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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

并行容器:

•ConcurrentQueue
•ConcurrentStack
•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
•ConcurrentDictionary 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。 关于CAS: •http://www.tuicool.com/articles/zuui6z
•http://www.360doc.com/content/11/0914/16/7656248_148221200.shtml 关于内存屏障 •http://en.wikipedia.org/wiki/Memory_barrier 用法与示例 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。 程序示例: using System;
using System.Text; using System.Threading.Tasks;
using System.Collections.Concurrent; namespace Sample4_1_concurrent_queue
{
class Program
{
internal static ConcurrentQueue<int> _TestQueue; class ThreadWork1 // producer
{
public ThreadWork1()
{ } public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = ; i < ; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestQueue.Enqueue(i);
}
System.Console.WriteLine("ThreadWork1 run } ");
}
} class ThreadWork2 // consumer
{
public ThreadWork2()
{ } public void run()
{
int i = ;
bool IsDequeuue = false;
System.Console.WriteLine("ThreadWork2 run { ");
for (; ; )
{
IsDequeuue = _TestQueue.TryDequeue(out i);
if (IsDequeuue)
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " ====="); if (i == )
break;
}
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()); _TestQueue = new ConcurrentQueue<int>(); Console.WriteLine("Sample 3-1 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 3-1 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。 程序示例: using System;
using System.Text; using System.Threading.Tasks;
using System.Collections.Concurrent; namespace Sample4_2_concurrent_stack
{
class Program
{
internal static ConcurrentStack<int> _TestStack; class ThreadWork1 // producer
{
public ThreadWork1()
{ } public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = ; i < ; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestStack.Push(i);
}
System.Console.WriteLine("ThreadWork1 run } ");
}
} class ThreadWork2 // consumer
{
public ThreadWork2()
{ } public void run()
{
int i = ;
bool IsDequeuue = false;
System.Console.WriteLine("ThreadWork2 run { ");
for (; ; )
{
IsDequeuue = _TestStack.TryPop(out i);
if (IsDequeuue)
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " =====" + i); if (i == )
break;
}
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()); _TestStack = new ConcurrentStack<int>(); Console.WriteLine("Sample 4-1 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 4-1 Main }"); Console.ReadKey();
}
}
} 测试中一个有趣的现象: 虽然生产者已经在栈中插入值已经到了25,但消费者第一个出栈的居然是4,而不是25。很像是出错了。但仔细想想入栈,出栈和打印语句是两个部分,而且并不是原子操作,出现这种现象应该也算正常。 Sample - Main {
Main t1 t2 started {
Main t1 t2 started }
Main wait t1 t2 end {
ThreadWork1 run {
ThreadWork1 producer:
ThreadWork2 run {
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork2 consumer: =====
ThreadWork2 consumer: =====
ThreadWork2 consumer: =====
ThreadWork2 consumer: =====
ThreadWork1 producer:
ThreadWork1 producer:
ThreadWork1 producer: 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。 程序示例: using System;
using System.Text; using System.Threading.Tasks;
using System.Collections.Concurrent; namespace Sample4_3_concurrent_bag
{
class Program
{
internal static ConcurrentBag<int> _TestBag; class ThreadWork1 // producer
{
public ThreadWork1()
{ } public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = ; i < ; i++)
{
System.Console.WriteLine("ThreadWork1 producer: " + i);
_TestBag.Add(i);
}
System.Console.WriteLine("ThreadWork1 run } ");
}
} class ThreadWork2 // consumer
{
public ThreadWork2()
{ } public void run()
{
int i = ;
int nCnt = ;
bool IsDequeuue = false;
System.Console.WriteLine("ThreadWork2 run { ");
for (;;)
{
IsDequeuue = _TestBag.TryTake(out i);
if (IsDequeuue)
{
System.Console.WriteLine("ThreadWork2 consumer: " + i * i + " =====" + i);
nCnt++;
} if (nCnt == )
break;
}
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()); _TestBag = new ConcurrentBag<int>(); Console.WriteLine("Sample 4-3 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 4-3 Main }"); Console.ReadKey();
}
}
} 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。 示例程序: 程序中,消费者线程完全使用 while (!_TestBCollection.IsCompleted) 作为退出运行的判断条件。 在Worker1中,有两条语句被注释掉了,当i 为50时设置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。 using System;
using System.Text; using System.Threading.Tasks;
using System.Collections.Concurrent; namespace Sample4_4_concurrent_bag
{
class Program
{
internal static BlockingCollection<int> _TestBCollection; class ThreadWork1 // producer
{
public ThreadWork1()
{ } public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = ; i < ; 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 = ;
int nCnt = ;
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();
}
}
} 当然可以尝试在Work1中注释掉 CompleteAdding 语句,此时Work2陷入循环无法退出。 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。 程序示例: using System;
using System.Text; using System.Threading.Tasks;
using System.Collections.Concurrent; namespace Sample4_5_concurrent_dictionary
{
class Program
{
internal static ConcurrentDictionary<int, int> _TestDictionary; class ThreadWork1 // producer
{
public ThreadWork1()
{ } public void run()
{
System.Console.WriteLine("ThreadWork1 run { ");
for (int i = ; i < ; 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 = , nCnt = ;
int nValue = ;
bool IsOk = false;
System.Console.WriteLine("ThreadWork2 run { ");
while (nCnt < )
{
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 = ; _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 }"); 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);
} Console.WriteLine("\n\nDictionary Count: " + _TestDictionary.Count); Console.WriteLine("Sample 4-5 Main }"); Console.ReadKey();
}
}
}

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