对于并行任务，与其相关紧密的就是对一些共享资源，数据结构的并行访问。经常要做的就是对一些队列进行加锁-解锁，然后执行类似插入，删除等等互斥操作。 .NetFramework 4.0 中提供了一些封装好的支持并行操作数据容器，可以减少并行编程的复杂程度。
基本信息
.NetFramework中并行集合的名字空间： System.Collections.Concurrent
并发容器
- ConcurrentQueue
- ConcurrentStack
- ConcurrentDictionary
- ConcurrentBag:一个无序的数据结构集，当不需要考虑顺序时非常有用。
- BlockingCollection与经典的阻塞队列数据结构类似
这些集合在某种程度上使用了无锁技术(CAS Compare-and-Swap和内存屏障Memory Barrier)，与加互斥锁相比获得了性能的提升。但在串行程序中，最好不用这些集合，它们必然会影响性能。
ConcurrentQueue
其完全无锁，但当CAS面临资源竞争失败时可能会陷入自旋并重试操作。
- Enqueue:在队尾插入元素
- TryDequeue:尝试删除队头元素，并通过out参数返回
- TryPeek:尝试将对头元素通过out参数返回，但不删除该元素。
class Program
{
internal static ConcurrentQueue<int> _TestQueue;
class ThreadWork1 // producer
{
public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = 0; i < 30; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestQueue.Enqueue(i);
}
System.Console.WriteLine("ThreadWork1 run } ");
}
}
class ThreadWork2 // consumer
{
public void run()
{
int i=0;
bool IsDequeuue = false;
System.Console.WriteLine("ThreadWork2 run { ");
for (;; i++)
{
IsDequeuue = _TestQueue.TryDequeue(out i);
if (IsDequeuue)
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " =====");
if (i == 29)
break;
}
System.Console.WriteLine("ThreadWork2 run } ");
}
}
static void StartT1()
{
ThreadWork1 work1 = new ThreadWork1();
work1.run();
}
static void StartT2()
{
ThreadWork2 work2 = new ThreadWork2();
work2.run();
}
public static void Main()
{
Task t1 = new Task(() => StartT1());
Task t2 = new Task(() => StartT2());
_TestQueue = new ConcurrentQueue<int>();
Console.WriteLine("Main {");
Console.WriteLine("Main t1 t2 started {");
t1.Start();
t2.Start();
Console.WriteLine("Main t1 t2 started }");
Console.WriteLine("Main wait t1 t2 end {");
Task.WaitAll(t1, t2);
Console.WriteLine("Main wait t1 t2 end }");
Console.WriteLine("Main }");
Console.ReadKey();
}
}
ConcurrentStack
其完全无锁，但当CAS面临资源竞争失败时可能会陷入自旋并重试操作。
- Push:向栈顶插入元素
- TryPop:从栈顶弹出元素，并且通过out 参数返回
- TryPeek:返回栈顶元素，但不弹出
ConcurrentBag
一个无序的集合，程序可以向其中插入元素，或删除元素。
在同一个线程中向集合插入，删除元素的效率很高。
- Add:向集合中插入元素
- TryTake:从集合中取出元素并删除
- TryPeek:从集合中取出元素，但不删除该元素。
BlockingCollection
一个支持界限和阻塞的容器
- Add:向容器中插入元素
- TryTake:从容器中取出元素并删除
- TryPeek:从容器中取出元素，但不删除。
- CompleteAdding:告诉容器，添加元素完成。此时如果还想继续添加会发生异常。
- IsCompleted:告诉消费线程，生产者线程还在继续运行中，任务还未完成。
要点一：消费者线程完全使用 while (!_TestBCollection.IsCompleted) 作为退出运行的判断条件
要点二:当BlockingCollection对象设置为CompleteAdding（.CompleteAdding()），但当继续向其中插入元素时，系统抛出异常，提示无法再继续插入。
class Program
{
internal static BlockingCollection<int> _TestBCollection;
class ThreadWork1 // producer
{
public ThreadWork1()
{ }
public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = 0; i < 100; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestBCollection.Add(i);
//if (i == 50)
// _TestBCollection.CompleteAdding();
}
_TestBCollection.CompleteAdding();
System.Console.WriteLine("ThreadWork1 run } ");
}
}
class ThreadWork2 // consumer
{
public ThreadWork2()
{ }
public void run()
{
int i = 0;
int nCnt = 0;
bool IsDequeuue = false;
System.Console.WriteLine("ThreadWork2 run { ");
while (!_TestBCollection.IsCompleted)
{
IsDequeuue = _TestBCollection.TryTake(out i);
if (IsDequeuue)
{
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " =====" + i);
nCnt++;
}
}
System.Console.WriteLine("ThreadWork2 run } ");
}
}
static void StartT1()
{
ThreadWork1 work1 = new ThreadWork1();
work1.run();
}
static void StartT2()
{
ThreadWork2 work2 = new ThreadWork2();
work2.run();
}
static void Main(string[] args)
{
Task t1 = new Task(() => StartT1());
Task t2 = new Task(() => StartT2());
_TestBCollection = new BlockingCollection<int>();
Console.WriteLine("Sample 4-4 Main {");
Console.WriteLine("Main t1 t2 started {");
t1.Start();
t2.Start();
Console.WriteLine("Main t1 t2 started }");
Console.WriteLine("Main wait t1 t2 end {");
Task.WaitAll(t1, t2);
Console.WriteLine("Main wait t1 t2 end }");
Console.WriteLine("Sample 4-4 Main }");
Console.ReadKey();
}
}
ConcurrentDictionary
对于读操作是完全无锁的，当很多线程要修改数据时，它会使用细粒度的锁。
- AddOrUpdate:如果键不存在，方法会在容器中添加新的键和值，如果存在，则更新现有的键和值。
- GetOrAdd:如果键不存在，方法会向容器中添加新的键和值，如果存在则返回现有的值，并不添加新值。
- TryAdd:尝试在容器中添加新的键和值。
- TryGetValue:尝试根据指定的键获得值。
- TryRemove:尝试删除指定的键。
- TryUpdate:有条件的更新当前键所对应的值。
- GetEnumerator:返回一个能够遍历整个容器的枚举器。
class Program
{
internal static ConcurrentDictionary<int, int> _TestDictionary;
class ThreadWork1 // producer
{
public ThreadWork1()
{ }
public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = 0; i < 100; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestDictionary.TryAdd(i, i);
}
System.Console.WriteLine("ThreadWork1 run } ");
}
}
class ThreadWork2 // consumer
{
public ThreadWork2()
{ }
public void run()
{
int i = 0, nCnt = 0;
int nValue = 0;
bool IsOk = false;
System.Console.WriteLine("ThreadWork2 run { ");
while (nCnt < 100)
{
IsOk = _TestDictionary.TryGetValue(i, out nValue);
if (IsOk)
{
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " =====" + i);
nValue = nValue * nValue;
_TestDictionary.AddOrUpdate(i, nValue, (key, value) => { return value = nValue; });
nCnt++;
i++;
}
}
System.Console.WriteLine("ThreadWork2 run } ");
}
}
static void StartT1()
{
ThreadWork1 work1 = new ThreadWork1();
work1.run();
}
static void StartT2()
{
ThreadWork2 work2 = new ThreadWork2();
work2.run();
}
static void Main(string[] args)
{
Task t1 = new Task(() => StartT1());
Task t2 = new Task(() => StartT2());
bool bIsNext = true;
int nValue = 0;
_TestDictionary = new ConcurrentDictionary<int, int>();
Console.WriteLine("Sample 4-5 Main {");
Console.WriteLine("Main t1 t2 started {");
t1.Start();
t2.Start();
Console.WriteLine("Main t1 t2 started }");
Console.WriteLine("Main wait t1 t2 end {");
Task.WaitAll(t1, t2);
Console.WriteLine("Main wait t1 t2 end }");
#region 其他
foreach (var pair in _TestDictionary)
{
Console.WriteLine(pair.Key + " : " + pair.Value);
}
System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<int, int>>
enumer = _TestDictionary.GetEnumerator();
while (bIsNext)
{
bIsNext = enumer.MoveNext();
Console.WriteLine("Key: " + enumer.Current.Key +
" Value: " + enumer.Current.Value);
_TestDictionary.TryRemove(enumer.Current.Key, out nValue);
}
#endregion
Console.WriteLine("
Dictionary Count: " + _TestDictionary.Count);
Console.WriteLine("Sample 4-5 Main }");
Console.ReadKey();
}
}
