Advanced Programming in the UNIX® Environment

ptg10805159

428 Thread Control Chapter 12

If we know that we don’t need the thread’s termination status at the time we create

the thread, we can arrange for the thread to start out in the detached state by modifying

thedetachstatethread attribute in the pthread_attr_tstructure. Wecan use the

pthread_attr_setdetachstatefunction to set thedetachstatethread attribute to

one of two legal values:PTHREAD_CREATE_DETACHED to start the thread in the

detached state orPTHREAD_CREATE_JOINABLEto start the thread normally, so its

termination status can be retrieved by the application.

#include <pthread.h>

int pthread_attr_getdetachstate(const pthread_attr_t *restrictattr,

int *detachstate);

int pthread_attr_setdetachstate(pthread_attr_t *attr,int detachstate);

Both return: 0 if OK, error number on failure

We can callpthread_attr_getdetachstateto obtain the currentdetachstate

attribute. The integer pointed to by the second argument is set to either

PTHREAD_CREATE_DETACHEDor PTHREAD_CREATE_JOINABLE,depending on the

value of the attribute in the givenpthread_attr_tstructure.

Example

Figure12.4 shows a function that can be used to create a thread in the detached state.

#include "apue.h"

#include <pthread.h>

int

makethread(void *(*fn)(void *), void *arg)

{

int err;

pthread_t tid;

pthread_attr_t attr;

err = pthread_attr_init(&attr);

if (err != 0)

return(err);

err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

if (err == 0)

err = pthread_create(&tid, &attr, fn, arg);

pthread_attr_destroy(&attr);

return(err);

}

Figure 12.4 Creating a thread in the detached state

Note that we ignorethe return value from the call topthread_attr_destroy.In

this case, we initialized the thread attributes properly,sopthread_attr_destroy

shouldn’t fail. Nonetheless, if it does fail, cleaning up would be difficult: we would

have to destroy the thread we just created, which might already be running,

asynchronous to the execution of this function. When we choose to ignorethe error