pthread_create(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON

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
       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         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
       attributes(7).

       ┌─────────────────┬───────────────┬─────────┐
       │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 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:

              ┌─────────────┬────────────────────┐
              │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;

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

           return uargv;
       }

       int
       main(int argc, char *argv[])
       {
           int s, opt, num_threads;
           pthread_attr_t attr;
           size_t 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 */

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

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

           for (int 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 (int 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         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 5.10 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/.

Linux                          2020-11-01              PTHREAD_CREATE(3)

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