File: [local] / prex / sys / sync / sem.c (download)
Revision 1.1.1.1 (vendor branch), Tue Aug 19 12:46:57 2008 UTC (16 years ago) by nbrk
Branch: MAIN, KOHSUKE
CVS Tags: PREX_0_8_BASE, HEAD Changes since 1.1: +0 -0 lines
Initial import of Prex, Portable Real-time Embedded POSIX microkernel system.
I have totally new directions in my development (more focused on real hardware, not virtual one).
Old hacks are available in prex-old module. They will be carefully re-designed and merged soon.
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/*-
* Copyright (c) 2005-2007, Kohsuke Ohtani
* 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. 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 THE AUTHOR 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.
*/
/*
* sem.c - semaphore support
*/
/*
* All of the Prex semaphore is un-named semaphore. Instead,
* the named semaphore is implemented by a file system server.
* In order to access the other task's semaphore, the task
* must have CAP_SEMAPHORE capability.
*/
#include <kernel.h>
#include <event.h>
#include <sched.h>
#include <kmem.h>
#include <thread.h>
#include <sync.h>
/*
* sem_init - initialize a semaphore.
*
* sem_init() creates a new semaphore if the specified
* semaphore does not exist yet. If the semaphore already
* exists, it is re-initialized only if nobody is waiting for
* it. The initial semaphore value is set to the requested
* value.
*/
int
sem_init(sem_t *sem, u_int value)
{
struct sem *s;
int err = 0;
if (value > MAXSEMVAL)
return EINVAL;
if (umem_copyin(sem, &s, sizeof(sem_t)))
return EFAULT;
/*
* An application can call sem_init() to reset the
* value of existing semaphore. So, we have to check
* whether the semaphore is already allocated.
*/
sched_lock();
if (sem_valid(s)) {
/*
* Semaphore already exists.
*/
if (s->task != cur_task() &&
!task_capable(CAP_SEMAPHORE))
err = EPERM;
else if (event_waiting(&s->event))
err = EBUSY;
else
s->value = value;
} else {
/*
* Create new semaphore.
*/
if ((s = kmem_alloc(sizeof(struct sem))) == NULL)
err = ENOSPC;
else {
event_init(&s->event, "semaphore");
s->task = cur_task();
s->value = value;
s->magic = SEM_MAGIC;
if (umem_copyout(&s, sem, sizeof(sem_t))) {
kmem_free(s);
err = EFAULT;
}
}
}
sched_unlock();
return err;
}
/*
* sem_copyin - copy a semaphore from user space.
*
* It also checks whether the passed semaphore is valid.
*/
static int
sem_copyin(sem_t *usem, sem_t *ksem)
{
sem_t s;
if (umem_copyin(usem, &s, sizeof(sem_t)))
return EFAULT;
if (!sem_valid(s))
return EINVAL;
/*
* Need a capability to access semaphores created
* by another task.
*/
if (s->task != cur_task() && !task_capable(CAP_SEMAPHORE))
return EPERM;
*ksem = s;
return 0;
}
/*
* Destroy a semaphore.
* If some thread is waiting for the specified semaphore,
* this routine fails with EBUSY.
*/
int
sem_destroy(sem_t *sem)
{
sem_t s;
int err;
sched_lock();
if ((err = sem_copyin(sem, &s))) {
sched_unlock();
return err;
}
if (event_waiting(&s->event) || s->value == 0) {
sched_unlock();
return EBUSY;
}
s->magic = 0;
kmem_free(s);
sched_unlock();
return 0;
}
/*
* sem_wait - lock a semaphore.
*
* The value of timeout is msec unit. 0 for no timeout.
*
* sem_wait() locks the semaphore referred by sem only if the
* semaphore value is currently positive. The thread will
* sleep while the semaphore value is zero. It decrements the
* semaphore value in return.
*
* If waiting thread receives any exception, this routine
* returns with EINTR in order to invoke exception
* handler. But, an application assumes this call does NOT
* return with error. So, system call stub routine must
* re-call automatically if it gets EINTR.
*/
int
sem_wait(sem_t *sem, u_long timeout)
{
sem_t s;
int err, rc;
sched_lock();
if ((err = sem_copyin(sem, &s)))
goto out;
while (s->value == 0) {
rc = sched_tsleep(&s->event, timeout);
if (rc == SLP_TIMEOUT) {
err = ETIMEDOUT;
goto out;
}
if (rc == SLP_INTR) {
err = EINTR;
goto out;
}
/* Kick scheduler */
sched_unlock();
sched_lock();
}
s->value--;
out:
sched_unlock();
return err;
}
/*
* Try to lock a semaphore.
* If the semaphore is already locked, it just returns EAGAIN.
*/
int
sem_trywait(sem_t *sem)
{
sem_t s;
int err;
sched_lock();
if ((err = sem_copyin(sem, &s))) {
sched_unlock();
return err;
}
if (s->value > 0)
s->value--;
else
err = EAGAIN;
sched_unlock();
return err;
}
/*
* Unlock a semaphore.
*
* If the semaphore value becomes non zero, then one of
* the threads blocked waiting for the semaphore will be
* unblocked. This is non-blocking operation.
*/
int
sem_post(sem_t *sem)
{
sem_t s;
int err;
sched_lock();
if ((err = sem_copyin(sem, &s))) {
sched_unlock();
return err;
}
if (s->value >= MAXSEMVAL) {
sched_unlock();
return ERANGE;
}
s->value++;
if (s->value > 0)
sched_wakeone(&s->event);
sched_unlock();
return 0;
}
/*
* Get the semaphore value.
*/
int
sem_getvalue(sem_t *sem, u_int *value)
{
sem_t s;
int err;
sched_lock();
if ((err = sem_copyin(sem, &s))) {
sched_unlock();
return err;
}
if (umem_copyout(&s->value, value, sizeof(int)))
err = EFAULT;
sched_unlock();
return err;
}