Multithreaded Programming Guide

Set Detach State


When a thread is created detached (PTHREAD_CREATE_DETACHED), its thread ID and other resources can be reused as soon as the thread terminates. Use pthread_attr_setdetachstate(3THR) when the calling thread does not want to wait for the thread to terminate.

When a thread is created nondetached (PTHREAD_CREATE_JOINABLE), it is assumed that you will be waiting for it. That is, it is assumed that you will be executing a pthread_join(3T)() on the thread.

Whether a thread is created detached or nondetached, the process does not exit until all threads have exited. See "Finishing Up" for a discussion of process termination caused by premature exit from main().


int	pthread_attr_setdetachstate(pthread_attr_t *tattr,int detachstate);
#include <pthread.h>

pthread_attr_t tattr;
int ret;

/* set the thread detach state */
ret = pthread_attr_setdetachstate(&tattr,PTHREAD_CREATE_DETACHED);

Note -

When there is no explicit synchronization to prevent it, a newly created, detached thread can die and have its thread ID reassigned to another new thread before its creator returns from pthread_create().

For nondetached (PTHREAD_CREATE_JOINABLE) threads, it is very important that some thread join with it after it terminates--otherwise the resources of that thread are not released for use by new threads. This commonly results in a memory leak. So when you do not want a thread to be joined, create it as a detached thread.

Example 3-1 Creating a Detached Thread

#include <pthread.h>

pthread_attr_t tattr;
pthread_t tid;
void *start_routine;
void arg
int ret;

/* initialized with default attributes */
ret = pthread_attr_init()(&tattr);
ret = pthread_attr_setdetachstate()(&tattr,PTHREAD_CREATE_DETACHED);
ret = pthread_create()(&tid, &tattr, start_routine, arg);

Return Values

pthread_attr_setdetachstate() returns zero after completing successfully. Any other returned value indicates that an error occurred. If the following condition occurs, the function fails and returns the corresponding value.


Indicates that the value of detachstate or tattr was not valid.