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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 3.27 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.