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using System;
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using System.Threading;
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namespace Implab.Parallels {
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public abstract class DispatchPool<TUnit> : IDisposable {
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readonly int m_minThreadsLimit;
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readonly int m_maxThreadsLimit;
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readonly int m_releaseTimeout = 1000; // the timeout while the working thread will wait for the new tasks before exit
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int m_threads; // the current size of the pool
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int m_maxRunningThreads; // the meximum reached size of the pool
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int m_exit; // the pool is going to shutdown, all unused workers are released
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readonly object m_signal = new object(); // used to pulse waiting threads
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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_minThreadsLimit = min;
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m_maxThreadsLimit = 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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m_minThreadsLimit = 0;
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m_maxThreadsLimit = Environment.ProcessorCount;
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}
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protected void InitPool() {
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for (int i = 0; i < m_minThreadsLimit; 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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Thread.MemoryBarrier();
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return m_threads;
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}
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}
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public int MaxRunningThreads {
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get {
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Thread.MemoryBarrier();
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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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Thread.MemoryBarrier();
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return m_exit == 1;
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}
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}
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protected abstract bool TryDequeue(out TUnit unit);
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bool Dequeue(out TUnit unit, int timeout) {
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int ts = Environment.TickCount;
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if (TryDequeue(out unit))
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return true;
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lock (m_signal) {
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while (!TryDequeue(out unit) && m_exit == 0)
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if(!Monitor.Wait(m_signal, Math.Max(0, ts + timeout - Environment.TickCount))) {
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// timeout
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return false;
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}
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// queue item or terminate
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Monitor.Pulse(m_signal);
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if (m_exit == 1)
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return false;
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}
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return true;
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}
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protected void SignalThread() {
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lock (m_signal) {
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Monitor.Pulse(m_signal);
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}
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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_threads;
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if (current >= m_maxThreadsLimit || m_exit == 1)
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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_threads, 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_threads, 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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Thread.MemoryBarrier();
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do {
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current = m_threads;
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if (current <= m_minThreadsLimit && m_exit == 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_threads, current - 1, current));
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last = (current == 1);
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return true;
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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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protected bool StartWorker() {
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if (AllocateThreadSlot()) {
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// slot successfully allocated
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var worker = new Thread(Worker);
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worker.IsBackground = true;
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worker.Start();
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return true;
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}
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return false;
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}
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protected abstract void InvokeUnit(TUnit unit);
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protected virtual void Worker() {
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TUnit unit;
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bool last;
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do {
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while (Dequeue(out unit, m_releaseTimeout)) {
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InvokeUnit(unit);
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}
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if(!ReleaseThreadSlot(out last))
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continue;
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// queue may be not empty
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if (last && TryDequeue(out unit)) {
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InvokeUnit(unit);
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if (AllocateThreadSlot(1))
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continue;
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// we can safely exit since pool is alive
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}
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break;
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} while(true);
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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 (0 == Interlocked.CompareExchange(ref m_exit, 1, 0)) { // implies memory barrier
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// wake sleeping threads
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SignalThread();
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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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