mirror of
https://github.com/xcp-ng/xenadmin.git
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bd36a85bff
Signed-off-by: Mihaela Stoica <mihaela.stoica@citrix.com>
239 lines
8.3 KiB
C#
239 lines
8.3 KiB
C#
/* Copyright (c) Citrix Systems Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms,
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* with or without modification, are permitted provided
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* that the following conditions are met:
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*
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* * Redistributions of source code must retain the above
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* copyright notice, this list of conditions and the
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* following disclaimer.
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* * Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the
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* following disclaimer in the documentation and/or other
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* materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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* CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
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* INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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using System;
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using System.Threading;
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using System.Collections.Generic;
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using System.Diagnostics;
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namespace XenAdmin
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{
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/// <summary>
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/// A class to throttle the updates to a particular class/component.
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///
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/// The purpose of the class is best described by example:
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/// It is used by <see cref="MainWindow"/> to control the refreshes to the TreeView.
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/// The refresh of the tree is slow and it is called all over the place.
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/// This class ensures there is always a small break between refreshes
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/// - the length of the break is calculated by <see cref="DelayCalculator"/>.
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///
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/// This class also allows consumers to specify a maximum time between updates.
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/// </summary>
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internal partial class UpdateManager : IDisposable
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{
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/// <summary>
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/// Used to ensure the maximum time between updates. (ms)
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/// </summary>
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private readonly int _longInterval;
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private bool _disposed;
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private Timer _shortIntervalTimer;
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private Timer _longIntervalTimer;
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private readonly DelayCalculator _delayCalculator = new DelayCalculator();
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private readonly object _lock = new object();
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/// <summary>
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/// A Boolean indicating whether an update is currently taking place.
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/// The _lock variable should be used when reading and writing to this variable.
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/// </summary>
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private bool _doingUpdate;
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/// <summary>
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/// A Boolean indicating whether an update request was received while the current update is taking place.
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/// The _lock variable should be used when reading and writing to this variable.
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/// </summary>
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private bool _anotherUpdateRequestOccurredDuringUpdate;
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/// <summary>
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/// Initializes a new instance of the <see cref="UpdateManager"/> class.
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/// </summary>
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/// <param name="longInterval">The maximum time between updates (ms). Specify 0 for no maximum value.</param>
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public UpdateManager(int longInterval)
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{
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_longInterval = longInterval;
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}
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/// <summary>
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/// Initializes a new instance of the <see cref="UpdateManager"/> class. There is no maximum time between updates specified.
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/// </summary>
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public UpdateManager()
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: this(0)
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{
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}
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/// <summary>
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/// Requests an update. The <see cref="Update"/> event occurs when an update should take place.
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/// </summary>
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public void RequestUpdate()
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{
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_delayCalculator.RegisterLatestUpdateRequest();
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RequestUpdate(null);
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}
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private void RequestUpdate(object state)
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{
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if (TryBeginUpdate())
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{
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// ensure update occurs on a new thread. This frees the calling thread up to continue.
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ThreadPool.QueueUserWorkItem(DoUpdate);
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}
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}
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private void DoUpdate(object state)
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{
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try
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{
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// stop watch to time how long an update takes.
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Stopwatch sw = Stopwatch.StartNew();
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OnUpdate(EventArgs.Empty);
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_delayCalculator.RegisterLatestUpdate(sw.ElapsedMilliseconds);
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}
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finally
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{
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// allow another request only after _delayCalculator.GetDelay() has elapsed.
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_shortIntervalTimer = new Timer(EndUpdate, null, _delayCalculator.GetDelay(), Timeout.Infinite);
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}
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}
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/// <summary>
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/// Tries to begin an Update.
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/// </summary>
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/// <returns>Returns false if an update is already underway.</returns>
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private bool TryBeginUpdate()
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{
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lock (_lock)
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{
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if (!_doingUpdate && !_disposed)
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{
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// now do an update so reset this variable.
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_anotherUpdateRequestOccurredDuringUpdate = false;
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DisposeTimer(_longIntervalTimer);
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_doingUpdate = true;
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return true;
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}
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// an update is taking place and another request has taken place.
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_anotherUpdateRequestOccurredDuringUpdate = true;
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return false;
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}
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}
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private void EndUpdate(object state)
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{
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lock (_lock)
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{
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_doingUpdate = false;
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DisposeTimer(_shortIntervalTimer);
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if (!_disposed)
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{
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if (_longInterval > 0)
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{
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_longIntervalTimer = new Timer(RequestUpdate, null, _longInterval, _longInterval);
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}
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if (_anotherUpdateRequestOccurredDuringUpdate)
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{
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// another update was requested during this update
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RequestUpdate();
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}
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}
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}
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}
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/// <summary>
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/// Raises the <see cref="Update"/> event.
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/// </summary>
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/// <param name="e">The <see cref="System.EventArgs"/> instance containing the event data.</param>
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protected virtual void OnUpdate(EventArgs e)
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{
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EventHandler handler = Update;
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if (handler != null)
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{
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handler(this, e);
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}
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}
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/// <summary>
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/// Releases unmanaged and - optionally - managed resources
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/// </summary>
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/// <param name="disposing"><c>true</c> to release both managed and unmanaged resources; <c>false</c> to release only unmanaged resources.</param>
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protected virtual void Dispose(bool disposing)
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{
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if (disposing)
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{
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lock (_lock)
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{
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if (!_disposed)
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{
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_disposed = true;
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DisposeTimer(_longIntervalTimer);
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DisposeTimer(_shortIntervalTimer);
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}
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}
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GC.SuppressFinalize(this);
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}
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}
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private static void DisposeTimer(Timer timer)
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{
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if (timer != null)
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{
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timer.Dispose();
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}
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}
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/// <summary>
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/// Occurs when an update should take place.
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/// </summary>
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public event EventHandler Update;
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#region IDisposable Members
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/// <summary>
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/// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
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/// </summary>
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public void Dispose()
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{
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Dispose(true);
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}
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#endregion
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}
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}
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