我一直在测试 System.Threading.Parallel 与 Threading 的性能,我很惊讶地看到 Parallel 完成任务比线程花费更长的时间。我确信这是由于我对 Parallel 的了解有限,而我刚刚开始阅读。
我想我会分享一些片段,如果有人可以向我指出并行代码与线程代码相比运行速度较慢。还尝试运行相同的比较来查找素数,并发现并行代码的完成时间比线程代码晚得多。
public class ThreadFactory
{
int workersCount;
private List<Thread> threads = new List<Thread>();
public ThreadFactory(int threadCount, int workCount, Action<int, int, string> action)
{
workersCount = threadCount;
int totalWorkLoad = workCount;
int workLoad = totalWorkLoad / workersCount;
int extraLoad = totalWorkLoad % workersCount;
for (int i = 0; i < workersCount; i++)
{
int min, max;
if (i < (workersCount - 1))
{
min = (i * workLoad);
max = ((i * workLoad) + workLoad - 1);
}
else
{
min = (i * workLoad);
max = (i * workLoad) + (workLoad - 1 + extraLoad);
}
string name = "Working Thread#" + i;
Thread worker = new Thread(() => { action(min, max, name); });
worker.Name = name;
threads.Add(worker);
}
}
public void StartWorking()
{
foreach (Thread thread in threads)
{
thread.Start();
}
foreach (Thread thread in threads)
{
thread.Join();
}
}
}
这是程序:
Stopwatch watch = new Stopwatch();
watch.Start();
int path = 1;
List<int> numbers = new List<int>(Enumerable.Range(0, 10000));
if (path == 1)
{
Parallel.ForEach(numbers, x =>
{
Console.WriteLine(x);
Thread.Sleep(1);
});
}
else
{
ThreadFactory workers = new ThreadFactory(10, numbers.Count, (min, max, text) => {
for (int i = min; i <= max; i++)
{
Console.WriteLine(numbers[i]);
Thread.Sleep(1);
}
});
workers.StartWorking();
}
watch.Stop();
Console.WriteLine(watch.Elapsed.TotalSeconds.ToString());
Console.ReadLine();
更新:
考虑到锁定:我尝试了以下代码段。同样的结果,Parallel 似乎完成得慢得多。
路径 = 1; 雪灵= 10000000;
List<int> numbers = new List<int>();
if (path == 1)
{
Parallel.For(0, cieling, x =>
{
lock (numbers)
{
numbers.Add(x);
}
});
}
else
{
ThreadFactory workers = new ThreadFactory(10, cieling, (min, max, text) =>
{
for (int i = min; i <= max; i++)
{
lock (numbers)
{
numbers.Add(i);
}
}
});
workers.StartWorking();
}
更新 2: 我的机器有四核处理器的快速更新。所以 Parallel 有 4 个内核可用。