704 lines
20 KiB
C
704 lines
20 KiB
C
/* GNU Objective C Runtime class related functions
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Copyright (C) 1993, 1995, 1996, 1997, 2001, 2002
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Free Software Foundation, Inc.
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Contributed by Kresten Krab Thorup and Dennis Glatting.
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Lock-free class table code designed and written from scratch by
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Nicola Pero, 2001.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under the
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terms of the GNU General Public License as published by the Free Software
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Foundation; either version 2, or (at your option) any later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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details.
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You should have received a copy of the GNU General Public License along with
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GCC; see the file COPYING. If not, write to the Free Software
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Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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/* As a special exception, if you link this library with files compiled with
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GCC to produce an executable, this does not cause the resulting executable
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to be covered by the GNU General Public License. This exception does not
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however invalidate any other reasons why the executable file might be
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covered by the GNU General Public License. */
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/*
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The code in this file critically affects class method invocation
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speed. This long preamble comment explains why, and the issues
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involved.
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One of the traditional weaknesses of the GNU Objective-C runtime is
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that class method invocations are slow. The reason is that when you
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write
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array = [NSArray new];
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this gets basically compiled into the equivalent of
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array = [(objc_get_class ("NSArray")) new];
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objc_get_class returns the class pointer corresponding to the string
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`NSArray'; and because of the lookup, the operation is more
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complicated and slow than a simple instance method invocation.
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Most high performance Objective-C code (using the GNU Objc runtime)
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I had the opportunity to read (or write) work around this problem by
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caching the class pointer:
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Class arrayClass = [NSArray class];
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... later on ...
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array = [arrayClass new];
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array = [arrayClass new];
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array = [arrayClass new];
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In this case, you always perform a class lookup (the first one), but
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then all the [arrayClass new] methods run exactly as fast as an
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instance method invocation. It helps if you have many class method
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invocations to the same class.
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The long-term solution to this problem would be to modify the
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compiler to output tables of class pointers corresponding to all the
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class method invocations, and to add code to the runtime to update
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these tables - that should in the end allow class method invocations
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to perform precisely as fast as instance method invocations, because
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no class lookup would be involved. I think the Apple Objective-C
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runtime uses this technique. Doing this involves synchronized
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modifications in the runtime and in the compiler.
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As a first medicine to the problem, I [NP] have redesigned and
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rewritten the way the runtime is performing class lookup. This
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doesn't give as much speed as the other (definitive) approach, but
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at least a class method invocation now takes approximately 4.5 times
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an instance method invocation on my machine (it would take approx 12
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times before the rewriting), which is a lot better.
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One of the main reason the new class lookup is so faster is because
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I implemented it in a way that can safely run multithreaded without
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using locks - a so-called `lock-free' data structure. The atomic
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operation is pointer assignment. The reason why in this problem
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lock-free data structures work so well is that you never remove
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classes from the table - and the difficult thing with lock-free data
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structures is freeing data when is removed from the structures. */
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#include "objc/runtime.h" /* the kitchen sink */
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#include "objc/sarray.h"
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#include "objc/objc.h"
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#include "objc/objc-api.h"
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#include "objc/thr.h"
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/* We use a table which maps a class name to the corresponding class
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* pointer. The first part of this file defines this table, and
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* functions to do basic operations on the table. The second part of
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* the file implements some higher level Objective-C functionality for
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* classes by using the functions provided in the first part to manage
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* the table. */
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/**
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** Class Table Internals
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**/
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/* A node holding a class */
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typedef struct class_node
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{
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struct class_node *next; /* Pointer to next entry on the list.
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NULL indicates end of list. */
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const char *name; /* The class name string */
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int length; /* The class name string length */
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Class pointer; /* The Class pointer */
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} *class_node_ptr;
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/* A table containing classes is a class_node_ptr (pointing to the
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first entry in the table - if it is NULL, then the table is
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empty). */
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/* We have 1024 tables. Each table contains all class names which
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have the same hash (which is a number between 0 and 1023). To look
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up a class_name, we compute its hash, and get the corresponding
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table. Once we have the table, we simply compare strings directly
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till we find the one which we want (using the length first). The
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number of tables is quite big on purpose (a normal big application
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has less than 1000 classes), so that you shouldn't normally get any
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collisions, and get away with a single comparison (which we can't
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avoid since we need to know that you have got the right thing). */
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#define CLASS_TABLE_SIZE 1024
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#define CLASS_TABLE_MASK 1023
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static class_node_ptr class_table_array[CLASS_TABLE_SIZE];
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/* The table writing mutex - we lock on writing to avoid conflicts
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between different writers, but we read without locks. That is
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possible because we assume pointer assignment to be an atomic
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operation. */
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static objc_mutex_t __class_table_lock = NULL;
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/* CLASS_TABLE_HASH is how we compute the hash of a class name. It is
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a macro - *not* a function - arguments *are* modified directly.
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INDEX should be a variable holding an int;
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HASH should be a variable holding an int;
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CLASS_NAME should be a variable holding a (char *) to the class_name.
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After the macro is executed, INDEX contains the length of the
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string, and HASH the computed hash of the string; CLASS_NAME is
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untouched. */
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#define CLASS_TABLE_HASH(INDEX, HASH, CLASS_NAME) \
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HASH = 0; \
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for (INDEX = 0; CLASS_NAME[INDEX] != '\0'; INDEX++) \
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{ \
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HASH = (HASH << 4) ^ (HASH >> 28) ^ CLASS_NAME[INDEX]; \
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} \
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\
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HASH = (HASH ^ (HASH >> 10) ^ (HASH >> 20)) & CLASS_TABLE_MASK;
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/* Setup the table. */
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static void
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class_table_setup (void)
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{
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/* Start - nothing in the table. */
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memset (class_table_array, 0, sizeof (class_node_ptr) * CLASS_TABLE_SIZE);
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/* The table writing mutex. */
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__class_table_lock = objc_mutex_allocate ();
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}
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/* Insert a class in the table (used when a new class is registered). */
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static void
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class_table_insert (const char *class_name, Class class_pointer)
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{
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int hash, length;
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class_node_ptr new_node;
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/* Find out the class name's hash and length. */
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CLASS_TABLE_HASH (length, hash, class_name);
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/* Prepare the new node holding the class. */
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new_node = objc_malloc (sizeof (struct class_node));
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new_node->name = class_name;
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new_node->length = length;
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new_node->pointer = class_pointer;
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/* Lock the table for modifications. */
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objc_mutex_lock (__class_table_lock);
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/* Insert the new node in the table at the beginning of the table at
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class_table_array[hash]. */
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new_node->next = class_table_array[hash];
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class_table_array[hash] = new_node;
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objc_mutex_unlock (__class_table_lock);
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}
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/* Replace a class in the table (used only by poseAs:). */
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static void
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class_table_replace (Class old_class_pointer, Class new_class_pointer)
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{
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int hash;
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class_node_ptr node;
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objc_mutex_lock (__class_table_lock);
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hash = 0;
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node = class_table_array[hash];
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while (hash < CLASS_TABLE_SIZE)
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{
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if (node == NULL)
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{
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hash++;
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if (hash < CLASS_TABLE_SIZE)
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{
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node = class_table_array[hash];
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}
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}
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else
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{
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Class class1 = node->pointer;
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if (class1 == old_class_pointer)
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{
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node->pointer = new_class_pointer;
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}
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node = node->next;
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}
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}
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objc_mutex_unlock (__class_table_lock);
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}
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/* Get a class from the table. This does not need mutex protection.
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Currently, this function is called each time you call a static
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method, this is why it must be very fast. */
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static inline Class
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class_table_get_safe (const char *class_name)
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{
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class_node_ptr node;
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int length, hash;
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/* Compute length and hash. */
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CLASS_TABLE_HASH (length, hash, class_name);
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node = class_table_array[hash];
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if (node != NULL)
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{
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do
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{
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if (node->length == length)
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{
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/* Compare the class names. */
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int i;
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for (i = 0; i < length; i++)
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{
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if ((node->name)[i] != class_name[i])
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{
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break;
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}
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}
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if (i == length)
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{
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/* They are equal! */
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return node->pointer;
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}
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}
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}
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while ((node = node->next) != NULL);
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}
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return Nil;
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}
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/* Enumerate over the class table. */
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struct class_table_enumerator
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{
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int hash;
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class_node_ptr node;
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};
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static Class
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class_table_next (struct class_table_enumerator **e)
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{
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struct class_table_enumerator *enumerator = *e;
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class_node_ptr next;
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if (enumerator == NULL)
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{
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*e = objc_malloc (sizeof (struct class_table_enumerator));
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enumerator = *e;
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enumerator->hash = 0;
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enumerator->node = NULL;
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next = class_table_array[enumerator->hash];
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}
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else
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{
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next = enumerator->node->next;
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}
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if (next != NULL)
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{
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enumerator->node = next;
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return enumerator->node->pointer;
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}
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else
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{
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enumerator->hash++;
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while (enumerator->hash < CLASS_TABLE_SIZE)
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{
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next = class_table_array[enumerator->hash];
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if (next != NULL)
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{
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enumerator->node = next;
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return enumerator->node->pointer;
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}
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enumerator->hash++;
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}
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/* Ok - table finished - done. */
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objc_free (enumerator);
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return Nil;
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}
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}
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#if 0 /* DEBUGGING FUNCTIONS */
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/* Debugging function - print the class table. */
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void
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class_table_print (void)
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{
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int i;
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for (i = 0; i < CLASS_TABLE_SIZE; i++)
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{
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class_node_ptr node;
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printf ("%d:\n", i);
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node = class_table_array[i];
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while (node != NULL)
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{
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printf ("\t%s\n", node->name);
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node = node->next;
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}
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}
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}
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/* Debugging function - print an histogram of number of classes in
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function of hash key values. Useful to evaluate the hash function
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in real cases. */
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void
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class_table_print_histogram (void)
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{
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int i, j;
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int counter = 0;
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for (i = 0; i < CLASS_TABLE_SIZE; i++)
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{
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class_node_ptr node;
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node = class_table_array[i];
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while (node != NULL)
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{
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counter++;
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node = node->next;
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}
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if (((i + 1) % 50) == 0)
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{
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printf ("%4d:", i + 1);
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for (j = 0; j < counter; j++)
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{
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printf ("X");
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}
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printf ("\n");
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counter = 0;
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}
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}
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printf ("%4d:", i + 1);
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for (j = 0; j < counter; j++)
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{
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printf ("X");
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}
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printf ("\n");
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}
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#endif /* DEBUGGING FUNCTIONS */
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/**
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** Objective-C runtime functions
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**/
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/* From now on, the only access to the class table data structure
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should be via the class_table_* functions. */
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/* This is a hook which is called by objc_get_class and
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objc_lookup_class if the runtime is not able to find the class.
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This may e.g. try to load in the class using dynamic loading. */
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Class (*_objc_lookup_class) (const char *name) = 0; /* !T:SAFE */
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/* True when class links has been resolved. */
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BOOL __objc_class_links_resolved = NO; /* !T:UNUSED */
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void
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__objc_init_class_tables (void)
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{
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/* Allocate the class hash table. */
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if (__class_table_lock)
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return;
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objc_mutex_lock (__objc_runtime_mutex);
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class_table_setup ();
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objc_mutex_unlock (__objc_runtime_mutex);
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}
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/* This function adds a class to the class hash table, and assigns the
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class a number, unless it's already known. */
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void
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__objc_add_class_to_hash (Class class)
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{
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Class h_class;
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objc_mutex_lock (__objc_runtime_mutex);
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/* Make sure the table is there. */
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assert (__class_table_lock);
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/* Make sure it's not a meta class. */
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assert (CLS_ISCLASS (class));
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/* Check to see if the class is already in the hash table. */
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h_class = class_table_get_safe (class->name);
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if (! h_class)
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{
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/* The class isn't in the hash table. Add the class and assign a class
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number. */
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static unsigned int class_number = 1;
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CLS_SETNUMBER (class, class_number);
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CLS_SETNUMBER (class->class_pointer, class_number);
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++class_number;
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class_table_insert (class->name, class);
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}
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objc_mutex_unlock (__objc_runtime_mutex);
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}
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/* Get the class object for the class named NAME. If NAME does not
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identify a known class, the hook _objc_lookup_class is called. If
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this fails, nil is returned. */
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Class
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objc_lookup_class (const char *name)
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{
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Class class;
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class = class_table_get_safe (name);
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if (class)
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return class;
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if (_objc_lookup_class)
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return (*_objc_lookup_class) (name);
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else
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return 0;
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}
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/* Get the class object for the class named NAME. If NAME does not
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identify a known class, the hook _objc_lookup_class is called. If
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this fails, an error message is issued and the system aborts. */
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Class
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objc_get_class (const char *name)
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{
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Class class;
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class = class_table_get_safe (name);
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if (class)
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return class;
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if (_objc_lookup_class)
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class = (*_objc_lookup_class) (name);
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if (class)
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return class;
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objc_error (nil, OBJC_ERR_BAD_CLASS,
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"objc runtime: cannot find class %s\n", name);
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return 0;
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}
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MetaClass
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objc_get_meta_class (const char *name)
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{
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return objc_get_class (name)->class_pointer;
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}
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/* This function provides a way to enumerate all the classes in the
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executable. Pass *ENUM_STATE == NULL to start the enumeration. The
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function will return 0 when there are no more classes.
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For example:
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id class;
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void *es = NULL;
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while ((class = objc_next_class (&es)))
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... do something with class;
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*/
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Class
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objc_next_class (void **enum_state)
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{
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Class class;
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objc_mutex_lock (__objc_runtime_mutex);
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/* Make sure the table is there. */
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assert (__class_table_lock);
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class = class_table_next ((struct class_table_enumerator **) enum_state);
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objc_mutex_unlock (__objc_runtime_mutex);
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return class;
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}
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/* Resolve super/subclass links for all classes. The only thing we
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can be sure of is that the class_pointer for class objects point to
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the right meta class objects. */
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void
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__objc_resolve_class_links (void)
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{
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struct class_table_enumerator *es = NULL;
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Class object_class = objc_get_class ("Object");
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Class class1;
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assert (object_class);
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objc_mutex_lock (__objc_runtime_mutex);
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/* Assign subclass links. */
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while ((class1 = class_table_next (&es)))
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{
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/* Make sure we have what we think we have. */
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assert (CLS_ISCLASS (class1));
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assert (CLS_ISMETA (class1->class_pointer));
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/* The class_pointer of all meta classes point to Object's meta
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class. */
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class1->class_pointer->class_pointer = object_class->class_pointer;
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if (! CLS_ISRESOLV (class1))
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{
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CLS_SETRESOLV (class1);
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CLS_SETRESOLV (class1->class_pointer);
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|
|
if (class1->super_class)
|
|
{
|
|
Class a_super_class
|
|
= objc_get_class ((char *) class1->super_class);
|
|
|
|
assert (a_super_class);
|
|
|
|
DEBUG_PRINTF ("making class connections for: %s\n",
|
|
class1->name);
|
|
|
|
/* Assign subclass links for superclass. */
|
|
class1->sibling_class = a_super_class->subclass_list;
|
|
a_super_class->subclass_list = class1;
|
|
|
|
/* Assign subclass links for meta class of superclass. */
|
|
if (a_super_class->class_pointer)
|
|
{
|
|
class1->class_pointer->sibling_class
|
|
= a_super_class->class_pointer->subclass_list;
|
|
a_super_class->class_pointer->subclass_list
|
|
= class1->class_pointer;
|
|
}
|
|
}
|
|
else /* A root class, make its meta object be a subclass of
|
|
Object. */
|
|
{
|
|
class1->class_pointer->sibling_class
|
|
= object_class->subclass_list;
|
|
object_class->subclass_list = class1->class_pointer;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Assign superclass links. */
|
|
es = NULL;
|
|
while ((class1 = class_table_next (&es)))
|
|
{
|
|
Class sub_class;
|
|
for (sub_class = class1->subclass_list; sub_class;
|
|
sub_class = sub_class->sibling_class)
|
|
{
|
|
sub_class->super_class = class1;
|
|
if (CLS_ISCLASS (sub_class))
|
|
sub_class->class_pointer->super_class = class1->class_pointer;
|
|
}
|
|
}
|
|
|
|
objc_mutex_unlock (__objc_runtime_mutex);
|
|
}
|
|
|
|
|
|
|
|
#define CLASSOF(c) ((c)->class_pointer)
|
|
|
|
Class
|
|
class_pose_as (Class impostor, Class super_class)
|
|
{
|
|
if (! CLS_ISRESOLV (impostor))
|
|
__objc_resolve_class_links ();
|
|
|
|
/* Preconditions */
|
|
assert (impostor);
|
|
assert (super_class);
|
|
assert (impostor->super_class == super_class);
|
|
assert (CLS_ISCLASS (impostor));
|
|
assert (CLS_ISCLASS (super_class));
|
|
assert (impostor->instance_size == super_class->instance_size);
|
|
|
|
{
|
|
Class *subclass = &(super_class->subclass_list);
|
|
|
|
/* Move subclasses of super_class to impostor. */
|
|
while (*subclass)
|
|
{
|
|
Class nextSub = (*subclass)->sibling_class;
|
|
|
|
if (*subclass != impostor)
|
|
{
|
|
Class sub = *subclass;
|
|
|
|
/* Classes */
|
|
sub->sibling_class = impostor->subclass_list;
|
|
sub->super_class = impostor;
|
|
impostor->subclass_list = sub;
|
|
|
|
/* It will happen that SUB is not a class object if it is
|
|
the top of the meta class hierarchy chain (root
|
|
meta-class objects inherit their class object). If
|
|
that is the case... don't mess with the meta-meta
|
|
class. */
|
|
if (CLS_ISCLASS (sub))
|
|
{
|
|
/* Meta classes */
|
|
CLASSOF (sub)->sibling_class =
|
|
CLASSOF (impostor)->subclass_list;
|
|
CLASSOF (sub)->super_class = CLASSOF (impostor);
|
|
CLASSOF (impostor)->subclass_list = CLASSOF (sub);
|
|
}
|
|
}
|
|
|
|
*subclass = nextSub;
|
|
}
|
|
|
|
/* Set subclasses of superclass to be impostor only. */
|
|
super_class->subclass_list = impostor;
|
|
CLASSOF (super_class)->subclass_list = CLASSOF (impostor);
|
|
|
|
/* Set impostor to have no sibling classes. */
|
|
impostor->sibling_class = 0;
|
|
CLASSOF (impostor)->sibling_class = 0;
|
|
}
|
|
|
|
/* Check relationship of impostor and super_class is kept. */
|
|
assert (impostor->super_class == super_class);
|
|
assert (CLASSOF (impostor)->super_class == CLASSOF (super_class));
|
|
|
|
/* This is how to update the lookup table. Regardless of what the
|
|
keys of the hashtable is, change all values that are superclass
|
|
into impostor. */
|
|
|
|
objc_mutex_lock (__objc_runtime_mutex);
|
|
|
|
class_table_replace (super_class, impostor);
|
|
|
|
objc_mutex_unlock (__objc_runtime_mutex);
|
|
|
|
/* Next, we update the dispatch tables... */
|
|
__objc_update_dispatch_table_for_class (CLASSOF (impostor));
|
|
__objc_update_dispatch_table_for_class (impostor);
|
|
|
|
return impostor;
|
|
}
|