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using System;
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using System.Threading;
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using Implab.Diagnostics;
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namespace Implab.Components {
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public class PollingComponent : RunnableComponent {
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readonly Timer m_timer;
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readonly Func<Func<ICancellationToken, IPromise>, IPromise> m_dispatcher;
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readonly TimeSpan m_interval;
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readonly object m_lock = new object();
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ActionTask m_pending;
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protected PollingComponent(TimeSpan interval, Func<Func<ICancellationToken, IPromise>, IPromise> dispatcher, bool initialized) : base(initialized) {
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m_timer = new Timer(OnInternalTick);
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m_interval = interval;
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m_dispatcher = dispatcher;
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}
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protected override IPromise OnStart() {
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m_timer.Change(TimeSpan.Zero, m_interval);
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return base.OnStart();
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}
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void OnInternalTick(object state) {
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if (StartTick()) {
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try {
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if (m_dispatcher != null) {
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var result = m_dispatcher(OnTick);
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m_pending.CancellationRequested(result.Cancel);
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AwaitTick(result);
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} else {
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AwaitTick(OnTick(m_pending));
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}
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} catch (Exception error) {
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HandleTickError(error);
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}
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}
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}
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/// <summary>
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/// Checks wheather there is no running handler in the component and marks that the handler is starting.
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/// </summary>
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/// <returns>boolean value, true - the new tick handler may be invoked, false - a tick handler is already running or a component isn't running.</returns>
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/// <remarks>
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/// If the component is stopping no new handlers can be run. Every successful call to this method must be completed with either AwaitTick or HandleTickError handlers.
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/// </remarks>
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protected virtual bool StartTick() {
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lock (m_lock) {
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if (State != ExecutionState.Running || m_pending != null)
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return false;
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// actually the component may be in a not running state here (stopping, disposed or what ever),
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// but OnStop method also locks on the same object and will handle operation in m_pending
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m_pending = new ActionTask(
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() => {
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// only one operation is running, it's safe to assing m_pending from it
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m_pending = null;
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},
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ex => {
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try {
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OnTickError(ex);
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// Analysis disable once EmptyGeneralCatchClause
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} catch {
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} finally {
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m_pending = null;
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}
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// suppress error
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},
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ex => {
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try {
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OnTickCancel(ex);
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// Analysis disable once EmptyGeneralCatchClause
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} catch {
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} finally {
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m_pending = null;
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}
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// supress cancellation
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},
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false
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);
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return true;
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}
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}
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/// <summary>
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/// Awaits the tick.
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/// </summary>
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/// <param name="tick">Tick.</param>
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/// <remarks>
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/// This method is called only after StartTick method and m_pending will hold the promise which should be fulfilled.
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/// </remarks>
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void AwaitTick(IPromise tick) {
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if (tick == null) {
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m_pending.Resolve();
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} else {
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tick.On(
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m_pending.Resolve,
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m_pending.Reject,
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m_pending.CancelOperation
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);
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}
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}
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/// <summary>
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/// Handles the tick error.
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/// </summary>
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/// <remarks>
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/// This method is called only after StartTick method and m_pending will hold the promise which should be fulfilled.
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/// </remarks>
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void HandleTickError(Exception error) {
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m_pending.Reject(error);
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}
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protected virtual void OnTickError(Exception error) {
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}
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protected virtual void OnTickCancel(Exception error) {
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}
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/// <summary>
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/// Invoked when the timer ticks, use this method to implement your logic
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/// </summary>
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protected virtual IPromise OnTick(ICancellationToken cancellationToken) {
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return Promise.Success;
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}
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protected override IPromise OnStop() {
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m_timer.Change(-1, -1);
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// the component is in the stopping state
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lock (m_lock) {
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// after this lock no more pending operations could be created
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var pending = m_pending;
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// m_pending could be fulfilled and set to null already
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if (pending != null) {
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pending.Cancel();
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return pending.Then(base.OnStop);
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}
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}
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return base.OnStop();
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}
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protected override void Dispose(bool disposing) {
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if (disposing)
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m_timer.Dispose();
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base.Dispose(disposing);
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}
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}
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}
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