PTHREAD_CREATE(3)          Linux Programmer's Manual         PTHREAD_CREATE(3)

       pthread_create - create a new thread

       #include <pthread.h>

       int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg);

       Compile and link with -pthread.

       The  pthread_create()  function  starts  a  new  thread  in the calling
       process.  The new thread starts execution by invoking  start_routine();
       arg is passed as the sole argument of start_routine().

       The new thread terminates in one of the following ways:

       * It  calls  pthread_exit(3),  specifying  an exit status value that is
         available  to  another  thread  in  the  same  process   that   calls

       * It  returns  from  start_routine().   This  is  equivalent to calling
         pthread_exit(3) with the value supplied in the return statement.

       * It is canceled (see pthread_cancel(3)).

       * Any of the threads in the process calls exit(3), or the  main  thread
         performs  a  return  from main().  This causes the termination of all
         threads in the process.

       The attr argument points to a pthread_attr_t structure  whose  contents
       are  used  at  thread creation time to determine attributes for the new
       thread; this structure is initialized  using  pthread_attr_init(3)  and
       related  functions.   If  attr is NULL, then the thread is created with
       default attributes.

       Before returning, a successful call to pthread_create() stores  the  ID
       of  the  new thread in the buffer pointed to by thread; this identifier
       is used to refer to the thread in subsequent calls  to  other  pthreads

       The  new  thread  inherits  a copy of the creating thread's signal mask
       (pthread_sigmask(3)).  The set of pending signals for the new thread is
       empty  (sigpending(2)).   The  new thread does not inherit the creating
       thread's alternate signal stack (sigaltstack(2)).

       The new thread inherits the calling thread's floating-point environment

       The  initial  value  of  the  new  thread's  CPU-time  clock  is 0 (see

   Linux-specific details
       The new thread inherits copies of the calling thread's capability  sets
       (see capabilities(7)) and CPU affinity mask (see sched_setaffinity(2)).

       On  success,  pthread_create() returns 0; on error, it returns an error
       number, and the contents of *thread are undefined.

       EAGAIN Insufficient resources to create another thread.

       EAGAIN A system-imposed limit on the number of threads was encountered.
              There  are  a  number of limits that may trigger this error: the
              RLIMIT_NPROC soft resource limit (set via  setrlimit(2)),  which
              limits  the  number of processes and threads for a real user ID,
              was reached; the kernel's system-wide limit  on  the  number  of
              processes and threads, /proc/sys/kernel/threads-max, was reached
              (see proc(5)); or the maximum  number  of  PIDs,  /proc/sys/ker-
              nel/pid_max, was reached (see proc(5)).

       EINVAL Invalid settings in attr.

       EPERM  No permission to set the scheduling policy and parameters speci-
              fied in attr.

       For an  explanation  of  the  terms  used  in  this  section,  see  at-

       |Interface        | Attribute     | Value   |
       |pthread_create() | Thread safety | MT-Safe |

       POSIX.1-2001, POSIX.1-2008.

       See  pthread_self(3)  for further information on the thread ID returned
       in *thread by pthread_create().  Unless real-time  scheduling  policies
       are  being employed, after a call to pthread_create(), it is indetermi-
       nate which thread--the caller or the new thread--will next execute.

       A thread may either be joinable or detached.  If a thread is  joinable,
       then  another thread can call pthread_join(3) to wait for the thread to
       terminate and fetch its exit status.  Only when a  terminated  joinable
       thread  has  been joined are the last of its resources released back to
       the system.  When a detached thread terminates, its resources are auto-
       matically  released back to the system: it is not possible to join with
       the thread in order to obtain its exit status.   Making  a  thread  de-
       tached is useful for some types of daemon threads whose exit status the
       application does not need to care about.  By default, a new  thread  is
       created  in  a joinable state, unless attr was set to create the thread
       in a detached state (using pthread_attr_setdetachstate(3)).

       Under the NPTL threading implementation, if the RLIMIT_STACK  soft  re-
       source  limit  at the time the program started has any value other than
       "unlimited", then it determines the default stack size of new  threads.
       Using pthread_attr_setstacksize(3), the stack size attribute can be ex-
       plicitly set in the attr argument used to create a thread, in order  to
       obtain  a  stack  size other than the default.  If the RLIMIT_STACK re-
       source limit is set to "unlimited", a per-architecture  value  is  used
       for the stack size.  Here is the value for a few architectures:

              |Architecture | Default stack size |
              |i386         |               2 MB |
              |IA-64        |              32 MB |
              |PowerPC      |               4 MB |
              |S/390        |               2 MB |
              |Sparc-32     |               2 MB |
              |Sparc-64     |               4 MB |
              |x86_64       |               2 MB |
       In  the  obsolete LinuxThreads implementation, each of the threads in a
       process has a different process ID.  This is in violation of the  POSIX
       threads  specification, and is the source of many other nonconformances
       to the standard; see pthreads(7).

       The program below demonstrates the use of pthread_create(), as well  as
       a number of other functions in the pthreads API.

       In  the  following run, on a system providing the NPTL threading imple-
       mentation, the stack size defaults to the value  given  by  the  "stack
       size" resource limit:

           $ ulimit -s
           8192            # The stack size limit is 8 MB (0x800000 bytes)
           $ ./a.out hola salut servus
           Thread 1: top of stack near 0xb7dd03b8; argv_string=hola
           Thread 2: top of stack near 0xb75cf3b8; argv_string=salut
           Thread 3: top of stack near 0xb6dce3b8; argv_string=servus
           Joined with thread 1; returned value was HOLA
           Joined with thread 2; returned value was SALUT
           Joined with thread 3; returned value was SERVUS

       In  the next run, the program explicitly sets a stack size of 1 MB (us-
       ing pthread_attr_setstacksize(3)) for the created threads:

           $ ./a.out -s 0x100000 hola salut servus
           Thread 1: top of stack near 0xb7d723b8; argv_string=hola
           Thread 2: top of stack near 0xb7c713b8; argv_string=salut
           Thread 3: top of stack near 0xb7b703b8; argv_string=servus
           Joined with thread 1; returned value was HOLA
           Joined with thread 2; returned value was SALUT
           Joined with thread 3; returned value was SERVUS

   Program source

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

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

       #define handle_error(msg) \
               do { perror(msg); exit(EXIT_FAILURE); } while (0)

       struct thread_info {    /* Used as argument to thread_start() */
           pthread_t thread_id;        /* ID returned by pthread_create() */
           int       thread_num;       /* Application-defined thread # */
           char     *argv_string;      /* From command-line argument */

       /* Thread start function: display address near top of our stack,
          and return upper-cased copy of argv_string */

       static void *
       thread_start(void *arg)
           struct thread_info *tinfo = arg;
           char *uargv, *p;

           printf("Thread %d: top of stack near %p; argv_string=%s\n",
                   tinfo->thread_num, &p, tinfo->argv_string);

           uargv = strdup(tinfo->argv_string);
           if (uargv == NULL)

           for (p = uargv; *p != '\0'; p++)
               *p = toupper(*p);

           return uargv;

       main(int argc, char *argv[])
           int s, tnum, opt, num_threads;
           struct thread_info *tinfo;
           pthread_attr_t attr;
           int stack_size;
           void *res;

           /* The "-s" option specifies a stack size for our threads */

           stack_size = -1;
           while ((opt = getopt(argc, argv, "s:")) != -1) {
               switch (opt) {
               case 's':
                   stack_size = strtoul(optarg, NULL, 0);

                   fprintf(stderr, "Usage: %s [-s stack-size] arg...\n",

           num_threads = argc - optind;

           /* Initialize thread creation attributes */

           s = pthread_attr_init(&attr);
           if (s != 0)
               handle_error_en(s, "pthread_attr_init");

           if (stack_size > 0) {
               s = pthread_attr_setstacksize(&attr, stack_size);
               if (s != 0)
                   handle_error_en(s, "pthread_attr_setstacksize");

           /* Allocate memory for pthread_create() arguments */

           tinfo = calloc(num_threads, sizeof(struct thread_info));
           if (tinfo == NULL)

           /* Create one thread for each command-line argument */

           for (tnum = 0; tnum < num_threads; tnum++) {
               tinfo[tnum].thread_num = tnum + 1;
               tinfo[tnum].argv_string = argv[optind + tnum];

               /* The pthread_create() call stores the thread ID into
                  corresponding element of tinfo[] */

               s = pthread_create(&tinfo[tnum].thread_id, &attr,
                                  &thread_start, &tinfo[tnum]);
               if (s != 0)
                   handle_error_en(s, "pthread_create");

           /* Destroy the thread attributes object, since it is no
              longer needed */

           s = pthread_attr_destroy(&attr);
           if (s != 0)
               handle_error_en(s, "pthread_attr_destroy");

           /* Now join with each thread, and display its returned value */

           for (tnum = 0; tnum < num_threads; tnum++) {
               s = pthread_join(tinfo[tnum].thread_id, &res);
               if (s != 0)
                   handle_error_en(s, "pthread_join");

               printf("Joined with thread %d; returned value was %s\n",
                       tinfo[tnum].thread_num, (char *) res);
               free(res);      /* Free memory allocated by thread */


       getrlimit(2), pthread_attr_init(3), pthread_cancel(3),
       pthread_detach(3), pthread_equal(3), pthread_exit(3),
       pthread_getattr_np(3), pthread_join(3), pthread_self(3),
       pthread_setattr_default_np(3), pthreads(7)

       This page is part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2018-04-30                 PTHREAD_CREATE(3)
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