537 lines
12 KiB
C
537 lines
12 KiB
C
/*
|
|
* Copyright (c) 1991, 1993
|
|
* The Regents of the University of California. All rights reserved.
|
|
*
|
|
* This code is derived from software contributed to Berkeley by
|
|
* The Mach Operating System project at Carnegie-Mellon University.
|
|
*
|
|
* 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 the University of
|
|
* California, Berkeley and its contributors.
|
|
* 4. 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 REGENTS 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 REGENTS 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.
|
|
*
|
|
* from: @(#)kern_lock.c 8.1 (Berkeley) 6/11/93
|
|
*
|
|
*
|
|
* Copyright (c) 1987, 1990 Carnegie-Mellon University.
|
|
* All rights reserved.
|
|
*
|
|
* Authors: Avadis Tevanian, Jr., Michael Wayne Young
|
|
*
|
|
* Permission to use, copy, modify and distribute this software and
|
|
* its documentation is hereby granted, provided that both the copyright
|
|
* notice and this permission notice appear in all copies of the
|
|
* software, derivative works or modified versions, and any portions
|
|
* thereof, and that both notices appear in supporting documentation.
|
|
*
|
|
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
|
|
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND
|
|
* FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
|
|
*
|
|
* Carnegie Mellon requests users of this software to return to
|
|
*
|
|
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
|
|
* School of Computer Science
|
|
* Carnegie Mellon University
|
|
* Pittsburgh PA 15213-3890
|
|
*
|
|
* any improvements or extensions that they make and grant Carnegie the
|
|
* rights to redistribute these changes.
|
|
*
|
|
* $Id: kern_lock.c,v 1.3 1995/01/09 16:05:30 davidg Exp $
|
|
*/
|
|
|
|
/*
|
|
* Locking primitives implementation
|
|
*/
|
|
|
|
#include <sys/param.h>
|
|
#include <sys/systm.h>
|
|
|
|
/* XXX */
|
|
#include <sys/proc.h>
|
|
|
|
#include <vm/vm.h>
|
|
|
|
typedef int *thread_t;
|
|
|
|
#define current_thread() ((thread_t)&curproc->p_thread)
|
|
/* XXX */
|
|
|
|
#if NCPUS > 1
|
|
|
|
/*
|
|
* Module: lock
|
|
* Function:
|
|
* Provide reader/writer sychronization.
|
|
* Implementation:
|
|
* Simple interlock on a bit. Readers first interlock
|
|
* increment the reader count, then let go. Writers hold
|
|
* the interlock (thus preventing further readers), and
|
|
* wait for already-accepted readers to go away.
|
|
*/
|
|
|
|
/*
|
|
* The simple-lock routines are the primitives out of which
|
|
* the lock package is built. The implementation is left
|
|
* to the machine-dependent code.
|
|
*/
|
|
|
|
#ifdef notdef
|
|
/*
|
|
* A sample implementation of simple locks.
|
|
* assumes:
|
|
* boolean_t test_and_set(boolean_t *)
|
|
* indivisibly sets the boolean to TRUE
|
|
* and returns its old value
|
|
* and that setting a boolean to FALSE is indivisible.
|
|
*/
|
|
/*
|
|
* simple_lock_init initializes a simple lock. A simple lock
|
|
* may only be used for exclusive locks.
|
|
*/
|
|
|
|
void
|
|
simple_lock_init(l)
|
|
simple_lock_t l;
|
|
{
|
|
*(boolean_t *) l = FALSE;
|
|
}
|
|
|
|
void
|
|
simple_lock(l)
|
|
simple_lock_t l;
|
|
{
|
|
while (test_and_set((boolean_t *) l))
|
|
continue;
|
|
}
|
|
|
|
void
|
|
simple_unlock(l)
|
|
simple_lock_t l;
|
|
{
|
|
*(boolean_t *) l = FALSE;
|
|
}
|
|
|
|
boolean_t
|
|
simple_lock_try(l)
|
|
simple_lock_t l;
|
|
{
|
|
return (!test_and_set((boolean_t *) l));
|
|
}
|
|
#endif /* notdef */
|
|
#endif /* NCPUS > 1 */
|
|
|
|
#if NCPUS > 1
|
|
int lock_wait_time = 100;
|
|
|
|
#else /* NCPUS > 1 */
|
|
|
|
/*
|
|
* It is silly to spin on a uni-processor as if we thought something magical
|
|
* would happen to the want_write bit while we are executing.
|
|
*/
|
|
int lock_wait_time = 0;
|
|
|
|
#endif /* NCPUS > 1 */
|
|
|
|
|
|
/*
|
|
* Routine: lock_init
|
|
* Function:
|
|
* Initialize a lock; required before use.
|
|
* Note that clients declare the "struct lock"
|
|
* variables and then initialize them, rather
|
|
* than getting a new one from this module.
|
|
*/
|
|
void
|
|
lock_init(l, can_sleep)
|
|
lock_t l;
|
|
boolean_t can_sleep;
|
|
{
|
|
bzero(l, sizeof(lock_data_t));
|
|
simple_lock_init(&l->interlock);
|
|
l->want_write = FALSE;
|
|
l->want_upgrade = FALSE;
|
|
l->read_count = 0;
|
|
l->can_sleep = can_sleep;
|
|
l->thread = (char *) -1; /* XXX */
|
|
l->recursion_depth = 0;
|
|
}
|
|
|
|
void
|
|
lock_sleepable(l, can_sleep)
|
|
lock_t l;
|
|
boolean_t can_sleep;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
l->can_sleep = can_sleep;
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
|
|
/*
|
|
* Sleep locks. These use the same data structure and algorithm
|
|
* as the spin locks, but the process sleeps while it is waiting
|
|
* for the lock. These work on uniprocessor systems.
|
|
*/
|
|
|
|
void
|
|
lock_write(l)
|
|
register lock_t l;
|
|
{
|
|
register int i;
|
|
|
|
simple_lock(&l->interlock);
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock.
|
|
*/
|
|
l->recursion_depth++;
|
|
simple_unlock(&l->interlock);
|
|
return;
|
|
}
|
|
/*
|
|
* Try to acquire the want_write bit.
|
|
*/
|
|
while (l->want_write) {
|
|
if ((i = lock_wait_time) > 0) {
|
|
simple_unlock(&l->interlock);
|
|
while (--i > 0 && l->want_write)
|
|
continue;
|
|
simple_lock(&l->interlock);
|
|
}
|
|
if (l->can_sleep && l->want_write) {
|
|
l->waiting = TRUE;
|
|
thread_sleep((int) l, &l->interlock, FALSE);
|
|
simple_lock(&l->interlock);
|
|
}
|
|
}
|
|
l->want_write = TRUE;
|
|
|
|
/* Wait for readers (and upgrades) to finish */
|
|
|
|
while ((l->read_count != 0) || l->want_upgrade) {
|
|
if ((i = lock_wait_time) > 0) {
|
|
simple_unlock(&l->interlock);
|
|
while (--i > 0 && (l->read_count != 0 ||
|
|
l->want_upgrade))
|
|
continue;
|
|
simple_lock(&l->interlock);
|
|
}
|
|
if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) {
|
|
l->waiting = TRUE;
|
|
thread_sleep((int) l, &l->interlock, FALSE);
|
|
simple_lock(&l->interlock);
|
|
}
|
|
}
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
void
|
|
lock_done(l)
|
|
register lock_t l;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
|
|
if (l->read_count != 0)
|
|
l->read_count--;
|
|
else if (l->recursion_depth != 0)
|
|
l->recursion_depth--;
|
|
else if (l->want_upgrade)
|
|
l->want_upgrade = FALSE;
|
|
else
|
|
l->want_write = FALSE;
|
|
|
|
if (l->waiting) {
|
|
l->waiting = FALSE;
|
|
thread_wakeup((int) l);
|
|
}
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
void
|
|
lock_read(l)
|
|
register lock_t l;
|
|
{
|
|
register int i;
|
|
|
|
simple_lock(&l->interlock);
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock.
|
|
*/
|
|
l->read_count++;
|
|
simple_unlock(&l->interlock);
|
|
return;
|
|
}
|
|
while (l->want_write || l->want_upgrade) {
|
|
if ((i = lock_wait_time) > 0) {
|
|
simple_unlock(&l->interlock);
|
|
while (--i > 0 && (l->want_write || l->want_upgrade))
|
|
continue;
|
|
simple_lock(&l->interlock);
|
|
}
|
|
if (l->can_sleep && (l->want_write || l->want_upgrade)) {
|
|
l->waiting = TRUE;
|
|
thread_sleep((int) l, &l->interlock, FALSE);
|
|
simple_lock(&l->interlock);
|
|
}
|
|
}
|
|
|
|
l->read_count++;
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
/*
|
|
* Routine: lock_read_to_write
|
|
* Function:
|
|
* Improves a read-only lock to one with
|
|
* write permission. If another reader has
|
|
* already requested an upgrade to a write lock,
|
|
* no lock is held upon return.
|
|
*
|
|
* Returns TRUE if the upgrade *failed*.
|
|
*/
|
|
boolean_t
|
|
lock_read_to_write(l)
|
|
register lock_t l;
|
|
{
|
|
register int i;
|
|
|
|
simple_lock(&l->interlock);
|
|
|
|
l->read_count--;
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock.
|
|
*/
|
|
l->recursion_depth++;
|
|
simple_unlock(&l->interlock);
|
|
return (FALSE);
|
|
}
|
|
if (l->want_upgrade) {
|
|
/*
|
|
* Someone else has requested upgrade. Since we've released a
|
|
* read lock, wake him up.
|
|
*/
|
|
if (l->waiting) {
|
|
l->waiting = FALSE;
|
|
thread_wakeup((int) l);
|
|
}
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
l->want_upgrade = TRUE;
|
|
|
|
while (l->read_count != 0) {
|
|
if ((i = lock_wait_time) > 0) {
|
|
simple_unlock(&l->interlock);
|
|
while (--i > 0 && l->read_count != 0)
|
|
continue;
|
|
simple_lock(&l->interlock);
|
|
}
|
|
if (l->can_sleep && l->read_count != 0) {
|
|
l->waiting = TRUE;
|
|
thread_sleep((int) l, &l->interlock, FALSE);
|
|
simple_lock(&l->interlock);
|
|
}
|
|
}
|
|
|
|
simple_unlock(&l->interlock);
|
|
return (FALSE);
|
|
}
|
|
|
|
void
|
|
lock_write_to_read(l)
|
|
register lock_t l;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
|
|
l->read_count++;
|
|
if (l->recursion_depth != 0)
|
|
l->recursion_depth--;
|
|
else if (l->want_upgrade)
|
|
l->want_upgrade = FALSE;
|
|
else
|
|
l->want_write = FALSE;
|
|
|
|
if (l->waiting) {
|
|
l->waiting = FALSE;
|
|
thread_wakeup((int) l);
|
|
}
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
|
|
/*
|
|
* Routine: lock_try_write
|
|
* Function:
|
|
* Tries to get a write lock.
|
|
*
|
|
* Returns FALSE if the lock is not held on return.
|
|
*/
|
|
|
|
boolean_t
|
|
lock_try_write(l)
|
|
register lock_t l;
|
|
{
|
|
|
|
simple_lock(&l->interlock);
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock
|
|
*/
|
|
l->recursion_depth++;
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
if (l->want_write || l->want_upgrade || l->read_count) {
|
|
/*
|
|
* Can't get lock.
|
|
*/
|
|
simple_unlock(&l->interlock);
|
|
return (FALSE);
|
|
}
|
|
/*
|
|
* Have lock.
|
|
*/
|
|
|
|
l->want_write = TRUE;
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
|
|
/*
|
|
* Routine: lock_try_read
|
|
* Function:
|
|
* Tries to get a read lock.
|
|
*
|
|
* Returns FALSE if the lock is not held on return.
|
|
*/
|
|
|
|
boolean_t
|
|
lock_try_read(l)
|
|
register lock_t l;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock
|
|
*/
|
|
l->read_count++;
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
if (l->want_write || l->want_upgrade) {
|
|
simple_unlock(&l->interlock);
|
|
return (FALSE);
|
|
}
|
|
l->read_count++;
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
|
|
/*
|
|
* Routine: lock_try_read_to_write
|
|
* Function:
|
|
* Improves a read-only lock to one with
|
|
* write permission. If another reader has
|
|
* already requested an upgrade to a write lock,
|
|
* the read lock is still held upon return.
|
|
*
|
|
* Returns FALSE if the upgrade *failed*.
|
|
*/
|
|
boolean_t
|
|
lock_try_read_to_write(l)
|
|
register lock_t l;
|
|
{
|
|
|
|
simple_lock(&l->interlock);
|
|
|
|
if (((thread_t) l->thread) == current_thread()) {
|
|
/*
|
|
* Recursive lock
|
|
*/
|
|
l->read_count--;
|
|
l->recursion_depth++;
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
if (l->want_upgrade) {
|
|
simple_unlock(&l->interlock);
|
|
return (FALSE);
|
|
}
|
|
l->want_upgrade = TRUE;
|
|
l->read_count--;
|
|
|
|
while (l->read_count != 0) {
|
|
l->waiting = TRUE;
|
|
thread_sleep((int) l, &l->interlock, FALSE);
|
|
simple_lock(&l->interlock);
|
|
}
|
|
|
|
simple_unlock(&l->interlock);
|
|
return (TRUE);
|
|
}
|
|
|
|
/*
|
|
* Allow a process that has a lock for write to acquire it
|
|
* recursively (for read, write, or update).
|
|
*/
|
|
void
|
|
lock_set_recursive(l)
|
|
lock_t l;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
if (!l->want_write) {
|
|
panic("lock_set_recursive: don't have write lock");
|
|
}
|
|
l->thread = (char *) current_thread();
|
|
simple_unlock(&l->interlock);
|
|
}
|
|
|
|
/*
|
|
* Prevent a lock from being re-acquired.
|
|
*/
|
|
void
|
|
lock_clear_recursive(l)
|
|
lock_t l;
|
|
{
|
|
simple_lock(&l->interlock);
|
|
if (((thread_t) l->thread) != current_thread()) {
|
|
panic("lock_clear_recursive: wrong thread");
|
|
}
|
|
if (l->recursion_depth == 0)
|
|
l->thread = (char *) -1; /* XXX */
|
|
simple_unlock(&l->interlock);
|
|
}
|