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Date: Sun, 24 Aug 1997 04:31:15 -0400 (EDT)
From: Bradley Dunn <bradley@dunn.org>
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Reply-To: Bradley Dunn <bradley@dunn.org>
To: freebsd-hackers@freebsd.org
Subject: pthread_join question
Message-ID: <Pine.BSF.3.96.970824041223.838A-100000@ns2.harborcom.net>
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Hi,

I just bought _Programming with POSIX Threads_ by Butenhof so I could
learn a little bit about threads. I have a question about pthread_join in
FreeBSD. It seems from looking at the source in
src/lib/libc_r/uthread/uthread_join.c
and from trying the test code on page 32 in the book that pthread_join
will always return -1 if an error occurs. The book says that Pthreads
doesn't use errno and returns the error directly. Can someone help me
understand this better?

Here is the code from the book:
#include <pthread.h>
#include <stdio.h>
#include <errno.h>

int main (int argc, char *argv[])
{
    pthread_t thread;
    int status;

    status = pthread_join (thread, NULL);
    if (status != 0)
	fprintf (stderr, "error %d: %s\n", status, strerror (status));
    return status;
}

The output is:
error -1: Unknown error: -1

If I modify the code so that it checks errno, I find that errno is
indeed ESRCH (and the source for pthread_join seems to indicate this is
normal behavior).

Oh, and another quick question. I compiled the program using:
cc -Wall -othread_error thread_error.c -lc_r
Is the '-lc_r' the correct way to get the thread functions linked in?

PS -- Please CC me as I am not on -hackers.

Thanks,
pbd
--
The more laws and order are made prominent, the more thieves and
robbers there will be.
                -- Lao Tsu