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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pthread_kill

pthread_kill(3T)														  pthread_kill(3T)

NAME

       pthread_kill() - send a signal to a thread

SYNOPSIS

PARAMETERS

	      thread	Thread to which the signal is to be delivered.

	      sig	Signal to be delivered to thread.

DESCRIPTION

       The  function  is  used	to  request  that a signal be delivered to thread.  The signal is asynchronously directed to thread in the calling
       process. The signal is handled in the context of the given thread; if the signal action results in the thread terminating or stopping, this
       action is applied to the whole process.

       If sig is zero, error checking is performed but a signal is not sent.

RETURN VALUE

       Upon successful completion, returns zero. Otherwise, an error number is returned to indicate the error (the variable is not set).

ERRORS

       If any of the following occur, the function returns the corresponding error number:

	      [EINVAL]	     sig is an invalid or unsupported signal number.

	      [ESRCH]	     No thread could be found corresponding to thread.

AUTHOR

       was derived from the IEEE POSIX P1003.1c standard.

SEE ALSO

       kill(2), sigaction(2), pthread_self(3T), raise(2).

STANDARDS CONFORMANCE

								  Pthread Library						  pthread_kill(3T)