58a7cc5d1b
o Runnable threads are now maintained in priority queues. The
implementation requires two things:
1.) The priority queues must be protected during insertion
and removal of threads. Since the kernel scheduler
must modify the priority queues, a spinlock for
protection cannot be used. The functions
_thread_kern_sched_defer() and _thread_kern_sched_undefer()
were added to {un}defer kernel scheduler activation.
2.) A thread (active) priority change can be performed only
when the thread is removed from the priority queue. The
implementation uses a threads active priority when
inserting it into the queue.
A by-product is that thread switches are much faster. A
separate queue is used for waiting and/or blocked threads,
and it is searched at most 2 times in the kernel scheduler
when there are active threads. It should be possible to
reduce this to once by combining polling of threads waiting
on I/O with the loop that looks for timed out threads and
the minimum timeout value.
o Functions to defer kernel scheduler activation were added. These
are _thread_kern_sched_defer() and _thread_kern_sched_undefer()
and may be called recursively. These routines do not block the
scheduling signal, but latch its occurrence. The signal handler
will not call the kernel scheduler when the running thread has
deferred scheduling, but it will be called when running thread
undefers scheduling.
o Added support for _POSIX_THREAD_PRIORITY_SCHEDULING. All the
POSIX routines required by this should now be implemented.
One note, SCHED_OTHER, SCHED_FIFO, and SCHED_RR are required
to be defined by including pthread.h. These defines are currently
in sched.h. I modified pthread.h to include sched.h but don't
know if this is the proper thing to do.
o Added support for priority protection and inheritence mutexes.
This allows definition of _POSIX_THREAD_PRIO_PROTECT and
_POSIX_THREAD_PRIO_INHERIT.
o Added additional error checks required by POSIX for mutexes and
condition variables.
o Provided a wrapper for sigpending which is marked as a hidden
syscall.
o Added a non-portable function as a debugging aid to allow an
application to monitor thread context switches. An application
can install a routine that gets called everytime a thread
(explicitly created by the application) gets context switched.
The routine gets passed the pthread IDs of the threads that are
being switched in and out.
Submitted by: Dan Eischen <eischen@vigrid.com>
Changes by me:
o Added a PS_SPINBLOCK state to deal with the priority inversion
problem most often (I think) seen by threads calling malloc/free/realloc.
o Dispatch signals to the running thread directly rather than at a
context switch to avoid the situation where the switch never occurs.
522 lines
13 KiB
C
522 lines
13 KiB
C
/*
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* Copyright (c) 1995 John Birrell <jb@cimlogic.com.au>.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by John Birrell.
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* 4. Neither the name of the author nor the names of any co-contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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*/
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#include <stdlib.h>
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#include <errno.h>
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#include <string.h>
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#ifdef _THREAD_SAFE
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#include <pthread.h>
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#include "pthread_private.h"
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/*
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* Prototypes
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*/
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static inline pthread_t cond_queue_deq(pthread_cond_t);
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static inline void cond_queue_remove(pthread_cond_t, pthread_t);
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static inline void cond_queue_enq(pthread_cond_t, pthread_t);
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int
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pthread_cond_init(pthread_cond_t * cond, const pthread_condattr_t * cond_attr)
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{
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enum pthread_cond_type type;
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pthread_cond_t pcond;
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int rval = 0;
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if (cond == NULL)
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rval = EINVAL;
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else {
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/*
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* Check if a pointer to a condition variable attribute
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* structure was passed by the caller:
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*/
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if (cond_attr != NULL && *cond_attr != NULL) {
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/* Default to a fast condition variable: */
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type = (*cond_attr)->c_type;
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} else {
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/* Default to a fast condition variable: */
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type = COND_TYPE_FAST;
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}
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/* Process according to condition variable type: */
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switch (type) {
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/* Fast condition variable: */
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case COND_TYPE_FAST:
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/* Nothing to do here. */
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break;
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/* Trap invalid condition variable types: */
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default:
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/* Return an invalid argument error: */
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rval = EINVAL;
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break;
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}
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/* Check for no errors: */
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if (rval == 0) {
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if ((pcond = (pthread_cond_t)
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malloc(sizeof(struct pthread_cond))) == NULL) {
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rval = ENOMEM;
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} else {
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/*
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* Initialise the condition variable
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* structure:
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*/
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TAILQ_INIT(&pcond->c_queue);
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pcond->c_flags |= COND_FLAGS_INITED;
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pcond->c_type = type;
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pcond->c_mutex = NULL;
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memset(&pcond->lock,0,sizeof(pcond->lock));
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*cond = pcond;
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}
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}
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}
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/* Return the completion status: */
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return (rval);
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}
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int
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pthread_cond_destroy(pthread_cond_t * cond)
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{
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int rval = 0;
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if (cond == NULL || *cond == NULL)
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rval = EINVAL;
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else {
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/*
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* Free the memory allocated for the condition
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* variable structure:
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*/
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free(*cond);
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/*
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* NULL the caller's pointer now that the condition
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* variable has been destroyed:
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*/
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*cond = NULL;
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}
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/* Return the completion status: */
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return (rval);
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}
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int
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pthread_cond_wait(pthread_cond_t * cond, pthread_mutex_t * mutex)
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{
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int rval = 0;
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int status;
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if (cond == NULL)
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rval = EINVAL;
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/*
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* If the condition variable is statically initialized,
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* perform the dynamic initialization:
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*/
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else if (*cond != NULL ||
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(rval = pthread_cond_init(cond,NULL)) == 0) {
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/* Process according to condition variable type: */
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switch ((*cond)->c_type) {
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/* Fast condition variable: */
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case COND_TYPE_FAST:
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if ((mutex == NULL) || (((*cond)->c_mutex != NULL) &&
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((*cond)->c_mutex != *mutex))) {
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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/* Return invalid argument error: */
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rval = EINVAL;
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} else {
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/* Reset the timeout flag: */
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_thread_run->timeout = 0;
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/*
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* Queue the running thread for the condition
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* variable:
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*/
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cond_queue_enq(*cond, _thread_run);
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/* Remember the mutex that is being used: */
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(*cond)->c_mutex = *mutex;
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/* Wait forever: */
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_thread_run->wakeup_time.tv_sec = -1;
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/* Unlock the mutex: */
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if ((rval = _mutex_cv_unlock(mutex)) != 0) {
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/*
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* Cannot unlock the mutex, so remove
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* the running thread from the condition
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* variable queue:
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*/
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cond_queue_remove(*cond, _thread_run);
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/* Check for no more waiters: */
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if (TAILQ_FIRST(&(*cond)->c_queue) ==
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NULL)
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(*cond)->c_mutex = NULL;
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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}
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else {
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/*
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* Schedule the next thread and unlock
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* the condition variable structure:
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*/
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_thread_kern_sched_state_unlock(PS_COND_WAIT,
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&(*cond)->lock, __FILE__, __LINE__);
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/* Lock the mutex: */
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rval = _mutex_cv_lock(mutex);
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}
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}
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break;
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/* Trap invalid condition variable types: */
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default:
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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/* Return an invalid argument error: */
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rval = EINVAL;
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break;
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}
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}
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/* Return the completion status: */
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return (rval);
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}
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int
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pthread_cond_timedwait(pthread_cond_t * cond, pthread_mutex_t * mutex,
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const struct timespec * abstime)
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{
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int rval = 0;
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int status;
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if (cond == NULL)
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rval = EINVAL;
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/*
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* If the condition variable is statically initialized,
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* perform the dynamic initialization:
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*/
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else if (*cond != NULL ||
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(rval = pthread_cond_init(cond,NULL)) == 0) {
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/* Process according to condition variable type: */
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switch ((*cond)->c_type) {
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/* Fast condition variable: */
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case COND_TYPE_FAST:
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if ((mutex == NULL) || (((*cond)->c_mutex != NULL) &&
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((*cond)->c_mutex != *mutex))) {
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/* Return invalid argument error: */
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rval = EINVAL;
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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} else {
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/* Set the wakeup time: */
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_thread_run->wakeup_time.tv_sec =
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abstime->tv_sec;
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_thread_run->wakeup_time.tv_nsec =
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abstime->tv_nsec;
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/* Reset the timeout flag: */
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_thread_run->timeout = 0;
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/*
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* Queue the running thread for the condition
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* variable:
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*/
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cond_queue_enq(*cond, _thread_run);
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/* Remember the mutex that is being used: */
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(*cond)->c_mutex = *mutex;
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/* Unlock the mutex: */
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if ((rval = _mutex_cv_unlock(mutex)) != 0) {
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/*
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* Cannot unlock the mutex, so remove
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* the running thread from the condition
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* variable queue:
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*/
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cond_queue_remove(*cond, _thread_run);
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/* Check for no more waiters: */
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if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
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(*cond)->c_mutex = NULL;
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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} else {
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/*
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* Schedule the next thread and unlock
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* the condition variable structure:
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*/
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_thread_kern_sched_state_unlock(PS_COND_WAIT,
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&(*cond)->lock, __FILE__, __LINE__);
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/* Check if the wait timedout: */
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if (_thread_run->timeout == 0) {
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/* Lock the mutex: */
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rval = _mutex_cv_lock(mutex);
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}
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else {
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/*
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* The wait timed out; remove
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* the thread from the condition
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* variable queue:
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*/
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cond_queue_remove(*cond,
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_thread_run);
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/* Check for no more waiters: */
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if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
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(*cond)->c_mutex = NULL;
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/* Unock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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/* Return a timeout error: */
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rval = ETIMEDOUT;
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/*
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* Lock the mutex and ignore
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* any errors:
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*/
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(void)_mutex_cv_lock(mutex);
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}
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}
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}
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break;
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/* Trap invalid condition variable types: */
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default:
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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/* Return an invalid argument error: */
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rval = EINVAL;
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break;
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}
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}
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/* Return the completion status: */
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return (rval);
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}
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int
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pthread_cond_signal(pthread_cond_t * cond)
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{
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int rval = 0;
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pthread_t pthread;
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if (cond == NULL || *cond == NULL)
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rval = EINVAL;
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else {
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/* Process according to condition variable type: */
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switch ((*cond)->c_type) {
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/* Fast condition variable: */
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case COND_TYPE_FAST:
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/*
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* Enter a loop to dequeue threads from the condition
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* queue until we find one that hasn't previously
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* timed out.
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*/
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while (((pthread = cond_queue_deq(*cond)) != NULL) &&
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(pthread->timeout != 0)) {
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}
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if (pthread != NULL)
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/* Allow the thread to run: */
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PTHREAD_NEW_STATE(pthread,PS_RUNNING);
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/* Check for no more waiters: */
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if (TAILQ_FIRST(&(*cond)->c_queue) == NULL)
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(*cond)->c_mutex = NULL;
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break;
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/* Trap invalid condition variable types: */
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default:
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/* Return an invalid argument error: */
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rval = EINVAL;
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break;
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}
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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}
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/* Return the completion status: */
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return (rval);
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}
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int
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pthread_cond_broadcast(pthread_cond_t * cond)
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{
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int rval = 0;
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pthread_t pthread;
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if (cond == NULL || *cond == NULL)
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rval = EINVAL;
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else {
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/*
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* Guard against preemption by a scheduling signal.
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* A change of thread state modifies the waiting
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* and priority queues. In addition, we must assure
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* that all threads currently waiting on the condition
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* variable are signaled and are not timedout by a
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* scheduling signal that causes a preemption.
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*/
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_thread_kern_sched_defer();
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/* Lock the condition variable structure: */
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_SPINLOCK(&(*cond)->lock);
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/* Process according to condition variable type: */
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switch ((*cond)->c_type) {
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/* Fast condition variable: */
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case COND_TYPE_FAST:
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/*
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* Enter a loop to bring all threads off the
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* condition queue:
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*/
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while ((pthread = cond_queue_deq(*cond)) != NULL) {
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/*
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* The thread is already running if the
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* timeout flag is set.
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*/
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if (pthread->timeout == 0)
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PTHREAD_NEW_STATE(pthread,PS_RUNNING);
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}
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/* There are no more waiting threads: */
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(*cond)->c_mutex = NULL;
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break;
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/* Trap invalid condition variable types: */
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default:
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/* Return an invalid argument error: */
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rval = EINVAL;
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break;
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}
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/* Unlock the condition variable structure: */
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_SPINUNLOCK(&(*cond)->lock);
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/* Reenable preemption and yield if necessary.
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*/
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_thread_kern_sched_undefer();
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}
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/* Return the completion status: */
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return (rval);
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}
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/*
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* Dequeue a waiting thread from the head of a condition queue in
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* descending priority order.
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*/
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static inline pthread_t
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cond_queue_deq(pthread_cond_t cond)
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{
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pthread_t pthread;
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if ((pthread = TAILQ_FIRST(&cond->c_queue)) != NULL) {
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TAILQ_REMOVE(&cond->c_queue, pthread, qe);
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pthread->flags &= ~PTHREAD_FLAGS_QUEUED;
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}
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return(pthread);
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}
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/*
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* Remove a waiting thread from a condition queue in descending priority
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* order.
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*/
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static inline void
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cond_queue_remove(pthread_cond_t cond, pthread_t pthread)
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{
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/*
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* Because pthread_cond_timedwait() can timeout as well
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* as be signaled by another thread, it is necessary to
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* guard against removing the thread from the queue if
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* it isn't in the queue.
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*/
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if (pthread->flags & PTHREAD_FLAGS_QUEUED) {
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TAILQ_REMOVE(&cond->c_queue, pthread, qe);
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pthread->flags &= ~PTHREAD_FLAGS_QUEUED;
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}
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}
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/*
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* Enqueue a waiting thread to a condition queue in descending priority
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* order.
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*/
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static inline void
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cond_queue_enq(pthread_cond_t cond, pthread_t pthread)
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{
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pthread_t tid = TAILQ_LAST(&cond->c_queue, cond_head);
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/*
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* For the common case of all threads having equal priority,
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* we perform a quick check against the priority of the thread
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* at the tail of the queue.
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*/
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if ((tid == NULL) || (pthread->active_priority <= tid->active_priority))
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TAILQ_INSERT_TAIL(&cond->c_queue, pthread, qe);
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else {
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tid = TAILQ_FIRST(&cond->c_queue);
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while (pthread->active_priority <= tid->active_priority)
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tid = TAILQ_NEXT(tid, qe);
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TAILQ_INSERT_BEFORE(tid, pthread, qe);
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}
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pthread->flags |= PTHREAD_FLAGS_QUEUED;
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}
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#endif
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