I want a function called on thread exit.
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I am trying to create my first a multi-threaded dev-studio library project. Is there a way to register a thread "cleanup" function that gets called each time a thread exits? Here are some constraints for any suggestions you provide me: 1) I think I want my library statically linked. I see that for DLLs, DllMain() gets called each time a thread "detaches". This might be an appropriate place for me to stick my clean-up code if I were writing a DLL, but I don't think I want a DLL. 2) I don't want users of my library to have to write any code to get the cleanup function called. It should all be completely hidden. 3) I really only need my cleanup function executed for exiting threads that previously used particular functions from my library. So I do have a place to register the thread-exit function if there is a way to do that at all. Thanks much for your help. Matt Busche
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I am trying to create my first a multi-threaded dev-studio library project. Is there a way to register a thread "cleanup" function that gets called each time a thread exits? Here are some constraints for any suggestions you provide me: 1) I think I want my library statically linked. I see that for DLLs, DllMain() gets called each time a thread "detaches". This might be an appropriate place for me to stick my clean-up code if I were writing a DLL, but I don't think I want a DLL. 2) I don't want users of my library to have to write any code to get the cleanup function called. It should all be completely hidden. 3) I really only need my cleanup function executed for exiting threads that previously used particular functions from my library. So I do have a place to register the thread-exit function if there is a way to do that at all. Thanks much for your help. Matt Busche
> Is there a way to register a thread "cleanup" function > that gets called each time a thread exits? Hm..the first solution that comes to my mind: Call
GetExitCodeThreadperiodically.DWORD dwExitCode;
GetExitCodeThread( hThread, &dwExitCode);if( dwExitCode == STILL_ACTIVE )
// thread still living
else
// thread terminated -> do your cleanupAnyway, why don't you simply call the cleanup routine at the end of
ThreadFunc(just before callingreturn)?DWORD WINAPI ThreadFunc( LPVOID lpParameter )
{
// do your workMyCleanUpRoutine();
return 0;
}Regards, RK
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> Is there a way to register a thread "cleanup" function > that gets called each time a thread exits? Hm..the first solution that comes to my mind: Call
GetExitCodeThreadperiodically.DWORD dwExitCode;
GetExitCodeThread( hThread, &dwExitCode);if( dwExitCode == STILL_ACTIVE )
// thread still living
else
// thread terminated -> do your cleanupAnyway, why don't you simply call the cleanup routine at the end of
ThreadFunc(just before callingreturn)?DWORD WINAPI ThreadFunc( LPVOID lpParameter )
{
// do your workMyCleanUpRoutine();
return 0;
}Regards, RK
Robert, I guess I'm not a big fan of polling. As for your second suggestion: I'm trying to write a library that other developers will use. My library won't be spawning threads -- the application written by someone else will. So to pursue your suggestion, I'd have to include in my library notes, "oh, and be sure to call MyCleanUpRoutine() before your thread exits. Don't really care for that either. I guess I'm going to have to figure out how to get a DLL to work for me instead. Actually, I think a DLL will work for me, but my initial attempts to create a DLL have not gone so well -- having problems getting global data from the DLL to link. :( Thanks much for your response. Matt Busche
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Robert, I guess I'm not a big fan of polling. As for your second suggestion: I'm trying to write a library that other developers will use. My library won't be spawning threads -- the application written by someone else will. So to pursue your suggestion, I'd have to include in my library notes, "oh, and be sure to call MyCleanUpRoutine() before your thread exits. Don't really care for that either. I guess I'm going to have to figure out how to get a DLL to work for me instead. Actually, I think a DLL will work for me, but my initial attempts to create a DLL have not gone so well -- having problems getting global data from the DLL to link. :( Thanks much for your response. Matt Busche
A *.dll would perfectly suit your needs. What you have to do is: 1.Create a *.dll and export all the functions you want your users to call 2.Make sure that the global data (if any) that simultanious threads can access (i.e. if two or more users at a time call the same function) is protected with syncronization objects like Critical sections 3.If your user calls LoadLibrary, your DllMain gets called with DLL_PROCESS_ATTACH, do some initialization, maybe keep reference count of attached clients, when your user calls FreeLibrary your DllMain gets called with reason DLL_PROCESS_DETACH. This is the place to call your CleanUpFunction() Summary: your user has only to call LoadLibrary on your *.dll, GetProcAddress on the function, and FreeLibrary to get detached from your lib. Peter Molnar
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A *.dll would perfectly suit your needs. What you have to do is: 1.Create a *.dll and export all the functions you want your users to call 2.Make sure that the global data (if any) that simultanious threads can access (i.e. if two or more users at a time call the same function) is protected with syncronization objects like Critical sections 3.If your user calls LoadLibrary, your DllMain gets called with DLL_PROCESS_ATTACH, do some initialization, maybe keep reference count of attached clients, when your user calls FreeLibrary your DllMain gets called with reason DLL_PROCESS_DETACH. This is the place to call your CleanUpFunction() Summary: your user has only to call LoadLibrary on your *.dll, GetProcAddress on the function, and FreeLibrary to get detached from your lib. Peter Molnar
Peter, Thanks for your reply. I actually started to do this and only just now discovered that this only works for RUN-TIME dynamic-linking of a DLL. (I.e., where you use the LoadLibrary call just like you said.) I saw some sample code on how to use LoadLibrary and GetProcAddress to call a single simple function from a DLL, but I'm not exporting a single simple function, I'm exporting a handfull of C++ concrete and abstract classes (along with all their numerous member methods and overloaded operators). It is not clear to me how you'd use run-time linking for such a library. Supppose Peter, you inherited from one of my abstract base-classes, then when you wrote your constructor, how would you call my base class constructor that is exported from my DLL? And even if it's possible, my whole objective is to make my software as easy as possible to use. I certainly wouldn't want my users to have to jump through any flaming hoops to call a base class constructor or call the "=" operator for a class. Here's a thought. What if I had two libraries? Library ALPHA has all my user visible software and could be built arbitrarily for either dynamic or static linkage. If built as a DLL it would be expected to be used with load-time dynamic-linkage. DLL BETA has nothing in it but a DllMain. Now, here's the trick: suppose DLL ALPHA secretly does a LoadLibrary call on BETA via some singleton constructor found in ALPHA. This singleton is instantiated the first time a user of ALHPA references resources that require thread initialization and cleanup activities. Then, I would presume that every subsequent thread spawn and delete would cause this DllMain in BETA to be invoked, would it not? I presume also that DllMain in BETA could invoke methods defined in ALPHA (to effect thread initialization and cleanup.) I'm going to investigate this idea further and maybe try it out. Let me know if I misunderstood the implications of your email. I've been battling this silly problem for a week now. If I don't come up with a better solution soon, I'll have to simply publish a threadCleanup method that must be called by users of my library on thread exit, but I really don't want to have to do this. Once again, thanks sincerely for your help. Matt
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A *.dll would perfectly suit your needs. What you have to do is: 1.Create a *.dll and export all the functions you want your users to call 2.Make sure that the global data (if any) that simultanious threads can access (i.e. if two or more users at a time call the same function) is protected with syncronization objects like Critical sections 3.If your user calls LoadLibrary, your DllMain gets called with DLL_PROCESS_ATTACH, do some initialization, maybe keep reference count of attached clients, when your user calls FreeLibrary your DllMain gets called with reason DLL_PROCESS_DETACH. This is the place to call your CleanUpFunction() Summary: your user has only to call LoadLibrary on your *.dll, GetProcAddress on the function, and FreeLibrary to get detached from your lib. Peter Molnar
Peter, OK, forget what I just wrote. If just found some words in the MSDN that would seem to imply that DllMain is used even if you use load time dynamic linking of the library. (Which I guess means that LoadLibrary must be invoked for you if you use load-time dynamic linking?) Let me know if I'm lost. Let me know if I'm not lost. I'm forging ahead. Matt