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 ('\0'). 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
 | Thread safety | MT-Safe

CONFORMING TO
These functions are nonstandard GNU extensions; hence the suffix "_np" (nonportable) in the names.

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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