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Full Discussion: Multiple instances of pthread
Top Forums Programming Multiple instances of pthread Post 302644409 by jim mcnamara on Monday 21st of May 2012 10:00:53 PM
Old 05-21-2012
Several points. Thread synchronization ( what you are asking about)
Code:
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_create(&tid, &attr, some_func, (void *)args);

This creates a detached thread - one that goes away when it hits a pthread_exit() statement or a return statement at the end of some_func();

The default pthread_create() call, by default, in most UNIXes, creates a joinable thread.
Not a detached thread like above.

So you do this for each thread:
Code:
pthread_t tid;
pthread_create(&tid, &attr, some_func, (void *)args);
pthread_join(tid, NULL);


The code blocks on pthread_join() until the child thread hits return or pthread_exit().
One type of thread you wait for (join) the other you do not care about.

You need to decide which one you want to use, there really aren't a lot of other choices.
You can set a global variable:
Code:
volatile int i_am_done=0;

and change the variable to let the parent know a detached thread completed.
Protect the volatile int with a mutex: pthread_mutex_lock & pthread_mutex_unlock calls, whenever you set or look at the variable.

And. pthread_kill is not always a great choice. All it does is to direct the signal to the thread. Example: SIGKILL (kill -9) destroys the entire process because the effect of the signal is to nuke the entire process. So signals do not behave the way you might believe a priori.
 

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LEARN ABOUT OPENDARWIN

pthread_equal

PTHREAD_EQUAL(3)					     Linux Programmer's Manual						  PTHREAD_EQUAL(3)

NAME

       pthread_equal - compare thread IDs

SYNOPSIS

       #include <pthread.h>

       int pthread_equal(pthread_t t1, pthread_t t2);

       Compile and link with -pthread.

DESCRIPTION

       The pthread_equal() function compares two thread identifiers.

RETURN VALUE

       If the two thread IDs are equal, pthread_equal() returns a nonzero value; otherwise, it returns 0.

ERRORS

       This function always succeeds.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------------+---------------+---------+
       |Interface	| Attribute	| Value   |
       +----------------+---------------+---------+
       |pthread_equal() | Thread safety | MT-Safe |
       +----------------+---------------+---------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

NOTES

       The  pthread_equal()  function  is  necessary  because thread IDs should be considered opaque: there is no portable way for applications to
       directly compare two pthread_t values.

SEE ALSO

       pthread_create(3), pthread_self(3), pthreads(7)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2015-08-08							  PTHREAD_EQUAL(3)
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