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Annotation of driverkit/libDriver/User/NXLock.m, revision 1.1.1.1

1.1       root        1: /*
                      2:  * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
                      3:  *
                      4:  * @APPLE_LICENSE_HEADER_START@
                      5:  * 
                      6:  * Portions Copyright (c) 1999 Apple Computer, Inc.  All Rights
                      7:  * Reserved.  This file contains Original Code and/or Modifications of
                      8:  * Original Code as defined in and that are subject to the Apple Public
                      9:  * Source License Version 1.1 (the "License").  You may not use this file
                     10:  * except in compliance with the License.  Please obtain a copy of the
                     11:  * License at http://www.apple.com/publicsource and read it before using
                     12:  * this file.
                     13:  * 
                     14:  * The Original Code and all software distributed under the License are
                     15:  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
                     16:  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
                     17:  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
                     18:  * FITNESS FOR A PARTICULAR PURPOSE OR NON- INFRINGEMENT.  Please see the
                     19:  * License for the specific language governing rights and limitations
                     20:  * under the License.
                     21:  * 
                     22:  * @APPLE_LICENSE_HEADER_END@
                     23:  */
                     24: /*     Copyright (c) 1991 NeXT Computer, Inc.  All rights reserved. 
                     25:  *
                     26:  * NXLock.m. Standard lock object, user version.
                     27:  *
                     28:  * HISTORY
                     29:  * 01-Aug-91    Doug Mitchell at NeXT
                     30:  *      Created. 
                     31:  */
                     32: 
                     33: #import <machkit/NXLock.h>
                     34: #import <mach/cthreads.h>
                     35: 
                     36: @implementation NXLock 
                     37: 
                     38: /*
                     39:  * _priv instance variable points to one of these.
                     40:  */
                     41: typedef struct {
                     42:        struct mutex            m;
                     43:        struct condition        c;
                     44:        BOOL                    locked;
                     45: } lock_priv_t;
                     46: 
                     47: - init
                     48: {      
                     49:        lock_priv_t *priv;
                     50: 
                     51:        [super init];
                     52:        priv = _priv = malloc(sizeof(lock_priv_t));
                     53:        mutex_init(&priv->m);
                     54:        condition_init(&priv->c);
                     55:        priv->locked = FALSE;
                     56:        return self;
                     57: }
                     58: 
                     59: - free 
                     60: {
                     61:        lock_priv_t *priv = _priv;
                     62: 
                     63:        mutex_clear(&priv->m);
                     64:        condition_clear(&priv->c);
                     65:        free(priv);
                     66:        return [super free];
                     67: }
                     68: 
                     69: - lock 
                     70: {
                     71:        lock_priv_t *priv = _priv;
                     72: 
                     73:        mutex_lock(&priv->m);
                     74:        while(priv->locked)
                     75:                condition_wait(&priv->c, &priv->m);
                     76:        priv->locked = TRUE;
                     77:        mutex_unlock(&priv->m); // allow others to acquire mutex & wait
                     78:        return self;
                     79: }
                     80: 
                     81: /*
                     82:  * acquire the mutex (quickly) and signal anyone in lock code above.
                     83:  * Note that we do not want or need condition_broadcast, since the one 
                     84:  * party to awake will reset locked and cause any other parties to
                     85:  * block in condition_wait again.
                     86:  */
                     87: - unlock 
                     88: {
                     89:        lock_priv_t *priv = _priv;
                     90: 
                     91:        mutex_lock(&priv->m);
                     92:        priv->locked = FALSE;
                     93:        condition_signal(&priv->c);
                     94:        mutex_unlock(&priv->m); // assume that signal delivery occurred
                     95:        return self;
                     96: }
                     97: @end

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