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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_runningThreads = 0;
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int m_maxRunningThreads = 0;
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int m_suspended = 0;
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int m_exitRequired = 0;
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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 ThreadCount {
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get {
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return m_runningThreads;
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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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protected virtual bool ExtendPool() {
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if (m_suspended > 0) {
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m_hasTasks.Set();
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return true;
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} else
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return StartWorker();
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}
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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 WakePool() {
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m_hasTasks.Set(); // wake sleeping thread;
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if (AllocateThreadSlot(1)) {
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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 void Suspend() {
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m_hasTasks.WaitOne();
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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_runningThreads;
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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_runningThreads, 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_runningThreads, 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_runningThreads;
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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_runningThreads, 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_runningThreads);
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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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bool FetchTask(out TUnit unit) {
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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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if (ReleaseThreadSlotAnyway()) // it was the last worker
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m_hasTasks.Dispose();
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else
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m_hasTasks.Set(); // wake next worker
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unit = default(TUnit);
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return false;
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}
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// fetch task
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if (TryDequeue(out unit)) {
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ExtendPool();
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return true;
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}
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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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if (ReleaseThreadSlot(out last)) {
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if (last && m_hasTasks.WaitOne(0)) {
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if (AllocateThreadSlot(1))
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continue; // spin again...
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else
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// we failed to reallocate slot for this thread
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// therefore we need to release the event
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m_hasTasks.Set();
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}
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return false;
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}
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// entering suspend state
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Interlocked.Increment(ref m_suspended);
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// keep this thread and wait
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Suspend();
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Interlocked.Decrement(ref m_suspended);
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} while (true);
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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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while (FetchTask(out unit))
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InvokeUnit(unit);
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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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m_hasTasks.Set();
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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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