calling pthread_self (on ubuntu), expensive? Post: 302427078

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Top Forums Programming calling pthread_self (on ubuntu), expensive? Post 302427078 by gorga on Thursday 3rd of June 2010 06:55:00 PM

06-03-2010

Registered User

Thanks for your replay Corona688.

I found similar code in glibc (tls.h)...

Code:

/* Return the TCB address of the current thread.  */
# define THREAD_SELF                                   \
  ({ tcbhead_t *__tcb;                                  \
     __asm__ ("movl %%gs:%c1,%0" : "=r" (__tcb)                      \
          : "i" (offsetof (tcbhead_t, tcb)));                  \
     __tcb;})

Which I believe is accessing the Thread Control Block of the running thread which resides here in the gs register, specifically the offset containing the tcb address, I think.

This should result in a pretty quick, "inexpensive" and scalable operation then. Wondered if there was a chance that another thread could overwrite the register where this value is written before the calling thread retrieved it, (the volatile keyword isn't used) but I suppose this function would be useless if that was a possibility. This function must be thread safe, right?

Cheers,

gorga

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LEARN ABOUT NETBSD

pthread_join

PTHREAD_JOIN(3) 					   BSD Library Functions Manual 					   PTHREAD_JOIN(3)

NAME

     pthread_join -- wait for thread termination

LIBRARY

     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS

     #include <pthread.h>

     int
     pthread_join(pthread_t thread, void **value_ptr);

DESCRIPTION

     The pthread_join() function suspends execution of the calling thread until the target thread terminates unless the target thread has already
     terminated.

     On return from a successful pthread_join() call with a non-NULL value_ptr argument, the value passed to pthread_exit() by the terminating
     thread is stored in the location referenced by value_ptr.	When a pthread_join() returns successfully, the target thread has been terminated.
     The results of multiple simultaneous calls to pthread_join() specifying the same target thread are undefined.  If the thread calling
     pthread_join() is cancelled, then the target thread is not detached.

     A thread that has exited but remains unjoined counts against _POSIX_THREAD_THREADS_MAX.

RETURN VALUES

     If successful,  the pthread_join() function will return zero.  Otherwise an error number will be returned to indicate the error.

ERRORS

     pthread_join() shall fail if:

     [EINVAL]		The value specified by thread does not refer to a joinable thread.

     [ESRCH]		No thread could be found corresponding to that specified by the given thread ID, thread.

     pthread_join() may fail if:

     [EDEADLK]		A deadlock was detected or the value of thread specifies the calling thread.

SEE ALSO

     wait(2), pthread_create(3)

STANDARDS

     The function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

BSD
								   July 9, 2010 							       BSD