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