线程池执行延迟疑问

Question

我已在循环中对 10 个委托调用 BeginInvoke。线程池不使用 10 个线程，而是仅使用两/三个线程来执行委托。有人可以解释一下原因吗？委托执行仅需几毫秒（不到 10 毫秒）。

当我在调用 BeginInvoke 之前记录线程池参数时，它表明最小线程 = 2、最大线程 = 500、可用线程 = 498。

---

当我调用以下托管 C++ 代码时，我遇到了问题。

void EventHelper::FireAndForget(Delegate^ d, ... array<Object^>^ args)
            {
                try
                {
                    if (d != nullptr)
                    {                                           
                        array<Delegate^>^ delegates = d->GetInvocationList();   

                        String^ message1 = String::Format("No of items in the event {0}",delegates.Length);
                        Log(LogMessageType::Information,"EventHelper.FireAndForget", message1);

                        // Iterating through the list of delegate methods.
                        for each(Delegate^ delegateMethod in delegates)
                        {
                            try
                            {
                                int minworkerThreads,maxworkerThreads,availworkerThreads, completionPortThreads;
                                ThreadPool::GetMinThreads(minworkerThreads, completionPortThreads);
                                ThreadPool::GetMaxThreads(maxworkerThreads, completionPortThreads);
                                ThreadPool::GetAvailableThreads(availworkerThreads, completionPortThreads);

                                String^ message = String::Format("FireAndForget Method {0}#{1} MinThreads - {2}, MaxThreads - {3} AvailableThreads - {4}",
                                                delegateMethod->Method->DeclaringType, delegateMethod->Method->Name, minworkerThreads, maxworkerThreads, availworkerThreads);

                                Log(LogMessageType::Information,"EventHelper.FireAndForget", message);

                                DynamicInvokeAsyncProc^ evtDelegate = gcnew DynamicInvokeAsyncProc(this, &EventHelper::OnTriggerEvent);
                                evtDelegate->BeginInvoke(delegateMethod, args, _dynamicAsyncResult, nullptr); //FIX_DEC_09 Handle Leak    
                            }
                            catch (Exception^ ex)
                            {
                                String^ message = String::Format("{0} : DynamicInvokeAsync of '{1}.{2}' failed", _id,
                                                                    delegateMethod->Method->DeclaringType, d->Method->Name);

                                Log(LogMessageType::Information,"EventHelper.FireAndForget", message);                              
                            }
                        }
                    }
                    else
                    {                   
                    }
                }
                catch (Exception^ e)
                {
                    Log(LogMessageType::Error, "EventHelper.FireAndForget", e->ToString());
                }

            }

---

这是委托中给出的方法

void EventHelper::OnTriggerEvent(Delegate^ delegateMethod, array<Object^>^ args)
            {
                try
                {
                    int minworkerThreads,maxworkerThreads,availworkerThreads, completionPortThreads;
                    ThreadPool::GetMinThreads(minworkerThreads, completionPortThreads);
                    ThreadPool::GetMaxThreads(maxworkerThreads, completionPortThreads);
                    ThreadPool::GetAvailableThreads(availworkerThreads, completionPortThreads);

                    String^ message = String::Format("OnTriggerEvent Method {0}#{1} MinThreads - {2}, MaxThreads - {3} AvailableThreads - {4}",
                                    delegateMethod->Method->DeclaringType, delegateMethod->Method->Name, minworkerThreads, maxworkerThreads, availworkerThreads);
                    Log(LogMessageType::Information,"EventHelper::OnTriggerEvent", message);

                    message = String::Format("Before Invoke Method {0}#{1}",
                                                delegateMethod->Method->DeclaringType, delegateMethod->Method->Name);
                    Log(LogMessageType::Information,"EventHelper::OnTriggerEvent", message);

                    // Dynamically invokes (late-bound) the method represented by the current delegate. 
                    delegateMethod->DynamicInvoke(args);
                    message = String::Format("After Invoke Method {0}#{1}",
                                                delegateMethod->Method->DeclaringType, delegateMethod->Method->Name);
                    Log(LogMessageType::Information,"EventHelper::OnTriggerEvent", message);
                }
                catch (Exception^ ex)
                {
                    Log(LogMessageType::Error, "EventHelper.OnTriggerEvent", ex->ToString());
                }
            }

Answer 1

您不希望为此创建 10 个线程。最佳情况是拥有与核心一样多的活动线程。您会发现 ThreadPool.MinThreads 等于 PC 上逻辑 CPU 的数量。

将创建其他线程，但线程池故意延迟创建。 Fx4中的算法得到了改进，请参见此页面< /a>.快速浏览一下底部的图片将帮助您理解其原理。

额外的线程仅有助于补偿阻塞的线程，但这很难完全正确。

Answer 2

线程池在启动新线程之前故意等待一段时间 - 如果委托无论如何都快速执行（听起来确实如此），那么在几个线程上执行它们比启动新线程更有效。

来自 ThreadPool 的文档：

当所有线程池线程都已完成时
分配给任务，线程池
不立即开始创建
新的空闲线程。为了避免
不必要地分配堆栈空间
对于线程，它会创建新的空闲
间隔的线程。间隔为
目前是半秒，尽管
可能会在未来版本中改变
.NET 框架..NET 框架。