pthread_create(3) — Linux manual page


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

NAME         top

       pthread_create - create a new thread

SYNOPSIS         top

       #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         top

       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

       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 (fenv(3)).

       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

RETURN VALUE         top

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

ERRORS         top

       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         top

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

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

CONFORMING TO         top

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

NOTES         top

       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

       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

       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:

              │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 │

BUGS         top

       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).

EXAMPLES         top

       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)

           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 */


SEE ALSO         top

       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         top

       This page is part of release 5.08 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                            2020-06-09                PTHREAD_CREATE(3)

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