man3/pthread_setname_np.3

   1 .\" Copyright (C) 2012 Chandan Apsangi <chandan.jc@gmail.com>
   2 .\" and Copyright (C) 2013 Michael Kerrisk <mtk.manpages@gmail.com>
   3 .\"
   4 .\" %%%LICENSE_START(VERBATIM)
   5 .\" Permission is granted to make and distribute verbatim copies of this
   6 .\" manual provided the copyright notice and this permission notice are
   7 .\" preserved on all copies.
   8 .\"
   9 .\" Permission is granted to copy and distribute modified versions of this
  10 .\" manual under the conditions for verbatim copying, provided that the
  11 .\" entire resulting derived work is distributed under the terms of a
  12 .\" permission notice identical to this one.
  13 .\"
  14 .\" Since the Linux kernel and libraries are constantly changing, this
  15 .\" manual page may be incorrect or out-of-date.  The author(s) assume no
  16 .\" responsibility for errors or omissions, or for damages resulting from
  17 .\" the use of the information contained herein.  The author(s) may not
  18 .\" have taken the same level of care in the production of this manual,
  19 .\" which is licensed free of charge, as they might when working
  20 .\" professionally.
  21 .\"
  22 .\" Formatted or processed versions of this manual, if unaccompanied by
  23 .\" the source, must acknowledge the copyright and authors of this work.
  24 .\" %%%LICENSE_END
  25 .\"
  26 .TH PTHREAD_SETNAME_NP 3 2019-03-06 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 pthread_setname_np, pthread_getname_np \- set/get the name of a thread
  29 .SH SYNOPSIS
  30 .nf
  31 .BR "#define _GNU_SOURCE" "             /* See feature_test_macros(7) */"
  32 .B #include <pthread.h>
  33 .BI "int pthread_setname_np(pthread_t " thread ", const char *" name ");
  34 .BI "int pthread_getname_np(pthread_t " thread ,
  35 .BI "                       char *" name ", size_t " len );
  36 .fi
  37 .PP
  38 Compile and link with \fI\-pthread\fP.
  39 .SH DESCRIPTION
  40 By default, all the threads created using
  41 .BR pthread_create ()
  42 inherit the program name.
  43 The
  44 .BR pthread_setname_np ()
  45 function can be used to set a unique name for a thread,
  46 which can be useful for debugging
  47 multithreaded applications.
  48 The thread name is a meaningful C language string, whose length is
  49 restricted to 16 characters, including the terminating null byte (\(aq\e0\(aq).
  50 The
  51 .I thread
  52 argument specifies the thread whose name is to be changed;
  53 .I name
  54 specifies the new name.
  55 .PP
  56 The
  57 .BR pthread_getname_np ()
  58 function can be used to retrieve the name of the thread.
  59 The
  60 .I thread
  61 argument specifies the thread whose name is to be retrieved.
  62 The buffer
  63 .I name
  64 is used to return the thread name;
  65 .I len
  66 specifies the number of bytes available in
  67 .IR name .
  68 The buffer specified by
  69 .I name
  70 should be at least 16 characters in length.
  71 The returned thread name in the output buffer will be null terminated.
  72 .SH RETURN VALUE
  73 On success, these functions return 0;
  74 on error, they return a nonzero error number.
  75 .SH ERRORS
  76 The
  77 .BR pthread_setname_np ()
  78 function can fail with the following error:
  79 .TP
  80 .B ERANGE
  81 The length of the string specified pointed to by
  82 .I name
  83 exceeds the allowed limit.
  84 .PP
  85 The
  86 .BR pthread_getname_np ()
  87 function can fail with the following error:
  88 .TP
  89 .B ERANGE
  90 The buffer specified by
  91 .I name
  92 and
  93 .I len
  94 is too small to hold the thread name.
  95 .PP
  96 If either of these functions fails to open
  97 .IR /proc/self/task/[tid]/comm ,
  98 then the call may fail with one of the errors described in
  99 .BR open (2).
 100 .SH VERSIONS
 101 These functions first appeared in glibc in version 2.12.
 102 .SH ATTRIBUTES
 103 For an explanation of the terms used in this section, see
 104 .BR attributes (7).
 105 .TS
 106 allbox;
 107 lbw21 lb lb
 108 l l l.
 109 Interface       Attribute       Value
 110 T{
 111 .BR pthread_setname_np (),
 112 .BR pthread_getname_np ()
 113 T}      Thread safety   MT-Safe
 114 .TE
 115 .sp 1
 116 .SH CONFORMING TO
 117 These functions are nonstandard GNU extensions;
 118 hence the suffix "_np" (nonportable) in the names.
 119 .SH NOTES
 120 .BR pthread_setname_np ()
 121 internally writes to the thread-specific
 122 .I comm
 123 file under the
 124 .IR /proc
 125 filesystem:
 126 .IR /proc/self/task/[tid]/comm .
 127 .BR pthread_getname_np ()
 128 retrieves it from the same location.
 129 .SH EXAMPLES
 130 .PP
 131 The program below demonstrates the use of
 132 .BR pthread_setname_np ()
 133 and
 134 .BR pthread_getname_np ().
 135 .PP
 136 The following shell session shows a sample run of the program:
 137 .PP
 138 .in +4n
 139 .EX
 140 .RB "$" " ./a.out"
 141 Created a thread. Default name is: a.out
 142 The thread name after setting it is THREADFOO.
 143 \fB^Z\fP                           # Suspend the program
 144 [1]+  Stopped           ./a.out
 145 .RB "$ " "ps H -C a.out -o 'pid tid cmd comm'"
 146   PID   TID CMD                         COMMAND
 147  5990  5990 ./a.out                     a.out
 148  5990  5991 ./a.out                     THREADFOO
 149 .RB "$ " "cat /proc/5990/task/5990/comm"
 150 a.out
 151 .RB "$ " "cat /proc/5990/task/5991/comm"
 152 THREADFOO
 153 .EE
 154 .in
 155 .SS Program source
 156 \&
 157 .EX
 158 #define _GNU_SOURCE
 159 #include <pthread.h>
 160 #include <stdio.h>
 161 #include <string.h>
 162 #include <unistd.h>
 163 #include <errno.h>
 164 #include <stdlib.h>
 165
 166 #define NAMELEN 16
 167
 168 #define errExitEN(en, msg) \e
 169             do { errno = en; perror(msg); exit(EXIT_FAILURE); \e
 170         } while (0)
 171
 172 static void *
 173 threadfunc(void *parm)
 174 {
 175     sleep(5);          // allow main program to set the thread name
 176     return NULL;
 177 }
 178
 179 int
 180 main(int argc, char **argv)
 181 {
 182     pthread_t thread;
 183     int rc;
 184     char thread_name[NAMELEN];
 185
 186     rc = pthread_create(&thread, NULL, threadfunc, NULL);
 187     if (rc != 0)
 188         errExitEN(rc, "pthread_create");
 189
 190     rc = pthread_getname_np(thread, thread_name, NAMELEN);
 191     if (rc != 0)
 192         errExitEN(rc, "pthread_getname_np");
 193
 194     printf("Created a thread. Default name is: %s\en", thread_name);
 195     rc = pthread_setname_np(thread, (argc > 1) ? argv[1] : "THREADFOO");
 196     if (rc != 0)
 197         errExitEN(rc, "pthread_setname_np");
 198
 199     sleep(2);
 200
 201     rc = pthread_getname_np(thread, thread_name,
 202                             (argc > 2) ? atoi(argv[1]) : NAMELEN);
 203     if (rc != 0)
 204         errExitEN(rc, "pthread_getname_np");
 205     printf("The thread name after setting it is %s.\en", thread_name);
 206
 207     rc = pthread_join(thread, NULL);
 208     if (rc != 0)
 209         errExitEN(rc, "pthread_join");
 210
 211     printf("Done\en");
 212     exit(EXIT_SUCCESS);
 213 }
 214 .EE
 215 .SH SEE ALSO
 216 .ad l
 217 .nh
 218 .BR prctl (2),
 219 .BR pthread_create (3),
 220 .BR pthreads (7)