I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
16  3160 
Ed Sutton <S_************ *@nomadics.com> wrote: Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
Yes - it's quite at liberty to do so.
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
Put a GC.KeepAlive(mu tex); at the end of your try block, and all should
be well.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
I just discovered it works in a release build if I add a mutex.Close()
after Application.Run ().
It appears I need to learn about how the GC works.
-Ed
Ed Sutton wrote: I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
Ed Sutton <S_************ *@nomadics.com> wrote: I just discovered it works in a release build if I add a mutex.Close()
after Application.Run ().
It appears I need to learn about how the GC works.
Basically the GC can tell that the mutex variable isn't used again
after it's created, so it's no longer considered "live".
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Hi John,
Thank you very much for your reply. Basically the GC can tell that the mutex variable isn't used again
after it's created, so it's no longer considered "live".
How you described it sounds very efficient. I guess my C++ experience
was leading me to think it would not be garbage collected until it went
out of scope. In most cases, I believe this type of thinking has not
gotten me into trouble.
However, I am beginning to think I have been lucky. I am concerned
about objects that I share between threads being garbage collected. My
objects that are declared static are ok. But I am starting to be
concerned about other objects that may not be static.
-Ed
Hi,
The garbage collector only collects objects which don't have at least one
valid reference. In your case there seems to be a valid reference because
Application.Run doens't return until the app quits and so mutex is a valid
though local variable.
The "problem" is with the compiler, it is the compiler that can see that you
don't use the created object. So in release build when optimizing, it sees
that mutex isn't used. Therefore there won't even be a local variable
"mutex" in the release build (ilasm). It creates the mutex but it doesn't
store its reference anywhere, which is the reason the gc collects it.
Putting mutex.Close after Application.Run is a good solution to prevent the
unwanted optimalization.
HTH,
greetings
"Ed Sutton" <S_************ *@nomadics.com> wrote in message
news:eM******** *****@TK2MSFTNG P11.phx.gbl... I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
Ed Sutton <S_************ *@nomadics.com> wrote: Basically the GC can tell that the mutex variable isn't used again
after it's created, so it's no longer considered "live".
How you described it sounds very efficient. I guess my C++ experience
was leading me to think it would not be garbage collected until it went
out of scope. In most cases, I believe this type of thinking has not
gotten me into trouble.
However, I am beginning to think I have been lucky. I am concerned
about objects that I share between threads being garbage collected. My
objects that are declared static are ok. But I am starting to be
concerned about other objects that may not be static.
The only time this is a concern is when an object being garbage
collected (or really, finalized - garbage collection itself is very
unlikely to cause you any problems) causes some side-effect which is
undesirable. Aside from this mutex case (and similar ones, eg "having a
file open for locking"), I don't think it's likely to be a problem for
you.
--
Jon Skeet - <sk***@pobox.co m> http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
Ed Sutton wrote: I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
The correct solution is:
[STAThread]
static void Main()
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
using(Mutex mutex = new Mutex(true, safeName, out firstInstance))
{
if(false == firstInstance)
return;
try
{
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
}
--
Greetings
Jochen
Do you need a memory-leak finder ? http://www.codeproject.com/tools/leakfinder.asp
Do you need daily reports from your server ? http://sourceforge.net/projects/srvreport/
Hmmm, How can the GC collect it when it's reference is not stored somewhere?
Did you actually look at the IL?
Not sure if you aren't confusing compiler with Jitter, but this has nothing
to do with the compiler and compiler optimizations, it's actually the Jitter
that 'sees' that the reference is not longer needed when Application.Run
returns, so it sets the reference to null when calling Application run, so
it's a runtime optimization.
When running in the debugger, the Jitter doesn't perform any kind of
"optimizations' , as such the mutex is maintained until main goes out of
scope.
Willy.
"BMermuys" <so*****@someon e.com> wrote in message
news:eB******** ******@TK2MSFTN GP12.phx.gbl... Hi,
The garbage collector only collects objects which don't have at least one
valid reference. In your case there seems to be a valid reference because
Application.Run doens't return until the app quits and so mutex is a valid
though local variable.
The "problem" is with the compiler, it is the compiler that can see that
you
don't use the created object. So in release build when optimizing, it
sees
that mutex isn't used. Therefore there won't even be a local variable
"mutex" in the release build (ilasm). It creates the mutex but it doesn't
store its reference anywhere, which is the reason the gc collects it.
Putting mutex.Close after Application.Run is a good solution to prevent
the
unwanted optimalization.
HTH,
greetings
"Ed Sutton" <S_************ *@nomadics.com> wrote in message
news:eM******** *****@TK2MSFTNG P11.phx.gbl... I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
Hi,
"Willy Denoyette [MVP]" <wi************ *@pandora.be> wrote in message
news:%2******** ********@TK2MSF TNGP12.phx.gbl. .. Hmmm, How can the GC collect it when it's reference is not stored
somewhere?
Maybe because there is a *managed heap* which keeps track of all created
objects. The GC checks each object on the managed heap to see if it has any
valid references, if there aren't it cleans up the object.
Did you actually look at the IL?
Not sure if you aren't confusing compiler with Jitter, but this has
nothing to do with the compiler and compiler optimizations, it's actually the
Jitter that 'sees' that the reference is not longer needed when Application.Run
returns, so it sets the reference to null when calling Application run, so
it's a runtime optimization.
When running in the debugger, the Jitter doesn't perform any kind of
"optimizations' , as such the mutex is maintained until main goes out of
scope.
I wouldn't answer such a question before looking at the ILASM. I wonder if
you looked ? And yes I mean the compiler and not the jitter and do know the
difference.
If you look at release ilasm you will see that the reference from the
created mutex isn't stored anywhere, there isn't even a local variable
'mutex' . This is a compiler optimalization that happens only in release
build.
Greetings
Willy.
"BMermuys" <so*****@someon e.com> wrote in message
news:eB******** ******@TK2MSFTN GP12.phx.gbl... Hi,
The garbage collector only collects objects which don't have at least
one valid reference. In your case there seems to be a valid reference
because Application.Run doens't return until the app quits and so mutex is a
valid though local variable.
The "problem" is with the compiler, it is the compiler that can see that
you
don't use the created object. So in release build when optimizing, it
sees
that mutex isn't used. Therefore there won't even be a local variable
"mutex" in the release build (ilasm). It creates the mutex but it
doesn't store its reference anywhere, which is the reason the gc collects it.
Putting mutex.Close after Application.Run is a good solution to prevent
the
unwanted optimalization.
HTH,
greetings
"Ed Sutton" <S_************ *@nomadics.com> wrote in message
news:eM******** *****@TK2MSFTNG P11.phx.gbl... I use a mutex to disallow starting a second application instance. This
did not work in a release build until I made it static member of my
MainForm class.
In a debug build, first instance got ownership, second did not and
terminated. In a release build, the second instance *also* got
ownership. I "fixed" it by making the mutex a static member of my
MainForm class.
Did the garbage collector eat my mutex because it is not referenced
again after Application.Run is called?
I could not reproduce this on a new simple WinForm project; I tried
making all the project setting the same. Here's the code that did not
work in release build.
[STAThread]
static void Main()
{
try
{
bool firstInstance = false;
string safeName = Application.Use rAppDataPath.Re place(@"\","_") ;
Mutex mutex = new Mutex(true, safeName, out firstInstance);
if(false == firstInstance)
{
return;
}
Application.Run (new FrmMain());
}
catch(Exception ex)
{
Err.Show(ex, "Caught an unexpected exception in FrmMain");
}
}
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