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using System;
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using System.Threading;
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using System.Threading.Tasks;
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namespace Implab.Components {
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public abstract class PollingComponent : RunnableComponent {
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readonly Timer m_timer;
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readonly CancellationTokenSource m_cancellation = new CancellationTokenSource();
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Task m_pending;
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Task m_poll;
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/// <summary>
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/// Poll interval in milliseconds.
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/// </summary>
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/// <returns></returns>
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public int Interval { get; set; }
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/// <summary>
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/// Delay to the first poll after start in milliseconds
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/// </summary>
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/// <returns></returns>
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public int Delay { get; set; }
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/// <summary>
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/// Indicates how to handle unhandled exceptions in <see cref="Poll()"/> method.
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/// </summary>
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/// <returns></returns>
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public bool FailOnError { get; set; }
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/// <summary>
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/// Event for the unhandled exceptions in <see cref="Poll()"/> method.
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/// </summary>
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public event EventHandler<UnhandledExceptionEventArgs> UnhandledException;
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protected PollingComponent(bool initialized) : base(initialized) {
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m_timer = new Timer(OnTimer);
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}
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protected override void RunInternal() {
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ScheduleNextPoll(Delay);
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}
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protected override async Task StopInternalAsync(CancellationToken ct) {
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// component in Stopping state, no new polls will be scheduled
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m_cancellation.Cancel();
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try {
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// await for pending poll
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await m_poll;
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} catch (OperationCanceledException) {
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// OK
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}
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}
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protected abstract Task Poll(CancellationToken ct);
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void ScheduleNextPoll(int timeout) {
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lock (SynchronizationObject) {
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if (State == ExecutionState.Running) {
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m_pending = Safe.CreateTask(m_cancellation.Token);
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m_poll = m_pending.Then(() => Poll(m_cancellation.Token));
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m_timer.Change(timeout, Timeout.Infinite);
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}
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}
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}
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async void OnTimer(object state) {
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try {
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m_pending.Start();
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await m_poll;
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ScheduleNextPoll(Interval);
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} catch (Exception e) {
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UnhandledException.DispatchEvent(this, new UnhandledExceptionEventArgs(e, false));
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if (FailOnError)
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Fail(e);
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else
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ScheduleNextPoll(Interval);
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}
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}
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protected override void Dispose(bool disposing) {
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if (disposing)
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Safe.Dispose(m_timer, m_cancellation);
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base.Dispose(disposing);
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}
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}
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}
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