man3/pthread_setname_np.3

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  26 .TH PTHREAD_SETNAME_NP 3 2015-07-23 "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\\0\(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 .SH NOTES
 119 .BR pthread_setname_np ()
 120 internally writes to the thread-specific
 121 .I comm
 122 file under the
 123 .IR /proc
 124 filesystem:
 125 .IR /proc/self/task/[tid]/comm .
 126 .BR pthread_getname_np ()
 127 retrieves it from the same location.
 128 .SH EXAMPLE
 129 .PP
 130 The program below demonstrates the use of
 131 .BR pthread_setname_np ()
 132 and
 133 .BR pthread_getname_np ().
 134 .PP
 135 The following shell session shows a sample run of the program:
 136 .in +4n
 137 .nf
 138
 139 .RB "$" " ./a.out"
 140 Created a thread. Default name is: a.out
 141 The thread name after setting it is THREADFOO.
 142 \fB^Z\fP                           # Suspend the program
 143 [1]+  Stopped           ./a.out
 144 .RB "$ " "ps H -C a.out -o 'pid tid cmd comm'"
 145   PID   TID CMD                         COMMAND
 146  5990  5990 ./a.out                     a.out
 147  5990  5991 ./a.out                     THREADFOO
 148 .RB "$ " "cat /proc/5990/task/5990/comm"
 149 a.out
 150 .RB "$ " "cat /proc/5990/task/5991/comm"
 151 THREADFOO
 152 .fi
 153 .in
 154 .SS Program source
 155 \&
 156 .EX
 157 #define _GNU_SOURCE
 158 #include <pthread.h>
 159 #include <stdio.h>
 160 #include <string.h>
 161 #include <unistd.h>
 162 #include <errno.h>
 163 #include <stdlib.h>
 164
 165 #define NAMELEN 16
 166
 167 #define errExitEN(en, msg) \\
 168             do { errno = en; perror(msg); exit(EXIT_FAILURE); \\
 169         } while (0)
 170
 171 static void *
 172 threadfunc(void *parm)
 173 {
 174     sleep(5);          // allow main program to set the thread name
 175     return NULL;
 176 }
 177
 178 int
 179 main(int argc, char **argv)
 180 {
 181     pthread_t thread;
 182     int rc;
 183     char thread_name[NAMELEN];
 184
 185     rc = pthread_create(&thread, NULL, threadfunc, NULL);
 186     if (rc != 0)
 187         errExitEN(rc, "pthread_create");
 188
 189     rc = pthread_getname_np(thread, thread_name, NAMELEN);
 190     if (rc != 0)
 191         errExitEN(rc, "pthread_getname_np");
 192
 193     printf("Created a thread. Default name is: %s\\n", thread_name);
 194     rc = pthread_setname_np(thread, (argc > 1) ? argv[1] : "THREADFOO");
 195     if (rc != 0)
 196         errExitEN(rc, "pthread_setname_np");
 197
 198     sleep(2);
 199
 200     rc = pthread_getname_np(thread, thread_name,
 201                             (argc > 2) ? atoi(argv[1]) : NAMELEN);
 202     if (rc != 0)
 203         errExitEN(rc, "pthread_getname_np");
 204     printf("The thread name after setting it is %s.\\n", thread_name);
 205
 206     rc = pthread_join(thread, NULL);
 207     if (rc != 0)
 208         errExitEN(rc, "pthread_join");
 209
 210     printf("Done\\n");
 211     exit(EXIT_SUCCESS);
 212 }
 213 .EE
 214 .SH SEE ALSO
 215 .ad l
 216 .nh
 217 .BR prctl (2),
 218 .BR pthread_create (3),
 219 .BR pthreads (7)