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PTHREADS(3)		  OpenBSD Programmer's Manual		   PTHREADS(3)

NAME
     pthreads - POSIX 1003.1c thread interface

DESCRIPTION
     A thread is a flow of control within a process.  Each thread represents a
     minimal amount of state; normally just the CPU state and a signal mask.
     All other process state (such as memory, file descriptors) is shared
     among all of the threads in the process.

     In OpenBSD, threads are implemented in a user-level library.  A program
     using these routines must be linked with the -pthread option.

     The SIGINFO signal can be sent to a threaded process to have the library
     show the state of all of its threads.  The information is sent to the
     process' controlling tty and describes each thread's ID, state (see
     Thread states), current priority, flags (see Thread flags), signal mask,
     and name (as set by pthread_set_name_np(3)).  If the environment variable
     PTHREAD_DEBUG is defined additional information is displayed.

     For the purpose of this document, the functions available are grouped in
     the following categories.	For further information, see the individual
     man page for each function.

	   -   Attribute Object Routines
	   -   Cleanup Routines
	   -   Condition Variable Routines
	   -   Mutex Routines
	   -   Non Portable Extensions
	   -   Per-Thread Context Routines
	   -   Read/Write Lock Routines
	   -   Thread Routines

   Attribute Object Routines
     The functions available are as follows:

     pthread_attr_init()	    Initialise a threads attribute object.
     pthread_attr_destroy()	    Destroy a threads attribute object.
     pthread_attr_getdetachstate()  Get detachstate attribute.
     pthread_attr_setdetachstate()  Set detachstate attribute.
     pthread_attr_getstack()	    Get stackaddr and stacksize attributes.
     pthread_attr_setstack()	    Set stackaddr and stacksize attributes.
     pthread_attr_getstackaddr()    Get stackaddr attribute.
     pthread_attr_setstackaddr()    Set stackaddr attribute.
     pthread_attr_getstacksize()    Get stacksize attribute.
     pthread_attr_setstacksize()    Set stacksize attribute.
     pthread_attr_getguardsize()    Get guardsize attribute.
     pthread_attr_setguardsize()    Set guardsize attribute.

   Cleanup Routines
     The functions available are as follows:

     pthread_atfork()	     Register fork handlers.
     pthread_cleanup_pop()   Call the first cleanup routine.
     pthread_cleanup_push()  Add a cleanup function for thread exit.

   Condition Variable Routines
     The functions available are as follows:

     pthread_cond_broadcast()  Unblock all threads waiting for a condition
			       variable.
     pthread_cond_destroy()    Destroy a condition variable.
     pthread_cond_init()       Create a condition variable.
     pthread_cond_signal()     Unblock a thread waiting for a condition
			       variable.
     pthread_cond_timedwait()  Wait on a condition variable for a specific
			       amount of time.
     pthread_cond_wait()       Wait on a condition variable.

   Mutex Routines
     The functions available are as follows:

     pthread_mutex_destroy()		 Free resources allocated for a mutex.
     pthread_mutex_init()		 Create a mutex.
     pthread_mutex_lock()		 Lock a mutex.
     pthread_mutex_trylock()		 Attempt to lock a mutex without
					 blocking.
     pthread_mutex_unlock()		 Unlock a mutex.
     pthread_mutexattr_init()		 Mutex attribute operations.
     pthread_mutexattr_destroy()	 Mutex attribute operations.
     pthread_mutexattr_getprioceiling()	 Mutex attribute operations.
     pthread_mutexattr_setprioceiling()	 Mutex attribute operations.
     pthread_mutexattr_getprotocol()	 Mutex attribute operations.
     pthread_mutexattr_setprotocol()	 Mutex attribute operations.
     pthread_mutexattr_gettype()	 Mutex attribute operations.
     pthread_mutexattr_settype()	 Mutex attribute operations.

   Non Portable Extensions
     The functions available are as follows:

     pthread_main_np()	       Identify the main thread.
     pthread_set_name_np()     Set the name of a thread.
     pthread_single_np()       Switch thread scheduling mode.
     pthread_multi_np()	       Switch thread scheduling mode.
     pthread_stackseg_np()     Return stack size and location.
     pthread_suspend_np()      Suspend given thread.
     pthread_suspend_all_np()  Suspend all threads except current thread.
     pthread_resume_np()       Resumes given thread.
     pthread_resume_all_np()   Resumes all suspended threads.
     pthread_yield()	       Yield control of the current thread.

   Per-Thread Context Routines
     The functions available are as follows:

     pthread_key_create()   Thread-specific data key creation.
     pthread_key_delete()   Delete a thread-specific data key.
     pthread_getspecific()  Get a thread-specific data value.
     pthread_setspecific()  Set a thread-specific data value.

   Read/Write Lock Routines
     The functions available are as follows:

     pthread_rwlock_destroy()	      Destroy a read/write lock.
     pthread_rwlock_init()	      Initialise a read/write lock.
     pthread_rwlock_rdlock()	      Acquire a read/write lock for reading.
     pthread_rwlock_unlock()	      Release a read/write lock.
     pthread_rwlock_wrlock()	      Acquire a read/write lock for writing.
     pthread_rwlockattr_destroy()     Destroy a read/write lock.
     pthread_rwlockattr_getpshared()  Get the process shared attribute.
     pthread_rwlockattr_init()	      Initialise a read/write lock.
     pthread_rwlockattr_setpshared()  Set the process shared attribute.

   Thread Routines
     The functions available are as follows:

     pthread_create()	       Create a new thread.
     pthread_cancel()	       Cancel execution of a thread.
     pthread_detach()	       Detach a thread.
     pthread_equal()	       Compare thread IDs.
     pthread_exit()	       Terminate the calling thread.
     pthread_getconcurrency()  Get level of concurrency.
     pthread_setconcurrency()  Set level of concurrency.
     pthread_join()	       Wait for thread termination.
     pthread_kill()	       Send a signal to a specific thread.
     pthread_once()	       Dynamic package initialisation.
     pthread_self()	       Get the calling thread's ID.
     pthread_setcancelstate()  Set cancelability state.
     pthread_setcanceltype()   Set cancelability state.
     pthread_testcancel()      Set cancelability state.
     pthread_sigmask()	       Examine/change a thread's signal mask.

   Thread states
     Threads can be in one of these states:

	   cond_wait	 Executing pthread_cond_wait(3) or
			 pthread_cond_timedwait(3).
	   dead		 Waiting for resource deallocation by the thread
			 garbage collector.
	   deadlock	 Waiting for a resource held by the thread itself.
	   fdlr_wait	 File descriptor read lock wait.
	   fdlw_wait	 File descriptor write lock wait.
	   fdr_wait	 Executing one of accept(2), read(2), readv(2),
			 recvfrom(2), recvmsg(2).
	   fdw_wait	 Executing one of connect(2), sendmsg(2), sendto(2),
			 write(2), writev(2).
	   file_wait	 Executing flockfile(3) or similar.
	   join		 Executing pthread_join(3).
	   mutex_wait	 Executing pthread_mutex_lock(3).
	   poll_wait	 Executing poll(2).
	   running	 Scheduled for, or engaged in, program execution.
	   select_wait	 Executing select(2).
	   sigsuspend	 Executing sigsuspend(2).
	   sigwait	 Executing sigwait(3).
	   sleep_wait	 Executing sleep(3) or nanosleep(2).
	   spinblock	 Waiting for a machine-level atomic lock.
	   suspended	 Suspended with pthread_suspend_np(3) or
			 pthread_suspend_all_np(3).
	   wait_wait	 Executing wait4(2) or similar.

   Thread flags
     The first three flags are one of:

	   p	Private, system thread (e.g., the garbage collector).
	   E, C, or c
		Thread is exiting (E), has a cancellation pending (C) (see
		pthread_cancel(3)), or is at a cancellation point (c).
	   t	Thread is being traced.

     The next 7 flags refer to thread attributes:

	   C	Thread is in the CONDQ.
	   R	Thread is in the WORKQ.
	   W	Thread is in the WAITQ.
	   P	Thread is in the PRIOQ.
	   d	Thread has been detached (see pthread_detach(3)).
	   i	Thread inherits scheduler properties.
	   f	Thread will save floating point context.

   Scheduling algorithm
     The scheduling algorithm used by the user-level thread library is roughly
     as follows:

     1.	  Threads each have a time slice credit which is debited by the actual
	  time the thread spends in running.  Freshly scheduled threads are
	  given a time slice credit of 100000 usec.
     2.	  Give an incremental priority update to run-enabled threads that have
	  not run since the last time that an incremental priority update was
	  given to them.
     3.	  Choose the next run-enabled thread with the highest priority, that
	  became inactive least recently, and has the largest remaining time
	  slice.

     When all threads are blocked, the process also blocks.  When there are no
     threads remaining, the process terminates with an exit code of zero.

   Thread stacks
     Each thread has (or should have) a different stack, whether it be
     provided by a user attribute, or provided automatically by the system.
     If a thread overflows its stack, unpredictable results may occur.
     System-allocated stacks (including that of the initial thread) are
     typically allocated in such a way that a SIGSEGV signal is delivered to
     the process when a stack overflows.

     Signals handlers are normally run on the stack of the currently executing
     thread.  Hence, if you want to handle the SIGSEGV signal, you should make
     use of sigaltstack(2) or sigprocmask(2).

   Thread safety
     The following functions are not thread safe:

     asctime(), basename(), catgets(), crypt(), ctime(), dbm_clearerr(),
     dbm_close(), dbm_delete(), dbm_error(), dbm_fetch(), dbm_firstkey(),
     dbm_nextkey(), dbm_open(), dbm_store(), dirname(), dlerror(), drand48(),
     ecvt(), encrypt(), endgrent(), endpwent(), fcvt(), ftw(), gcvt(),
     getc_unlocked(), getchar_unlocked(), getenv(), getgrent(), getgrgid(),
     getgrnam(), gethostbyaddr(), gethostbyname(), gethostent(), getlogin(),
     getnetbyaddr(), getnetbyname(), getnetent(), getopt(), getprotobyname(),
     getprotobynumber(), getprotoent(), getpwent(), getpwnam(), getpwuid(),
     getservbyname(), getservbyport(), getservent(), gmtime(), hcreate(),
     hdestroy(), hsearch(), inet_ntoa(), l64a(), lgamma(), lgammaf(),
     localeconv(), localtime(), lrand48(), mrand48(), nftw(), nl_langinfo(),
     putc_unlocked(), putchar_unlocked(), putenv(), rand(), readdir(),
     setenv(), setgrent(), setkey(), setpwent(), strerror(), strtok(),
     ttyname(), unsetenv(),

     The ctermid() and tmpnam() functions are not thread safe when passed a
     NULL argument.

ENVIRONMENT
     PTHREAD_DEBUG     Enables verbose SIGINFO signal output.

     LIBPTHREAD_DEBUG  Display thread status every time the garbage collection
		       thread runs, approximately once every 10 seconds.  The
		       status display verbosity is controlled by the
		       PTHREAD_DEBUG environment variable.

SEE ALSO
     pthread_atfork(3), pthread_attr_init(3), pthread_attr_setdetachstate(3),
     pthread_attr_setguardsize(3), pthread_attr_setstack(3),
     pthread_attr_setstackaddr(3), pthread_attr_setstacksize(3),
     pthread_cancel(3), pthread_cleanup_pop(3), pthread_cleanup_push(3),
     pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_init(3),
     pthread_cond_signal(3), pthread_cond_timedwait(3), pthread_cond_wait(3),
     pthread_create(3), pthread_detach(3), pthread_equal(3), pthread_exit(3),
     pthread_getspecific(3), pthread_join(3), pthread_key_create(3),
     pthread_key_delete(3), pthread_kill(3), pthread_main_np(3),
     pthread_mutex_destroy(3), pthread_mutex_init(3), pthread_mutex_lock(3),
     pthread_mutex_trylock(3), pthread_mutex_unlock(3), pthread_mutexattr(3),
     pthread_once(3), pthread_resume_all_np(3), pthread_resume_np(3),
     pthread_rwlock_destroy(3), pthread_rwlock_init(3),
     pthread_rwlock_rdlock(3), pthread_rwlock_unlock(3),
     pthread_rwlock_wrlock(3), pthread_rwlockattr_destroy(3),
     pthread_rwlockattr_getpshared(3), pthread_rwlockattr_init(3),
     pthread_rwlockattr_setpshared(3), pthread_schedparam(3), pthread_self(3),
     pthread_set_name_np(3), pthread_setspecific(3), pthread_sigmask(3),
     pthread_single_np(3), pthread_stackseg_np(3), pthread_suspend_all_np(3),
     pthread_suspend_np(3), pthread_testcancel(3), pthread_yield(3)

STANDARDS
     The user-level thread library provides functions that conform to ISO/IEC
     9945-1 ANSI/IEEE (``POSIX'') Std 1003.1 Second Edition 1996-07-12.

AUTHORS
     John Birrell (jb@freebsd.org) wrote the majority of the user level thread
     library.

BUGS
     The library contains a scheduler that uses the process virtual interval
     timer to pre-empt running threads.	 This means that using setitimer(2) to
     alter the process virtual timer will have undefined effects.  The
     SIGVTALRM will never be delivered to threads in a process.

     Some pthread functions fail to work correctly when linked using the -g
     option to cc(1) or gcc(1).	 The problems do not occur when linked using
     the -ggdb option.

OpenBSD 4.9		       December 18, 2008		   OpenBSD 4.9
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