www.pudn.com > shijiantongbu.zip > previnst.pas

unit previnst; 
 
{Unit PREVINST.pas -  
Include this unit in your project file (.dpr) to keep multiple instances  
  of your application from running.  Works the same way as the standard method  
  of using mutexes, except uses a semaphore and stores the application handle in  
  the semaphore's count so we can get it to show the original instance.  
  You would call it like this: 
 
  program Project1;  
 
uses  
   Forms,  
   Unit1 in 'Unit1.pas',  
   PREVINST in 'PREVINST.pas';  
 
begin  
    if not HavePrevInstance(Application.Handle, 'SOmeWEIRDnameFoRTheSemaphOre') then  
    begin  
     Application.Initialize;  
   Application.CreateForm(TForm1, Form1);  
   Application.Run;  
    end; 
  end.}  
 
interface  
 
uses Windows;  
 
function HavePrevInstance(AppHandle: THandle; UniqueName: String): boolean;  
 
implementation  
 
function HavePrevInstance(AppHandle: THandle; UniqueName: String): boolean;  
const  
  ERROR_ALREADY_EXISTS = 183; //Not in Windows.pas - dont know why  
  SEMAPHORE_ALL_ACCESS = STANDARD_RIGHTS_REQUIRED or SYNCHRONIZE or 3; //Ditto  
  WM_SYSCOMMAND = 274; //Define here so dont have to include Messages.pas  
var  
  MyHandle: THandle;  
begin  
  Result := False; //Set Initial Result to false  
  //Now we create the semaphore and store the applications handle as its count adding one to it so we can keep toggling it back and forth  
  MyHandle := CreateSemaphore(nil, AppHandle + 1, AppHandle + 1, PChar(UniqueName));  
  //The following will be true if an instance of out app is already running 
  if (MyHandle <> 0) and (GetLastError = ERROR_ALREADY_EXISTS) then  
  begin  
    Result := True; //Set to result to true  
    //Now we open the semaphore to get its handle  
    MyHandle := OpenSemaphore(SEMAPHORE_ALL_ACCESS, False, PChar(UniqueName));  
    //at this point MyHandle is our app handle plus one. now we reduce count by one to get back our original handle  
    WaitForSingleObject(MyHandle, 0);  
    //This replaces the value of MyHandle with the Application handle of the prev instance and pushes our count back up again  
    ReleaseSemaphore(MyHandle, 1, @MyHandle);  
    //now we have the handle to the previous instance - do whatever you want  
    //This is what I usually do but you could pop up a messagebox or whatever  
    if IsIconic(MyHandle) then  
     PostMessage(MyHandle, WM_SYSCOMMAND, SC_RESTORE, 0)  
    else  
     SetForeGroundWindow(MyHandle);  
  end;  
end;  
 
end.