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

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_setaffin-
       ity(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).

       +-----------------+---------------+---------+
       |Interface	 | Attribute	 | Value   |
       +-----------------+---------------+---------+
       |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)).

       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.

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
",
		   tinfo->thread_num, &p, tinfo->argv_string);

	   uargv = strdup(tinfo->argv_string);
	   if (uargv == NULL)
	       handle_error("strdup");

	   for (p = uargv; *p != ''; 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...
",
			   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
",
		       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 4.15 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								    2017-09-15							 PTHREAD_CREATE(3)