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Runtime系列文章总字数为10w+,写技术文章不容易,希望各位能帮忙点个Star,谢谢!
文中写道
类的本质是结构体,在结构体中包含一些成员变量,例如method list 、ivar list 等,
这些都是结构体的一部分,method、protocol、property的实现这些都可以放到类中,
所有对象调用同一份即可...
1.文中说明的methodlist 和metod 有什么不同
2.文中说明的对象是类对象 or 实例对象
3.若是实例对象,那么实例对象的私有方法,对应的也就是实例对象的methodlist 是做如何处理的呢?
你好,在你的pdf的Message Forward中描述到:
可以通过重写resolveInstanceMethod:和resolveClassMethod:方法,动态添加未实现的方法。其中第一个是添加实例方法,第二个是添加类方法。这两个方法都有一个BOOL返回值,返回NO则进入消息转发机制。
实际上,不论你返回yes或者no,都会重新搜索一遍是否已经添加了方法,当第二次搜索没有时,才会进入消息转发,具体的源码(objc-723)如下:
IMP lookUpImpOrForward(Class cls, SEL sel, id inst,
bool initialize, bool cache, bool resolver)
{
IMP imp = nil;
bool triedResolver = NO;
runtimeLock.assertUnlocked();
// Optimistic cache lookup
if (cache) {
imp = cache_getImp(cls, sel);
if (imp) return imp;
}
// runtimeLock is held during isRealized and isInitialized checking
// to prevent races against concurrent realization.
// runtimeLock is held during method search to make
// method-lookup + cache-fill atomic with respect to method addition.
// Otherwise, a category could be added but ignored indefinitely because
// the cache was re-filled with the old value after the cache flush on
// behalf of the category.
runtimeLock.read();
if (!cls->isRealized()) {
// Drop the read-lock and acquire the write-lock.
// realizeClass() checks isRealized() again to prevent
// a race while the lock is down.
runtimeLock.unlockRead();
runtimeLock.write();
realizeClass(cls);
runtimeLock.unlockWrite();
runtimeLock.read();
}
if (initialize && !cls->isInitialized()) {
runtimeLock.unlockRead();
_class_initialize (_class_getNonMetaClass(cls, inst));
runtimeLock.read();
// If sel == initialize, _class_initialize will send +initialize and
// then the messenger will send +initialize again after this
// procedure finishes. Of course, if this is not being called
// from the messenger then it won't happen. 2778172
}
retry:
runtimeLock.assertReading();
// Try this class's cache.
imp = cache_getImp(cls, sel);
if (imp) goto done;
// Try this class's method lists.
{
Method meth = getMethodNoSuper_nolock(cls, sel);
if (meth) {
log_and_fill_cache(cls, meth->imp, sel, inst, cls);
imp = meth->imp;
goto done;
}
}
// Try superclass caches and method lists.
{
unsigned attempts = unreasonableClassCount();
for (Class curClass = cls->superclass;
curClass != nil;
curClass = curClass->superclass)
{
// Halt if there is a cycle in the superclass chain.
if (--attempts == 0) {
_objc_fatal("Memory corruption in class list.");
}
// Superclass cache.
imp = cache_getImp(curClass, sel);
if (imp) {
if (imp != (IMP)_objc_msgForward_impcache) {
// Found the method in a superclass. Cache it in this class.
log_and_fill_cache(cls, imp, sel, inst, curClass);
goto done;
}
else {
// Found a forward:: entry in a superclass.
// Stop searching, but don't cache yet; call method
// resolver for this class first.
break;
}
}
// Superclass method list.
Method meth = getMethodNoSuper_nolock(curClass, sel);
if (meth) {
log_and_fill_cache(cls, meth->imp, sel, inst, curClass);
imp = meth->imp;
goto done;
}
}
}
// No implementation found. Try method resolver once.
if (resolver && !triedResolver) {
runtimeLock.unlockRead();
_class_resolveMethod(cls, sel, inst);
runtimeLock.read();
// Don't cache the result; we don't hold the lock so it may have
// changed already. Re-do the search from scratch instead.
triedResolver = YES;
goto retry;
}
// No implementation found, and method resolver didn't help.
// Use forwarding.
imp = (IMP)_objc_msgForward_impcache;
cache_fill(cls, sel, imp, inst);
done:
runtimeLock.unlockRead();
return imp;
}
可以看到,动态解析时,会goto retry
。 可以新建工程尝试添加方法后返回NO
。
建议文中比较下它们的区别和联系。
我联系上下文想了下,method应该是表达了IMP和SEL的映射关系,对吗?
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