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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  subse-
       quent 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 capabili-
       ties(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 con-
       tents of *thread are undefined.

ERRORS
       EAGAIN Insufficient  resources  to create another thread, or a system-imposed limit on the
	      number of threads was encountered.  The latter case may  occur  in  two  ways:  the
	      RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which limits the number of
	      process for a real user ID, was reached; or the kernel's system-wide limit  on  the
	      number of threads, /proc/sys/kernel/threads-max, was reached.

       EINVAL Invalid settings in attr.

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

CONFORMING TO
       POSIX.1-2001.

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 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 explic-
       itly 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 dif-
       ferent 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 1MB (using pthread_attr_set-
       stacksize(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), pthreads(7)

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at
       http://www.kernel.org/doc/man-pages/.

Linux					    2012-08-03				PTHREAD_CREATE(3)
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