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本系列博客是本人的源码阅读笔记,如果有 iOS 开发者在看 runtime 的,欢迎大家多多交流。为了方便讨论,本人新建了一个微信群(iOS技术讨论群),想要加入的,请添加本人微信:zhujinhui207407,【加我前请备注:ios 】,本人博客http://www.kyson.cn 也在不停的更新中,欢迎一起讨论
本文完整版详见笔者小专栏:https://xiaozhuanlan.com/runtime
背景
在前面的文章中,笔者有做过如下打印信息:
if (0 == strncmp(subcls->nameForLogging(), "Person", 5)) {
printf("subcls:%s,superclass:%s hasCustomAllocZone:%d\n",subcls->nameForLogging(),supercls->nameForLogging(),subcls->ISA()->hasCustomAWZ());
}
用于更好的观察代码的属性,有了这些信息的提示,我们能更好的了解runtime的原理。那么runtime本身有没有类似的打印日志信息用于调试或者观察呢,答案是肯定的,笔者暂时给其起个名字叫“日志打印系统”。这个名字不是笔者随便提出的,而是经过对其代码分析后得出的。因为这套系统是有着较为清晰的设计的,接下来笔者带大家来了解一下。
入口
这里先给大家普及一个知识,函数
void _objc_init(void)
{
static bool initialized = false;
if (initialized) return;
initialized = true;
environ_init();
tls_init();
static_init();
lock_init();
exception_init();
_dyld_objc_notify_register(&map_2_images, load_images, unmap_image);
}
是runtime启动后执行的第一个函数。关于这个知识点,这里笔者先简单提一下,具体的分析会在后面的文章中提出。void _objc_init(void)
函数位于文件objc_os.mm
中,而这个函数中的这句代码:
environ_init();
即是对log系统的初始化,我们看看里面的代码。
void environ_init(void)
{
if (issetugid()) {
// All environment variables are silently ignored when setuid or setgid
// This includes OBJC_HELP and OBJC_PRINT_OPTIONS themselves.
return;
}
bool PrintHelp = false;
bool PrintOptions = false;
bool maybeMallocDebugging = false;
// Scan environ[] directly instead of calling getenv() a lot.
// This optimizes the case where none are set.
for (char **p = *_NSGetEnviron(); *p != nil; p++) {
if (0 == strncmp(*p, "Malloc", 6) || 0 == strncmp(*p, "DYLD", 4) ||
0 == strncmp(*p, "NSZombiesEnabled", 16))
{
maybeMallocDebugging = true;
}
if (0 != strncmp(*p, "OBJC_", 5)) continue;
if (0 == strncmp(*p, "OBJC_HELP=", 10)) {
PrintHelp = true;
continue;
}
if (0 == strncmp(*p, "OBJC_PRINT_OPTIONS=", 19)) {
PrintOptions = true;
continue;
}
const char *value = strchr(*p, '=');
if (!*value) continue;
value++;
for (size_t i = 0; i < sizeof(Settings)/sizeof(Settings[0]); i++) {
const option_t *opt = &Settings[i];
if ((size_t)(value - *p) == 1+opt->envlen &&
0 == strncmp(*p, opt->env, opt->envlen))
{
*opt->var = (0 == strcmp(value, "YES"));
break;
}
}
}
// Special case: enable some autorelease pool debugging
// when some malloc debugging is enabled
// and OBJC_DEBUG_POOL_ALLOCATION is not set to something other than NO.
if (maybeMallocDebugging) {
const char *insert = getenv("DYLD_INSERT_LIBRARIES");
const char *zombie = getenv("NSZombiesEnabled");
const char *pooldebug = getenv("OBJC_DEBUG_POOL_ALLOCATION");
if ((getenv("MallocStackLogging")
|| getenv("MallocStackLoggingNoCompact")
|| (zombie && (*zombie == 'Y' || *zombie == 'y'))
|| (insert && strstr(insert, "libgmalloc")))
&&
(!pooldebug || 0 == strcmp(pooldebug, "YES")))
{
DebugPoolAllocation = true;
}
}
// Print OBJC_HELP and OBJC_PRINT_OPTIONS output.
if (PrintHelp || PrintOptions) {
if (PrintHelp) {
_objc_inform("Objective-C runtime debugging. Set variable=YES to enable.");
_objc_inform("OBJC_HELP: describe available environment variables");
if (PrintOptions) {
_objc_inform("OBJC_HELP is set");
}
_objc_inform("OBJC_PRINT_OPTIONS: list which options are set");
}
if (PrintOptions) {
_objc_inform("OBJC_PRINT_OPTIONS is set");
}
for (size_t i = 0; i < sizeof(Settings)/sizeof(Settings[0]); i++) {
const option_t *opt = &Settings[i];
if (PrintHelp) _objc_inform("%s: %s", opt->env, opt->help);
if (PrintOptions && *opt->var) _objc_inform("%s is set", opt->env);
}
}
}
对以上代码做个解释:
issetugid
该方法在苹果API Reference中有介绍:issetugid,大概意思是判断当前App的uid或者gid有没有发生变化。这里返回的是NO,继续看后面的代码。
issetugid
_NSGetEnviron
获取Xcode中的环境变量,类似的函数还有:
extern char ***_NSGetArgv(void);
extern int *_NSGetArgc(void);
extern char **_NSGetProgname(void);
这几个函数笔者就不多做介绍了,这里告诉大家如何在Xcode中设置参数,使得_NSGetEnviron
能读取到。
1.选择Edit Scheme
2.在Arguments中的Environment Variables中添加相应环境变量即可
接下来的代码都是对环境变量进行读取以及和Settings里的变量进行比对了:
for (size_t i = 0; i < sizeof(Settings)/sizeof(Settings[0]); i++) {
const option_t *opt = &Settings[i];
if ((size_t)(value - *p) == 1+opt->envlen &&
0 == strncmp(*p, opt->env, opt->envlen))
{
*opt->var = (0 == strcmp(value, "YES"));
break;
}
}
Settings
即是本地的变量文件,我们点击进入看一下:
const option_t Settings[] = {
#define OPTION(var, env, help) option_t{&var, #env, help, strlen(#env)},
#include "objc-env.h"
#undef OPTION
};
可以发现,其环境变量都是在objc-env.h
中进行设置的,而该文件的内容如下:
OPTION( PrintImages, OBJC_PRINT_IMAGES, "log image and library names as they are loaded")
OPTION( PrintImageTimes, OBJC_PRINT_IMAGE_TIMES, "measure duration of image loading steps")
OPTION( PrintLoading, OBJC_PRINT_LOAD_METHODS, "log calls to class and category +load methods")
OPTION( PrintInitializing, OBJC_PRINT_INITIALIZE_METHODS, "log calls to class +initialize methods")
OPTION( PrintResolving, OBJC_PRINT_RESOLVED_METHODS, "log methods created by +resolveClassMethod: and +resolveInstanceMethod:")
OPTION( PrintConnecting, OBJC_PRINT_CLASS_SETUP, "log progress of class and category setup")
OPTION( PrintProtocols, OBJC_PRINT_PROTOCOL_SETUP, "log progress of protocol setup")
OPTION( PrintIvars, OBJC_PRINT_IVAR_SETUP, "log processing of non-fragile ivars")
OPTION( PrintVtables, OBJC_PRINT_VTABLE_SETUP, "log processing of class vtables")
OPTION( PrintVtableImages, OBJC_PRINT_VTABLE_IMAGES, "print vtable images showing overridden methods")
OPTION( PrintCaches, OBJC_PRINT_CACHE_SETUP, "log processing of method caches")
OPTION( PrintFuture, OBJC_PRINT_FUTURE_CLASSES, "log use of future classes for toll-free bridging")
OPTION( PrintPreopt, OBJC_PRINT_PREOPTIMIZATION, "log preoptimization courtesy of dyld shared cache")
OPTION( PrintCxxCtors, OBJC_PRINT_CXX_CTORS, "log calls to C++ ctors and dtors for instance variables")
OPTION( PrintExceptions, OBJC_PRINT_EXCEPTIONS, "log exception handling")
OPTION( PrintExceptionThrow, OBJC_PRINT_EXCEPTION_THROW, "log backtrace of every objc_exception_throw()")
OPTION( PrintAltHandlers, OBJC_PRINT_ALT_HANDLERS, "log processing of exception alt handlers")
OPTION( PrintReplacedMethods, OBJC_PRINT_REPLACED_METHODS, "log methods replaced by category implementations")
OPTION( PrintDeprecation, OBJC_PRINT_DEPRECATION_WARNINGS, "warn about calls to deprecated runtime functions")
OPTION( PrintPoolHiwat, OBJC_PRINT_POOL_HIGHWATER, "log high-water marks for autorelease pools")
OPTION( PrintCustomRR, OBJC_PRINT_CUSTOM_RR, "log classes with un-optimized custom retain/release methods")
OPTION( PrintCustomAWZ, OBJC_PRINT_CUSTOM_AWZ, "log classes with un-optimized custom allocWithZone methods")
OPTION( PrintRawIsa, OBJC_PRINT_RAW_ISA, "log classes that require raw pointer isa fields")
OPTION( DebugUnload, OBJC_DEBUG_UNLOAD, "warn about poorly-behaving bundles when unloaded")
OPTION( DebugFragileSuperclasses, OBJC_DEBUG_FRAGILE_SUPERCLASSES, "warn about subclasses that may have been broken by subsequent changes to superclasses")
OPTION( DebugNilSync, OBJC_DEBUG_NIL_SYNC, "warn about @synchronized(nil), which does no synchronization")
OPTION( DebugNonFragileIvars, OBJC_DEBUG_NONFRAGILE_IVARS, "capriciously rearrange non-fragile ivars")
OPTION( DebugAltHandlers, OBJC_DEBUG_ALT_HANDLERS, "record more info about bad alt handler use")
OPTION( DebugMissingPools, OBJC_DEBUG_MISSING_POOLS, "warn about autorelease with no pool in place, which may be a leak")
OPTION( DebugPoolAllocation, OBJC_DEBUG_POOL_ALLOCATION, "halt when autorelease pools are popped out of order, and allow heap debuggers to track autorelease pools")
OPTION( DebugDuplicateClasses, OBJC_DEBUG_DUPLICATE_CLASSES, "halt when multiple classes with the same name are present")
OPTION( DebugDontCrash, OBJC_DEBUG_DONT_CRASH, "halt the process by exiting instead of crashing")
OPTION( DisableVtables, OBJC_DISABLE_VTABLES, "disable vtable dispatch")
OPTION( DisablePreopt, OBJC_DISABLE_PREOPTIMIZATION, "disable preoptimization courtesy of dyld shared cache")
OPTION( DisableTaggedPointers, OBJC_DISABLE_TAGGED_POINTERS, "disable tagged pointer optimization of NSNumber et al.")
OPTION( DisableNonpointerIsa, OBJC_DISABLE_NONPOINTER_ISA, "disable non-pointer isa fields")
设置里面的任何一个变量为YES,即可观察对应的代码。下面笔者举个例子,查看awz的设置过程:
OPTION( PrintCustomAWZ, OBJC_PRINT_CUSTOM_AWZ, "log classes with un-optimized custom allocWithZone methods")
运行项目可以看到xcode中有如下日志:
全局搜索CUSTOM AWZ:
可以看到日志打印函数在文件objc-runtime-new.mm
中:
void
objc_class::printCustomAWZ(bool inherited)
{
assert(PrintCustomAWZ);
assert(hasCustomAWZ());
_objc_inform("CUSTOM AWZ: %s%s%s", nameForLogging(),
isMetaClass() ? " (meta)" : "",
inherited ? " (inherited)" : "");
}
打断点查看其调用栈可以发现,其被
objc_class::setInitialized()
调用:
有了这些日志,我们阅读runtime源代码就更方便啦。
总结
本文介绍了runtime中的日志系统,希望对大家有所帮助。
本文完整版详见笔者小专栏:https://xiaozhuanlan.com/runtime
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