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freebsd-dev/lib/libc_r/uthread/uthread_cond.c
John Birrell 02292f131a In the words of the author: 
o The polling mechanism for I/O readiness was changed from
    select() to poll().  In additon, a wrapped version of poll()
    is now provided.

  o The wrapped select routine now converts each fd_set to a
    poll array so that the thread scheduler doesn't have to
    perform a bitwise search for selected fds each time file
    descriptors are polled for I/O readiness.

  o The thread scheduler was modified to use a new queue (_workq)
    for threads that need work.  Threads waiting for I/O readiness
    and spinblocks are added to the work queue in addition to the
    waiting queue.  This reduces the time spent forming/searching
    the array of file descriptors being polled.

  o The waiting queue (_waitingq) is now maintained in order of
    thread wakeup time.  This allows the thread scheduler to
    find the nearest wakeup time by looking at the first thread
    in the queue instead of searching the entire queue.

  o Removed file descriptor locking for select/poll routines.  An
    application should not rely on the threads library for providing
    this locking; if necessary, the application should use mutexes
    to protect selecting/polling of file descriptors.

  o Retrieve and use the kernel clock rate/resolution at startup
    instead of hardcoding the clock resolution to 10 msec (tested
    with kernel running at 1000 HZ).

  o All queues have been changed to use queue.h macros.  These
    include the queues of all threads, dead threads, and threads
    waiting for file descriptor locks.

  o Added reinitialization of the GC mutex and condition variable
    after a fork.  Also prevented reallocation of the ready queue
    after a fork.

  o Prevented the wrapped close routine from closing the thread
    kernel pipes.

  o Initialized file descriptor table for stdio entries at thread
    init.

  o Provided additional flags to indicate to what queues threads
    belong.

  o Moved TAILQ initialization for statically allocated mutex and
    condition variables to after the spinlock.

  o Added dispatching of signals to pthread_kill.  Removing the
    dispatching of signals from thread activation broke sigsuspend
    when pthread_kill was used to send a signal to a thread.

  o Temporarily set the state of a thread to PS_SUSPENDED when it
    is first created and placed in the list of threads so that it
    will not be accidentally scheduled before becoming a member
    of one of the scheduling queues.

  o Change the signal handler to queue signals to the thread kernel
    pipe if the scheduling queues are protected.  When scheduling
    queues are unprotected, signals are then dequeued and handled.

  o Ensured that all installed signal handlers block the scheduling
    signal and that the scheduling signal handler blocks all
    other signals.  This ensures that the signal handler is only
    interruptible for and by non-scheduling signals.  An atomic
    lock is used to decide which instance of the signal handler
    will handle pending signals.

  o Removed _lock_thread_list and _unlock_thread_list as they are
    no longer used to protect the thread list.

  o Added missing RCS IDs to modified files.

  o Added checks for appropriate queue membership and activity when
    adding, removing, and searching the scheduling queues.  These
    checks add very little overhead and are enabled when compiled
    with _PTHREADS_INVARIANTS defined.  Suggested and implemented
    by Tor Egge with some modification by me.

  o Close a race condition in uthread_close.  (Tor Egge)

  o Protect the scheduling queues while modifying them in
    pthread_cond_signal and _thread_fd_unlock.  (Tor Egge)

  o Ensure that when a thread gets a mutex, the mutex is on that
    threads list of owned mutexes.  (Tor Egge)

  o Set the kernel-in-scheduler flag in _thread_kern_sched_state
    and _thread_kern_sched_state_unlock to prevent a scheduling
    signal from calling the scheduler again.  (Tor Egge)

  o Don't use TAILQ_FOREACH macro while searching the waiting
    queue for threads in a sigwait state, because a change of
    state destroys the TAILQ link.  It is actually safe to do
    so, though, because once a sigwaiting thread is found, the
    loop ends and the function returns.  (Tor Egge)

  o When dispatching signals to threads, make the thread inherit
    the signal deferral flag of the currently running thread.
    (Tor Egge)

Submitted by: Daniel Eischen <eischen@vigrid.com> and
              Tor Egge <Tor.Egge@fast.no>
1999-06-20 08:28:48 +00:00

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/*
* Copyright (c) 1995 John Birrell <jb@cimlogic.com.au>.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by John Birrell.
* 4. Neither the name of the author nor the names of any co-contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id$
*/
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#ifdef _THREAD_SAFE
#include <pthread.h>
#include "pthread_private.h"
/*
* Prototypes
*/
static inline pthread_t cond_queue_deq(pthread_cond_t);
static inline void cond_queue_remove(pthread_cond_t, pthread_t);
static inline void cond_queue_enq(pthread_cond_t, pthread_t);
/* Reinitialize a condition variable to defaults. */
int
_cond_reinit(pthread_cond_t * cond)
{
int ret = 0;
if (cond == NULL)
ret = EINVAL;
else if (*cond == NULL)
ret = pthread_cond_init(cond, NULL);
else {
/*
* Initialize the condition variable structure:
*/
TAILQ_INIT(&(*cond)->c_queue);
(*cond)->c_flags = COND_FLAGS_INITED;
(*cond)->c_type = COND_TYPE_FAST;
(*cond)->c_mutex = NULL;
memset(&(*cond)->lock, 0, sizeof((*cond)->lock));
}
return (ret);
}
int
pthread_cond_init(pthread_cond_t * cond, const pthread_condattr_t * cond_attr)
{
enum pthread_cond_type type;
pthread_cond_t pcond;
int rval = 0;
if (cond == NULL)
rval = EINVAL;
else {
/*
* Check if a pointer to a condition variable attribute
* structure was passed by the caller:
*/
if (cond_attr != NULL && *cond_attr != NULL) {
/* Default to a fast condition variable: */
type = (*cond_attr)->c_type;
} else {
/* Default to a fast condition variable: */
type = COND_TYPE_FAST;
}
/* Process according to condition variable type: */
switch (type) {
/* Fast condition variable: */
case COND_TYPE_FAST:
/* Nothing to do here. */
break;
/* Trap invalid condition variable types: */
default:
/* Return an invalid argument error: */
rval = EINVAL;
break;
}
/* Check for no errors: */
if (rval == 0) {
if ((pcond = (pthread_cond_t)
malloc(sizeof(struct pthread_cond))) == NULL) {
rval = ENOMEM;
} else {
/*
* Initialise the condition variable
* structure:
*/
TAILQ_INIT(&pcond->c_queue);
pcond->c_flags |= COND_FLAGS_INITED;
pcond->c_type = type;
pcond->c_mutex = NULL;
memset(&pcond->lock,0,sizeof(pcond->lock));
*cond = pcond;
}
}
}
/* Return the completion status: */
return (rval);
}
int
pthread_cond_destroy(pthread_cond_t * cond)
{
int rval = 0;
if (cond == NULL || *cond == NULL)
rval = EINVAL;
else {
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/*
* Free the memory allocated for the condition
* variable structure:
*/
free(*cond);
/*
* NULL the caller's pointer now that the condition
* variable has been destroyed:
*/
*cond = NULL;
}
/* Return the completion status: */
return (rval);
}
int
pthread_cond_wait(pthread_cond_t * cond, pthread_mutex_t * mutex)
{
int rval = 0;
int status;
if (cond == NULL)
rval = EINVAL;
/*
* If the condition variable is statically initialized,
* perform the dynamic initialization:
*/
else if (*cond != NULL ||
(rval = pthread_cond_init(cond,NULL)) == 0) {
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/*
* If the condvar was statically allocated, properly
* initialize the tail queue.
*/
if (((*cond)->c_flags & COND_FLAGS_INITED) == 0) {
TAILQ_INIT(&(*cond)->c_queue);
(*cond)->c_flags |= COND_FLAGS_INITED;
}
/* Process according to condition variable type: */
switch ((*cond)->c_type) {
/* Fast condition variable: */
case COND_TYPE_FAST:
if ((mutex == NULL) || (((*cond)->c_mutex != NULL) &&
((*cond)->c_mutex != *mutex))) {
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/* Return invalid argument error: */
rval = EINVAL;
} else {
/* Reset the timeout flag: */
_thread_run->timeout = 0;
/*
* Queue the running thread for the condition
* variable:
*/
cond_queue_enq(*cond, _thread_run);
/* Remember the mutex that is being used: */
(*cond)->c_mutex = *mutex;
/* Wait forever: */
_thread_run->wakeup_time.tv_sec = -1;
/* Unlock the mutex: */
if ((rval = _mutex_cv_unlock(mutex)) != 0) {
/*
* Cannot unlock the mutex, so remove
* the running thread from the condition
* variable queue:
*/
cond_queue_remove(*cond, _thread_run);
/* Check for no more waiters: */
if (TAILQ_FIRST(&(*cond)->c_queue) ==
NULL)
(*cond)->c_mutex = NULL;
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
}
else {
/*
* Schedule the next thread and unlock
* the condition variable structure:
*/
_thread_kern_sched_state_unlock(PS_COND_WAIT,
&(*cond)->lock, __FILE__, __LINE__);
/* Lock the mutex: */
rval = _mutex_cv_lock(mutex);
}
}
break;
/* Trap invalid condition variable types: */
default:
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/* Return an invalid argument error: */
rval = EINVAL;
break;
}
}
/* Return the completion status: */
return (rval);
}
int
pthread_cond_timedwait(pthread_cond_t * cond, pthread_mutex_t * mutex,
const struct timespec * abstime)
{
int rval = 0;
int status;
if (cond == NULL)
rval = EINVAL;
/*
* If the condition variable is statically initialized,
* perform the dynamic initialization:
*/
else if (*cond != NULL ||
(rval = pthread_cond_init(cond,NULL)) == 0) {
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/*
* If the condvar was statically allocated, properly
* initialize the tail queue.
*/
if (((*cond)->c_flags & COND_FLAGS_INITED) == 0) {
TAILQ_INIT(&(*cond)->c_queue);
(*cond)->c_flags |= COND_FLAGS_INITED;
}
/* Process according to condition variable type: */
switch ((*cond)->c_type) {
/* Fast condition variable: */
case COND_TYPE_FAST:
if ((mutex == NULL) || (((*cond)->c_mutex != NULL) &&
((*cond)->c_mutex != *mutex))) {
/* Return invalid argument error: */
rval = EINVAL;
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
} else {
/* Set the wakeup time: */
_thread_run->wakeup_time.tv_sec =
abstime->tv_sec;
_thread_run->wakeup_time.tv_nsec =
abstime->tv_nsec;
/* Reset the timeout flag: */
_thread_run->timeout = 0;
/*
* Queue the running thread for the condition
* variable:
*/
cond_queue_enq(*cond, _thread_run);
/* Remember the mutex that is being used: */
(*cond)->c_mutex = *mutex;
/* Unlock the mutex: */
if ((rval = _mutex_cv_unlock(mutex)) != 0) {
/*
* Cannot unlock the mutex, so remove
* the running thread from the condition
* variable queue:
*/
cond_queue_remove(*cond, _thread_run);
/* Check for no more waiters: */
if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
(*cond)->c_mutex = NULL;
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
} else {
/*
* Schedule the next thread and unlock
* the condition variable structure:
*/
_thread_kern_sched_state_unlock(PS_COND_WAIT,
&(*cond)->lock, __FILE__, __LINE__);
/* Check if the wait timedout: */
if (_thread_run->timeout == 0) {
/* Lock the mutex: */
rval = _mutex_cv_lock(mutex);
}
else {
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/*
* The wait timed out; remove
* the thread from the condition
* variable queue:
*/
cond_queue_remove(*cond,
_thread_run);
/* Check for no more waiters: */
if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
(*cond)->c_mutex = NULL;
/* Unock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/* Return a timeout error: */
rval = ETIMEDOUT;
/*
* Lock the mutex and ignore
* any errors:
*/
(void)_mutex_cv_lock(mutex);
}
}
}
break;
/* Trap invalid condition variable types: */
default:
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/* Return an invalid argument error: */
rval = EINVAL;
break;
}
}
/* Return the completion status: */
return (rval);
}
int
pthread_cond_signal(pthread_cond_t * cond)
{
int rval = 0;
pthread_t pthread;
if (cond == NULL || *cond == NULL)
rval = EINVAL;
else {
/*
* Defer signals to protect the scheduling queues
* from access by the signal handler:
*/
_thread_kern_sig_defer();
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/* Process according to condition variable type: */
switch ((*cond)->c_type) {
/* Fast condition variable: */
case COND_TYPE_FAST:
/*
* Enter a loop to dequeue threads from the condition
* queue until we find one that hasn't previously
* timed out.
*/
while (((pthread = cond_queue_deq(*cond)) != NULL) &&
(pthread->timeout != 0)) {
}
if (pthread != NULL)
/* Allow the thread to run: */
PTHREAD_NEW_STATE(pthread,PS_RUNNING);
/* Check for no more waiters: */
if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
(*cond)->c_mutex = NULL;
break;
/* Trap invalid condition variable types: */
default:
/* Return an invalid argument error: */
rval = EINVAL;
break;
}
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/*
* Undefer and handle pending signals, yielding if
* necessary:
*/
_thread_kern_sig_undefer();
}
/* Return the completion status: */
return (rval);
}
int
pthread_cond_broadcast(pthread_cond_t * cond)
{
int rval = 0;
pthread_t pthread;
if (cond == NULL || *cond == NULL)
rval = EINVAL;
else {
/*
* Defer signals to protect the scheduling queues
* from access by the signal handler:
*/
_thread_kern_sig_defer();
/* Lock the condition variable structure: */
_SPINLOCK(&(*cond)->lock);
/* Process according to condition variable type: */
switch ((*cond)->c_type) {
/* Fast condition variable: */
case COND_TYPE_FAST:
/*
* Enter a loop to bring all threads off the
* condition queue:
*/
while ((pthread = cond_queue_deq(*cond)) != NULL) {
/*
* The thread is already running if the
* timeout flag is set.
*/
if (pthread->timeout == 0)
PTHREAD_NEW_STATE(pthread,PS_RUNNING);
}
/* There are no more waiting threads: */
(*cond)->c_mutex = NULL;
break;
/* Trap invalid condition variable types: */
default:
/* Return an invalid argument error: */
rval = EINVAL;
break;
}
/* Unlock the condition variable structure: */
_SPINUNLOCK(&(*cond)->lock);
/*
* Undefer and handle pending signals, yielding if
* necessary:
*/
_thread_kern_sig_undefer();
}
/* Return the completion status: */
return (rval);
}
/*
* Dequeue a waiting thread from the head of a condition queue in
* descending priority order.
*/
static inline pthread_t
cond_queue_deq(pthread_cond_t cond)
{
pthread_t pthread;
if ((pthread = TAILQ_FIRST(&cond->c_queue)) != NULL) {
TAILQ_REMOVE(&cond->c_queue, pthread, qe);
pthread->flags &= ~PTHREAD_FLAGS_IN_CONDQ;
}
return(pthread);
}
/*
* Remove a waiting thread from a condition queue in descending priority
* order.
*/
static inline void
cond_queue_remove(pthread_cond_t cond, pthread_t pthread)
{
/*
* Because pthread_cond_timedwait() can timeout as well
* as be signaled by another thread, it is necessary to
* guard against removing the thread from the queue if
* it isn't in the queue.
*/
if (pthread->flags & PTHREAD_FLAGS_IN_CONDQ) {
TAILQ_REMOVE(&cond->c_queue, pthread, qe);
pthread->flags &= ~PTHREAD_FLAGS_IN_CONDQ;
}
}
/*
* Enqueue a waiting thread to a condition queue in descending priority
* order.
*/
static inline void
cond_queue_enq(pthread_cond_t cond, pthread_t pthread)
{
pthread_t tid = TAILQ_LAST(&cond->c_queue, cond_head);
/*
* For the common case of all threads having equal priority,
* we perform a quick check against the priority of the thread
* at the tail of the queue.
*/
if ((tid == NULL) || (pthread->active_priority <= tid->active_priority))
TAILQ_INSERT_TAIL(&cond->c_queue, pthread, qe);
else {
tid = TAILQ_FIRST(&cond->c_queue);
while (pthread->active_priority <= tid->active_priority)
tid = TAILQ_NEXT(tid, qe);
TAILQ_INSERT_BEFORE(tid, pthread, qe);
}
pthread->flags |= PTHREAD_FLAGS_IN_CONDQ;
}
#endif
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