BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  TCriticalSection does not work?          BorlandTalk.com Forum Index -> C++ Builder (VCL Components Usage) View previous topic :: View next topic   Author Message Cagatay Undeger Guest Posted: Sat Jan 24, 2004 2:00 pm    Post subject: TCriticalSection does not work? Hi, I am trying to use critical sections for non blocking socket programming, but they are not functioning? For example, the below code should be blocked, but it is not. TCriticalSection * critical = new TCriticalSection (); critical->Enter(); critical->Enter(); ShowMessage("Critical section does not wor !"); This one also should block but it is not again? TCOMCriticalSection * critical = new TCOMCriticalSection(); TCOMCriticalSection::Lock * lock1 = new TCOMCriticalSection::Lock ( *critical ); TCOMCriticalSection::Lock * lock2 = new TCOMCriticalSection::Lock ( *critical ); kind regards, Cagatay Back to top Tomasz Piasecki Guest Posted: Sat Jan 24, 2004 2:28 pm    Post subject: Re: TCriticalSection does not work? Cagatay Undeger wrote: Quote: TCriticalSection * critical = new TCriticalSection (); critical->Enter(); critical->Enter(); ShowMessage("Critical section does not wor !"); read about critical sections in winapi help. Critical sections are specially made in this way that entering it in thread that already has entered it does not have effect - just for avoiding thread lock-ups. TP. -- Quote: _ _ _ | _____ _| |_| | __ (o) | | __ __ @poczta.onet.pl | | | | |o | | |/o |/ _| | |_|_|_| _| |__/|_| |_|__|__||_| Tomasz Piasecki | Back to top Cagatay Undeger Guest Posted: Sat Jan 24, 2004 9:48 pm    Post subject: Re: TCriticalSection does not work? I think non blocking server socket uses just one thread, so critical sections does not work. Thank you, "Tomasz Piasecki" <mtbrider (AT) _-nospam-_ (DOT) poczta.onet.pl> wrote Quote: Cagatay Undeger wrote: TCriticalSection * critical = new TCriticalSection (); critical->Enter(); critical->Enter(); ShowMessage("Critical section does not wor !"); read about critical sections in winapi help. Critical sections are specially made in this way that entering it in thread that already has entered it does not have effect - just for avoiding thread lock-ups. TP. -- | _ _ _ | | _____ _| |_| | __ (o) | | __ __ @poczta.onet.pl | | | | | |o | | |/o |/ _| | | |_|_|_| _| |__/|_| |_|__|__||_| Tomasz Piasecki | Back to top Remy Lebeau (TeamB) Guest Posted: Sat Jan 24, 2004 10:55 pm    Post subject: Re: TCriticalSection does not work? "Cagatay Undeger" <cagatay (AT) interaktif (DOT) gen.tr> wrote Quote: I am trying to use critical sections for non blocking socket programming, but they are not functioning? Yes, they do work. You are just using them incorrectly. Quote: For example, the below code should be blocked, but it is not. It appears that you are creating new critical section instances each time you want to apply a lock. You should not be doing that. Critical sections, mutexes, semiphores, TMultiReadExclusiveWriteSynchronizer, all of these synch objects have one thing in common - every time you want to support locking/unlocking of shared resources somewhere, you are supposed to be sharing a common instance. You are not supposed to be creating new instances each time you want to lock something, that defeats the whole purpose. Synch locks only work correctly when multiple threads are trying to access and lock/unlock the same sych object, not their own individual sych objects. Gambit Back to top Cagatay Undeger Guest Posted: Sun Jan 25, 2004 1:08 pm    Post subject: Re: TCriticalSection does not work? Sorry, I didn't informed clearly that the code I sent was just a test sample, not the way I use. I always have one instance within an application. I was expecting that 2 sequential enters on a single critical section will block itself. Thank you Cagatay "Remy Lebeau (TeamB)" <gambit47.no.spam (AT) no (DOT) spam.yahoo.com> wrote Quote: "Cagatay Undeger" <cagatay (AT) interaktif (DOT) gen.tr> wrote in message news:40127a7a (AT) newsgroups (DOT) borland.com... I am trying to use critical sections for non blocking socket programming, but they are not functioning? Yes, they do work. You are just using them incorrectly. For example, the below code should be blocked, but it is not. It appears that you are creating new critical section instances each time you want to apply a lock. You should not be doing that. Critical sections, mutexes, semiphores, TMultiReadExclusiveWriteSynchronizer, all of these synch objects have one thing in common - every time you want to support locking/unlocking of shared resources somewhere, you are supposed to be sharing a common instance. You are not supposed to be creating new instances each time you want to lock something, that defeats the whole purpose. Synch locks only work correctly when multiple threads are trying to access and lock/unlock the same sych object, not their own individual sych objects. Gambit Back to top Tomasz Piasecki Guest Posted: Sun Jan 25, 2004 1:28 pm    Post subject: Re: TCriticalSection does not work? Cagatay Undeger wrote: Quote: I think non blocking server socket uses just one thread, so critical sections does not work. I don't understand you. TCriticalSection is a wrapper of WinAPI CRITICAL_SECTION and it has nothing to do with client socket. The code you presented does just what it should do. And as far as I know, nonblocking socket runs in separate thread, not in main thread. That's why it is nonblocking. TP. -- Quote: _ _ _ | _____ _| |_| | __ (o) | | __ __ @poczta.onet.pl | | | | |o | | |/o |/ _| | |_|_|_| _| |__/|_| |_|__|__||_| Tomasz Piasecki | Back to top Tomasz Piasecki Guest Posted: Sun Jan 25, 2004 1:30 pm    Post subject: Re: TCriticalSection does not work? Cagatay Undeger wrote: Quote: I was expecting that 2 sequential enters on a single critical section will They don't if you enter critical section twice in the same thread. If you enter it in one thread, then trying to enter it in second thread will lock this thread until first one leaves critical section. TP. -- Quote: _ _ _ | _____ _| |_| | __ (o) | | __ __ @poczta.onet.pl | | | | |o | | |/o |/ _| | |_|_|_| _| |__/|_| |_|__|__||_| Tomasz Piasecki | Back to top Remy Lebeau (TeamB) Guest Posted: Sun Jan 25, 2004 10:56 pm    Post subject: Re: TCriticalSection does not work? "Cagatay Undeger" <cagatay (AT) interaktif (DOT) gen.tr> wrote Quote: I was expecting that 2 sequential enters on a single critical section will block itself. If it allowed that in the manner that you have shown, then you would deadlock your code. Which is exactly why synch objects do not allow a thread to obtain the lock more than once at a time. If a thread already has the lock, further attempts to obtain the lock from within the same thread will have no effect. 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