/// <summary>
/// Updates the current trigger timer using the specified trigger.
/// </summary>
/// <param name="trigger">The trigger information.</param>
private void OnUpdateTimer(CrawlerTrigger trigger)
{
// Synchronize access.
lock (this.sync)
{
// Get the current time;
DateTime now = DateTime.Now;
// Set the current trigger.
this.timerTrigger = trigger;
// If the trigger timestamp does not meet the minimum trigger delay.
if (now + this.minimumTriggerDelay > trigger.Timestamp)
{
// Disable the timer.
this.timer.Change(Timeout.Infinite, Timeout.Infinite);
// Execute the trigger now on the thread pool.
ThreadPool.QueueUserWorkItem(this.OnTrigger);
}
else
{
// Update the timer.
this.timer.Change((long)trigger.Timestamp.Subtract(now).TotalMilliseconds, Timeout.Infinite);
}
}
}
/// <summary>
/// An event handler called when the trigger timer expires.
/// </summary>
/// <param name="state">The state.</param>
private void OnTrigger(object state)
{
// The current trigger.
KeyValuePair<DateTime, CrawlerTrigger> first;
// Synchronize access.
lock (this.sync)
{
// If the trigger list is empty, do nothing.
if (this.timeline.Count == 0) return;
// Get the first trigger.
first = this.timeline.First();
// Check the timer has been triggered for the current timer trigger. Otherwise, return.
if (!object.ReferenceEquals(this.timerTrigger, first.Value)) return;
// Remove the first trigger from the list.
if (!this.timeline.Remove(first.Key)) throw new InvalidOperationException("Internal task scheduler exception: cannot remove an existing trigger.");
// Set the current timer trigger to null.
this.timerTrigger = null;
// If the trigger list is not empty.
if (this.timeline.Count > 0)
{
// Get the next trigger.
KeyValuePair<DateTime, CrawlerTrigger> next = this.timeline.First();
// Update the timer.
this.OnUpdateTimer(next.Value);
}
}
// Execute the current trigger.
first.Value.Execute();
}
/// <summary>
/// Removes a trigger from the tasks timeline.
/// </summary>
/// <param name="trigger">The trigger.</param>
public void RemoveTrigger(CrawlerTrigger trigger)
{
// Synchronize access.
lock (this.sync)
{
// Check the trigger list is not empty.
if (this.timeline.Count == 0) throw new InvalidOperationException("Internal task scheduler exception: cannot remove a trigger because the trigger list is empty.");
// Get the first trigger.
KeyValuePair<DateTime, CrawlerTrigger> first = this.timeline.First();
// Remove the trigger.
if (!this.timeline.Remove(trigger.Timestamp)) throw new InvalidOperationException("Internal task schedule exception: cannot remove a trigger because it could not be found.");
// If the trigger is the first trigger.
if (object.ReferenceEquals(first.Value, trigger))
{
// If the trigger list is empty.
if (this.timeline.Count == 0)
{
// Disable the timer.
this.timer.Change(Timeout.Infinite, Timeout.Infinite);
}
else
{
// Get the next trigger.
KeyValuePair<DateTime, CrawlerTrigger> next = this.timeline.First();
// Update the timer.
this.OnUpdateTimer(next.Value);
}
}
}
}
/// <summary>
/// Adds the specified trigger to the timeline.
/// </summary>
/// <param name="trigger">The trigger.</param>
/// <param name="timestamp">The timeline timestamp.</param>
private void OnAddTriggerSafe(CrawlerTrigger trigger, out DateTime timestamp)
{
// Synchronize access.
lock (this.sync)
{
// Get the trigger timestamp.
timestamp = trigger.Timestamp;
// If the timestamp exists.
while (this.timeline.ContainsKey(timestamp))
{
// Increment the timestamp.
timestamp.AddTicks(1);
}
// Add the trigger.
this.timeline.Add(timestamp, trigger);
}
}
/// <summary>
/// Adds a new trigger to the tasks timeline.
/// </summary>
/// <param name="trigger">The trigger.</param>
/// <param name="timestamp">The timeline timestamp.</param>
public void AddTrigger(CrawlerTrigger trigger, out DateTime timestamp)
{
// Synchronize access.
lock (this.sync)
{
// If the timeline is empty.
if (this.timeline.Count == 0)
{
// Add the trigger to the timeline.
this.OnAddTriggerSafe(trigger, out timestamp);
// Update the timer.
this.OnUpdateTimer(trigger);
}
else
{
// The first trigger.
KeyValuePair<DateTime, CrawlerTrigger> first = this.timeline.First();
// Add the trigger to the triggers list.
this.OnAddTriggerSafe(trigger, out timestamp);
// If the timestamp of the current schedule is smaller than the timestamp of the first schedule.
if (trigger.Timestamp < first.Key)
{
// Update the timer.
this.OnUpdateTimer(trigger);
}
}
}
}
