cs350/kern/thread/synch.c

/*
 * Copyright (c) 2000, 2001, 2002, 2003, 2004, 2005, 2008, 2009
 *	The President and Fellows of Harvard College.
 *
 * 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 University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY 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 UNIVERSITY 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.
 */

/*
 * Synchronization primitives.
 * The specifications of the functions are in synch.h.
 */

#include <types.h>
#include <lib.h>
#include <spinlock.h>
#include <wchan.h>
#include <thread.h>
#include <current.h>
#include <synch.h>

////////////////////////////////////////////////////////////
//
// Semaphore.

struct semaphore *
sem_create(const char *name, int initial_count)
{
        struct semaphore *sem;

        KASSERT(initial_count >= 0);

        sem = kmalloc(sizeof(struct semaphore));
        if (sem == NULL) {
                return NULL;
        }

        sem->sem_name = kstrdup(name);
        if (sem->sem_name == NULL) {
                kfree(sem);
                return NULL;
        }

	sem->sem_wchan = wchan_create(sem->sem_name);
	if (sem->sem_wchan == NULL) {
		kfree(sem->sem_name);
		kfree(sem);
		return NULL;
	}

	spinlock_init(&sem->sem_lock);
        sem->sem_count = initial_count;

        return sem;
}

void
sem_destroy(struct semaphore *sem)
{
        KASSERT(sem != NULL);

	/* wchan_cleanup will assert if anyone's waiting on it */
	spinlock_cleanup(&sem->sem_lock);
	wchan_destroy(sem->sem_wchan);
        kfree(sem->sem_name);
        kfree(sem);
}

void
P(struct semaphore *sem)
{
        KASSERT(sem != NULL);

        /*
         * May not block in an interrupt handler.
         *
         * For robustness, always check, even if we can actually
         * complete the P without blocking.
         */
        KASSERT(curthread->t_in_interrupt == false);

	spinlock_acquire(&sem->sem_lock);
        while (sem->sem_count == 0) {
		/*
		 * Bridge to the wchan lock, so if someone else comes
		 * along in V right this instant the wakeup can't go
		 * through on the wchan until we've finished going to
		 * sleep. Note that wchan_sleep unlocks the wchan.
		 *
		 * Note that we don't maintain strict FIFO ordering of
		 * threads going through the semaphore; that is, we
		 * might "get" it on the first try even if other
		 * threads are waiting. Apparently according to some
		 * textbooks semaphores must for some reason have
		 * strict ordering. Too bad. :-)
		 *
		 * Exercise: how would you implement strict FIFO
		 * ordering?
		 */
		wchan_lock(sem->sem_wchan);
		spinlock_release(&sem->sem_lock);
                wchan_sleep(sem->sem_wchan);

		spinlock_acquire(&sem->sem_lock);
        }
        KASSERT(sem->sem_count > 0);
        sem->sem_count--;
	spinlock_release(&sem->sem_lock);
}

void
V(struct semaphore *sem)
{
        KASSERT(sem != NULL);

	spinlock_acquire(&sem->sem_lock);

        sem->sem_count++;
        KASSERT(sem->sem_count > 0);
	wchan_wakeone(sem->sem_wchan);

	spinlock_release(&sem->sem_lock);
}

////////////////////////////////////////////////////////////
//
// Lock.

struct lock * lock_create(const char * name)
{
  struct lock * lock = kmalloc(sizeof(struct lock));
  
  if (lock == NULL)
  {
    return NULL;
  }

  lock->lk_name = kstrdup(name);
  
  struct wchan * wc = wchan_create(lock->lk_name);
  
  if (lock->lk_name == NULL || wc == NULL)
  {
    kfree(lock->lk_name);
    kfree(lock);
    kfree(wc);
    return NULL;
  }
  
  spinlock_init(&(lock->spin));
  lock->owner = NULL;
  lock->wc = wc;
    
  return lock;
}

void lock_destroy(struct lock * lock)
{
  KASSERT(lock);
  
  spinlock_cleanup(&(lock->spin));
  wchan_destroy(lock->wc);
  kfree(lock->lk_name);
  kfree(lock);
}

void lock_acquire(struct lock * lock)
{
  KASSERT(lock);
  KASSERT(!(lock_do_i_hold(lock)));

  spinlock_acquire(&(lock->spin));
  
  while (lock->owner)
  {
    wchan_lock(lock->wc);
    spinlock_release(&(lock->spin));
    wchan_sleep(lock->wc);
    spinlock_acquire(&(lock->spin));
  }
  
  lock->owner = curthread;
  spinlock_release(&(lock->spin));
}

void lock_release(struct lock * lock)
{
  KASSERT(lock);
  KASSERT(lock_do_i_hold(lock));
  
  spinlock_acquire(&(lock->spin));
  lock->owner = NULL;
  wchan_wakeone(lock->wc);
  spinlock_release(&(lock->spin));
}

bool lock_do_i_hold(struct lock * lock)
{
  KASSERT(lock);
  
  return (lock->owner == curthread);
}

////////////////////////////////////////////////////////////
//
// CV


struct cv * cv_create(const char * name)
{
  struct cv * cv = kmalloc(sizeof(struct cv));
  
  if (cv == NULL)
  {
    return NULL;
  }
  
  cv->cv_name = kstrdup(name);
  struct wchan * wc = wchan_create(cv->cv_name);
  
  if (cv->cv_name == NULL || wc == NULL)
  {
    kfree(cv->cv_name);
    kfree(cv);
    kfree(wc);
    return NULL;
  }

  cv->wc = wc;
  return cv;
}

void cv_destroy(struct cv * cv)
{
  KASSERT(cv);
  
  wchan_destroy(cv->wc);
  kfree(cv->cv_name);
  kfree(cv);
}

void cv_wait(struct cv * cv, struct lock * lock)
{
  KASSERT(lock_do_i_hold(lock));
  
  wchan_lock(cv->wc);
  lock_release(lock);
  wchan_sleep(cv->wc);
  lock_acquire(lock);
}

void
cv_signal(struct cv * cv, struct lock * lock)
{
  KASSERT(lock_do_i_hold(lock));
  KASSERT(cv);
  
  wchan_wakeone(cv->wc);
}

void
cv_broadcast(struct cv * cv, struct lock * lock)
{
	KASSERT(lock_do_i_hold(lock));
	KASSERT(cv);
	
	wchan_wakeall(cv->wc);
}