238 lines
9.2 KiB
Objective-C
238 lines
9.2 KiB
Objective-C
// Protocol Buffers - Google's data interchange format
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// Copyright 2008 Google Inc. All rights reserved.
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// https://developers.google.com/protocol-buffers/
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#import "GPBRootObject_PackagePrivate.h"
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#import <objc/runtime.h>
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#import <CoreFoundation/CoreFoundation.h>
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#import "GPBDescriptor.h"
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#import "GPBExtensionRegistry.h"
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#import "GPBUtilities_PackagePrivate.h"
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@interface GPBExtensionDescriptor (GPBRootObject)
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// Get singletonName as a c string.
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- (const char *)singletonNameC;
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@end
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@implementation GPBRootObject
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// Taken from http://www.burtleburtle.net/bob/hash/doobs.html
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// Public Domain
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static uint32_t jenkins_one_at_a_time_hash(const char *key) {
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uint32_t hash = 0;
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for (uint32_t i = 0; key[i] != '\0'; ++i) {
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hash += key[i];
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hash += (hash << 10);
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hash ^= (hash >> 6);
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}
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hash += (hash << 3);
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hash ^= (hash >> 11);
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hash += (hash << 15);
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return hash;
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}
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// Key methods for our custom CFDictionary.
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// Note that the dictionary lasts for the lifetime of our app, so no need
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// to worry about deallocation. All of the items are added to it at
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// startup, and so the keys don't need to be retained/released.
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// Keys are NULL terminated char *.
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static const void *GPBRootExtensionKeyRetain(CFAllocatorRef allocator,
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const void *value) {
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#pragma unused(allocator)
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return value;
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}
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static void GPBRootExtensionKeyRelease(CFAllocatorRef allocator,
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const void *value) {
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#pragma unused(allocator)
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#pragma unused(value)
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}
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static CFStringRef GPBRootExtensionCopyKeyDescription(const void *value) {
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const char *key = (const char *)value;
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return CFStringCreateWithCString(kCFAllocatorDefault, key,
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kCFStringEncodingUTF8);
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}
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static Boolean GPBRootExtensionKeyEqual(const void *value1,
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const void *value2) {
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const char *key1 = (const char *)value1;
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const char *key2 = (const char *)value2;
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return strcmp(key1, key2) == 0;
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}
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static CFHashCode GPBRootExtensionKeyHash(const void *value) {
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const char *key = (const char *)value;
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return jenkins_one_at_a_time_hash(key);
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}
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// NOTE: OSSpinLock may seem like a good fit here but Apple engineers have
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// pointed out that they are vulnerable to live locking on iOS in cases of
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// priority inversion:
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// http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
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// https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html
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static dispatch_semaphore_t gExtensionSingletonDictionarySemaphore;
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static CFMutableDictionaryRef gExtensionSingletonDictionary = NULL;
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static GPBExtensionRegistry *gDefaultExtensionRegistry = NULL;
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+ (void)initialize {
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// Ensure the global is started up.
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if (!gExtensionSingletonDictionary) {
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gExtensionSingletonDictionarySemaphore = dispatch_semaphore_create(1);
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CFDictionaryKeyCallBacks keyCallBacks = {
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// See description above for reason for using custom dictionary.
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0,
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GPBRootExtensionKeyRetain,
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GPBRootExtensionKeyRelease,
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GPBRootExtensionCopyKeyDescription,
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GPBRootExtensionKeyEqual,
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GPBRootExtensionKeyHash,
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};
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gExtensionSingletonDictionary =
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CFDictionaryCreateMutable(kCFAllocatorDefault, 0, &keyCallBacks,
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&kCFTypeDictionaryValueCallBacks);
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gDefaultExtensionRegistry = [[GPBExtensionRegistry alloc] init];
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}
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if ([self superclass] == [GPBRootObject class]) {
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// This is here to start up all the per file "Root" subclasses.
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// This must be done in initialize to enforce thread safety of start up of
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// the protocol buffer library.
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[self extensionRegistry];
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}
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}
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+ (GPBExtensionRegistry *)extensionRegistry {
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// Is overridden in all the subclasses that provide extensions to provide the
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// per class one.
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return gDefaultExtensionRegistry;
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}
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+ (void)globallyRegisterExtension:(GPBExtensionDescriptor *)field {
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const char *key = [field singletonNameC];
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dispatch_semaphore_wait(gExtensionSingletonDictionarySemaphore,
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DISPATCH_TIME_FOREVER);
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CFDictionarySetValue(gExtensionSingletonDictionary, key, field);
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dispatch_semaphore_signal(gExtensionSingletonDictionarySemaphore);
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}
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static id ExtensionForName(id self, SEL _cmd) {
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// Really fast way of doing "classname_selName".
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// This came up as a hotspot (creation of NSString *) when accessing a
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// lot of extensions.
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const char *selName = sel_getName(_cmd);
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if (selName[0] == '_') {
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return nil; // Apple internal selector.
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}
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size_t selNameLen = 0;
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while (1) {
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char c = selName[selNameLen];
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if (c == '\0') { // String end.
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break;
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}
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if (c == ':') {
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return nil; // Selector took an arg, not one of the runtime methods.
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}
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++selNameLen;
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}
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const char *className = class_getName(self);
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size_t classNameLen = strlen(className);
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char key[classNameLen + selNameLen + 2];
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memcpy(key, className, classNameLen);
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key[classNameLen] = '_';
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memcpy(&key[classNameLen + 1], selName, selNameLen);
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key[classNameLen + 1 + selNameLen] = '\0';
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// NOTE: Even though this method is called from another C function,
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// gExtensionSingletonDictionarySemaphore and gExtensionSingletonDictionary
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// will always be initialized. This is because this call flow is just to
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// lookup the Extension, meaning the code is calling an Extension class
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// message on a Message or Root class. This guarantees that the class was
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// initialized and Message classes ensure their Root was also initialized.
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NSAssert(gExtensionSingletonDictionary, @"Startup order broken!");
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dispatch_semaphore_wait(gExtensionSingletonDictionarySemaphore,
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DISPATCH_TIME_FOREVER);
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id extension = (id)CFDictionaryGetValue(gExtensionSingletonDictionary, key);
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// We can't remove the key from the dictionary here (as an optimization),
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// two threads could have gone into +resolveClassMethod: for the same method,
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// and ended up here; there's no way to ensure both return YES without letting
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// both try to wire in the method.
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dispatch_semaphore_signal(gExtensionSingletonDictionarySemaphore);
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return extension;
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}
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BOOL GPBResolveExtensionClassMethod(Class self, SEL sel) {
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// Another option would be to register the extensions with the class at
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// globallyRegisterExtension:
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// Timing the two solutions, this solution turned out to be much faster
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// and reduced startup time, and runtime memory.
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// The advantage to globallyRegisterExtension is that it would reduce the
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// size of the protos somewhat because the singletonNameC wouldn't need
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// to include the class name. For a class with a lot of extensions it
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// can add up. You could also significantly reduce the code complexity of this
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// file.
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id extension = ExtensionForName(self, sel);
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if (extension != nil) {
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const char *encoding =
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GPBMessageEncodingForSelector(@selector(getClassValue), NO);
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Class metaClass = objc_getMetaClass(class_getName(self));
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IMP imp = imp_implementationWithBlock(^(id obj) {
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#pragma unused(obj)
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return extension;
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});
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BOOL methodAdded = class_addMethod(metaClass, sel, imp, encoding);
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// class_addMethod() is documented as also failing if the method was already
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// added; so we check if the method is already there and return success so
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// the method dispatch will still happen. Why would it already be added?
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// Two threads could cause the same method to be bound at the same time,
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// but only one will actually bind it; the other still needs to return true
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// so things will dispatch.
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if (!methodAdded) {
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methodAdded = GPBClassHasSel(metaClass, sel);
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}
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return methodAdded;
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}
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return NO;
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}
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+ (BOOL)resolveClassMethod:(SEL)sel {
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if (GPBResolveExtensionClassMethod(self, sel)) {
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return YES;
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}
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return [super resolveClassMethod:sel];
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}
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@end
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