CODEWITHSUNDEEP
androidmultithreadingdelphi
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wBB

Reputation: 851

Terminating a thread in Delphi 10 with Android

I'm creating a thread with the basic settings indicated below. Apparently everything is working fine, but when I run MyThread.Terminate I noticed that Destroy does not run. Destroy is only executed when closing the main application.

What is the correct way to end a thread?

BASIC THREAD

// MyThread "TPoolingThread"
constructor TPoolingThread.Create;
begin
   inherited Create(True);

   // Initializing something
end;

destructor TPoolingThread.Destroy;
begin
   inherited Destroy;
end;

procedure TPoolingThread.Execute;
begin
   try
      while (not Terminated) do begin
         sleep(100);
         // do something
      end;
   finally
      if not Terminated then
         Terminate;
   end;
end;

EXECUTING THREAD

// Main Application 

   //////////////////////////////////////////
   // Create and Start
   MyThread := TPoolingThread.Create;

   if Assigned(MyThread.FatalException) then
      raise MyThread.FatalException;

   MyThread.Start;

   //////////////////////////////////////////
   // Stop
   MyThread.Terminate;

Upvotes: 1

Views: 1073

Answers (1)

user5150422
user5150422

Reputation:

I'd like to preface my answer by defining 'ending a thread'. I'm going to assume that by 'ending a thread' you mean to stop your loop in the TPoolingThread.Execute procedure.

Terminating the thread

The method you use to terminate your thread is perfectly acceptable. Now as to why it is, allow me to show you this snippet:

Version 1

In a Try-Finally construct, the Finally statement is guaranteed to be executed absolutely regardless of what happens in the try clause. However, the Finally clause does not actually handle any exceptions - the program will terminate if no Except clause is found (see notes below).

Therefore if your code within your loop throws an exception, you tell your TPoolingThread object that it has been terminated.

Why destroy isn't getting called

As Remy Lebeau and Dalija Prasnikar suggest. Terminate is not supposed to call destroy:

System.Classes.TThread.Terminate:

Signals the thread to terminate by setting the Terminated property to true. Terminate sets the thread's Terminated property to true, signaling that the thread should be terminated as soon as possible.

For Terminate to work, the thread's Execute method and any methods that Execute calls should check Terminated periodically and exit when it's true.

I will leave you this link if you want to find out more about ARC in Delphi for Android development.

Upvotes: 1

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