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NAME

       pthread_create - create a new thread

SYNOPSIS

       #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.

DESCRIPTION

       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 pthread_join(3).

       * 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 functions.

       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 (fenv(3)).

       The initial value of the new thread's CPU-time clock is 0 (see pthread_getcpuclockid(3)).

   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)).

RETURN VALUE

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

ERRORS

       EAGAIN Insufficient  resources  to create another thread, or a system-imposed limit on the
              number of threads was encountered.  The latter case may  occur  in  two  ways:  the
              RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which limits the number of
              process for a real user ID, was reached; or the kernel's system-wide limit  on  the
              number of threads, /proc/sys/kernel/threads-max, was reached.

       EINVAL Invalid settings in attr.

       EPERM  No permission to set the scheduling policy and parameters specified in attr.

CONFORMING TO

       POSIX.1-2001.

NOTES

       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 indeterminate 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
       automatically released back to the system: it is not possible to join with the  thread  in
       order  to  obtain  its  exit status.  Making a thread detached 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)).

       On Linux/x86-32, the default stack size for a new thread is 2 megabytes.  Under  the  NPTL
       threading  implementation, if the RLIMIT_STACK soft resource 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
       explicitly set in the attr argument used to create a thread, in order to  obtain  a  stack
       size other than the default.

EXAMPLE

       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 implementation,  the  stack
       size defaults to the value given by the "stack size" resource limit:

           $ ulimit -s
           8192            # The stack size limit is 8 MB (0x80000 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  1MB  (using
       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 = (struct thread_info *) 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)
               handle_error("strdup");

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

           return uargv;
       }

       int
       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);
                   break;

               default:
                   fprintf(stderr, "Usage: %s [-s stack-size] arg...\n",
                           argv[0]);
                   exit(EXIT_FAILURE);
               }
           }

           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)
               handle_error("calloc");

           /* 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 */
           }

           free(tinfo);
           exit(EXIT_SUCCESS);
       }

BUGS

       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).

SEE ALSO

       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), pthreads(7)

COLOPHON

       This page is part of release 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.