好的,情况如下：我的主要/ UI线程(称之为Thread1)用于从phsycial文档扫描程序中获取一批图像.获取批次后,会启动一个单独的“后台”线程(称为Thread2)来处理并保存该批次中的图像.
Thread2(“后台”线程)使用Parallel.For循环,与正常For循环相比,可将图像处理/保存时间缩短70％.但是,它似乎也是最大化我的所有处理器,因此Thread1无法开始获取任何更多的图像,直到Parallel.For循环完成.
有没有办法“限制”一个Parallel.For循环,以便它不会最大化我的处理器？或者设置处理优先级？我尝试设置Thread2.Priority = ThreadPriority.Lowest,但这似乎不会影响循环.或者我误解了Parallel.For循环是如何工作的？是以某种方式阻止Thread1？
public void SaveWithSettings(bool save) // method in Thread1
{
....
Thread thr = new Thread(ThreadWork); // creating new thread (Thread 2)
thr.Priority = ThreadPriority.Lowest; // does nothing?
thr.Start(new SaveContainer(sc)); // pass a copy as paramater
// misc stuff to make scanning possible again
numBgw++;
twain.RemoveAllImages(); // clear images
imagelist.Clear(); // clear imagelist images
.... // etc. this all appears to process fine while Thread2 is processing
}
这是我的ThreadWork方法：
private void ThreadWork(object data) // executing in Thread2
{
SaveContainer sc = data as SaveContainer; // holds images
bool[] blankIndex = new bool[sc.imagelist.Count]; // to use in Parallel.For loop
for (int i = 0; i < sc.imagelist.Count; i++)
blankIndex[i] = false; // set default value to false (not blank)
Parallel.For(0,sc.imagelist.Count,i => // loop to mark blank images
{
bool x = false; // local vars make loop more efficient
x = sc.IsBlankImage((short)i); // check if image at index i is blank
blankIndex[i] = x; // set if image is blank
}
.... // other image processing steps
}
解决方法
public static void PriorityParallelForeach<T>(this IEnumerable<T> source,Action<T> action,ThreadPriority threadPriority,int? maxDegreeOfParallelism = null)
{
if (maxDegreeOfParallelism == null || maxDegreeOfParallelism<1)
{
maxDegreeOfParallelism = Environment.ProcessorCount;
}
var blockingQueue = new BlockingCollection<T>(new ConcurrentQueue<T>(source));
blockingQueue.CompleteAdding();
var tasks = new List<Task>() ;
for (int i = 0; i < maxDegreeOfParallelism; i++)
{
tasks.Add(Task.Factory.StartNew(() =>
{
while (!blockingQueue.IsCompleted)
{
T item;
try
{
item = blockingQueue.Take();
}
catch (InvalidOperationException)
{
// collection was already empty
break;
}
action(item);
}
},CancellationToken.None,TaskCreationOptions.None,new PriorityScheduler(threadPriority)));
}
Task.WaitAll(tasks.ToArray());
}
要不就：
Parallel.ForEach(testList,item =>
{
var privIoUsePrio = Thread.CurrentThread.Priority;
// Set your desired priority
Thread.CurrentThread.Priority = ThreadPriority.Lowest;
TestCalc(item);
//Reset privIoUse priority of the TPL Thread
Thread.CurrentThread.Priority = privIoUsePrio;
});
