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2 shortcuts, 1 instance

Posted on 2004-09-17
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Last Modified: 2010-04-05
I asked a variant of this question at

"A single hotkey doing wakeup and global duty"
http://www.experts-exchange.com/Programming/Programming_Platforms/Win_Prog/Q_21122673.html

and accepted the answer - that it was basically a matter of using a mutex to enforce a single instance and passing through an indication of which shortcut key was used via SendMessage.

However, I started thinking <g> and it seems to me that enforcing a single instance via a mutex is inefficient.  My concern is that a second copy of the exe (MyMegaApp) is actually loaded into memory BEFORE it gets killed (after detecting the mutex).

How about this. The shortcut keys actually call a small "loader" app. It is that app which then "spawns" MyMegaApp but ONLY if needed (ie no mutex). Some sort of WinExecAndWait or is CreateProcess what I need?. We still use a SendMessage to send the arguments.. hmm, would it be better to use a more general interprocess communications approach (so I can send more stuff).

Anyone care to look at the previous answer and improve on it, given these ideas?

Thanks



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Question by:Mutley2003
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8 Comments
 
LVL 34

Expert Comment

by:Slick812
ID: 12090373
hello  Mutley2003, , I am not sure that I am getting what you want or need to have done? you say something about -
"is actually loaded into memory BEFORE it gets killed"
and why do you have a problem with this? are you getting complaints form users about system error of running out of memory when your program loads? or some memory problems?
anyway, here is a EE question that shows a better (in my opinion) mutex for single instance  PLUS it sends the first parameter to the running program! -

http://www.experts-exchange.com/Programming/Programming_Languages/Delphi/Q_20623659.html

if you think you need a "Small Program" to run and  do the mutext thing and then launch your program, I could do an API program of 20 Kb or so to test the mutext, and then run your other program, but I can not at this point see any need for a  WinExecAndWait or a CreateProcess and a wait. . . you should just use a shellexecute if there is no mutext, but it seems, like this could cause other problems, if you need one program inorder to launch another (the main) program,
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LVL 34

Expert Comment

by:Slick812
ID: 12090387
oh yea, , It is my impression that if you never call the

  Application.Initialize;
  Application.CreateForm(TForm1, Form1);

the Application and "Form" are not loaded into a Memory block, so none of the Form's class is ever given any memory for functioning
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Author Comment

by:Mutley2003
ID: 12090783
hi Slick812

http://www.experts-exchange.com/Programming/Programming_Languages/Delphi/Q_20623659.html

does a nice job of passing string data via WM_COPYDATA, thanks.

I guess I don't understand enough about how windows loads an exe .. you say

"It is my impression that if you never call the

  Application.Initialize;
  Application.CreateForm(TForm1, Form1);

the Application and "Form" are not loaded into a Memory block, so none of the Form's class is ever given any memory for functioning"

well, there would not be any dynamic memory allocations obviously, but I would have thought that all the code and data gets loaded ... that is, an "image" of the exe.

How to test this?

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LVL 34

Accepted Solution

by:
Slick812 earned 2000 total points
ID: 12091956
Yea, I spoke to soon, sleepy I guess :-) , the exe is loaded into the programs Instance on start of program , , , Sorry

so you want some way to NOT load your program, if a Mutex is up??
I think I would have a "Small" GUI program (only code for the basic Form) and then move all of my "Large Code" or whatever makes your program into a MegaApp into several DLL's and then if your program Runs, you then load the DLLs (this would make "Updating" your App easier also). .  However, It would probally take alot of work to do this. . . .

If you just want a "Small" do nothing app that ONLY tests for the Mutex, you might try something like this, Here is some code for a .DPR  file in delphi, there is NO GUI, no windows are created, the user sees NOTHING (well and error message is it craps out), all it does is Open a mutex and if there is no mutex then it starts a program. . . . . . .




program preMutex;

uses
  SysUtils,
  ShellApi, Windows;

var
hMutex: Cardinal;
i: Integer;
StartApp, ParamS1: String;

begin
hMutex := OpenMutex(MUTEX_ALL_ACCESS,False,'h8J3Cn90?%x7');
if hMutex = 0 then
  begin
  for i := 1 to ParamCount do
    ParamS1 := ParamS1+'"'+ParamStr(i)+'" ';
  StartApp := ExtractFilePath(ParamStr(0))+'WesThumbs.exe';
  if ShellExecute(0,'open',PChar(StartApp),PChar(ParamS1),nil,SW_SHOWDEFAULT) < 33 then
    MessageBox(0, PChar('ERROR - Could NOT start program'#10+StartApp),
               'ERROR Program was NOT Started', MB_ICONERROR or MB_TOPMOST);;
  end else
  CloseHandle(hMutex);
end.


this DOES NOT send the parameters to an already running program,
if you need that, you can get the code for that at the other EE question
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LVL 34

Expert Comment

by:Slick812
ID: 12091959
Oh this DOES not set a Mutex if there is Not one, so you will still need to set the mutex in your MegaApp
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Author Comment

by:Mutley2003
ID: 12094187
Slick812,
maybe I am sleepy too (or just thick<g>).. but you have shown me how to start an app if there is no mutex, cool.

If there is a mutex, then OK we send stuff to the already running instance (via WM_COPYDATA) .  There is still the issue of how to "wake up" that instance. Maybe it is just something in the WM_COPYDATA event handler to make a form visible/active

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LVL 34

Expert Comment

by:Slick812
ID: 12094229
????
OK, I have NO IDEA what your program may or may not be doing. . .I don't know if it is minimized or hidden or whatever. So when you get the WM_COPYDATA message you can use the parameters in the TWmCopyData to indicate "Different" types of WM_COPYDATA data, if you need to do that,, , , ,
 but as for your "Wake Up" the main app, , well yes, you can do code to do whatever you need if minimized or hidden or small or whatever


procedure TForm1.GetCopyData(var Msg: TWmCopyData);
var
i: Integer;
PrePc, ScanPc: PChar;
Str1: String;
begin
// add a test and then a change when you get a WM_COPYDATA message

if  not Visible then Show;
if mininized then Maximize;
if IsSmall then MakeBig;

Msg.Result := 0;
if StrLen(PChar(msg.CopyDataStruct^.lpData)) > 0 then
              begin
              Msg.Result := 17;
              if msg.CopyDataStruct^.dwData = 1 then
                begin
                Str1 := PChar(msg.CopyDataStruct^.lpData);
                Form1.Label3.Caption := Str1;
                end
             end;

end;
0
 

Author Comment

by:Mutley2003
ID: 12094341
thanks Slick812 .. I have plenty to work with now
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