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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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PTHREAD_ATTR_GET_NP(3)					   BSD Library Functions Manual 				    PTHREAD_ATTR_GET_NP(3)

NAME
pthread_attr_get_np -- get attributes of existing thread LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_attr_get_np(pthread_t thread, pthread_attr_t *attr); int pthread_getattr_np(pthread_t thread, pthread_attr_t *attr); DESCRIPTION
The pthread_attr_get_np() and pthread_getattr_np() functions can be used to retrieve attributes of a running thread. The result is stored to attr. For pthread_attr_get_np() attr should be initialized prior to the call by using pthread_attr_init(3). pthread_getattr_np() does this auto- matically. For both functions attr should be freed when it is not in use anymore with pthread_attr_destroy(3). Most fields of attr are the same ones provided during thread creation time as a parameter to pthread_create(3). The exceptions include: o The detach state -- a joinable thread may have detached itself after the creation. o The guard size, which may vary if the application has allocated its own thread stack. o The stack address and size; pthread_attr_get_np() will always return the thread's real stack address and size, regardless of the values in the original attributes structure. The returned pthread_attr_t structure is supposed to be used in conjunction with the pthread_attr_get*() functions to retrieve individual values from the structure. When the returned attr is no longer needed, it should be destroyed by using pthread_attr_destroy(3). RETURN VALUES
Upon successful completion, pthread_attr_get_np() and pthread_getattr_np() return 0. Otherwise an error number is returned to indicate the error. COMPATIBILITY
The pthread_attr_get_np() and pthread_getattr_np() functions are non-standard extensions. ERRORS
The pthread_attr_get_np() and pthread_getattr_np() functions will fail if: [ENOMEM] Insufficient memory. [ESRCH] Non-existent thread. SEE ALSO
pthread(3), pthread_attr(3) BSD
August 6, 2010 BSD
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