pthread_setname_np (3)

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Copyright (C) 2012 Chandan Apsangi <chandan.jc@gmail.com>
and Copyright (C) 2013 Michael Kerrisk <mtk.manpages@gmail.com>

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(The comments found at the beginning of the groff file "man3/pthread_setname_np.3".)

NAME

pthread_setname_np, pthread_getname_np - set/get the name of a thread

SYNOPSIS

#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <pthread.h>
int pthread_setname_np(pthread_t thread, const char *name);
int pthread_getname_np(pthread_t thread,
                       char *name, size_t len);

Compile and link with -pthread.

DESCRIPTION

By default, all the threads created using pthread_create() inherit the program name. The pthread_setname_np() function can be used to set a unique name for a thread, which can be useful for debugging multithreaded applications. The thread name is a meaningful C language string, whose length is restricted to 16 characters, including the terminating null byte (aq\0aq). The thread argument specifies the thread whose name is to be changed; name specifies the new name.
The pthread_getname_np() function can be used to retrieve the name of the thread. The thread argument specifies the thread whose name is to be retrieved. The buffer name is used to return the thread name; len specifies the number of bytes available in name. The buffer specified by name should be at least 16 characters in length. The returned thread name in the output buffer will be null terminated.

RETURN VALUE

On success, these functions return 0; on error, they return a nonzero error number.

ERRORS

The pthread_setname_np() function can fail with the following error:

ERANGE

The length of the string specified pointed to by name exceeds the allowed limit.

The pthread_getname_np() function can fail with the following error:

ERANGE

The buffer specified by name and len is too small to hold the thread name.

If either of these functions fails to open /proc/self/task/[tid]/comm, then the call may fail with one of the errors described in open(2).

VERSIONS

These functions first appeared in glibc in version 2.12.

ATTRIBUTES

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

Interface	Attribute	Value
pthread_setname_np(), pthread_getname_np()	Thread safety	MT-Safe

CONFORMING TO

These functions are nonstandard GNU extensions.

NOTES

pthread_setname_np() internally writes to the thread-specific comm file under the /proc filesystem: /proc/self/task/[tid]/comm. pthread_getname_np() retrieves it from the same location.

EXAMPLE

The program below demonstrates the use of pthread_setname_np() and pthread_getname_np().
The following shell session shows a sample run of the program:

$ ./a.out
Created a thread. Default name is: a.out
The thread name after setting it is THREADFOO.
^Z                           # Suspend the program
[1]+  Stopped           ./a.out
$ ps H -C a.out -o 'pid tid cmd comm'
  PID   TID CMD                         COMMAND
 5990  5990 ./a.out                     a.out
 5990  5991 ./a.out                     THREADFOO
$ cat /proc/5990/task/5990/comm
a.out
$ cat /proc/5990/task/5991/comm
THREADFOO

Program source

#define _GNU_SOURCE
#include <pthread.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>

#define NAMELEN 16

#define errExitEN(en, msg) \
            do { errno = en; perror(msg); exit(EXIT_FAILURE); \
        } while (0)

static void *
threadfunc(void *parm)
{
    sleep(5);          // allow main program to set the thread name
    return NULL;
}

int
main(int argc, char **argv)
{
    pthread_t thread;
    int rc;
    char thread_name[NAMELEN];

    rc = pthread_create(&thread, NULL, threadfunc, NULL);
    if (rc != 0)
        errExitEN(rc, "pthread_create");

    rc = pthread_getname_np(thread, thread_name, NAMELEN);
    if (rc != 0)
        errExitEN(rc, "pthread_getname_np");

    printf("Created a thread. Default name is: %s\n", thread_name);
    rc = pthread_setname_np(thread, (argc > 1) ? argv[1] : "THREADFOO");
    if (rc != 0)
        errExitEN(rc, "pthread_setname_np");

    sleep(2);

    rc = pthread_getname_np(thread, thread_name,
                            (argc > 2) ? atoi(argv[1]) : NAMELEN);
    if (rc != 0)
        errExitEN(rc, "pthread_getname_np");
    printf("The thread name after setting it is %s.\n", thread_name);

    rc = pthread_join(thread, NULL);
    if (rc != 0)
        errExitEN(rc, "pthread_join");

    printf("Done\n");
    exit(EXIT_SUCCESS);
}

SEE ALSO

prctl(2), pthread_create(3), pthreads(7)

COLOPHON

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