Return to objc-dispatch.c CVS log

Up to [Apple Darwin 0.x] / objc

Annotation of objc/objc-dispatch.c, 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 1.0 (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: /*
        !            25:  *     objc-dispatch.c
        !            26:  *     Copyright 1988, NeXT, Inc.
        !            27:  *     Author: s.naroff & s.stone
        !            28:  *
        !            29:  *     Purpose: Compute implementation for method, and dispatch there,
        !            30:  *              leaving all arguments undisturbed on the stack.
        !            31:  *
        !            32:  *     Implementation:
        !            33:  *
        !            34:  *     - caches are maintained on a `per-class' basis.
        !            35:  *     - caches are allocated dynamically, sized proportional to all the
        !            36:  *     methods that the class can respond to.
        !            37:  *     - cache entries cost 4 bytes each. This saves memory and enables
        !            38:  *     a cache load to be accomplished in an atomic assignment operation,
        !            39:  *     removing the expensive `tas' operation. Because a cache load in the
        !            40:  *     Stepstone messager consisted of 3 assignment operations <cls,sel,imp>   
        !            41:  *     they needed this instruction to enforce concurrency lockouts on 
        !            42:  *     cache slot access. This insured the `integrity' of the cache
        !            43:  *     when sending messages from interrupt handlers. This makes the 
        !            44:  *     dispatcher more portable, considering many machines do not have or
        !            45:  *     support (i.e. apollo) this instruction.
        !            46:  *     - this cache supports collision resolution. Because we can estimate 
        !            47:  *     the number of elements in the cache (and are concerned about data 
        !            48:  *     space overhead), we use a simple open-addressing method called 
        !            49:  *     `linear probing'. If all probes are filled, we replace one of them.
        !            50:  *     In this implementation, the length of a chain will be 8.
        !            51:  *     - _msgSuper DOES NOT depend on retreiving `self' from the previous
        !            52:  *     stack frame.
        !            53:  */
        !            54: 
        !            55: #ifdef SHLIB
        !            56: #import "shlib.h"
        !            57: #endif SHLIB
        !            58: 
        !            59: #include "objc.h"
        !            60: #include "objc-private.h"
        !            61: #include "objc-dispatch.h"
        !            62: extern id (*_objc_msgPreop)(MSG, int, int);
        !            63: 
        !            64: #define JMP(imp) \
        !            65:        /* load function address */ \
        !            66:        asm ("movel %0,a0" : "=m" (imp)); \
        !            67:        /* restore a1...for methods that return > 8 bytes quantities */ \
        !            68:        asm ("movel %0,a1" : "=m" (save_a1)); \
        !            69:        /* unlink stack frame */ \
        !            70:         asm ("unlk a6"); \
        !            71:        /* go to method */ \
        !            72:        asm ("jmp a0@");                 
        !            73: 
        !            74: #if 0
        !            75: /* 
        !            76:  * Implement [anObject aSelector] 
        !            77:  */
        !            78: id objc_msgSend(id self, SEL sel, ...) 
        !            79: { 
        !            80:        Class cls; 
        !            81:        Method *buckets;
        !            82:        int index, mask, i;
        !            83:        IMP imp;
        !            84:        void *save_a1;
        !            85: 
        !            86:        asm ("movel a1,%0" : "=m" (save_a1));
        !            87: 
        !            88:        /* This provides the innocuous semantics for nil messages.
        !            89:         * Changing this to an error would reliably trap messages
        !            90:         * to nil objects.
        !            91:         */
        !            92:        if (self == nil)
        !            93:                return nil;
        !            94: 
        !            95:        cls = self->isa;
        !            96: 
        !            97:        mask = cls->cache->mask;
        !            98:        buckets = cls->cache->buckets;
        !            99: 
        !           100:        index = sel & mask;
        !           101:        for (;;) {
        !           102:            if (buckets[index] && (buckets[index]->method_name == sel))
        !           103:              goto cacheHit;
        !           104:            if (! buckets[index]) goto cacheMiss;
        !           105:            index++;
        !           106:            index &= mask;
        !           107:        }
        !           108: cacheMiss:
        !           109:        imp = _class_lookupMethodAndLoadCache(cls, sel);
        !           110: 
        !           111:        if (_objc_msgPreop)
        !           112:          (*_objc_msgPreop)(GETFRAME(self), NO, NO);
        !           113: 
        !           114:        JMP(imp);
        !           115: 
        !           116: cacheHit:
        !           117:        imp = buckets[index]->method_imp;
        !           118: 
        !           119:        if (_objc_msgPreop)
        !           120:          (*_objc_msgPreop)(GETFRAME(self), NO, YES);
        !           121: 
        !           122:        JMP(imp);
        !           123: }
        !           124: #endif
        !           125: /* 
        !           126:  * Implement [super aSelector] 
        !           127:  */
        !           128: id objc_msgSendSuper(struct objc_super *caller, SEL sel, ...)
        !           129: {
        !           130:        id self; Class cls;
        !           131:        Method *buckets;
        !           132:        int index, mask, i;
        !           133:        IMP imp;
        !           134:        void *save_a1;
        !           135: 
        !           136:        asm ("movel a1,%0" : "=m" (save_a1));
        !           137: 
        !           138:        /* Fetch the caller's value for "self". */
        !           139:        cls = caller->class;
        !           140: 
        !           141:        /* replace `caller' with the real receiver */
        !           142:        caller = (struct objc_super *)self = caller->receiver;
        !           143: 
        !           144:        /* Unlikely, but not impossible */
        !           145:        if (self == nil)
        !           146:                return nil;
        !           147: 
        !           148:        mask = cls->cache->mask;
        !           149:        buckets = cls->cache->buckets;
        !           150: 
        !           151:        index = sel & mask;
        !           152:        for (;;) {
        !           153:            if (buckets[index] && (buckets[index]->method_name == sel))
        !           154:              goto cacheHit;
        !           155:            if (! buckets[index]) goto cacheMiss;
        !           156:            index++;
        !           157:            index &= mask;
        !           158:        }
        !           159: 
        !           160: cacheMiss:
        !           161:        imp = _class_lookupMethodAndLoadCache(cls, sel);
        !           162: 
        !           163:        if (_objc_msgPreop)
        !           164:          (*_objc_msgPreop)(GETFRAME(self), YES, NO);
        !           165: 
        !           166:        JMP(imp);
        !           167: 
        !           168: cacheHit:
        !           169:        imp = buckets[index]->method_imp;
        !           170: 
        !           171:        if (_objc_msgPreop)
        !           172:          (*_objc_msgPreop)(GETFRAME(self), YES, YES);
        !           173: 
        !           174:        JMP(imp);
        !           175: }
        !           176: 

This archive runs on limited infrastructure. Preserving old code on modern bandwidth. Automated agents are requested to crawl responsibly.