How to block until an event is fired in c

Question

After asking this question  I am wondering if it is possible to wait for an event to be fired  and then get the event data and return part of it  Sort of like this   private event MyEventHandler event  public string ReadLine    return event waitForValue   Message        event  My String       elsewhere    var resp   ReadLine      Please make sure whatever solution you provide returns the value directly rather than getting it from something else  I m asking if the method above is available in some way  I know about Auto ManuelResetEvent  but I don t know that they return the value directly like I did above    Update  I declared an event using MyEventHandler  which contains a Message field   I have a method in another thread called ReadLine waiting for the event to fire  When the event fires the WaitForValue method  part of the event handling scene  returns the event args  which contains the message  The message is then returned by ReadLine to whatever had called it    The accepted answer to that question I asked was what I did  but it just doesn t feel quite right  It almost feels like something could happen to the data between the ManuelResetEvent firing and the program retrieving the data and returning it   Update  The main problem with the Auto ManualResetEvent is that it is too vulnerable  A thread could wait for the event  and then not give enough time for anyone else to get it before changing it to something else  Is there a way to use locks or something else  Maybe using get and set statements

User · Answer

A very easy kind of event you can wait for is the ManualResetEvent, and even better, the ManualResetEventSlim.

They have a WaitOne() method that does exactly that. You can wait forever, or set a timeout, or a "cancellation token" which is a way for you to decide to stop waiting for the event (if you want to cancel your work, or your app is asked to exit).

You fire them calling Set().

Here is the doc.

User · Answer

If the current method is async then you can use TaskCompletionSource  Create a field that the event handler and the current method can access       TaskCompletionSource lt bool gt  tcs   null       private async void Button Click object sender  RoutedEventArgs e                tcs   new TaskCompletionSource lt bool gt             await tcs Task          WelcomeTitle Text    Finished work              private void Button Click2 object sender  RoutedEventArgs e                tcs  TrySetResult true           This example uses a form that has a textblock named WelcomeTitle and two buttons   When the first button is clicked it starts the click event but stops at the await line  When the second button is clicked the task is completed and the WelcomeTitle text is updated   If you want to timeout as well then change  await tcs Task    to  await Task WhenAny tcs Task  Task Delay 25000    if  tcs Task IsCompleted      WelcomeTitle Text    Task Completed   else     WelcomeTitle Text    Task Timed Out

User · Answer

You can use  ManualResetEvent  Reset the event before you fire secondary thread and then use the WaitOne   method to block the current thread  You can then have secondary thread set the ManualResetEvent which would cause the main thread to continue  Something like this   ManualResetEvent oSignalEvent   new ManualResetEvent false    void SecondThread          DoStuff     oSignalEvent Set       void Main          DoStuff       Call second thread     System Threading Thread oSecondThread   new System Threading Thread SecondThread       oSecondThread Start         oSignalEvent WaitOne      This thread will block here until the reset event is sent      oSignalEvent Reset          Do more stuff

User · Answer

If you re happy to use the Microsoft Reactive Extensions  then this can work nicely   public class Foo       public delegate void MyEventHandler object source  MessageEventArgs args       public event MyEventHandler  event      public string ReadLine                 return Observable              FromEventPattern lt MyEventHandler  MessageEventArgs gt                   h   gt  this  event    h                  h   gt  this  event -  h               Select ep   gt  ep EventArgs Message               First              public void SendLine string message                 event this  new MessageEventArgs     Message   message              public class MessageEventArgs   EventArgs       public string Message      I can use it like this   var foo   new Foo     ThreadPoolScheduler Instance      Schedule          TimeSpan FromSeconds 5 0                gt  foo SendLine  Bar       var resp   foo ReadLine     Console WriteLine resp     I needed to call the SendLine message on a different thread to avoid locking  but this code shows that it works as expected

[c#] How to block until an event is fired in c#

Examples related to c#

Examples related to events