Step by step

Folks,

This code below implement a singleton structure for the aplication, and that need to be implemented on the DPR file of the project:

 Delphi | 
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uses Windows;
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function AppSingleton(ACheckPath: boolean = false): boolean;
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var
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  s: string;
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  i, iLast: Cardinal;
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begin
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  s := ParamStr(0);
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  iLast := 1;
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  case Integer(ACheckPath) of
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    0: for i := 1 to Length(s) do if s[i] = '\' then iLast := i;
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    1: for i := 1 to Length(s) do if s[i] in [':','\','.',' '] then s[i] := '_';
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  end;
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  Result := (CreateMutex(nil, true, PChar(Cardinal(@s) + (iLast - 1))) <> 0) and
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    (GetLastError = 0);
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end;

I use the CreateMutex API that works as a semaphore, if open, the application is unique, if closed the application is already running.

I wrote a condition to check the full path of the application for the Mutex call, so if you want to check the full path use the funciotn with param as True, the default is False and the check will be only on the application exe name.

A little detail about checking the functionality of this function:
Under debug mode the checkout on full path mode will fail and more then one application can be raised. This problem is because the relationship of the application with other program, so the CreateMutex API understand the Process ID is diferent from others.

Tags: AppSingleton, CreateMutex, Delphi, Usefull Function

This entry was posted on Thursday, July 3rd, 2008 at 6:02 pm and is filed under articles. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.