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using System;
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using Implab.Parallels;
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using System.Threading;
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using System.Reflection;
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namespace Implab {
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public abstract class AbstractPromise<THandler> {
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const int UNRESOLVED_SATE = 0;
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const int TRANSITIONAL_STATE = 1;
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const int SUCCEEDED_STATE = 2;
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const int REJECTED_STATE = 3;
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const int CANCELLED_STATE = 4;
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const int RESERVED_HANDLERS_COUNT = 4;
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int m_state;
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Exception m_error;
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int m_handlersCount;
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readonly THandler[] m_handlers = new THandler[RESERVED_HANDLERS_COUNT];
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MTQueue<THandler> m_extraHandlers;
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int m_handlerPointer = -1;
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int m_handlersCommited;
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#region state managment
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bool BeginTransit() {
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return UNRESOLVED_SATE == Interlocked.CompareExchange(ref m_state, TRANSITIONAL_STATE, UNRESOLVED_SATE);
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}
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void CompleteTransit(int state) {
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if (TRANSITIONAL_STATE != Interlocked.CompareExchange(ref m_state, state, TRANSITIONAL_STATE))
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throw new InvalidOperationException("Can't complete transition when the object isn't in the transitional state");
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}
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void WaitTransition() {
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while (m_state == TRANSITIONAL_STATE) {
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Thread.MemoryBarrier();
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}
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}
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protected void BeginSetResult() {
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if (!BeginTransit()) {
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WaitTransition();
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if (m_state != CANCELLED_STATE)
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throw new InvalidOperationException("The promise is already resolved");
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}
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}
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protected void EndSetResult() {
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CompleteTransit(SUCCEEDED_STATE);
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OnSuccess();
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}
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/// <summary>
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/// Выполняет обещание, сообщая об ошибке
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/// </summary>
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/// <remarks>
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/// Поскольку обещание должно работать в многопточной среде, при его выполнении сразу несколько потоков
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/// могу вернуть ошибку, при этом только первая будет использована в качестве результата, остальные
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/// будут проигнорированы.
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/// </remarks>
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/// <param name="error">Исключение возникшее при выполнении операции</param>
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/// <exception cref="InvalidOperationException">Данное обещание уже выполнено</exception>
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protected void SetError(Exception error) {
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if (BeginTransit()) {
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m_error = error is PromiseTransientException ? error.InnerException : error;
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CompleteTransit(REJECTED_STATE);
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OnError();
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} else {
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WaitTransition();
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if (m_state == SUCCEEDED_STATE)
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throw new InvalidOperationException("The promise is already resolved");
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}
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}
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/// <summary>
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/// Отменяет операцию, если это возможно.
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/// </summary>
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/// <remarks>Для определения была ли операция отменена следует использовать свойство <see cref="IsCancelled"/>.</remarks>
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protected void SetCancelled() {
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if (BeginTransit()) {
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CompleteTransit(CANCELLED_STATE);
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OnCancelled();
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}
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}
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protected abstract void SignalSuccess(THandler handler);
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protected abstract void SignalError(THandler handler, Exception error);
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protected abstract void SignalCancelled(THandler handler);
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void OnSuccess() {
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var hp = m_handlerPointer;
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var slot = hp +1 ;
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while (slot < m_handlersCommited) {
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if (Interlocked.CompareExchange(ref m_handlerPointer, slot, hp) == hp) {
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SignalSuccess(m_handlers[slot]);
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}
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hp = m_handlerPointer;
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slot = hp +1 ;
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}
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if (m_extraHandlers != null) {
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THandler handler;
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while (m_extraHandlers.TryDequeue(out handler))
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SignalSuccess(handler);
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}
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}
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void OnError() {
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var hp = m_handlerPointer;
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var slot = hp +1 ;
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while (slot < m_handlersCommited) {
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if (Interlocked.CompareExchange(ref m_handlerPointer, slot, hp) == hp) {
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SignalError(m_handlers[slot],m_error);
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}
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hp = m_handlerPointer;
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slot = hp +1 ;
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}
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if (m_extraHandlers != null) {
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THandler handler;
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while (m_extraHandlers.TryDequeue(out handler))
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SignalError(handler, m_error);
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}
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}
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void OnCancelled() {
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var hp = m_handlerPointer;
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var slot = hp +1 ;
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while (slot < m_handlersCommited) {
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if (Interlocked.CompareExchange(ref m_handlerPointer, slot, hp) == hp) {
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SignalCancelled(m_handlers[slot]);
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}
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hp = m_handlerPointer;
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slot = hp +1 ;
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}
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if (m_extraHandlers != null) {
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THandler handler;
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while (m_extraHandlers.TryDequeue(out handler))
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SignalCancelled(handler);
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}
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}
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#endregion
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protected abstract void Listen(PromiseEventType events, Action handler);
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#region synchronization traits
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protected void WaitResult(int timeout) {
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if (!IsResolved) {
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var lk = new object();
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Listen(PromiseEventType.All, () => {
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lock(lk) {
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Monitor.Pulse(lk);
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}
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});
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lock (lk) {
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while(!IsResolved) {
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if(!Monitor.Wait(lk,timeout))
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throw new TimeoutException();
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}
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}
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}
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switch (m_state) {
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case SUCCEEDED_STATE:
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return;
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case CANCELLED_STATE:
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throw new OperationCanceledException();
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case REJECTED_STATE:
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throw new TargetInvocationException(m_error);
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default:
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throw new ApplicationException(String.Format("Invalid promise state {0}", m_state));
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}
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}
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#endregion
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#region handlers managment
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protected void AddHandler(THandler handler) {
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if (m_state > 1) {
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// the promise is in the resolved state, just invoke the handler
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InvokeHandler(handler);
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} else {
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var slot = Interlocked.Increment(ref m_handlersCount) - 1;
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if (slot < RESERVED_HANDLERS_COUNT) {
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m_handlers[slot] = handler;
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while (slot != Interlocked.CompareExchange(ref m_handlersCommited, slot + 1, slot)) {
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}
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if (m_state > 1) {
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do {
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var hp = m_handlerPointer;
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slot = hp + 1;
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if (slot < m_handlersCommited) {
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if (Interlocked.CompareExchange(ref m_handlerPointer, slot, hp) != hp)
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continue;
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InvokeHandler(m_handlers[slot]);
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}
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break;
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} while(true);
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}
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} else {
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if (slot == RESERVED_HANDLERS_COUNT) {
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m_extraHandlers = new MTQueue<THandler>();
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} else {
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while (m_extraHandlers == null)
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Thread.MemoryBarrier();
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}
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m_extraHandlers.Enqueue(handler);
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if (m_state > 1 && m_extraHandlers.TryDequeue(out handler))
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// if the promise have been resolved while we was adding the handler to the queue
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// we can't guarantee that someone is still processing it
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// therefore we need to fetch a handler from the queue and execute it
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// note that fetched handler may be not the one that we have added
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// even we can fetch no handlers at all :)
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InvokeHandler(handler);
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}
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}
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}
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protected void InvokeHandler(THandler handler) {
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switch (m_state) {
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case SUCCEEDED_STATE:
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SignalSuccess(handler);
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break;
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case CANCELLED_STATE:
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SignalCancelled(handler);
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break;
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case REJECTED_STATE:
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SignalError(handler, m_error);
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break;
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default:
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throw new Exception(String.Format("Invalid promise state {0}", m_state));
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}
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}
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#endregion
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#region IPromise implementation
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public void Join(int timeout) {
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WaitResult(timeout);
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}
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public void Join() {
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WaitResult(-1);
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}
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public bool IsResolved {
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get {
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Thread.MemoryBarrier();
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return m_state > 1;
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}
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}
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public bool IsCancelled {
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get {
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Thread.MemoryBarrier();
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return m_state == CANCELLED_STATE;
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}
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}
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#endregion
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#region ICancellable implementation
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public void Cancel() {
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SetCancelled();
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}
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#endregion
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}
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}
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