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I'm using the code from following posting to avoid running multiple instances of my app. I'm running an MFC SDI application. Where is the ideal location to create and release the mutex?
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Subject: Re: Avoiding multiple instances of an application.
Sender: John Uhlenbrock
Date: 15:53 7 Aug '01
I've seen a few examples to avoid multiple instances of an application. In fact, there are a few of them here on code project. However, they all seem like a lot of code, when there is an easy solution like:
HANDLE hMutex = CreateMutex( NULL, TRUE, "MVD Load Utility" );
if( (hMutex == NULL) || (GetLastError() == ERROR_ALREADY_EXISTS) )
{
AfxMessageBox( "Two copies of this program are not allowed to run at the same time." );
return FALSE;
}
Marcus
Make no little plans; they have no magic to stir your blood to action. Make big plans, aim high in work and hope
-- Daniel Burnham
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CWinApp::InitInstance
Nish
p.s. Of course that will be the CWinApp derived class in your case...
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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Nish,
thanks for the quick response. do I make the mutex's handle a member of my CWinApp derived class. then how (and where) should I realease it?
Marcus
Make no little plans; they have no magic to stir your blood to action. Make big plans, aim high in work and hope
-- Daniel Burnham
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No need to release it. The system does it for you when the program exits.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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great... thanks.
As a side note, I have to say THANKS to everyone at CodeProject, and everyone that uses CodeProject. I started using VC++ in September on my first real project at work. Coming from Visual Basic, I was a little intimidated making the transition, but CP has really made it less painless, and even enjoyable experience. Thanks for help everyone.
Marcus
Make no little plans; they have no magic to stir your blood to action. Make big plans, aim high in work and hope
-- Daniel Burnham
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Marcus, I think there's a flaw in your piece of code. Instead of
CreateMutex( NULL, TRUE, "MVD Load Utility" ) you should use
CreateMutex( NULL, FALSE, "MVD Load Utility" ); Good luck.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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thanks. I read the MSDN on CreateMutex, but I can't make heads or tails of what the difference is.
BTW - in your previous example, how did you get the code to appear in beige?
Marcus
Make no little plans; they have no magic to stir your blood to action. Make big plans, aim high in work and hope
-- Daniel Burnham
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thanks. I read the MSDN on CreateMutex, but I can't make heads or tails of what the difference is.
The difference is that when bInitialOwner is set to TRUE, the system gives ownership to the first process that creates the mutex, as if it has subsequently called WaitForSingleObject on the mutex handle. As ownership is not needed for your purposes (you are only resorting to mutexes as a convenient way to share global identifier across proceses), bInitialOwner is best left as FALSE (moreover, you'd have to expliciy call RelaseMutex later, which is not the same as closing the handle). Pff, what a messy explanation, hope you've understand something of it 
To get the beige background enclose your code between <pre> and </pre> tags.
Regards
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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If his program exits, he need not call ReleaseMutex as the mutex object itself gets destroyed [or am I highly erroneous here?]
Nish
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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"highly erroneous"? that sounds painful!
Sorry to dissapoint you all with my lack of a witty or poignant signature.
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Hi Nish,
Well, the thing is a little tricky, because the documentation is not conclusive on this. I haven't found nowehere that closing a mutex handle implies also releasing it, so to the best of my knowledge not calling ReleaseMutex is undefined behavior (though it is perfectly possible that everything works nevertheless).
All in all, as the guy didn't need ownership at all, I think it is better to remain on the safe side and simply setting bInitialOwner to FALSE
Regards,
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Thanks for your thoughts and time Joaquín!
I guess you were correct in your advice to him 
Regards
Nish
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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Mutexes are automatically released.
Here is a quote from Helen Custler's Inside Windows NT book which talks about this history of mutants and mutexes in NT.
"The name /mutant/ has a colorful [sic] history. Early in Windows NT's development, Dave Cutler created a kernel mutex object that implemented low-level mutual exclusion. Later he discovered that OS/2 required a version of the mutual-exclusion semaphore with additional semantics, which Dave considered "brain-damaged" and which was incompatible with the original object. (Specifically, a thread could abandon the object and leave it inaccessible.) So he created an OS/2 version of the mutex and gave it the name /mutant/. Later Dave modified the mutant object to remove the OS/2 semantics, allowing the Win32 subsystem to use the object. The Win32 API calls the modified object /mutex/, but the native services retain the name /mutant/."
Tim Smith
Descartes Systems Sciences, Inc.
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Beautiful piece of wisdom
Anyway, I wouldn't rely on only this paragraph to merrily abandon mutexes unreleased, withouth stronger confirmation from the documentation.
Regards,
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Joaquín... You have shed some light in this dark world of mine.  It made as much sense as it could for a beginner C++ programmer.
where can I find the docs on how to use other tags (or are there any other)
thanks again.
Marcus
Make no little plans; they have no magic to stir your blood to action. Make big plans, aim high in work and hope
-- Daniel Burnham
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Apart from <pre> you can use <code> to get an effect like this.
If you're including code of yours that may have the character '<', replace those with the escape sequence <
Also, you can use regular HTML tags as well.
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Marcus2001 wrote:
where can I find the docs on how to use other tags
In the VC forum FAQ
--Mike--
My really out-of-date homepage
"Hey, you wanna go to the Espresso Pump and get sugared up on mochas?"
-- Willow Rosenberg
Sonork - 100.10414 AcidHelm
Big fan of Alyson Hannigan.
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Use the <pre> tags!
this is between two 'pre' tags
Nish
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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I am trying to see if the "enter" key is hit when some object has the focus. I have tried many things and all other keys are gotten except for the "enter."
Thanks.
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over-ride PreTranslateMessage
Nish
Sonork ID 100.9786 voidmain
www.busterboy.org
If you don't find me on CP, I'll be at Bob's HungOut
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As nish says, PreTranslate message is the way to go,
if (pMsg->message == WM_KEYDOWN)
{
if (GetFocus() != GetDlgItem(IDC_ASSAY) && pMsg->wParam == VK_ENTER)
{
Roger Allen
Sonork 100.10016
If I'm not breathing, I'm either dead or holding my breath.
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I have a simple CListCtrl that allows the user to edit the item (0). To do this the user needs to click on the item once or twice to get into "Edit" mode.
Is there a way to allow the user other ways to get into edit mode? Like pressing the right arrow key (VK_RIGHT) or something?
-kg
Ken Goguen
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Sure, you can use something like this in the appropriate handler:
int nItem=m_list.GetNextItem(-1,LVNI_SELECTED);
if(nItem>=0){
GotoDlgCtrl(&m_list);
m_list.EditLabel(nItem);
}
Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo
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Sometimes we over look the simple things. Thanks.
-kg
Ken Goguen
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