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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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using System.Threading;
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using System.Diagnostics;
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namespace Implab.Parallels {
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public abstract class DispatchPool<TUnit> : IDisposable {
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readonly int m_minThreads;
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readonly int m_maxThreads;
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int m_createdThreads = 0; // the current size of the pool
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int m_activeThreads = 0; // the count of threads which are active
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int m_sleepingThreads = 0; // the count of currently inactive threads
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int m_maxRunningThreads = 0; // the meximum reached size of the pool
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int m_exitRequired = 0; // the pool is going to shutdown, all unused workers are released
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int m_releaseTimeout = 100; // the timeout while the working thread will wait for the new tasks before exit
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int m_wakeEvents = 0; // the count of wake events
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AutoResetEvent m_hasTasks = new AutoResetEvent(false);
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protected DispatchPool(int min, int max) {
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if (min < 0)
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throw new ArgumentOutOfRangeException("min");
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if (max <= 0)
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throw new ArgumentOutOfRangeException("max");
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if (min > max)
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min = max;
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m_minThreads = min;
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m_maxThreads = max;
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}
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protected DispatchPool(int threads)
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: this(threads, threads) {
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}
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protected DispatchPool() {
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int maxThreads, maxCP;
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ThreadPool.GetMaxThreads(out maxThreads, out maxCP);
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m_minThreads = 0;
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m_maxThreads = maxThreads;
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}
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protected void InitPool() {
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for (int i = 0; i < m_minThreads; i++)
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StartWorker();
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}
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public int PoolSize {
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get {
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return m_createdThreads;
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}
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}
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public int ActiveThreads {
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get {
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return m_activeThreads;
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}
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}
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public int MaxRunningThreads {
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get {
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return m_maxRunningThreads;
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}
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}
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protected bool IsDisposed {
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get {
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return m_exitRequired != 0;
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}
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}
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protected abstract bool TryDequeue(out TUnit unit);
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#region thread execution traits
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int SignalThread() {
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var signals = Interlocked.Increment(ref m_wakeEvents);
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if(signals == 1)
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m_hasTasks.Set();
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return signals;
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}
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bool FetchSignalOrWait(int timeout) {
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var start = Environment.TickCount;
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// означает, что поток владеет блокировкой и при успешном получении сигнала должен
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// ее вернуть, чтобы другой ожидающий поток смог
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bool hasLock = false;
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do {
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int signals;
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do {
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signals = m_wakeEvents;
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if (signals == 0)
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break;
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} while (Interlocked.CompareExchange(ref m_wakeEvents, signals - 1, signals) != signals);
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if (signals >= 1) {
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if (signals > 1 && hasLock)
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m_hasTasks.Set();
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return true;
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}
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if (timeout != -1)
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timeout = Math.Max(0, timeout - (Environment.TickCount - start));
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// если сигналов больше не осталось, то первый поток, который дошел сюда сбросит событие
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// и уйдет на пустой цикл, после чего заблокируется
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hasLock = true;
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} while (m_hasTasks.WaitOne(timeout));
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return false;
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}
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bool Sleep(int timeout) {
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Interlocked.Increment(ref m_sleepingThreads);
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if (FetchSignalOrWait(timeout)) {
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Interlocked.Decrement(ref m_sleepingThreads);
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return true;
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} else {
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Interlocked.Decrement(ref m_sleepingThreads);
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return false;
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}
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}
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#endregion
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/// <summary>
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/// Запускает либо новый поток, если раньше не было ни одного потока, либо устанавливает событие пробуждение одного спящего потока
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/// </summary>
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protected void GrowPool() {
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if (m_exitRequired != 0)
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return;
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if (m_sleepingThreads > m_wakeEvents) {
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//Console.WriteLine("Waking threads (sleeps {0}, pending {1})", m_sleepingThreads, m_wakeEvents);
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// all sleeping threads may gone
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SignalThread(); // wake a sleeping thread;
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// we can't check whether signal has been processed
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// anyway it may take some time for the thread to start
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// we will ensure that at least one thread is running
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EnsurePoolIsAlive();
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} else {
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// if there is no sleeping threads in the pool
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if (!StartWorker()) {
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// we haven't started a new thread, but the current can be on the way to terminate and it can't process the queue
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// send it a signal to spin again
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SignalThread();
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EnsurePoolIsAlive();
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}
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}
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}
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protected void EnsurePoolIsAlive() {
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if (AllocateThreadSlot(1)) {
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// if there were no threads in the pool
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var worker = new Thread(this.Worker);
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worker.IsBackground = true;
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worker.Start();
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}
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}
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protected virtual bool Suspend() {
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//no tasks left, exit if the thread is no longer needed
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bool last;
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bool requestExit;
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// if threads have a timeout before releasing
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if (m_releaseTimeout > 0)
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requestExit = !Sleep(m_releaseTimeout);
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else
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requestExit = true;
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if (!requestExit)
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return true;
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// release unsused thread
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if (requestExit && ReleaseThreadSlot(out last)) {
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// in case at the moment the last thread was being released
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// a new task was added to the queue, we need to try
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// to revoke the thread to avoid the situation when the task is left unprocessed
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if (last && FetchSignalOrWait(0)) { // FetchSignalOrWait(0) will fetch pending task or will return false
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SignalThread(); // since FetchSignalOrWait(0) has fetched the signal we need to reschedule it
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return AllocateThreadSlot(1); // ensure that at least one thread is alive
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}
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return false;
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}
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// wait till infinity
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Sleep(-1);
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return true;
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}
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#region thread slots traits
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bool AllocateThreadSlot() {
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int current;
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// use spins to allocate slot for the new thread
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do {
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current = m_createdThreads;
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if (current >= m_maxThreads || m_exitRequired != 0)
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// no more slots left or the pool has been disposed
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return false;
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} while (current != Interlocked.CompareExchange(ref m_createdThreads, current + 1, current));
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UpdateMaxThreads(current + 1);
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return true;
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}
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bool AllocateThreadSlot(int desired) {
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if (desired - 1 != Interlocked.CompareExchange(ref m_createdThreads, desired, desired - 1))
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return false;
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UpdateMaxThreads(desired);
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return true;
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}
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bool ReleaseThreadSlot(out bool last) {
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last = false;
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int current;
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// use spins to release slot for the new thread
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do {
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current = m_createdThreads;
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if (current <= m_minThreads && m_exitRequired == 0)
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// the thread is reserved
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return false;
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} while (current != Interlocked.CompareExchange(ref m_createdThreads, current - 1, current));
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last = (current == 1);
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return true;
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}
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/// <summary>
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/// releases thread slot unconditionally, used during cleanup
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/// </summary>
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/// <returns>true - no more threads left</returns>
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bool ReleaseThreadSlotAnyway() {
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var left = Interlocked.Decrement(ref m_createdThreads);
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return left == 0;
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}
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void UpdateMaxThreads(int count) {
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int max;
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do {
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max = m_maxRunningThreads;
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if (max >= count)
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break;
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} while(max != Interlocked.CompareExchange(ref m_maxRunningThreads, count, max));
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}
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#endregion
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bool StartWorker() {
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if (AllocateThreadSlot()) {
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// slot successfully allocated
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var worker = new Thread(this.Worker);
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worker.IsBackground = true;
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worker.Start();
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return true;
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} else {
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return false;
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}
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}
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protected abstract void InvokeUnit(TUnit unit);
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void Worker() {
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TUnit unit;
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//Console.WriteLine("{0}: Active", Thread.CurrentThread.ManagedThreadId);
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Interlocked.Increment(ref m_activeThreads);
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do {
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// exit if requested
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if (m_exitRequired != 0) {
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// release the thread slot
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Interlocked.Decrement(ref m_activeThreads);
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if (ReleaseThreadSlotAnyway()) // it was the last worker
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m_hasTasks.Dispose();
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else
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SignalThread(); // wake next worker
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break;
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}
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// fetch task
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if (TryDequeue(out unit)) {
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InvokeUnit(unit);
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continue;
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}
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Interlocked.Decrement(ref m_activeThreads);
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// entering suspend state
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// keep this thread and wait
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if (!Suspend())
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break;
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//Console.WriteLine("{0}: Awake", Thread.CurrentThread.ManagedThreadId);
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Interlocked.Increment(ref m_activeThreads);
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} while (true);
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//Console.WriteLine("{0}: Exited", Thread.CurrentThread.ManagedThreadId);
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}
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protected virtual void Dispose(bool disposing) {
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if (disposing) {
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if (m_exitRequired == 0) {
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if (Interlocked.CompareExchange(ref m_exitRequired, 1, 0) != 0)
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return;
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// wake sleeping threads
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if (m_createdThreads > 0)
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SignalThread();
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else
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m_hasTasks.Dispose();
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GC.SuppressFinalize(this);
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}
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}
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}
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public void Dispose() {
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Dispose(true);
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}
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~DispatchPool() {
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Dispose(false);
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}
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}
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}
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