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_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/ker-
	      nel/pid_max, was reached (see proc(5)).

       EINVAL Invalid settings in attr.

       EPERM  No permission to set the scheduling policy and parameters speci-
	      fied 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 indetermi-
       nate 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 auto-
       matically  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 cre-
       ate 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	imple-
       mentation,  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 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 = 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 4.10 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				  2016-12-12		     PTHREAD_CREATE(3)