Re: critical section

["Ye Liu" <yliu at tibco dot com>]

In the book of "Programming with POSIX Threads",  the author metioned

"You cannot lock a mutex when the calling thread already has that mutex locked."

My previous understanding is "a mutex cannot be locked twice", which obviously
is wrong.

If I use a non-recursive mutex, when a thread try to lock the mutex which is
already locked by another one, what happens to the calling thread? Spin or
yield?

--ye

Scott McCaskill wrote:

> It looks like you're trying to make a non-recursive mutex (can only be
> locked once by any thread, including the mutex owner).  pthread_mutex can
> already do this; is there some reason you're not using it this way directly?
> See pthread_mutexattr_settype().
>
> ----- Original Message -----
> From: "Ye Liu" <yliu@tibco.com>
> To: "win32-pthread" <pthreads-win32@sourceware.cygnus.com>
> Sent: Tuesday, July 31, 2001 4:27 PM
> Subject: critical section
>
> > Greets,
> >
> > When I impelement the critical section using mutex, I have the following
> > code:
> >
> > /*    TIBMutex.h    */
> > #ifndef _TIBMutex_H_
> > #define _TIBMutex_H_
> > class TIBMutex
> > {
> > public:
> >     TIBMutex();
> >      ~TIBMutex();
> >      void acquire();
> >      void acquire_yield();
> >      void release();
> >      int tryacquire();
> >
> > private:
> >     pthread_mutex_t m_Mutex;
> >     pthread_mutexattr_t m_MutexAttr;
> >     void init_MutexAttr();
> >     int m_Count;
> > };
> >
> > /*    TIBMutex.cpp    */
> > TIBMutex::TIBMutex()
> > {
> >  m_Count = 0;
> >  if  (pthread_mutex_init(&m_Mutex, &m_MutexAttr))
> >     /* error handling...*/
> > }
> >
> > inline void TIBMutex::acquire()
> > {
> >  while (m_Count);
> >
> >  if (pthread_mutex_lock(&m_Mutex))
> >  {
> >      /* error handling...*/
> >  }
> >  ++m_Count;
> >  return;
> > }
> >
> > inline void TIBMutex::release()
> > {
> >  if (pthread_mutex_unlock(&m_Mutex))
> >  {
> >     /* error handling...*/
> >  }
> >  --m_Count;
> > }
> >
> > My questions are:
> >
> > 1. Do I need use a condition variable here because I use m_Count as 0/1
> > signal?
> >
> > 2. In the acquire(), when m_Count is not 0, the waiting thread should
> > "spin" there as the above or yield like the following acquire_yield()
> >
> > inline void TIBMutex::acquire_yield()
> > {
> >  while (m_Count)
> >   shed_yield();
> >  if (pthread_mutex_lock(&m_Mutex))
> >  {
> >     /* error handling...*/
> >  }
> >  ++m_Count;
> >  return;
> > }
> >
> >
> > --
> > Ye Liu
> > Tel(O) 650-846-5228
> >
> >
> >

--
Ye Liu
Tel(O) 650-846-5228