ++i)
{
_processors[i] = Task.Factory.StartNew(processBlocks);
}
}
private void initWorkItems()
{
for (int i = 0; i < _workPool.BoundedCapacity; ++i)
{
_workPool.Add(new WorkItem());
}
}
private void enqueueBlocks()
{
int index = 0;
while (true)
{
T data = _read();
if (data == null)
{
_inputQueue.CompleteAdding();
_outputQueue.Enqueue(index, null); // Special terminator WorkItem.
break;
}
WorkItem workItem = _workPool.Take();
workItem.Data = data;
workItem.Index = index++;
_inputQueue.Add(workItem);
}
}
private void dequeueBlocks()
{
int index = 0; // Next required index.
int last = int.MaxValue;
while (true)
{
KeyValuePair<int, T> workItem;
_outputQueue.WaitForNewItem(); // There will always be at least one item - the sentinel item.
while (_outputQueue.TryPeek(out workItem))
{
if (workItem.Value == null) // The sentinel item has a null value to indicate that it's the sentinel.
{
last = workItem.Key; // The sentinel's key is the index of the last block + 1.
}
else if (workItem.Key == index) // Is this block the next one that we want?
{
// Even if new items are added to the queue while we're here, the new items will be lower priority.
// Therefore it is safe to assume that the item we will dequeue now is the same one we peeked at.
_outputQueue.TryDequeue(out workItem);
Contract.Assume(workItem.Key == index);
_workPool.Add(new WorkItem()); // Free up a work pool item.
_write(workItem.Value);
++index;
}
else // If it's not the block we want, we know we'll get a new item at some point.
{
_outputQueue.WaitForNewItem();
}
if (index == last)
{
return;
}
}
}
}
private void processBlocks()
{
foreach (var block in _inputQueue.GetConsumingEnumerable())
{
var processedData = _process(block.Data);
_outputQueue.Enqueue(block.Index, processedData);
}
}
public bool WaitForFinished(int maxMillisecondsToWait) // Can be Timeout.Infinite.
{
return _dequeuer.Wait(maxMillisecondsToWait);
}
private sealed class WorkItem // Note: This is mutable.
{
public T Data { get; set; }
public int Index { get; set; }
}
private readonly Task[] _processors;
private readonly Task _dequeuer;
private readonly BlockingCollection<WorkItem> _workPool;
private readonly BlockingCollection<WorkItem> _inputQueue;
private readonly ConcurrentPriorityQueue<int, T> _outputQueue;
private readonly Read _read;
private readonly Process _process;
private readonly Write _write;
}
}
优先队列(改编自微软):
using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Threading;
namespace ConsoleApplication1
{
/// <summary>Provides a thread-safe priority queue data structure.</summary>
/// <typeparam name="TKey">Specifies the type of keys used to prioritize values.</typeparam>
/// <typeparam name="TValue">Specifies the type of elements in the queue.</typeparam>
[SuppressMessage("Microsoft.Naming", "CA1711:IdentifiersShouldNotHaveIncorrectSuffix")]
[SuppressMessage("Microsoft.Naming", "CA1710:IdentifiersShouldHaveCorrectSuffix")]
[DebuggerDisplay("Count={Count}")]
public sealed class ConcurrentPriorityQueue<TKey, TValue> :
IProducerConsumerCollection<KeyValuePair<TKey,TValue>>
where TKey : IComparable<TKey>
{
/// <summary>Initializes a new instance of the ConcurrentPriorityQueue class.</summary>
public ConcurrentPriorityQueue() {}
/// <summary>Initializes a new instance of the ConcurrentPriorityQueue class that contains elements copied from the specified collection.</summary>
/// <param name="collection">The collection whose elements are copied to the new ConcurrentPriorityQueue.</param>
[SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures")]
public ConcurrentPriorityQueue(IEnumerable<KeyValuePair<TKey, TValue>> collection)
{
if (collection == null) throw new ArgumentNullException("collection");
foreach (var item in collection) _minHeap.Insert(item);
}
/// <summary>Adds the key/value pair to the priority queue.</summary>
/// <param name="priority">The priority of the item to be added.</param>
/// <param name="value">The item to be added.</param>
public void Enqueue(TKey priority, TValue value)
{
Enqueue(new KeyValuePair<TKey, TValue>(priority, value));
}
/// <summary>Adds the key/value pair to the priority queue.</summary>
/// <param name="item">The key/value pair to be added to the queue.</param>
public void Enqueue(KeyValuePair<TKey, TValue> item)
{
lock (_syncLock)
{
_minHeap.Insert(item);
_newItem.Set();
}
}
/// <summary>Waits for a new item to appear.</summary>
public void WaitForNewItem()
{
_newItem.WaitOne();
}
/// <summary>Attempts to remove and return the next prioritized item in the queue.</summary>
/// <param name="result">
/// When this method returns, if the operation was successful, result contains the object removed. If
/// no object was available to be removed, the value is unspecified.
/// </param>
/// <returns>
/// true if an element was removed and returned from the queue succesfully; otherwise, false.
/// </returns>
public bool TryDequeue(out KeyValuePair<TKey, TValue> result)
{
result = default(KeyValuePair<TKey, TValue>);
lock (_syncLock)
{
if (_minHeap.Count > 0)
{
result = _minHeap.Remove();
return true;
}
}
return false;
}
/// <summary>Attempts to return the next prioritized item in the queue.</summary>
/// <param name="result">
/// When this method returns, if the operation was successful, result contains the object.
/// The queue was not modified by the operation.
/// </param>
/// <returns>
/// true if an element was returned from the queue succesfully; otherwise, false.
/// </returns>
public bool TryPeek(out KeyValuePair<TKey, TValue> result)
{
result = default(KeyValuePair<TKey, TValue>);
lock (_syncLock)
{
if (_minHeap.Count > 0)
{
result = _minHeap.Peek();
return true;
}
}
return false;
}
/// <summary>Empties the queue.</summary>
public void Clear() { lock(_syncLock) _minHeap.Clear(); }
/// <summary>Gets whether the queue is empty.</summary>
public bool IsEmpty { get { return Count == 0; } }
/// <summary>Gets the number of elements contained in the queue.</summary>
public int Count
{
get { lock (_syncLock) return _minHeap.Count; }
}
/// <summary>Copies the elements of the collection to an array, starting at a particular array index.</summary>
/// <param name="array">
/// The one-dimensional array that is the destination of the elements copied from the queue.
/// </param>
/// <param name="index">
/// The zero-based index in array at which copying begins.
/// </param>
/// <remarks>The elements will not be copied to the array in any guaranteed order.</remarks>
public void CopyTo(KeyValuePair<TKey, TValue>[] array, int index)
{
lock (_syncLock) _minHeap.Items.CopyTo(array, index);
}
/// <summary>Copies the elements stored in the queue to a new array.</summary>
/// <returns>A new array containing a snapshot of elements copied from the queue.</returns>
public KeyValuePair<TKey, TValue>[] ToArray()
{
lock (_syncLock)
{
var clonedHeap = new MinBinaryHeap(_minHeap);
var result = new KeyValuePair<TKey, TValue>[_minHeap.Count];
for (int i = 0; i < result.Length; i++)
{
result[i] = clonedHeap.Remove();
}
return result;
}
}
/// <summary>Attempts to add an item in the queue.</summary>
/// <param name="item">The key/value pair to be added.</param>
/// <returns>
/// true if the pair was added; otherwise, false.
/// </returns>
bool IProducerConsumerCollection<KeyValuePair<TKey, TValue>>.TryAdd(KeyValuePair<TKey, TValue> item)
{
Enqueue(item);
return true;
}
/// <summary>Attempts to remove and return the next prioritized item in the queue.</summary>
/// <param name="item">
/// When this method returns, if the operation was successful, result contains the object removed. If
/// no object was available to be removed, the value is unspecified.
/// </param>
/// <returns>
/// true if an element was removed and returned from the queue succesfully; otherwise, false.
/// </returns>
bool IProducerConsumerCollection<KeyValuePair<TKey, TValue>>.TryTake(out KeyValuePair<TKey, TValue> item)
{
return TryDequeue(out item);
}
/// <summary>Returns an enumerator that iterates through the collection.</summary>
/// <returns>An enumerator for the contents of the queue.</returns>
/// <remarks>
/// The enumeration represents a moment-in-time snapshot of the contents of the queue. It does not
/// reflect any updates to the collection after GetEnumerator was called. The enumerator is safe to
/// use concurrently with reads from and writes to the queue.
/// </remarks>
public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
{
var arr = ToArray();
return ((IEnumerable<KeyValuePair<TKey, TValue>>)arr).GetEnumerator();
}
/// <summary>Returns an enumerator that iterates through a collection.</summary>
/// <returns>An IEnumerator that can be used to iterate through the collection.</returns>
IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); }
/// <summary>Copies the elements of the collection to an array, starting at a particular array index.</summary>
/// <param name="array">
/// The one-dimensional array that is the destination of the elements copied from the queue.
/// </param>
/// <param name="index">
/// The zero-based index in array at which copying begins.
/// </param>
void ICollection.CopyTo(Array array, int index)
{
lock (_syncLock) ((ICollection)_minHeap.Items).CopyTo(array, index);
}
/// <summary>
/// Gets a value indicating whether access to the ICollection is synchronized with the SyncRoot.
/// </summary>
bool ICollection.IsSynchronized { get { return true; } }
/// <summary>
/// Gets an object that can be used to synchronize access to the collection.
/// </summary>
object ICollection.SyncRoot { get { return _syncLock; } }
/// <summary>Implements a binary heap that prioritizes smaller values.</summary>
private sealed class MinBinaryHeap
{
private readonly List<KeyValuePair<TKey, TValue>> _items;
/// <summary>Initializes an empty heap.</summary>
public MinBinaryHeap()
{
_items = new List<KeyValuePair<TKey, TValue>>();
}
/// <summary>Initializes a heap as a copy of another heap instance.</summary>
/// <param name="heapToCopy">The heap to copy.</param>
/// <remarks>Key/Value values are not deep cloned.</remarks>
public MinBinaryHeap(MinBinaryHeap heapToCopy)
{
_items = new List<KeyValuePair<TKey, TValue>>(heapToCopy.Items);
}
/// <summary>Empties the heap.</summary>
public void Clear() { _items.Clear(); }
/// <summary>Adds an item to the heap.</summary>
public void Insert(KeyValuePair<TKey,TValue> entry)
{
// Add the item to the list, making sure to keep track of where it was added.
_items.Add(entry);
int pos = _items.Count - 1;
// If the new item is the only item, we're done.
if (pos == 0) return;
// Otherwise, perform log(n) operations, walking up the tree, swapping
// where necessary based on key values
while (pos > 0)
{
// Get the next position to check
int nextPos = (pos-1) / 2;
// Extract the entry at the next position
var toCheck = _items[nextPos];
// Compare that entry to our new one. If our entry has a smaller key, move it up.
// Otherwise, we're done.
if (entry.Key.CompareTo(toCheck.Key) < 0)
{
_items[pos] = toCheck;
pos = nextPos;
}
else break;
}
// Make sure we put this entry back in, just in case
_items[pos] = entry;
}
/// <summary>Returns the entry at the top of the heap.</summary>
public KeyValuePair<TKey, TValue> Peek()
{
// Returns the first item
if (_items.Count == 0) throw new InvalidOperationException("The heap is empty.");
return _items[0];
}
/// <summary>Removes the entry at the top of the heap.</summary>
public KeyValuePair<TKey, TValue> Remove()
{
// Get the first item and save it for later (this is what will be returned).
if (_items.Count == 0) throw new InvalidOperationException("The heap is empty.");
KeyValuePair<TKey, TValue> toReturn = _items[0];
// Remove the first item if there will only be 0 or 1 items left after doing so.
if (_items.Count <= 2) _items.RemoveAt(0);
// A reheapify will be required for the removal
else
{
// Remove the first item and move the last item to the front.
_items[0] = _items[_items.Count - 1];
_items.RemoveAt(_items.Count - 1);
// Start reheapify
int current = 0, possibleSwap = 0;
// Keep going until the tree is a heap
while (true)
{
// Get the positions of the node's children
int leftChildPos = 2 * current + 1;
int rightChildPos = leftChildPos + 1;
// Should we swap with the left child?
if (leftChildPos < _items.Count)
{
// Get the two entries to compare (node and its left child)
var entry1 = _items[current];
var entry2 = _items[leftChildPos];
// If the child has a lower key than the parent, set that as a possible swap
if (entry2.Key.CompareTo(entry1.Key) < 0) possibleSwap = leftChildPos;
}
else break; // if can't swap this, we're done
// Should we swap with the right child? Note that now we check with the possible swap
// position (which might be current and might be left child).
if (rightChildPos < _items.Count)
{
// Get the two entries to compare (node and its left child)
var entry1 = _items[possibleSwap];
var entry2 = _items[rightChildPos];
// If the child has a lower key than the parent, set that as a possible swap
if (entry2.Key.CompareTo(entry1.Key) < 0) possibleSwap = rightChildPos;
}
// Now swap current and possible swap if necessary
if (current != possibleSwap)
{
var temp = _items[current];
_items[current] = _items[possibleSwap];
_items[possibleSwap] = temp;
}
else break; // if nothing to swap, we're done
// Update current to the location of the swap
current = possibleSwap;
}
}
// Return the item from the heap
return toReturn;
}
/// <summary>Gets the number of objects stored in the heap.</summary>
public int Count { get { return _items.Count; } }
internal List<KeyValuePair<TKey, TValue>> Items { get { return _items; } }
}
private readonly AutoResetEvent _newItem = new AutoResetEvent(false);
private readonly object _syncLock = new object();
private readonly MinBinaryHeap _minHeap = new MinBinaryHeap();
}
}
测试程序:
using System;
using System.Diagnostics;
using System.Threading;
namespace Demo
{
public static class Program
{
private static void Main(string[] args)
{
_rng = new Random(34324);
int threadCount = 8;
int maxBlocks = 200;
ThreadPool.SetMinThreads(threadCount + 2, 4); // Kludge!
var stopwatch = new Stopwatch();
_numBlocks = maxBlocks;
stopwatch.Restart();
var processor = new ParallelBlockProcessor<byte[]>(read, process, write, threadCount);
processor.WaitForFinished(Timeout.Infinite);
Console.WriteLine("'n'nFinished in " + stopwatch.Elapsed + "'n'n");
}
private static byte[] read()
{
if (_numBlocks-- == 0)
{
return null;
}
var result = new byte[128];
result[0] = (byte)_numBlocks;
Console.WriteLine("Supplied input: " + _numBlocks);
return result;
}
private static byte[] process(byte[] data)
{
if (data[0] == 190)/*!*/
{
Thread.Sleep(5000);
}
Thread.Sleep(10 + _rng.Next(50));
Console.WriteLine("Processed: " + data[0]);
return data;
}
private static void write(byte[] data)
{
Console.WriteLine("Received output: " + data[0]);
}
private static Random _rng;
private static int _numBlocks;
}
}
您可以使用CountdownEVent，它允许您等待多个线程。
的例子:static CountdownEvent _countdown = new CountdownEvent (3);
static void Main()
{
new Thread (SaySomething).Start ("I am thread 1");
new Thread (SaySomething).Start ("I am thread 2");
new Thread (SaySomething).Start ("I am thread 3");
_countdown.Wait(); // Blocks until Signal has been called 3 times
Console.WriteLine ("All threads have finished speaking!");
}
static void SaySomething (object thing)
{
Thread.Sleep (1000);
Console.WriteLine (thing);
_countdown.Signal();
}
这段代码不保证线程1-3将按照这个顺序执行，但是如果你先调用信号方法，我相信应该解决这个问题
另一个更有效的方法是寻求实现Monitor.Pulse()和Monitor.Wait()机制，您可以将其与Thread结合使用。睡眠在理论上是指当一个线程完成执行临界区(在你的例子中是一个帧)时，让它进入睡眠状态。在一个线程完成对帧的处理后，将该线程置于睡眠状态，并对等待的线程进行脉冲操作，直到所有帧都完成，然后唤醒线程....线程很棘手，因为很难知道它们何时会完成执行。