本章内容
- objc初始化的时候都做了什么
- map_images的分析
- load_images的分析
本章目的
了解从dyld到objc后,objc都做了什么,此过程也是pre-main的过程。我们已经从dyld的加载过程知道了objc最关键的两个函数执行。但是不清楚这两个函数具体的内容是什么。本章中最主要的需要了解map_images函数
objc_init源码 分析
该方法可以算是objc的开始地方, 里面包含了各种初始化。以及沟通dyld的执行回调。请看源码注释,先了解大概,然后一个一个方法进行剖析,只分析前面几个就行了,其他都不怎么重要
void _objc_init(void)
{
// 保证初始化方法只执行一次
static bool initialized = false;
if (initialized) return;
initialized = true;
// fixme defer initialization until an objc-using image is found?
// 读取影响运行时的环境变量,例如,我们可以根据这个方法打印出那些关键key
environ_init();
// 关于线程key的锁定,tls(thread_local_storage)。例如,每个线程数据的析构函数
tls_init();
// 运行c++静态构造函数。在dyld调用之前,objc自己调用其构造函数
static_init();
// 运行时环境初始化,主要是建表
runtime_init();
// 异常处理初始化
exception_init();
#if __OBJC2__
// 缓存条件初始化
cache_t::init();
#endif
// 启动回调机制,通常不做什么,因为所有初始化都是惰性的
// 但对于某些进程,我们要立马加载trampoline dylib
_imp_implementationWithBlock_init();
// 注册dyld与objc的通知,&map_images,加一个&符号是代表同步进行
// map_images是很耗时的操作,而映射镜像是很重要的必须保证dyld与objc的函数指针同步
_dyld_objc_notify_register(&map_images, load_images, unmap_image);
#if __OBJC2__
didCallDyldNotifyRegister = true;
#endif
}
environ_init 分析
源码就不再发出来,有兴趣自行查看,在这个方法我们可以打印出相关的环境变量。用于控制台输出,设置方式如下:Edit Scheme
-> Run
-> Arguments
-> Environment Variables
。
至于打印其影响环境变量的方式有两种:
- 运行源码环境,并且把这个代码的条件语句删除。
2. 终端输入export OBJC_HELP=1
举例说明
例如关键字OBJC_PRINT_LOAD_METHODS
效果就是打印出所有的load方法,或者OBJC_PRINT_INITIALIZE_METHODS
是打印initialize方法,你只要按照上面的进行查看就会有其备注
tls_init 分析
这个方法,没什么看的,源码就是根据条件语句执行一个方法而已,pthread_key_init_np
就是为了TLS_DIRECT_KEY
设置析构函数。我们不必关心这个函数,或许以后会说关于tls的内容,但不是现在
void tls_init(void)
{
// 其实就是走这个方法,看宏定义是存在 __PTK_FRAMEWORK_OBJC_KEY0这个key的
#if SUPPORT_DIRECT_THREAD_KEYS
pthread_key_init_np(TLS_DIRECT_KEY, &_objc_pthread_destroyspecific);
#else
_objc_pthread_key = tls_create(&_objc_pthread_destroyspecific);
#endif
}
static_init 分析
苹果给我们的这个函数的注释是:运行c++静态构造函数,libc在dyld调用静态构造函数之前调用_objc_init(),所以我们必须自己做。
而从objc源码调试的时候也已经证明了一个顺序,c++函数是在load方法之前调用的。注意,我说的意思C++构造函数是在objc源码中,如果说是我们实际开发的时候是不可能写在源码中的。所以实际开发中顺序是先load调用再是c++(此时的c++是dyld发起的)例如:
其结果是
runtime_init 分析
这是运行时做准备,也就是运行时的初始化。我们都知道runtime维护了几张表,其中这个初始化就是表的创建。其本质都是类ExplicitInit
。这只是其中两张表,类表(全局的所有已加载或未加载的类)没有在这里创建
void runtime_init(void)
{
// 创建分类的表
objc::unattachedCategories.init(32);
// 创建已分配的类、元类的表
objc::allocatedClasses.init();
}
map_images 镜像文件加载分析
这个函数为什么这么重要,我们知道,编译时(1. LLVM去分配mach-o的东西,其中包括ro的数据分配,这些跟我们没什么关系,因为ro是已经加载好的数据不能够更改存放在磁盘中)我们就已经确定了我们项目工程里面创建的类,方法等等内存大小且分配好地址(其实不完全正确,因为当有load方法的时候就有可能打破这种格局,在类的加载里面会描述)在mach-o里面了。启动后dyld(2. 将mach-o的文件去加载,可以看上一篇内容)去链接镜像文件,初始化主程序等等内容并去勾起objc的初始化。而在这个函数中,又做了什么,需要看源码去研究。我们直接看函数map_images_nolock
,因为map_images就是去调用它,其实map_images_nolock也不怎么重要
map_images_nolock
了解一下,去创建了几张表,一个是关联对象的表初始化,一个是散列表(用来存储引用计数、弱引用,相当于包含了,引用计数表,和弱引用表)初始化,AutoreleasePoolPage表初始化(这几张表是runtime去维护的),当然后面也会创建一个类表。这个函数其实不怎么重要,真正重要的就是_read_images
函数,这个函数你也可以当做中间过渡流程。下面的源码,我能备注的都备注,你不需要了解这个函数的任何东西,么意义
void map_images_nolock(unsigned mhCount, const char * const mhPaths[], const struct mach_header * const mhdrs[])
{
// 第一次进来,一直到镜像文件被读取才行
static bool firstTime = YES;
header_info *hList[mhCount];
// 这个是所有mach-o里面我们项目中的镜像文件的数量
uint32_t hCount;
//下面代码就是统计mach-o里面的各种数量,sel,message等等
size_t selrefCount = 0;
// Perform first-time initialization if necessary.
// This function is called before ordinary library initializers.
// fixme defer initialization until an objc-using image is found?
if (firstTime) {
//做了一些初始化,我们记得共享缓存那些东西,它里面就是获取共享缓存占用的内存区域然后做了一些操作,也搞了一些我们上面介绍过的环境变量等等去进行控制,对我们没什么意义
preopt_init();
}
//这个也是环境变量,如果我们设置的话就会打印一些东西,像这种我不再备注
if (PrintImages) {
_objc_inform("IMAGES: processing %u newly-mapped images...\n", mhCount);
}
// Find all images with Objective-C metadata.
hCount = 0;
// Count classes. Size various table based on the total.
int totalClasses = 0;
int unoptimizedTotalClasses = 0;
{
uint32_t i = mhCount;
while (i--) {
//你可以理解为mach-o的header,也就是头,都是通过这样方式访问mach-o
const headerType *mhdr = (const headerType *)mhdrs[i];
auto hi = addHeader(mhdr, mhPaths[i], totalClasses, unoptimizedTotalClasses);
if (!hi) {
// no objc data in this entry
continue;
}
if (mhdr->filetype == MH_EXECUTE) {
// Size some data structures based on main executable's size
#if __OBJC2__
// If dyld3 optimized the main executable, then there shouldn't
// be any selrefs needed in the dynamic map so we can just init
// to a 0 sized map
// 这里不重要,就是看看mach-o里面有没有选择器
if ( !hi->hasPreoptimizedSelectors() ) {
size_t count;
_getObjc2SelectorRefs(hi, &count);
selrefCount += count;
_getObjc2MessageRefs(hi, &count);
selrefCount += count;
}
#else
_getObjcSelectorRefs(hi, &selrefCount);
#endif
#if SUPPORT_GC_COMPAT
// Halt if this is a GC app.
if (shouldRejectGCApp(hi)) {
_objc_fatal_with_reason
(OBJC_EXIT_REASON_GC_NOT_SUPPORTED,
OS_REASON_FLAG_CONSISTENT_FAILURE,
"Objective-C garbage collection "
"is no longer supported.");
}
#endif
}
hList[hCount++] = hi;
if (PrintImages) {
_objc_inform("IMAGES: loading image for %s%s%s%s%s\n",
hi->fname(),
mhdr->filetype == MH_BUNDLE ? " (bundle)" : "",
hi->info()->isReplacement() ? " (replacement)" : "",
hi->info()->hasCategoryClassProperties() ? " (has class properties)" : "",
hi->info()->optimizedByDyld()?" (preoptimized)":"");
}
}
}
// Perform one-time runtime initialization that must be deferred until
// the executable itself is found. This needs to be done before
// further initialization.
// (The executable may not be present in this infoList if the
// executable does not contain Objective-C code but Objective-C
// is dynamically loaded later.
//不重要,不需要了解,照着备注看看就行
//执行一次性的运行时初始化,该初始化必须延迟到找到可执行文件本身。这需要在进一步初始化之前完成。(如果可执行文件不包含Objective-C代码,但是Objective-C稍后会动态加载,那么这个可执行文件可能不会出现在这个infoList中。
if (firstTime) {
sel_init(selrefCount);
// 建表的函数
arr_init();
#if SUPPORT_GC_COMPAT
// Reject any GC images linked to the main executable.
// We already rejected the app itself above.
// Images loaded after launch will be rejected by dyld.
for (uint32_t i = 0; i < hCount; i++) {
auto hi = hList[i];
auto mh = hi->mhdr();
if (mh->filetype != MH_EXECUTE && shouldRejectGCImage(mh)) {
_objc_fatal_with_reason
(OBJC_EXIT_REASON_GC_NOT_SUPPORTED,
OS_REASON_FLAG_CONSISTENT_FAILURE,
"%s requires Objective-C garbage collection "
"which is no longer supported.", hi->fname());
}
}
#endif
#if TARGET_OS_OSX
// Disable +initialize fork safety if the app is too old (< 10.13).
// Disable +initialize fork safety if the app has a
// __DATA,__objc_fork_ok section.
// if(!dyld_program_sdk_at_least(dyld_platform_version_macOS_10_13)) {
// DisableInitializeForkSafety = true;
// if (PrintInitializing) {
// _objc_inform("INITIALIZE: disabling +initialize fork "
// "safety enforcement because the app is "
// "too old.)");
// }
// }
for (uint32_t i = 0; i < hCount; i++) {
auto hi = hList[i];
auto mh = hi->mhdr();
if (mh->filetype != MH_EXECUTE) continue;
unsigned long size;
if (getsectiondata(hi->mhdr(), "__DATA", "__objc_fork_ok", &size)) {
DisableInitializeForkSafety = true;
if (PrintInitializing) {
_objc_inform("INITIALIZE: disabling +initialize fork "
"safety enforcement because the app has "
"a __DATA,__objc_fork_ok section");
}
}
break; // assume only one MH_EXECUTE image
}
#endif
}
//该函数才是核心,因为它是去设置镜像文件,读取到内存等等。上面的知道着没用
if (hCount > 0) {
_read_images(hList, hCount, totalClasses, unoptimizedTotalClasses);
}
firstTime = NO;
// Call image load funcs after everything is set up.
// 经历过读取,才能去调用,例如load方法
for (auto func : loadImageFuncs) {
for (uint32_t i = 0; i < mhCount; i++) {
func(mhdrs[i]);
}
}
}
_read_images
该函数才是map_images流程的核心开始。很重要了,它做了很多事情,去读取mach-o,以header开始进行读取。你可以直接理解为读取镜像文件到内存中去。它大致分为以下几个步骤:
-
第一次进来的时候去创建一个类表,该类表包含了类名等(不是runtime的,是全局的已经被加载或没被加载的类,我说的加载不加载意思是是否被实现,其实像其他语言一样类的内存大小等在编译阶段就已经确定了,之所以说OC是运行时动态,因为提供api去改变类的结构,但是你要知道,改变的结构是指的rw,并不是ro。ro在编译后就已经确定),略微重要,需要知道类表创建
-
将mach-o已经编译后的sel,进行修复。不重要
-
先将所有的类都加到1流程锁创建的大类表中,并且将类的地址和名字进行绑定,也就是给类赋予名字。然后将混乱错误类处理(就是我们删除的类,但是删除后内存中依旧有这块地址没被清除,我们成为futureClass。)略微重要,需要知道类被加表,以及赋予名字
-
修复一些重映射类,就是重映射没被加载进来的,不重要
-
修复objc_msgSend_fixup,不重要
-
看看有没有协议,如果有的话修复一下。可以当做发现协议,不重要
-
修复重映射协议,不重要
-
对分类进行处理,但是在启动的时候并不会走,也就是说分类加载并不在这时候,不重要
-
对非懒加载类进行处理,里面包含了类的实现。重要
-
如果有3流程的错误类被修复了,会进行优化。不重要
源码
源码太长可以不看
void _read_images(header_info **hList, uint32_t hCount, int totalClasses, int unoptimizedTotalClasses)
{
header_info *hi;
uint32_t hIndex;
size_t count;
size_t i;
Class *resolvedFutureClasses = nil;
size_t resolvedFutureClassCount = 0;
static bool doneOnce;
bool launchTime = NO;
TimeLogger ts(PrintImageTimes);
runtimeLock.assertLocked();
#define EACH_HEADER \
hIndex = 0; \
hIndex < hCount && (hi = hList[hIndex]); \
hIndex++
// 1.第一次进来
if (!doneOnce) {
doneOnce = YES;
launchTime = YES;
#if SUPPORT_NONPOINTER_ISA
// Disable non-pointer isa under some conditions.
# if SUPPORT_INDEXED_ISA
// Disable nonpointer isa if any image contains old Swift code
for (EACH_HEADER) {
if (hi->info()->containsSwift() &&
hi->info()->swiftUnstableVersion() < objc_image_info::SwiftVersion3)
{
DisableNonpointerIsa = true;
if (PrintRawIsa) {
_objc_inform("RAW ISA: disabling non-pointer isa because "
"the app or a framework contains Swift code "
"older than Swift 3.0");
}
break;
}
}
# endif
# if TARGET_OS_OSX
// Disable non-pointer isa if the app is too old
// (linked before OS X 10.11)
// if (!dyld_program_sdk_at_least(dyld_platform_version_macOS_10_11)) {
// DisableNonpointerIsa = true;
// if (PrintRawIsa) {
// _objc_inform("RAW ISA: disabling non-pointer isa because "
// "the app is too old.");
// }
// }
// Disable non-pointer isa if the app has a __DATA,__objc_rawisa section
// New apps that load old extensions may need this.
for (EACH_HEADER) {
if (hi->mhdr()->filetype != MH_EXECUTE) continue;
unsigned long size;
if (getsectiondata(hi->mhdr(), "__DATA", "__objc_rawisa", &size)) {
DisableNonpointerIsa = true;
if (PrintRawIsa) {
_objc_inform("RAW ISA: disabling non-pointer isa because "
"the app has a __DATA,__objc_rawisa section");
}
}
break; // assume only one MH_EXECUTE image
}
# endif
#endif
if (DisableTaggedPointers) {
disableTaggedPointers();
}
initializeTaggedPointerObfuscator();
if (PrintConnecting) {
_objc_inform("CLASS: found %d classes during launch", totalClasses);
}
// namedClasses
// Preoptimized classes don't go in this table.
// 4/3 is NXMapTable's load factor
// objc::unattachedCategories.init(32);
// objc::allocatedClasses.init();
int namedClassesSize =
(isPreoptimized() ? unoptimizedTotalClasses : totalClasses) * 4 / 3;
//gdb_objc_realized_classes
gdb_objc_realized_classes =
NXCreateMapTable(NXStrValueMapPrototype, namedClassesSize);
ts.log("IMAGE TIMES: first time tasks");
}
// Fix up @selector references
// 2.将mach-o的sel也就是预编译与编译后的sel进行比对修复
static size_t UnfixedSelectors;
{
mutex_locker_t lock(selLock);
for (EACH_HEADER) {
if (hi->hasPreoptimizedSelectors()) continue;
bool isBundle = hi->isBundle();
SEL *sels = _getObjc2SelectorRefs(hi, &count);
UnfixedSelectors += count;
for (i = 0; i < count; i++) {
const char *name = sel_cname(sels[i]);
SEL sel = sel_registerNameNoLock(name, isBundle);
if (sels[i] != sel) {
sels[i] = sel;
}
}
}
}
ts.log("IMAGE TIMES: fix up selector references");
// Discover classes. Fix up unresolved future classes. Mark bundle classes.
bool hasDyldRoots = dyld_shared_cache_some_image_overridden();
// 3.对一些错误混乱的类处理
for (EACH_HEADER) {
if (! mustReadClasses(hi, hasDyldRoots)) {
// Image is sufficiently optimized that we need not call readClass()
continue;
}
classref_t const *classlist = _getObjc2ClassList(hi, &count);
bool headerIsBundle = hi->isBundle();
bool headerIsPreoptimized = hi->hasPreoptimizedClasses();
for (i = 0; i < count; i++) {
Class cls = (Class)classlist[i];
Class newCls = readClass(cls, headerIsBundle, headerIsPreoptimized);
if (newCls != cls && newCls) {
// Class was moved but not deleted. Currently this occurs
// only when the new class resolved a future class.
// Non-lazily realize the class below.
resolvedFutureClasses = (Class *) realloc(resolvedFutureClasses,
(resolvedFutureClassCount+1) * sizeof(Class));
resolvedFutureClasses[resolvedFutureClassCount++] = newCls;
}
}
}
ts.log("IMAGE TIMES: discover classes");
// Fix up remapped classes
// Class list and nonlazy class list remain unremapped.
// Class refs and super refs are remapped for message dispatching.
// 4.修复重映射一些没有被镜像文件加载进来的类
if (!noClassesRemapped()) {
for (EACH_HEADER) {
Class *classrefs = _getObjc2ClassRefs(hi, &count);
for (i = 0; i < count; i++) {
remapClassRef(&classrefs[i]);
}
// fixme why doesn't test future1 catch the absence of this?
classrefs = _getObjc2SuperRefs(hi, &count);
for (i = 0; i < count; i++) {
remapClassRef(&classrefs[i]);
}
}
}
ts.log("IMAGE TIMES: remap classes");
#if SUPPORT_FIXUP
// Fix up old objc_msgSend_fixup call sites
// 5.修复一些消息
for (EACH_HEADER) {
message_ref_t *refs = _getObjc2MessageRefs(hi, &count);
if (count == 0) continue;
if (PrintVtables) {
_objc_inform("VTABLES: repairing %zu unsupported vtable dispatch "
"call sites in %s", count, hi->fname());
}
for (i = 0; i < count; i++) {
fixupMessageRef(refs+i);
}
}
ts.log("IMAGE TIMES: fix up objc_msgSend_fixup");
#endif
// Discover protocols. Fix up protocol refs.
// 6.如果类里面有协议,读取一下
for (EACH_HEADER) {
extern objc_class OBJC_CLASS_$_Protocol;
Class cls = (Class)&OBJC_CLASS_$_Protocol;
ASSERT(cls);
NXMapTable *protocol_map = protocols();
bool isPreoptimized = hi->hasPreoptimizedProtocols();
// Skip reading protocols if this is an image from the shared cache
// and we support roots
// Note, after launch we do need to walk the protocol as the protocol
// in the shared cache is marked with isCanonical() and that may not
// be true if some non-shared cache binary was chosen as the canonical
// definition
if (launchTime && isPreoptimized) {
if (PrintProtocols) {
_objc_inform("PROTOCOLS: Skipping reading protocols in image: %s",
hi->fname());
}
continue;
}
bool isBundle = hi->isBundle();
protocol_t * const *protolist = _getObjc2ProtocolList(hi, &count);
for (i = 0; i < count; i++) {
readProtocol(protolist[i], cls, protocol_map,
isPreoptimized, isBundle);
}
}
ts.log("IMAGE TIMES: discover protocols");
// Fix up @protocol references
// Preoptimized images may have the right
// answer already but we don't know for sure.
// 7.修复一些没有被加载的协议
for (EACH_HEADER) {
// At launch time, we know preoptimized image refs are pointing at the
// shared cache definition of a protocol. We can skip the check on
// launch, but have to visit @protocol refs for shared cache images
// loaded later.
if (launchTime && hi->isPreoptimized())
continue;
protocol_t **protolist = _getObjc2ProtocolRefs(hi, &count);
for (i = 0; i < count; i++) {
remapProtocolRef(&protolist[i]);
}
}
ts.log("IMAGE TIMES: fix up @protocol references");
// Discover categories. Only do this after the initial category
// attachment has been done. For categories present at startup,
// discovery is deferred until the first load_images call after
// the call to _dyld_objc_notify_register completes. rdar://problem/53119145
// 8.对于分类的处理,这里条件为默认false
if (didInitialAttachCategories) {
for (EACH_HEADER) {
load_categories_nolock(hi);
}
}
ts.log("IMAGE TIMES: discover categories");
// Category discovery MUST BE Late to avoid potential races
// when other threads call the new category code before
// this thread finishes its fixups.
// +load handled by prepare_load_methods()
// Realize non-lazy classes (for +load methods and static instances)
// 9.对于哪些非懒加载类的加载处理(懒加载类与非懒加载类,加载的时机其实不同)
for (EACH_HEADER) {
classref_t const *classlist = hi->nlclslist(&count);
for (i = 0; i < count; i++) {
Class cls = remapClass(classlist[i]);
if (!cls) continue;
addClassTableEntry(cls);
if (cls->isSwiftStable()) {
if (cls->swiftMetadataInitializer()) {
_objc_fatal("Swift class %s with a metadata initializer "
"is not allowed to be non-lazy",
cls->nameForLogging());
}
// fixme also disallow relocatable classes
// We can't disallow all Swift classes because of
// classes like Swift.__EmptyArrayStorage
}
realizeClassWithoutSwift(cls, nil);
}
}
ts.log("IMAGE TIMES: realize non-lazy classes");
// Realize newly-resolved future classes, in case CF manipulates them
// 10.上面3的时候如果有类是混乱后被修复,优化一下被侵犯的类
if (resolvedFutureClasses) {
for (i = 0; i < resolvedFutureClassCount; i++) {
Class cls = resolvedFutureClasses[i];
if (cls->isSwiftStable()) {
_objc_fatal("Swift class is not allowed to be future");
}
realizeClassWithoutSwift(cls, nil);
cls->setInstancesRequireRawIsaRecursively(false/*inherited*/);
}
free(resolvedFutureClasses);
}
ts.log("IMAGE TIMES: realize future classes");
if (DebugNonFragileIvars) {
realizeAllClasses();
}
// Print preoptimization statistics
// 如果说我们设置环境变量OBJC_PRINT_PREOPTIMIZATION这个值会进行打印
if (PrintPreopt) {
static unsigned int PreoptTotalMethodLists;
static unsigned int PreoptOptimizedMethodLists;
static unsigned int PreoptTotalClasses;
static unsigned int PreoptOptimizedClasses;
for (EACH_HEADER) {
if (hi->hasPreoptimizedSelectors()) {
_objc_inform("PREOPTIMIZATION: honoring preoptimized selectors "
"in %s", hi->fname());
}
else if (hi->info()->optimizedByDyld()) {
_objc_inform("PREOPTIMIZATION: IGNORING preoptimized selectors "
"in %s", hi->fname());
}
classref_t const *classlist = _getObjc2ClassList(hi, &count);
for (i = 0; i < count; i++) {
Class cls = remapClass(classlist[i]);
if (!cls) continue;
PreoptTotalClasses++;
if (hi->hasPreoptimizedClasses()) {
PreoptOptimizedClasses++;
}
const method_list_t *mlist;
if ((mlist = cls->bits.safe_ro()->baseMethods())) {
PreoptTotalMethodLists++;
if (mlist->isFixedUp()) {
PreoptOptimizedMethodLists++;
}
}
if ((mlist = cls->ISA()->bits.safe_ro()->baseMethods())) {
PreoptTotalMethodLists++;
if (mlist->isFixedUp()) {
PreoptOptimizedMethodLists++;
}
}
}
}
_objc_inform("PREOPTIMIZATION: %zu selector references not "
"pre-optimized", UnfixedSelectors);
_objc_inform("PREOPTIMIZATION: %u/%u (%.3g%%) method lists pre-sorted",
PreoptOptimizedMethodLists, PreoptTotalMethodLists,
PreoptTotalMethodLists
? 100.0*PreoptOptimizedMethodLists/PreoptTotalMethodLists
: 0.0);
_objc_inform("PREOPTIMIZATION: %u/%u (%.3g%%) classes pre-registered",
PreoptOptimizedClasses, PreoptTotalClasses,
PreoptTotalClasses
? 100.0*PreoptOptimizedClasses/PreoptTotalClasses
: 0.0);
_objc_inform("PREOPTIMIZATION: %zu protocol references not "
"pre-optimized", UnfixedProtocolReferences);
}
#undef EACH_HEADER
}
load_images ,load方法的加载调用
该方法包含了所有文件的load的方法的加载调用。其实最主要的也是调用load方法。(插一句题外话,就是当类与分类同时实现load方法的时候,也就打破了类的加载,进而分类的加载会从此处去进行。但是又有一种情况就是,当超过一个分类实现load方法,也就是两个及以上的时候虽说还会从此处走,但是走的方式又有所不同。)
void load_images(const char *path __unused, const struct mach_header *mh)
{
// 当完成dyld通知注册回调后,这里看函数名意思是加载所有的分类,但是是这样吗?
//
if (!didInitialAttachCategories && didCallDyldNotifyRegister) {
didInitialAttachCategories = true;
loadAllCategories();
}
// Return without taking locks if there are no +load methods here.
if (!hasLoadMethods((const headerType *)mh)) return;
recursive_mutex_locker_t lock(loadMethodLock);
// 去准备分类方法,看备注就知道
// Discover load methods
{
mutex_locker_t lock2(runtimeLock);
prepare_load_methods((const headerType *)mh);
}
// 这个没什么看的,就是去调用load方法了,但是先调用类的,再按顺序调用分类的
// Call +load methods (without runtimeLock - re-entrant)
call_load_methods();
}
loadAllCategories 分析
这个方法不重要,只执行了一次,我分析过,当类和分类同时实现load方法的时候才会进入这个方法,这一块跟分类加载有关,这里不做分析。而循环执行的是296次,可能不准确,不过无所谓,反正是玩的而已
static void loadAllCategories() {
mutex_locker_t lock(runtimeLock);
// 执行了296次
for (auto *hi = FirstHeader; hi != NULL; hi = hi->getNext()) {
// 对于某种情况下,我们自己创建的分类加载会走这里,这里不做分析
load_categories_nolock(hi);
}
}
prepare_load_methods load方法的准备
这个方法是load的方法的准备,也跟我们分类加载的某种情况有关,在以后我会补上分类加载篇章。先看看源码里面备注能理解就理解不能的话,没有关系。
void prepare_load_methods(const headerType *mhdr)
{
size_t count, i;
runtimeLock.assertLocked();
// 获取非懒加载的类表
classref_t const *classlist =
_getObjc2NonlazyClassList(mhdr, &count);
// 将类加如需要执行load方法的表中,有兴趣看里面的add_class_to_loadable_list方法
for (i = 0; i < count; i++) {
schedule_class_load(remapClass(classlist[i]));
}
// 获取非懒加载的分类列表
category_t * const *categorylist = _getObjc2NonlazyCategoryList(mhdr, &count);
for (i = 0; i < count; i++) {
category_t *cat = categorylist[i];
Class cls = remapClass(cat->cls);
if (!cls) continue; // category for ignored weak-linked class
/** 这里你可以写跟我一样的测试代码,进行打印看看
const char *clsName = cls -> nonlazyMangledName();
const char *perosn = "Person";
const char *teacher = "Teacher";
if (strcmp(clsName, perosn) == 0 || strcmp(clsName, teacher) == 0)
{
printf("-------%s----%s\n", __func__,clsName);
}
*/
if (cls->isSwiftStable()) {
_objc_fatal("Swift class extensions and categories on Swift "
"classes are not allowed to have +load methods");
}
// 如果说对于非懒加载的分类它的类没有实现的话去实现
// 类被动实现
realizeClassWithoutSwift(cls, nil);
ASSERT(cls->ISA()->isRealized());
// 与类的add_class_to_loadable_list对照
add_category_to_loadable_list(cat);
}
}