Do C Timers elapse on a separate thread

Question

Does a System Timers Timer elapse on a separate thread than the thread that created it   Lets say I have a class with a timer that fires every 5 seconds  When the timer fires  in the elapsed method  some object is modified  Lets say it takes a long time to modify this object  like 10 seconds  Is it possible that I will run into thread collisions in this scenario

User · Accepted Answer

For System Timers Timer   See Brian Gideon s answer below  For System Threading Timer   MSDN Documentation on Timers states      The System Threading Timer class makes   callbacks on a ThreadPool thread and   does not use the event model at all    So indeed the timer elapses on a different thread

User · Answer

It depends   The System Timers Timer has two modes of operation     If SynchronizingObject is set to an ISynchronizeInvoke instance then the Elapsed event will execute on the thread hosting the synchronizing object   Usually these ISynchronizeInvoke instances are none other than plain old Control and Form instances that we are all familiar with   So in that case the Elapsed event is invoked on the UI thread and it behaves similar to the System Windows Forms Timer   Otherwise  it really depends on the specific ISynchronizeInvoke instance that was used   If SynchronizingObject is null then the Elapsed event is invoked on a ThreadPool thread and it behaves similar to the System Threading Timer  In fact  it actually uses a System Threading Timer behind the scenes and does the marshaling operation after it receives the timer callback if needed

User · Answer

If the elapsed event takes longer then the interval  it will create another thread to raise the elapsed event  But there is a workaround for this  static void timer Elapsed object sender  ElapsedEventArgs e                try            timer Stop           Thread Sleep 2000                 Debug WriteLine Thread CurrentThread ManagedThreadId               finally           timer Start

User · Answer

For System Timers Timer  on separate thread  if SynchronizingObject is not set       static System Timers Timer DummyTimer   null       static void Main string   args                try                        Console WriteLine  Main Thread Id      System Threading Thread CurrentThread ManagedThreadId                DummyTimer   new System Timers Timer 1000   5      5 sec interval             DummyTimer Enabled   true              DummyTimer Elapsed    new System Timers ElapsedEventHandler OnDummyTimerFired               DummyTimer AutoReset   true               DummyTimer Start                 Console WriteLine  Hit any key to exit                Console ReadLine                      catch  Exception Ex                        Console WriteLine Ex Message                      return             static void OnDummyTimerFired object Sender  System Timers ElapsedEventArgs e                Console WriteLine System Threading Thread CurrentThread ManagedThreadId           return          Output you d see if DummyTimer fired on 5 seconds interval   Main Thread Id  9    12    12    12    12    12           So  as seen  OnDummyTimerFired is executed on Workers thread    No  further complication - If you reduce interval to say 10 ms    Main Thread Id  9    11    13    12    22    17           This is because if prev execution of OnDummyTimerFired isn t done when next tick is fired  then  NET would create a new thread to do this job   Complicating things further   The System Timers Timer class provides an easy way to deal with this dilemma   it exposes a public SynchronizingObject property  Setting this property to an instance of a Windows Form  or a control on a Windows Form  will ensure that the code in your Elapsed event handler runs on the same thread on which the SynchronizingObject was instantiated    http   msdn microsoft com en-us magazine cc164015 aspx S2

User · Answer

Each elapsed event will fire in the same thread unless a previous Elapsed is still running   So it handles the collision for you  try putting this in a console  static void Main string   args        Debug WriteLine Thread CurrentThread ManagedThreadId       var timer   new Timer 1000       timer Elapsed    timer Elapsed      timer Start        Console ReadLine       static void timer Elapsed object sender  ElapsedEventArgs e        Thread Sleep 2000       Debug WriteLine Thread CurrentThread ManagedThreadId       you will get something like this  10 6 12 6 12   where 10 is the calling thread and 6 and 12 are firing from the bg elapsed event  If you remove the Thread Sleep 2000   you will get something like this  10 6 6 6 6   Since there are no collisions   But this still leaves u with a problem  if u are firing the event every 5 seconds and it takes 10 seconds to edit u need some locking to skip some edits

[c#] Do C# Timers elapse on a separate thread?

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