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author | Ulrich Drepper <drepper@redhat.com> | 1998-03-11 12:42:25 +0000 |
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committer | Ulrich Drepper <drepper@redhat.com> | 1998-03-11 12:42:25 +0000 |
commit | 5afdca0087dad2994ad4fcdfe7f489f4dbcab7b3 (patch) | |
tree | c9c82db2ff92537b921361a02a284b0e18a594b8 /linuxthreads/man/pthread_cond_init.man | |
parent | 3d76e7784700c20fc222920b2a22baba006daa15 (diff) | |
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LinuxThreads library.
1998-03-11 00:42 Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
* linuxthreads/manager.c: Enable resetting of the thread
scheduling policy to SCHED_OTHER when the parent thread
has a different one.
1998-02-01 13:51 Ulrich Drepper <drepper@cygnus.com>
* sysdeps/unix/sysv/linux/bits/posix_opt.h: Define
_POSIX_ASYNCHRONOUS_IO.
* sysdeps/pthread/pthread.h: Define bits for Unix98 variants of
mutexes.
* mutex.c: Implement new mutex types.
* internals.h: Include <signal.h>.
* libpthread.map: Add __erno_location and __h_errno_location.
* errno.c: Return pointer to variable actually in use. This might
not be the one in the thread structure.
* internals.h (struct _pthread_descr_struct): Add new fields p_errnop
and p_h_errnop.
* manager.c (__pthread_manager): Set p_errnop and p_h_errnop member
of manager thread structure.
(pthread_handle_create): Set p_errnop and p_h_errnop members for new
thread.
* pthread.c: Adapt initializer for thread structures.
(__pthread_initial_thread): Set p_errnop and p_h_errnop member.
(__pthread_reset_main_thread): Reset p_errnop and p_h_errnop of
current thread to global variables.
1998-01-31 17:27 Ulrich Drepper <drepper@cygnus.com>
* rwlock.c: New file.
* Makefile (libpthread-routines): Add rwlock.
* sysdeps/pthread/pthread.h: Define data structures and declare
functions.
* libpthread.map: Add new functions.
1997-12-18 13:50 Philip Blundell <pb@nexus.co.uk>
* sysdeps/arm/pt-machine.h: New file; add ARM support.
* sysdeps/arm/Implies: likewise.
* README: Document it.
1997-12-13 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* signals.c: Remove unneeded initializer for sigwaited, saving a
1997-04-11 01:18 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* semaphore.c (sem_init): Set sem_spinlock only if available.
1997-12-04 01:48 Ulrich Drepper <drepper@cygnus.com>
* mutex.c: Implement PTHREAD_MUTEX_CHECKERROR.
* sysdeps/pthread/pthread.h: Define PTHREAD_MUTEX_CHECKERROR.
* Makefile: Update from LinuxThreads 0.7.
* internals.h. Likewise.
* manager.c: Likewise.
* mutex.c: Likewise.
* pthread.c: Likewise.
* signals.c: Likewise.
* specific.c: Likewise.
* Examples/ex3.c: Likewise.
1997-11-20 18:13 Ulrich Drepper <drepper@cygnus.com>
* pthread.c (__pthread_reset_main_thread): Close pipe only if still
open.
1997-10-29 05:38 Ulrich Drepper <drepper@cygnus.com>
* wrapsyscall.c: Add socket functions which are also cancelation
points.
1997-10-19 21:40 Wolfram Gloger <wg@wolfram.dent.med.uni-muenchen.de>
* specific.c (__libc_internal_tsd_set, __libc_internal_tsd_get):
New functions for fast thread specific data within libc.
* internals.h: Add new array p_libc_specific to struct
_pthread_descr_struct.
* sysdeps/pthread/bits/libc-lock.h: Declare new functions.
1997-10-13 05:39 Ulrich Drepper <drepper@cygnus.com>
* semaphore.h: Add __BEGIN_DECLS/__END_DECLS.
Reported by Ralf Corsepius <corsepiu@faw.uni-ulm.de>.
1997-08-29 03:05 Ulrich Drepper <drepper@cygnus.com>
* internals.h (struct _pthread_descr_struct): Add definitions for
two-level specific key handling.
* manager.c (pthread_handle_create): Initialize specific memory array.
* specific.c: Implement two-level key handling.
* weaks.c: Don't provide dummy key handling.
* sysdeps/pthread/bits/libc-lock.h: Typedef __libc_lock_t (no #define).
Add definition of __libc_key_t.
* sysdeps/unix/sysv/linux/bits/local_lim.h: Define PTHREAD_KEYS_MAX
as 1024.
Add definition of _POSIX_THREAD_DESTRUCTOR_ITERATIONS and
PTHREAD_DESTRUCTOR_ITERATIONS.
* manager.c (pthread_handle_create): Compare mmap result with
MAP_FAILED.
* ptfork.c: Rename to __pthread_atfork and make old name a weak alias.
* sysdeps/pthread/bits/pthread.h: Add prototype for __pthread_atfork.
1997-08-22 19:04 Richard Henderson <rth@cygnus.com>
sysdeps/sparc -> sysdeps/sparc/sparc32
sysdeps/sparc64 -> sysdeps/sparc/sparc64
* internals.h: Change definition of THREAD_SELF to be an expression,
not a statement that did a return.
* sysdeps/alpha/pt-machine.h (THREAD_SELF): Update accordingly.
* sysdeps/sparc/sparc32/pt-machine.h (THREAD_SELF, INIT_THREAD_SELF):
Follow Solaris and use a "system reserved" register (%g6) to hold
the thread descriptor.
* sysdeps/sparc/sparc64/pt-machine.h: Likewise.
1997-08-03 00:09 Ulrich Drepper <drepper@cygnus.com>
* mutex.c: Correct pthread_once. Patch by Xavier Leroy.
* sysdeps/pthread/pthread.h: Add prototype for __pthread_once.
* sysdeps/pthread/bits/pthread.h: Add macros for __libc_once.
* semaphore.c: Include spinlock.h only when needed.
* specific.c (__pthread_setsepcific, __pthread_getspecific): Reject
keys for entries not in use.
* weaks.c: Implement key handling functions for real.
1997-06-29 01:04 Richard Henderson <richard@gnu.ai.mit.edu>
Initial sparc64-linux support:
* linuxthreads/sysdeps/sparc64/Implies: New file.
* linuxthreads/sysdeps/sparc64/pt-machine.h: Likewise.
1997-06-29 00:48 Ulrich Drepper <drepper@cygnus.com>
* semaphore.c: Include spinlock.h at correct place.
Patch by HJ Lu.
1997-06-13 10:06 Richard Henderson <rth@tamu.edu>
The Great Bit File Move:
* sysdeps/alpha/semaphorebits.h: -> .../bits/semaphore.h.
* sysdeps/powerpc/semaphorebits.h: Likewise.
* sysdeps/pthread/cmpxchg/semaphorebits.h: Likewise.
* sysdeps/pthread/no-cmpxchg/semaphorebits.h: Likewise.
* sysdeps/pthread/libc-lock.h: -> bits/
* sysdeps/pthread/stdio-lock.h: Likewise.
* sysdeps/unix/sysv/linux/local_lim.h: Likewise.
* sysdeps/unix/sysv/linux/posix_opt.h: Likewise.
* semaphore.h: Likewise.
* sysdeps/pthread/pthread.h: Likewise.
* lockfile.c: <foo.h> -> <bits/foo.h>.
* semaphore.h: Likewise.
* Makefile: (headers): foo.h -> bits/foo.h.
* sysdeps/pthread/Makefile: Likewise.
1997-04-11 01:18 Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
* semaphore.c (sem_init): Set sem_spinlock only if available.
* sysdeps/m68k/pt-machine.h (testandset, __compare_and_swap): Fix
asm constraints.
1997-04-09 03:00 Ulrich Drepper <drepper@cygnus.com>
Update from LinuxThreads 0.6.
* attr.c (pthread_attr_getdetachstate): Use __sched_get_priority_max
and __sched_get_priority_min instead of names without `__'.
* manager.c: Rewrite large parts to implement opaque pthread_t.
* cancel.c: Adapt for opaque pthread_t type.
* condvar.c: Likewise.
* errno.c: Likewise.
* join.c: Likewise.
* mutex.c: Likewise.
* pthread.c: Likewise.
* signals.c: Likewise.
* specific.c: Likewise.
* restart.h: Likewise.
* queue.h: Likewise.
* Examples/ex3.c: Likewise.
* Examples/ex4.c: Likewise.
* sysdeps/pthread/pthread.h: Likewise.
* pthread.c: Accumulate time for all threads in thread manager.
* semaphore.c: Implement fallback implementation for architectures
sometimes missing compare-exchange operations.
* cancel.c (pthread_cancel): Validate handle argument.
* join.c (pthread_join): Likewise.
(pthread_detach): Likewise.
* signals.c (pthread_kill): Likewise.
* spinlock.h (acquire): Use __sched_yield not sched_yield.
* queue.h (enqueue): Enqueue thread according to priority.
* internals.c (struct pthread_start_args): New struct for passing
args to cloning function.
(struct _pthread): Rename to _pthread_descr_struct and adapt for
opaque pthread_t.
* Examples/Makefile (clean): Pass -f option to rm.
* sysdeps/i386/pt-machine.h: Add check for compare-exchange instruction
and define TEST_FOR_COMPARE_AND_SWAP.
* sysdeps/i386/i486/pt-machine.h: Removed.
* sysdeps/unix/sysv/linux/local_lim.h (PTHREAD_THREADS_MAX): Increase
to 1024.
1997-04-04 16:38 Ulrich Drepper <drepper@cygnus.com>
* restart.h (suspend): Clear p_signal before suspending.
(suspend_with_cancellation): Likewise.
Patch by Xavier Leroy <Xavier.Leroy@inria.fr>.
* weaks.c: Make __pthread_key_create return 1.
* sysdeps/pthread/libc-lock.h: Define __libc_key_create,
__libc_getspecific, __libc_setspecific, and __libc_key_t.
* sysdeps/pthread/stdio-lock.h: Don't care for implementation not
using libio.
1997-03-19 15:13 Miguel de Icaza <miguel@nuclecu.unam.mx>
* sysdeps/sparc/pt-machine (RELEASE): Fix.
1997-03-01 07:55 Geoff Keating <geoffk@ozemail.com.au>
* sysdeps/powerpc/Implies: Added.
* sysdeps/powerpc/pt-machine.h: Added.
* sysdeps/powerpc/semaphorebits.h: Added.
1997-01-22 01:22 Ulrich Drepper <drepper@cygnus.com>
* linuxtheads/pthread.c (__pthread_initial_thread): Correct
initializer.
(__pthread_manager_thread): Likewise.
Reported by Andreas Jaeger.
1997-01-18 22:15 Richard Henderson <rth@tamu.edu>
Since sigset_t no longer fits in a register, we can't pass in the
thread's initial mask so easily. Take this opportunity to simplify
the clone implementation by only accepting a single void* argument.
* linuxthreads/manager.c (__pthread_manager): Put thread vitals
in the thread struct instead of as arguments through clone.
(pthread_start_thread): Look for them there.
* linuxthreads/internals.h (struct _pthread): Add p_initial_fn,
p_initial_fn_arg, p_initial_mask. Fix __pthread_manager proto.
* linuxthreads/pthread.c (pthread_initialize_manager): Revise
clone invocation.
Diffstat (limited to 'linuxthreads/man/pthread_cond_init.man')
-rw-r--r-- | linuxthreads/man/pthread_cond_init.man | 235 |
1 files changed, 235 insertions, 0 deletions
diff --git a/linuxthreads/man/pthread_cond_init.man b/linuxthreads/man/pthread_cond_init.man new file mode 100644 index 0000000000..b803f08361 --- /dev/null +++ b/linuxthreads/man/pthread_cond_init.man @@ -0,0 +1,235 @@ +.TH PTHREAD_COND 3 LinuxThreads + +.XREF pthread_cond_signal +.XREF pthread_cond_broadcast +.XREF pthread_cond_wait +.XREF pthread_cond_timedwait +.XREF pthread_cond_destroy + +.SH NAME +pthread_cond_init, pthread_cond_destroy, pthread_cond_signal, pthread_cond_broadcast, pthread_cond_wait, pthread_cond_timedwait \- operations on conditions + +.SH SYNOPSIS +#include <pthread.h> + +pthread_cond_t cond = PTHREAD_COND_INITIALIZER; + +int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr); + +int pthread_cond_signal(pthread_cond_t *cond); + +int pthread_cond_broadcast(pthread_cond_t *cond); + +int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex); + +int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec *abstime); + +int pthread_cond_destroy(pthread_cond_t *cond); + +.SH DESCRIPTION + +A condition (short for ``condition variable'') is a synchronization +device that allows threads to suspend execution and relinquish the +processors until some predicate on shared data is satisfied. The basic +operations on conditions are: signal the condition (when the +predicate becomes true), and wait for the condition, suspending the +thread execution until another thread signals the condition. + +A condition variable must always be associated with a mutex, to avoid +the race condition where a thread prepares to wait on a condition +variable and another thread signals the condition just before the +first thread actually waits on it. + +!pthread_cond_init! initializes the condition variable |cond|, using the +condition attributes specified in |cond_attr|, or default attributes +if |cond_attr| is !NULL!. The LinuxThreads implementation supports no +attributes for conditions, hence the |cond_attr| parameter is actually +ignored. + +Variables of type !pthread_cond_t! can also be initialized +statically, using the constant !PTHREAD_COND_INITIALIZER!. + +!pthread_cond_signal! restarts one of the threads that are waiting on +the condition variable |cond|. If no threads are waiting on |cond|, +nothing happens. If several threads are waiting on |cond|, exactly one +is restarted, but it is not specified which. + +!pthread_cond_broadcast! restarts all the threads that are waiting on +the condition variable |cond|. Nothing happens if no threads are +waiting on |cond|. + +!pthread_cond_wait! atomically unlocks the |mutex| (as per +!pthread_unlock_mutex!) and waits for the condition variable |cond| to +be signaled. The thread execution is suspended and does not consume +any CPU time until the condition variable is signaled. The |mutex| +must be locked by the calling thread on entrance to +!pthread_cond_wait!. Before returning to the calling thread, +!pthread_cond_wait! re-acquires |mutex| (as per !pthread_lock_mutex!). + +Unlocking the mutex and suspending on the condition variable is done +atomically. Thus, if all threads always acquire the mutex before +signaling the condition, this guarantees that the condition cannot be +signaled (and thus ignored) between the time a thread locks the mutex +and the time it waits on the condition variable. + +!pthread_cond_timedwait! atomically unlocks |mutex| and waits on +|cond|, as !pthread_cond_wait! does, but it also bounds the duration +of the wait. If |cond| has not been signaled within the amount of time +specified by |abstime|, the mutex |mutex| is re-acquired and +!pthread_cond_timedwait! returns the error !ETIMEDOUT!. +The |abstime| parameter specifies an absolute time, with the same +origin as !time!(2) and !gettimeofday!(2): an |abstime| of 0 +corresponds to 00:00:00 GMT, January 1, 1970. + +!pthread_cond_destroy! destroys a condition variable, freeing the +resources it might hold. No threads must be waiting on the condition +variable on entrance to !pthread_cond_destroy!. In the LinuxThreads +implementation, no resources are associated with condition variables, +thus !pthread_cond_destroy! actually does nothing except checking that +the condition has no waiting threads. + +.SH CANCELLATION + +!pthread_cond_wait! and !pthread_cond_timedwait! are cancellation +points. If a thread is cancelled while suspended in one of these +functions, the thread immediately resumes execution, then locks again +the |mutex| argument to !pthread_cond_wait! and +!pthread_cond_timedwait!, and finally executes the cancellation. +Consequently, cleanup handlers are assured that |mutex| is locked when +they are called. + +.SH "ASYNC-SIGNAL SAFETY" + +The condition functions are not async-signal safe, and should not be +called from a signal handler. In particular, calling +!pthread_cond_signal! or !pthread_cond_broadcast! from a signal +handler may deadlock the calling thread. + +.SH "RETURN VALUE" + +All condition variable functions return 0 on success and a non-zero +error code on error. + +.SH ERRORS + +!pthread_cond_init!, !pthread_cond_signal!, !pthread_cond_broadcast!, +and !pthread_cond_wait! never return an error code. + +The !pthread_cond_timedwait! function returns the following error codes +on error: +.RS +.TP +!ETIMEDOUT! +the condition variable was not signaled until the timeout specified by +|abstime| + +.TP +!EINTR! +!pthread_cond_timedwait! was interrupted by a signal +.RE + +The !pthread_cond_destroy! function returns the following error code +on error: +.RS +.TP +!EBUSY! +some threads are currently waiting on |cond|. +.RE + +.SH AUTHOR +Xavier Leroy <Xavier.Leroy@inria.fr> + +.SH "SEE ALSO" +!pthread_condattr_init!(3), +!pthread_mutex_lock!(3), +!pthread_mutex_unlock!(3), +!gettimeofday!(2), +!nanosleep!(2). + +.SH EXAMPLE + +Consider two shared variables |x| and |y|, protected by the mutex |mut|, +and a condition variable |cond| that is to be signaled whenever |x| +becomes greater than |y|. + +.RS +.ft 3 +.nf +.sp +int x,y; +pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER; +pthread_cond_t cond = PTHREAD_COND_INITIALIZER; +.ft +.LP +.RE +.fi + +Waiting until |x| is greater than |y| is performed as follows: + +.RS +.ft 3 +.nf +.sp +pthread_mutex_lock(&mut); +while (x <= y) { + pthread_cond_wait(&cond, &mut); +} +/* operate on x and y */ +pthread_mutex_unlock(&mut); +.ft +.LP +.RE +.fi + +Modifications on |x| and |y| that may cause |x| to become greater than +|y| should signal the condition if needed: + +.RS +.ft 3 +.nf +.sp +pthread_mutex_lock(&mut); +/* modify x and y */ +if (x > y) pthread_mutex_broadcast(&cond); +pthread_mutex_unlock(&mut); +.ft +.LP +.RE +.fi + +If it can be proved that at most one waiting thread needs to be waken +up (for instance, if there are only two threads communicating through +|x| and |y|), !pthread_cond_signal! can be used as a slightly more +efficient alternative to !pthread_cond_broadcast!. In doubt, use +!pthread_cond_broadcast!. + +To wait for |x| to becomes greater than |y| with a timeout of 5 +seconds, do: + +.RS +.ft 3 +.nf +.sp +struct timeval now; +struct timespec timeout; +int retcode; + +pthread_mutex_lock(&mut); +gettimeofday(&now); +timeout.tv_sec = now.tv_sec + 5; +timeout.tv_nsec = now.tv_usec * 1000; +retcode = 0; +while (x <= y && retcode != ETIMEDOUT) { + retcode = pthread_cond_timedwait(&cond, &mut, &timeout); +} +if (retcode == ETIMEDOUT) { + /* timeout occurred */ +} else { + /* operate on x and y */ +} +pthread_mutex_unlock(&mut); +.ft +.LP +.RE +.fi + |