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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 MOJAVE

pthread_attr_getdetachstate

PTHREAD_ATTR(3) 					   BSD Library Functions Manual 					   PTHREAD_ATTR(3)

NAME

     pthread_attr_getdetachstate, pthread_attr_setdetachstate -- thread attribute operations

SYNOPSIS

     #include <pthread.h>

     int
     pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detachstate);

     int
     pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);

DESCRIPTION

     Thread attributes are used to specify parameters to pthread_create().  One attribute object can be used in multiple calls to
     pthread_create(), with or without modifications between calls.

     One of these thread attributes governs the creation state of the new thread. The new thread can be either created "detached" or "joinable".
     The constants corresponding to these states are PTHREAD_CREATE_DETACHED and PTHREAD_CREATE_JOINABLE respectively.	Creating a "joinable"
     thread allows the user to call pthread_join() and pthread_detach(), with the new thread's ID. A "detached" thread's ID cannot be used with
     pthread_join() and pthread_detach().  The default value for the "detachstate" attribute is PTHREAD_CREATE_JOINABLE.

     The pthread_attr_setdetachstate() function sets the thread's "detachstate" attribute.

     The "detachstate" attribute is set within the attr argument, which can subsequently be used as an argument to pthread_create().

RETURN VALUES

     If successful, these functions return 0.  Otherwise, an error number is returned to indicate the error.  pthread_attr_getdetachstate(), on
     success, will copy the value of the thread's "detachstate" attribute to the location pointed to by the second function parameter.

ERRORS

     pthread_attr_getdetachstate() will fail if:

     [EINVAL]		Invalid value for attr

     pthread_attr_setdetachstate() will fail if:

     [EINVAL]		Invalid value for attr or detachstate.

SEE ALSO

     pthread_create(3), pthread_join(3), pthread_attr_init(3), pthread_detach(3)

STANDARDS

     pthread_attr_setdetachstate(), pthread_attr_getdetachstate() conform to ISO/IEC 9945-1:1996 (``POSIX.1'')

BSD
								 December 31, 2007							       BSD
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