Zygote——Native
2017-08-22 本文已影响0人
开开向前冲
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注：限于作者水平有限，文中有不对的地方还请指教
我刚开始接触Android 是作为一名APP开发者，因此在刚开始看到 Zygote 时，并不明白它是什么，
现在我在这里记录一下自己对于 Zygote 的理解；
Zygote —— 进程起源地
1.Zygote 启动：init.zygote32.rc
/system/core/rootdir/init.zygote32.rc
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
class main
socket zygote stream 660 root system
onrestart write /sys/android_power/request_state wake
onrestart write /sys/power/state on
onrestart restart media
onrestart restart netd
/system/bin/app_process是Zygote进程的可执行程序，后续都是启动参数；
app_process的源码路径：
/frameworks/base/cmds/app_process/app_main.cpp
1-1. main方法
int main(int argc, char* const argv[])
{
if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) < 0) {//Selinux相关，防止动态更改权限
// Older kernels don't understand PR_SET_NO_NEW_PRIVS and return
// EINVAL. Don't die on such kernels.
if (errno != EINVAL) { //老版本内核一直返回EINVAL
LOG_ALWAYS_FATAL("PR_SET_NO_NEW_PRIVS failed: %s", strerror(errno));
return 12;
}
}
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0] //忽略第一个参数
argc--; //参数个数减一
argv++; //指向argv[1]
// Everything up to '--' or first non '-' arg goes to the vm.
//
// The first argument after the VM args is the "parent dir", which
// is currently unused.
//
// After the parent dir, we expect one or more the following internal
// arguments :
//
// --zygote : Start in zygote mode
// --start-system-server : Start the system server.
// --application : Start in application (stand alone, non zygote) mode.
// --nice-name : The nice name for this process.
//
// For non zygote starts, these arguments will be followed by
// the main class name. All remaining arguments are passed to
// the main method of this class.
//
// For zygote starts, all remaining arguments are passed to the zygote.
// main function.
//
// Note that we must copy argument string values since we will rewrite the
// entire argument block when we apply the nice name to argv0.
int i;
for (i = 0; i < argc; i++) {
if (argv[i][0] != '-') {
break;
}
if (argv[i][1] == '-' && argv[i][2] == 0) {
++i; // Skip --.
break;
}
runtime.addOption(strdup(argv[i]));
}
// Parse runtime arguments. Stop at first unrecognized option.
bool zygote = false;
bool startSystemServer = false;
bool application = false;
String8 niceName;
String8 className;
++i; // Skip unused "parent dir" argument.
while (i < argc) {
const char* arg = argv[i++];
if (strcmp(arg, "--zygote") == 0) {
zygote = true;
niceName = ZYGOTE_NICE_NAME;
} else if (strcmp(arg, "--start-system-server") == 0) {
startSystemServer = true;
} else if (strcmp(arg, "--application") == 0) {
application = true;
} else if (strncmp(arg, "--nice-name=", 12) == 0) {
niceName.setTo(arg + 12);
} else if (strncmp(arg, "--", 2) != 0) {
className.setTo(arg);
break;
} else {
--i;
break;
}
}
Vector<String8> args;
if (!className.isEmpty()) {
// We're not in zygote mode, the only argument we need to pass
// to RuntimeInit is the application argument.
//
// The Remainder of args get passed to startup class main(). Make
// copies of them before we overwrite them with the process name.
args.add(application ? String8("application") : String8("tool"));
runtime.setClassNameAndArgs(className, argc - i, argv + i);
} else {
// We're in zygote mode.
maybeCreateDalvikCache();
if (startSystemServer) {
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
ABI_LIST_PROPERTY);
return 11;
}
String8 abiFlag("--abi-list=");
abiFlag.append(prop);
args.add(abiFlag);
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string());
set_process_name(niceName.string());
}
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
} else if (className) {
runtime.start("com.android.internal.os.RuntimeInit", args, zygote);
} else {
fprintf(stderr, "Error: no class name or --zygote supplied.\n");
app_usage();
LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
return 10;
}
}
对于init.zygote32.rc中service Zygote 的参数已经在main方法的注释中都有讲解；
" -Xzygote"是VM参数；
"/system/bin"是可执行程序app_process的父目录，可以不关注；
"--zygote" : Start in zygote mode
"--start-system-server" : Start the system server.
"--application" : Start in application (stand alone, non zygote) mode.
"--nice-name" : The nice name for this process.
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
第一个参数从"/system/bin/app_process"算起，argc = 5（参数长度），argv = argv[0] = "/system/bin/app_process"
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0]
argc--; //参数个数减一
argv++; //指向argv[1]
上述代码执行完成后，
argc = 4 argv指向参数原始参数的argv[1]，即argv = "-Xzygote"
上面忽略第一个参数的原因相比你已经了解——当实参传给main函数之后，argv的第一个元素指向程序的名字或者一个空字符串，接下来的元素依次传递给命令行提供的实参，最后一个指针之后的元素保证为0。
接下来是一个循环
int i;
for (i = 0; i < argc; i++) {
if (argv[i][0] != '-') { //argv[i]是一个字符串数组，所以此时是判断参数头部是否带有"-"
break;
}
if (argv[i][1] == '-' && argv[i][2] == 0) {
++i; // Skip --.
break;
}
runtime.addOption(strdup(argv[i]));//这个循环的核心就是执行这段代码，从判断条件中知道
//只有 "-Xzygote"符合要求，即给虚拟机设置参数
}
上述代码循环是在判断第二个参数时退出的，循环退出时i = 1，argc = 4
// Parse runtime arguments. Stop at first unrecognized option.
bool zygote = false;
bool startSystemServer = false;
bool application = false;
String8 niceName;
String8 className;
++i; // Skip unused "parent dir" argument. //此时i = 2
while (i < argc) { //argc = 4
const char* arg = argv[i++]; //从argv[2]开始算起，即跳过了/system/bin
if (strcmp(arg, "--zygote") == 0) {
zygote = true;
niceName = ZYGOTE_NICE_NAME;
} else if (strcmp(arg, "--start-system-server") == 0) {
startSystemServer = true;
} else if (strcmp(arg, "--application") == 0) {
application = true;
} else if (strncmp(arg, "--nice-name=", 12) == 0) {
niceName.setTo(arg + 12);
} else if (strncmp(arg, "--", 2) != 0) {
className.setTo(arg);
break;
} else {
--i;
break;
}
}
上述这段代码很简单，就是根据传递的argv参数来设置几个变量，后续肯定会根据这个几个变量来执行相关操作；一共循环两次，上述代码执行完成后i = 4，但是argv的指向-Xzygote；循环结束后，变量的值如下：
zygote = true;
niceName = ZYGOTE_NICE_NAME;
startSystemServer = true;
循环结束后会根据上述赋值的变量来进行一些初始化操作，代码如下：
Vector<String8> args; //该变量后续会作为AppRuntime 的启动参数传递
if (!className.isEmpty()) { //className 在上述代码中没有赋值，所以className 为空
// We're not in zygote mode, the only argument we need to pass
// to RuntimeInit is the application argument.
//
// The Remainder of args get passed to startup class main(). Make
// copies of them before we overwrite them with the process name.
args.add(application ? String8("application") : String8("tool"));
runtime.setClassNameAndArgs(className, argc - i, argv + i);
} else { //className 为空，走该流程==================>>
// We're in zygote mode.
maybeCreateDalvikCache(); //创建虚拟机Cache 文件，目录在/data/dalvik-cache/下，
// 我的机器是arm架构，所以在这个目录下生成一个arm的文件夹，里面存放的都是一些dex文件；
if (startSystemServer) {
args.add(String8("start-system-server"));//添加start-system-server参数
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) {
LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
ABI_LIST_PROPERTY);
return 11;
}
String8 abiFlag("--abi-list=");
abiFlag.append(prop);
args.add(abiFlag);
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) {
runtime.setArgv0(niceName.string());
set_process_name(niceName.string());
}
1-2. maybeCreateDalvikCache() 方法
static void maybeCreateDalvikCache() {
#if defined(__aarch64__)
static const char kInstructionSet[] = "arm64";
#elif defined(__x86_64__)
static const char kInstructionSet[] = "x86_64";
#elif defined(__arm__)
static const char kInstructionSet[] = "arm";
#elif defined(__i386__)
static const char kInstructionSet[] = "x86";
#elif defined (__mips__)
static const char kInstructionSet[] = "mips";
#else
#error "Unknown instruction set"
#endif
const char* androidRoot = getenv("ANDROID_DATA");
LOG_ALWAYS_FATAL_IF(androidRoot == NULL, "ANDROID_DATA environment variable unset");
char dalvikCacheDir[PATH_MAX];
const int numChars = snprintf(dalvikCacheDir, PATH_MAX,
"%s/dalvik-cache/%s", androidRoot, kInstructionSet);//dalvikCacheDir最终为/data/dalvik-cache/arm
LOG_ALWAYS_FATAL_IF((numChars >= PATH_MAX || numChars < 0),
"Error constructing dalvik cache : %s", strerror(errno));
int result = mkdir(dalvikCacheDir, 0711);
LOG_ALWAYS_FATAL_IF((result < 0 && errno != EEXIST),
"Error creating cache dir %s : %s", dalvikCacheDir, strerror(errno));
// We always perform these steps because the directory might
// already exist, with wider permissions and a different owner
// than we'd like.
result = chown(dalvikCacheDir, AID_ROOT, AID_ROOT);//修改用户和用户主组为ROOT
LOG_ALWAYS_FATAL_IF((result < 0), "Error changing dalvik-cache ownership : %s", strerror(errno));
result = chmod(dalvikCacheDir, 0711);
LOG_ALWAYS_FATAL_IF((result < 0),
"Error changing dalvik-cache permissions : %s", strerror(errno));
}
maybeCreateDalvikCache 完成的功能如下：
1. 设置虚拟机指令集；
2. 创建虚拟机缓存目录；目录为/data/dalvik-cache/arm，后面的arm是根据签名机器指令集赋值的；我的机器为arm；
3. 修改目录的USER和GROUP 为ROOT 用户；
4. 修改目录权限为"0711"（-rwx--x--x），即目录拥有者有读写执行权限，其他用户只有执行权限；
maybeCreateDalvikCache 后：
if (startSystemServer) {
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX];
if (property_get(ABI_LIST_PROPERTY, prop, NULL) == 0) { //根据ABI_LIST_PROPERTY属性获取abi-list参数
LOG_ALWAYS_FATAL("app_process: Unable to determine ABI list from property %s.",
ABI_LIST_PROPERTY);
return 11;
}
String8 abiFlag("--abi-list=");
abiFlag.append(prop);
args.add(abiFlag);// 添加abi-list参数
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) { //开机执行这句代码前i = 4,argc = 4，所以下面程序不会执行，
//即没有参数需要添加了，如果还有参数会接着添加
args.add(String8(argv[i]));//将参数添加到args，再传给Runtime
}
......
......
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args);//启动ZygoteInit，接收上面传递过来的参数args，
//即从init.rc传递过来的参数；
} else if (className) {
runtime.start("com.android.internal.os.RuntimeInit", args);//调用AndroidRuntime的start方法
//启动RuntimeInit
} else {
fprintf(stderr, "Error: no class name or --zygote supplied.\n");
app_usage();
LOG_ALWAYS_FATAL("app_process: no class name or --zygote supplied.");
return 10;
}
注：这里所说的过程是第一次开机Zygote 的处理过程，参数也是开机过程从init.rc中传递的参数，我尝试使用adb install 安装应用，也会调用Zygote，但是参数和上述描述不一样；
到此app_main的main方法执行结束，程序将继续执行AndroidRuntime的start方法；
2. AndroidRuntime
frameworks/base/core/jni/AndroidRuntime.cpp
2-1. AndroidRuntime::start(const char* className, const Vector<String8>& options)
/*
* Start the Android runtime. This involves starting the virtual machine
* and calling the "static void main(String[] args)" method in the class
* named by "className".
*
* Passes the main function two arguments, the class name and the specified
* options string.
*/
void AndroidRuntime::start(const char* className, const Vector<String8>& options)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",
className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");//初始化字符串startSystemServer，
//判断从app_main传递过来的参数是否带有该参数
/*
* 'startSystemServer == true' means runtime is obsolete and not run from
* init.rc anymore, so we print out the boot start event here.
*/
for (size_t i = 0; i < options.size(); ++i) {
if (options[i] == startSystemServer) {//判断参数
/* track our progress through the boot sequence */
const int LOG_BOOT_PROGRESS_START = 3000;
LOG_EVENT_LONG(LOG_BOOT_PROGRESS_START, ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
}
}
const char* rootDir = getenv("ANDROID_ROOT");//获取ANDROID_ROOT环境变量，
//adb shell 到手机里面echo $ANDROID_ROOT，得出该环境变量为 "/system"
if (rootDir == NULL) {//第一次进来为空，先设置rootDir 为"/system"
rootDir = "/system";
if (!hasDir("/system")) {
LOG_FATAL("No root directory specified, and /android does not exist.");
return;
}
setenv("ANDROID_ROOT", rootDir, 1);
}
//const char* kernelHack = getenv("LD_ASSUME_KERNEL");
//ALOGD("Found LD_ASSUME_KERNEL='%s'\n", kernelHack);
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env) != 0) { //核心，启动虚拟机，该方法中会配置各种JVM参数，
//最终会调用JNI_CreateJavaVM方法创建JVM
return;
}
onVmCreated(env);
/*
* Register android functions.
*/
if (startReg(env) < 0) {//核心中的核心，注册JNI方法，什么Binder，各种核心库的JNI基本都在这里注册
ALOGE("Unable to register all android natives\n");
return;
}
/*
* We want to call main() with a String array with arguments in it.
* At present we have two arguments, the class name and an option string.
* Create an array to hold them.
*/
jclass stringClass;
jobjectArray strArray;
jstring classNameStr;
stringClass = env->FindClass("java/lang/String");
assert(stringClass != NULL);
strArray = env->NewObjectArray(options.size() + 1, stringClass, NULL);
assert(strArray != NULL);
classNameStr = env->NewStringUTF(className);
assert(classNameStr != NULL);
env->SetObjectArrayElement(strArray, 0, classNameStr);
for (size_t i = 0; i < options.size(); ++i) {
jstring optionsStr = env->NewStringUTF(options.itemAt(i).string());
assert(optionsStr != NULL);
env->SetObjectArrayElement(strArray, i + 1, optionsStr);
}
/*
* Start VM. This thread becomes the main thread of the VM, and will
* not return until the VM exits.
*/
char* slashClassName = toSlashClassName(className);//className从app_main.cpp传递过来的，
//为"com.android.internal.os.ZygoteInit"，
//toSlashClassName将className中的字符串替换为"/"来满足FindClass(slashClassName)
//对参数的需求来获取java class 对象
jclass startClass = env->FindClass(slashClassName);
if (startClass == NULL) {
ALOGE("JavaVM unable to locate class '%s'\n", slashClassName);
/* keep going */
} else {
jmethodID startMeth = env->GetStaticMethodID(startClass, "main",
"([Ljava/lang/String;)V"); //获取Java层ZygoteInit的"main"方法ID
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
env->CallStaticVoidMethod(startClass, startMeth, strArray);//执行Java层ZygoteInit "main"方法，
//终于看到了指向Java层的曙光；
#if 0
if (env->ExceptionCheck())
threadExitUncaughtException(env);
#endif
}
}
free(slashClassName);
ALOGD("Shutting down VM\n");
if (mJavaVM->DetachCurrentThread() != JNI_OK)
ALOGW("Warning: unable to detach main thread\n");
if (mJavaVM->DestroyJavaVM() != 0)
ALOGW("Warning: VM did not shut down cleanly\n");
}
本来我们应该继续往下跳转到ZygoteInit.java的main方法，但是我觉得AndroidRuntime中有几个重要的方法需要记住，在此先说说，Java层的ZygoteInit放到下一篇再说：
2-2. int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv)
/*
* Start the Dalvik Virtual Machine.
*
* Various arguments, most determined by system properties, are passed in.
* The "mOptions" vector is updated.
*
* CAUTION: when adding options in here, be careful not to put the
* char buffer inside a nested scope. Adding the buffer to the
* options using mOptions.add() does not copy the buffer, so if the
* buffer goes out of scope the option may be overwritten. It's best
* to put the buffer at the top of the function so that it is more
* unlikely that someone will surround it in a scope at a later time
* and thus introduce a bug.
*
* Returns 0 on success.
*/
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv)
{
int result = -1;
JavaVMInitArgs initArgs;
char zygoteMaxFailedBootsBuf[sizeof("-XzygoteMaxFailedBoots")-1 + PROPERTY_VALUE_MAX];
char propBuf[PROPERTY_VALUE_MAX];
char stackTraceFileBuf[sizeof("-Xstacktracefile:")-1 + PROPERTY_VALUE_MAX];
char dexoptFlagsBuf[PROPERTY_VALUE_MAX];
char enableAssertBuf[sizeof("-ea:")-1 + PROPERTY_VALUE_MAX];
char jniOptsBuf[sizeof("-Xjniopts:")-1 + PROPERTY_VALUE_MAX];
char heapstartsizeOptsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
char heapsizeOptsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
char heapgrowthlimitOptsBuf[sizeof("-XX:HeapGrowthLimit=")-1 + PROPERTY_VALUE_MAX];
char heapminfreeOptsBuf[sizeof("-XX:HeapMinFree=")-1 + PROPERTY_VALUE_MAX];
char heapmaxfreeOptsBuf[sizeof("-XX:HeapMaxFree=")-1 + PROPERTY_VALUE_MAX];
char gctypeOptsBuf[sizeof("-Xgc:")-1 + PROPERTY_VALUE_MAX];
char backgroundgcOptsBuf[sizeof("-XX:BackgroundGC=")-1 + PROPERTY_VALUE_MAX];
char heaptargetutilizationOptsBuf[sizeof("-XX:HeapTargetUtilization=")-1 + PROPERTY_VALUE_MAX];
char jitcodecachesizeOptsBuf[sizeof("-Xjitcodecachesize:")-1 + PROPERTY_VALUE_MAX];
char dalvikVmLibBuf[PROPERTY_VALUE_MAX];
char dex2oatXmsImageFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmxImageFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmsFlagsBuf[sizeof("-Xms")-1 + PROPERTY_VALUE_MAX];
char dex2oatXmxFlagsBuf[sizeof("-Xmx")-1 + PROPERTY_VALUE_MAX];
char dex2oatCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
char dex2oatImageCompilerFilterBuf[sizeof("--compiler-filter=")-1 + PROPERTY_VALUE_MAX];
char dex2oatFlagsBuf[PROPERTY_VALUE_MAX];
char dex2oatImageFlagsBuf[PROPERTY_VALUE_MAX];
char extraOptsBuf[PROPERTY_VALUE_MAX];
char voldDecryptBuf[PROPERTY_VALUE_MAX];
enum {
kEMDefault,
kEMIntPortable,
kEMIntFast,
kEMJitCompiler,
} executionMode = kEMDefault;
char profilePeriod[sizeof("-Xprofile-period:")-1 + PROPERTY_VALUE_MAX];
char profileDuration[sizeof("-Xprofile-duration:")-1 + PROPERTY_VALUE_MAX];
char profileInterval[sizeof("-Xprofile-interval:")-1 + PROPERTY_VALUE_MAX];
char profileBackoff[sizeof("-Xprofile-backoff:")-1 + PROPERTY_VALUE_MAX];
char profileTopKThreshold[sizeof("-Xprofile-top-k-threshold:")-1 + PROPERTY_VALUE_MAX];
char profileTopKChangeThreshold[sizeof("-Xprofile-top-k-change-threshold:")-1 +
PROPERTY_VALUE_MAX];
char profileType[sizeof("-Xprofile-type:")-1 + PROPERTY_VALUE_MAX];
char profileMaxStackDepth[sizeof("-Xprofile-max-stack-depth:")-1 + PROPERTY_VALUE_MAX];
char langOption[sizeof("-Duser.language=") + 3];
char regionOption[sizeof("-Duser.region=") + 3];
char lockProfThresholdBuf[sizeof("-Xlockprofthreshold:")-1 + PROPERTY_VALUE_MAX];
char jitOpBuf[sizeof("-Xjitop:")-1 + PROPERTY_VALUE_MAX];
char jitMethodBuf[sizeof("-Xjitmethod:")-1 + PROPERTY_VALUE_MAX];
char nativeBridgeLibrary[sizeof("-XX:NativeBridge=") + PROPERTY_VALUE_MAX];
......
property_get("dalvik.vm.checkjni", propBuf, "");
......
parseRuntimeOption("dalvik.vm.heapsize", heapsizeOptsBuf, "-Xmx", "16m");
......
}
/*
* Reads a "property" into "buffer" with a default of "defaultArg". If
* the property is non-empty, it is treated as a runtime option such
* as "-Xmx32m".
*
* The "runtimeArg" is a prefix for the option such as "-Xms" or "-Xmx".
*
* If an argument is found, it is added to mOptions.
*
* If an option is found, it is added to mOptions and true is
* returned. Otherwise false is returned.
*/
bool AndroidRuntime::parseRuntimeOption(const char* property,
char* buffer,
const char* runtimeArg,
const char* defaultArg)
{
strcpy(buffer, runtimeArg);
size_t runtimeArgLen = strlen(runtimeArg);
property_get(property, buffer+runtimeArgLen, defaultArg);
if (buffer[runtimeArgLen] == '\0') {
return false;
}
addOption(buffer);
return true;
}
这里对于Java Dalvik 参数配置，大部分都是通过获取系统属性来赋值；对此不需要详解；
2-3. int AndroidRuntime::startReg(JNIEnv* env)
/*
* Register android native functions with the VM.
*/
/*static*/
int AndroidRuntime::startReg(JNIEnv* env)
{
/*
* This hook causes all future threads created in this process to be
* attached to the JavaVM. (This needs to go away in favor of JNI
* Attach calls.)
*/
androidSetCreateThreadFunc((android_create_thread_fn) javaCreateThreadEtc);
ALOGV("--- registering native functions ---\n");
/*
* Every "register" function calls one or more things that return
* a local reference (e.g. FindClass). Because we haven't really
* started the VM yet, they're all getting stored in the base frame
* and never released. Use Push/Pop to manage the storage.
*/
env->PushLocalFrame(200);
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {//注册JNI方法，很重要，gRegJNI是方法表
env->PopLocalFrame(NULL);
return -1;
}
env->PopLocalFrame(NULL);
//createJavaThread("fubar", quickTest, (void*) "hello");
return 0;
}
2-4. gRegJNI 方法表
static const RegJNIRec gRegJNI[] = {
REG_JNI(register_com_android_internal_os_RuntimeInit),
REG_JNI(register_android_os_SystemClock),
REG_JNI(register_android_util_EventLog),
REG_JNI(register_android_os_Process),
REG_JNI(register_android_os_SystemProperties),
REG_JNI(register_android_os_Binder),
REG_JNI(register_android_os_Parcel),
REG_JNI(register_android_graphics_Graphics),
REG_JNI(register_android_view_DisplayEventReceiver),
REG_JNI(register_android_view_RenderNode),
REG_JNI(register_android_view_RenderNodeAnimator),
REG_JNI(register_android_view_GraphicBuffer),
REG_JNI(register_android_view_GLES20Canvas),
REG_JNI(register_android_view_HardwareLayer),
REG_JNI(register_android_view_Surface),
REG_JNI(register_android_view_SurfaceControl),
REG_JNI(register_android_view_SurfaceSession),
REG_JNI(register_android_view_TextureView),
REG_JNI(register_com_android_internal_view_animation_NativeInterpolatorFactoryHelper),
REG_JNI(register_com_google_android_gles_jni_EGLImpl),
REG_JNI(register_com_google_android_gles_jni_GLImpl),
REG_JNI(register_android_opengl_jni_EGL14),
REG_JNI(register_android_opengl_jni_EGLExt),
REG_JNI(register_android_opengl_jni_GLES10),
REG_JNI(register_android_opengl_jni_GLES10Ext),
REG_JNI(register_android_opengl_jni_GLES11),
REG_JNI(register_android_opengl_jni_GLES11Ext),
REG_JNI(register_android_opengl_jni_GLES20),
REG_JNI(register_android_opengl_jni_GLES30),
REG_JNI(register_android_opengl_jni_GLES31),
REG_JNI(register_android_opengl_jni_GLES31Ext),
REG_JNI(register_android_graphics_Bitmap),
REG_JNI(register_android_graphics_BitmapFactory),
REG_JNI(register_android_graphics_BitmapRegionDecoder),
REG_JNI(register_android_graphics_Camera),
REG_JNI(register_android_graphics_CreateJavaOutputStreamAdaptor),
REG_JNI(register_android_graphics_Canvas),
REG_JNI(register_android_graphics_CanvasProperty),
REG_JNI(register_android_graphics_ColorFilter),
REG_JNI(register_android_graphics_DrawFilter),
REG_JNI(register_android_graphics_FontFamily),
REG_JNI(register_android_graphics_Movie),
REG_JNI(register_android_graphics_NinePatch),
REG_JNI(register_android_graphics_Paint),
REG_JNI(register_android_graphics_Path),
REG_JNI(register_android_graphics_PathMeasure),
REG_JNI(register_android_graphics_PathEffect),
REG_JNI(register_android_graphics_Picture),
REG_JNI(register_android_graphics_PorterDuff),
REG_JNI(register_android_graphics_Rasterizer),
REG_JNI(register_android_graphics_Region),
REG_JNI(register_android_graphics_Shader),
REG_JNI(register_android_graphics_SurfaceTexture),
REG_JNI(register_android_graphics_Typeface),
REG_JNI(register_android_graphics_pdf_PdfRenderer),
REG_JNI(register_android_database_CursorWindow),
REG_JNI(register_android_database_SQLiteConnection),
REG_JNI(register_android_database_SQLiteGlobal),
REG_JNI(register_android_database_SQLiteDebug),
REG_JNI(register_android_os_Debug),
REG_JNI(register_android_os_FileObserver),
REG_JNI(register_android_os_MessageQueue),
REG_JNI(register_android_os_SELinux),
REG_JNI(register_android_os_Trace),
REG_JNI(register_android_os_UEventObserver),
REG_JNI(register_android_net_NetworkUtils),
REG_JNI(register_com_android_internal_os_ZygoteInit),
REG_JNI(register_com_android_internal_os_Zygote),
REG_JNI(register_android_hardware_Camera),
REG_JNI(register_android_hardware_camera2_legacy_PerfMeasurement),
REG_JNI(register_android_hardware_camera2_DngCreator),
REG_JNI(register_android_hardware_SensorManager),
REG_JNI(register_android_hardware_SerialPort),
REG_JNI(register_android_media_AudioRecord),
REG_JNI(register_android_media_AudioSystem),
REG_JNI(register_android_media_AudioTrack),
REG_JNI(register_android_media_ToneGenerator),
REG_JNI(register_android_opengl_classes),
REG_JNI(register_android_server_NetworkManagementSocketTagger),
REG_JNI(register_android_app_ActivityThread),
REG_JNI(register_android_app_NativeActivity),
REG_JNI(register_android_view_InputChannel),
REG_JNI(register_android_view_InputEventReceiver),
REG_JNI(register_android_view_InputEventSender),
REG_JNI(register_android_view_InputQueue),
REG_JNI(register_android_view_KeyEvent),
};
限于篇幅原因我删除了很多，这里注册的这些JNI方法都很重要很重要很重要，比如Binder，Camera，EGL 等等；
这篇文章描述有点杂，贴的代码中有很多注释，很多是Google 原生的注释我没删除，因为我觉得这些注释简单明了。
总结：app_process进程主要是根据init.rc脚本来设置参数，然后调用到Java层的ZygoteInit；
