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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.

       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/kernel/pid_max, was reached (see proc(5)).

       EINVAL Invalid settings in attr.

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

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌─────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├─────────────────┼───────────────┼─────────┤
       │pthread_create() │ Thread safety │ MT-Safe │
       └─────────────────┴───────────────┴─────────┘

CONFORMING TO

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

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)).

       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.  If the RLIMIT_STACK resource limit is set to
       "unlimited", a per-architecture value is used for the stack size.  Here is the value for a
       few architectures:

              ┌─────────────┬────────────────────┐
              │ArchitectureDefault 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 │
              └─────────────┴────────────────────┘

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).

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 (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  (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 = 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);
       }

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), pthread_setattr_default_np(3), pthreads(7)

COLOPHON

       This page is part of release 5.02 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 https://www.kernel.org/doc/man-pages/.