Re: Memory leak in pthread_setcanceltype()?

[reentrant <reentrant at yahoo dot com>]

I don't know for a fact, but I'd be leary about calling pthread_mutex_destroy()
on a mutex not initialized with pthread_mutex_init() (i.e. initialied with
PTHREAD_MUTEX_INITIALIZER).  It feels like free()ing a pointer to a char array
allocated on the stack to me.  I certainly wouldn't depend on calling
pthread_mutex_destroy() on a mutex not initialized via pthread_mutex_init() to
be portable.

From the sound of it, to be safe I'd personally recommend avoiding the
PTHREAD_MUTEX_INITIALIZER and use pthread_mutex_init() to initialize and
pthread_mutex_destroy() to destroy.

I've used a mutex class since 11/99 that does exactly that without any flags
from purify or boundschecker (but using a 10/99 pthreads snapshot...).

Dave

--- Ross Johnson <rpj@ise.canberra.edu.au> wrote:
> Hi,
> 
> I could be wrong since C++ is not a strongpoint for me, but your Mutex
> class constructs the mutex as a PTHREAD_MUTEX_INITIALIZER but you
> don't call pthread_mutex_destroy() in the destructor. The way that
> pthreads-win32 implements static initialised mutexes is to calloc
> the mutex struct the first time pthread_mutex_lock() is called on
> that mutex. Perhaps other Pthreads implementations don't require
> this but I think destroying a static mutex is legal and portable.
> 
> Ross
> 
> Alastair Hume wrote:
> > 
> > Hello,
> > 
> > I'm using Pthreads win32 (snapshot 2000-09-08) with Visual C++ (6.0) and
> > Windows2000 and I am getting lots of memory leaks flagged by Purify and
> > BoundsChecker.  I'm using the precompiled DLL obtained from
> > <ftp://sources.redhat.com/pub/pthreads-win32/dll-latest>.
> > 
> > These leaks occur in (at least) calls to phread_mutex_lock(),
> > pthread_cond_wait() and pthread_cond_timedwait() and at typically about 28
> > bytes per leak.
> > 
> > Purify reports these memory leaks as:
> > 
> > MLK: Memory leak of 28 bytes from 1 block allocated in
> pthread_setcanceltype
> >         Distribution of leaked blocks
> >                 28 bytes from 1 block of 28 bytes (0x02105db0)
> >         Allocation location
> >             calloc         [msvcrt.DLL]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             SDSUtility::Mutex::lock(void) [SDSUtility_Mutex.cpp:61]
> >                 {
> >                 #ifdef _MT
> > 
> >              =>     pthread_mutex_lock( &m_objectMutex );
> > 
> >                 #endif
> >                 }
> > and:
> > 
> > MLK: Memory leak of 20 bytes from 1 block allocated in
> pthread_setcanceltype
> >         Distribution of leaked blocks
> >                 20 bytes from 1 block of 20 bytes (0x02106200)
> >         Allocation location
> >             calloc         [msvcrt.DLL]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             pthread_setcanceltype [pthreadVSE.dll]
> >             SDSDataStore::Query::waitForTrigger(void)
> > [SDSDataStore_Query.cpp:136]
> >                     if( !m_triggered && !m_terminated )
> >                     {
> >              =>         pthread_cond_wait( &m_triggered_cond, &m_mutex );
> >                     }
> > 
> > BoundsChecker reports the first leak as:
> > 
> > Bounds checker reports this as:
> > 
> > Memory leak: 28 bytes allocated by calloc in
> PTHREADVSE.DLL!00002AC1,HANDLE:
> > 0x00303A10
> > PTHREADVSE.DLL!00002AC1()       (unknown)       (unknown)
> > PTHREADVSE.DLL!00002AC1()       (unknown)       (unknown)
> > PTHREADVSE.DLL!00002AC1()       (unknown)       (unknown)
> > SDSUtility::Mutex::lock()
> > C:\Scorpion\source\SDSUtility\SDSUtility_Mutex.cpp      61
> > 
> > Does anybody know if this is a known problem?  Can anybody point me to
> > something I could be doing wrong to cause this problem.  I have tried using
> > both the VSE and VCE versions.  I also hacked up a simple program which
> > locks and unlocks a pthread mutex and purify does not find any leaks in it
> > so it is likely to be something within my more complicated program but I'm
> > not sure what I can do to release memory allocated by a call to
> > pthread_mutex_lock() - have I missed something?
> > 
> > Below is my implementation of my Mutex class whose lock() methods creates
> > the first leak listed above, just incase anybody can see anything obviously
> > stupid in this.
> > 
> > Any help in pointing me in the right direction would be very much
> > appreciated.
> > 
> > Thanks,
> > 
> > Ally Hume
> > Concept Systems Limited
> > 
> > Mutex.h
> > 
> > #include <pthread.h>
> > 
> > class Mutex
> > {
> > public:
> > 
> >     /// Constructor
> >     Mutex();
> > 
> >     /// Destructor
> >     ~Mutex();
> > 
> >     /**
> >     *** Locks the mutex.  Blocks until the lock is obtained
> >     **/
> >     void lock();
> > 
> >     /**
> >     *** Unlocks the mutex
> >     **/
> >     void unlock();
> > 
> > private:
> > 
> >     // Synchronization object
> > 
> > #ifdef _MT
> > 
> >     pthread_mutex_t    m_objectMutex;                       ///< global
> > object mutex
> > 
> > #endif
> > 
> > };
> > 
> > Mutex.cpp
> > 
> > /// Constructor
> > Mutex::Mutex()
> > #ifdef _MT
> >     : m_objectMutex( PTHREAD_MUTEX_INITIALIZER )
> > #endif
> > {
> > }
> > 
> > /// Destructor
> > Mutex::~Mutex()
> > {
> > }
> > 
> > /**
> > *** Locks the mutex.  Blocks until the lock is obtained
> > **/
> > void
> > Mutex::lock()
> > {
> > #ifdef _MT
> > 
> >     pthread_mutex_lock( &m_objectMutex );
> > 
> > #endif
> > }
> > 
> > /**
> > *** Unlocks the mutex
> > **/
> > void
> > Mutex::unlock()
> > {
> > #ifdef _MT
> > 
> >     pthread_mutex_unlock( &m_objectMutex );
> > 
> > #endif
> > }


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