Advanced Delphi :: 
In this article you'll learn how to "run-once enable" a Delphi application that can check for its previous (running) instance. Along the process, several techniques of implementing such a check will be discussed; as well as how to bring your already running application to the foreground, if a user tries to run it "one more time". By the end of the article you'll have a copy-to-go code to control the behavior of your application's multiple instances: with the option to limit the number of running instances.
In this article you'll learn how to "run-once enable" a Delphi application that can check for its previous (running) instance. Along the process, several techniques of implementing such a check will be discussed; as well as how to bring your already running application to the foreground, if a user tries to run it "one more time". By the end of the article you'll have a copy-to-go code to control the behavior of your application's multiple instances: with the option to limit the number of running instances.
Related: TInstance Control | Using WMCopyData to communicate between applications | Creating a Splash Screen
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if (Mutex = 0) OR (GetLastError = ERROR_ALREADY_EXISTS) then
begin
SendMessage(HWND_BROADCAST, MyMsg, 0,0);
end
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there should be PostMessage instead of SendMessage:p