checkprevious.pas

利用内存映射原理实现的同时只能运行一个实例的例子

unit CheckPrevious;

interface

uses
  Windows, SysUtils;

function RestoreIfRunning(const AppHandle: THandle; MaxInstances: integer = 1): Boolean;

implementation

type
  PInstanceInfo = ^TInstanceInfo;
  TInstanceInfo = packed record
    PreviousHandle : THandle;
    RunCounter : integer;
  end;

var
  MappingHandle: THandle;
  InstanceInfo: PInstanceInfo;
  MappingName: string;
  RemoveMe: Boolean = True;

function RestoreIfRunning(const AppHandle: THandle; MaxInstances: Integer = 1): Boolean;
begin
  Result := True;
  MappingName :=StringReplace(ParamStr(0),'\','',[rfReplaceAll, rfIgnoreCase]);
  MappingHandle := CreateFileMapping($FFFFFFFF,
                                     nil,
                                     PAGE_READWRITE,
                                     0,
                                     SizeOf(TInstanceInfo),
                                     PChar(MappingName));
  if MappingHandle = 0 then
    RaiseLastOSError
  else
  begin
    if GetLastError <> ERROR_ALREADY_EXISTS then
    begin
      InstanceInfo := MapViewOfFile(MappingHandle,
                                    FILE_MAP_ALL_ACCESS,
                                    0,
                                    0,
                                    SizeOf(TInstanceInfo));
      InstanceInfo^.PreviousHandle := AppHandle;
      InstanceInfo^.RunCounter := 1;
      Result := False;
    end
    else
    begin
      MappingHandle := OpenFileMapping(FILE_MAP_ALL_ACCESS, False, PChar(MappingName));
      if MappingHandle <> 0 then
      begin
        InstanceInfo := MapViewOfFile(MappingHandle,
                                      FILE_MAP_ALL_ACCESS,
                                      0,
                                      0,
                                      SizeOf(TInstanceInfo));
        if InstanceInfo^.RunCounter >= MaxInstances then
        begin
          RemoveMe := False;
          if IsIconic(InstanceInfo^.PreviousHandle) then
            ShowWindow(InstanceInfo^.PreviousHandle, SW_RESTORE);
          SetForegroundWindow(InstanceInfo^.PreviousHandle);
        end
        else
        begin
          InstanceInfo^.PreviousHandle := AppHandle;
          InstanceInfo^.RunCounter := 1 + InstanceInfo^.RunCounter;
          Result := False;
        end
      end;
    end;
  end;
end;

initialization

finalization
  //remove one instance
  if RemoveMe then
  begin
    MappingHandle:= OpenFileMapping(FILE_MAP_ALL_ACCESS, False, PChar(MappingName));
    if MappingHandle <> 0 then
    begin
      InstanceInfo := MapViewOfFile(MappingHandle,
                                  FILE_MAP_ALL_ACCESS,
                                  0,
                                  0,
                                  SizeOf(TInstanceInfo));
      InstanceInfo^.RunCounter := -1 + InstanceInfo^.RunCounter;
    end
    else
      RaiseLastOSError;
  end;

  if Assigned(InstanceInfo) then UnmapViewOfFile(InstanceInfo);
  if MappingHandle <> 0 then CloseHandle(MappingHandle);
end.