的Parallel.For失败(C#) [英] Parallel.For fail (C#)
问题描述
我写了一些代码:
class Program
{
public const int count = 3000;
static List<int> list = new List<int>();
static void DoWork(int i)
{
list.Add(i);
}
static void Main(string[] args)
{
while (true)
{
Stopwatch s = new Stopwatch();
s.Start();
Parallel.For(0, count + 1, DoWork);
s.Stop();
Console.WriteLine("\n Elapsed: " + s.Elapsed.ToString());
Console.WriteLine("Expected: {0}", count + 1);
Console.WriteLine("count: {0}", list.Count);
Console.ReadKey();
list = new List<int>();
}
}
}
但结果没有预期(
but results are not expected(
Console.WriteLine调用之前,并非所有的周期完成
Not all of the cycles are finished before Console.WriteLine calls
什么是使用并行的问题。对于?
What is the problem with using Parallel.For?
推荐答案
您正在运行到什么叫做的竞争条件,由于列表集合在.NET是不是线程安全的,这是如添加()
不是原子操作基本上调用Add()方法在一个线程可以破坏另一个线程的Add()完成之前,你需要为你的代码是线程安全的并发收集。
You're running into what's known as a Race Condition. Since the List collection in .Net isn't thread safe, it's operations such as Add()
aren't atomic. Basically a call to Add() on one thread can destroy another thread's Add() before it is complete. You need a thread-safe concurrent collection for your code.
试试这个:使用System.Threading.Tasks
Try this:
using System.Threading.Tasks;
class Program
{
public const int count = 3000;
static ConcurrentBag<int> bag = new ConcurrentBag<int>();
static void DoWork(int i)
{
bag.Add(i);
}
static void Main(string[] args)
{
while (true)
{
Stopwatch s = new Stopwatch();
s.Start();
Parallel.For(0, count + 1, DoWork);
s.Stop();
Console.WriteLine("\n Elapsed: " + s.Elapsed.ToString());
Console.WriteLine("Expected: {0}", count + 1);
Console.WriteLine("count: {0}", bag.Count);
Console.ReadKey();
bag = new ConcurrentBag<int>();
}
}
}
的
ConcurrentBag是最接近一个线程安全的列表。只要记住,因为我们正在处理的未知调度,整数不会为了。
The ConcurrentBag is the closest thing to a thread-safe list. Just remember since we are dealing with unknown scheduling, the integers won't be in order.
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