1.开机启动Zygote进程
在线源码查看：http://androidxref.com/6.0.0_r1/xref/
Zygote进程是由init进程通过解析init.zygote.rc文件创建的，Zygote所对应的可执行程序是app_process，所对应的源文件是app_main.cpp，进程名为zygote
//源码文件：/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
2.执行app_main.cpp中的main方法
//资源文件：/frameworks/base/cmds/app_process/app_main.cpp
//line186
int main(int argc, char* const argv[])
{
//line197 AppRuntime继承AndroidRuntime
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
//line248 匹配上面rc中的"--zygote"，将zygote标志位设置为true
if (strcmp(arg, "--zygote") == 0) {
zygote = true;
niceName = ZYGOTE_NICE_NAME;
}
//line306 运行AndroidRuntime.cpp的start方法
if (zygote) {
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
}
}
3.AndroidRuntime::start
//xref: /frameworks/base/core/jni/AndroidRuntime.cpp
//1007
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
//line1051 startReg：JNI方法注册，Java才能调到Native方法
/*
* Register android functions.
*/
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
}
//line1440
/*
* Register android native functions with the VM.
*/
/*static*/ int AndroidRuntime::startReg(JNIEnv* env)
{
//line1459 注册JNI方法
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
env->PopLocalFrame(NULL);
return -1;
}
}
//line1283
static int register_jni_procs(const RegJNIRec array[], size_t count, JNIEnv* env)
{
//循环注册JNI方法
for (size_t i = 0; i < count; i++) {
if (array[i].mProc(env) < 0) {
#ifndef NDEBUG
ALOGD("----------!!! %s failed to load\n", array[i].mName);
#endif
return -1;
}
}
return 0;
}
//line1296 要注册JNI的数组
static const RegJNIRec gRegJNI[] = {
//line1312
REG_JNI(register_android_os_Binder)
}
4.register_android_os_Binder
//xref: /frameworks/base/core/jni/android_util_Binder.cpp
//line1282
int register_android_os_Binder(JNIEnv* env)
{
if (int_register_android_os_Binder(env) < 0)
return -1;
if (int_register_android_os_BinderInternal(env) < 0)
return -1;
if (int_register_android_os_BinderProxy(env) < 0)
return -1;
}
三个方法都是完成Java层和Native层能够相互调用
int_register_android_os_Binder
//xref: /frameworks/base/core/jni/android_util_Binder.cpp
//line843
static const JNINativeMethod gBinderMethods[] = {
/* name, signature, funcPtr */
{ "getCallingPid", "()I", (void*)android_os_Binder_getCallingPid },
{ "getCallingUid", "()I", (void*)android_os_Binder_getCallingUid },
{ "clearCallingIdentity", "()J", (void*)android_os_Binder_clearCallingIdentity },
{ "restoreCallingIdentity", "(J)V", (void*)android_os_Binder_restoreCallingIdentity },
{ "setThreadStrictModePolicy", "(I)V", (void*)android_os_Binder_setThreadStrictModePolicy },
{ "getThreadStrictModePolicy", "()I", (void*)android_os_Binder_getThreadStrictModePolicy },
{ "flushPendingCommands", "()V", (void*)android_os_Binder_flushPendingCommands },
{ "init", "()V", (void*)android_os_Binder_init },
{ "destroy", "()V", (void*)android_os_Binder_destroy },
{ "blockUntilThreadAvailable", "()V", (void*)android_os_Binder_blockUntilThreadAvailable }
};
const char* const kBinderPathName = "android/os/Binder";
static int int_register_android_os_Binder(JNIEnv* env)
{
//查找文件"android/os/Binder"，拿到对应的class对象
jclass clazz = FindClassOrDie(env, kBinderPathName);
//通过gBinderOffsets结构体，保存Java层Binder类的信息，为JNI层访问Java层提供通道
gBinderOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
gBinderOffsets.mExecTransact = GetMethodIDOrDie(env, clazz, "execTransact", "(IJJI)Z");
gBinderOffsets.mObject = GetFieldIDOrDie(env, clazz, "mObject", "J");
//通过RegisterMethodsOrDie将gBinderMethods数组完成映射关系，从而为Java层访问JNI层提供通道
return RegisterMethodsOrDie(
env, kBinderPathName,
gBinderMethods, NELEM(gBinderMethods));
}
int_register_android_os_BinderInternal
static const JNINativeMethod gBinderInternalMethods[] = {
/* name, signature, funcPtr */
{ "getContextObject", "()Landroid/os/IBinder;", (void*)android_os_BinderInternal_getContextObject },
{ "joinThreadPool", "()V", (void*)android_os_BinderInternal_joinThreadPool },
{ "disableBackgroundScheduling", "(Z)V", (void*)android_os_BinderInternal_disableBackgroundScheduling },
{ "handleGc", "()V", (void*)android_os_BinderInternal_handleGc }
};
const char* const kBinderInternalPathName = "com/android/internal/os/BinderInternal";
static int int_register_android_os_BinderInternal(JNIEnv* env)
{
//查找文件"com/android/internal/os/BinderInternal"，拿到对应的class对象
jclass clazz = FindClassOrDie(env, kBinderInternalPathName);
//通过gBinderOffsets结构体，保存Java层BinderInternal类的信息，为JNI层访问Java层提供通道
gBinderInternalOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
gBinderInternalOffsets.mForceGc = GetStaticMethodIDOrDie(env, clazz, "forceBinderGc", "()V");
//通过RegisterMethodsOrDie将gBinderInternalMethods数组完成映射关系，从而为Java层访问JNI层提供通道
return RegisterMethodsOrDie(
env, kBinderInternalPathName,
gBinderInternalMethods, NELEM(gBinderInternalMethods));
}
int_register_android_os_BinderProxy
static const JNINativeMethod gBinderProxyMethods[] = {
/* name, signature, funcPtr */
{"pingBinder", "()Z", (void*)android_os_BinderProxy_pingBinder},
{"isBinderAlive", "()Z", (void*)android_os_BinderProxy_isBinderAlive},
{"getInterfaceDescriptor", "()Ljava/lang/String;", (void*)android_os_BinderProxy_getInterfaceDescriptor},
{"transactNative", "(ILandroid/os/Parcel;Landroid/os/Parcel;I)Z", (void*)android_os_BinderProxy_transact},
{"linkToDeath", "(Landroid/os/IBinder$DeathRecipient;I)V", (void*)android_os_BinderProxy_linkToDeath},
{"unlinkToDeath", "(Landroid/os/IBinder$DeathRecipient;I)Z", (void*)android_os_BinderProxy_unlinkToDeath},
{"destroy", "()V", (void*)android_os_BinderProxy_destroy},
};
const char* const kBinderProxyPathName = "android/os/BinderProxy";
static int int_register_android_os_BinderProxy(JNIEnv* env)
{
//查找文件"android/os/BinderProxy"，拿到对应的class对象
jclass clazz = FindClassOrDie(env, "java/lang/Error");
gErrorOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
clazz = FindClassOrDie(env, kBinderProxyPathName);
//通过gBinderOffsets结构体，保存Java层BinderProxy类的信息，为JNI层访问Java层提供通道
gBinderProxyOffsets.mClass = MakeGlobalRefOrDie(env, clazz);
gBinderProxyOffsets.mConstructor = GetMethodIDOrDie(env, clazz, "<init>", "()V");
gBinderProxyOffsets.mSendDeathNotice = GetStaticMethodIDOrDie(env, clazz, "sendDeathNotice",(Landroid/os/IBinder$DeathRecipient;)V");
gBinderProxyOffsets.mObject = GetFieldIDOrDie(env, clazz, "mObject", "J");
gBinderProxyOffsets.mSelf = GetFieldIDOrDie(env, clazz, "mSelf",
"Ljava/lang/ref/WeakReference;");
gBinderProxyOffsets.mOrgue = GetFieldIDOrDie(env, clazz, "mOrgue", "J");
clazz = FindClassOrDie(env, "java/lang/Class");
gClassOffsets.mGetName = GetMethodIDOrDie(env, clazz, "getName", "()Ljava/lang/String;");
//通过RegisterMethodsOrDie将gBinderProxyMethods数组完成映射关系，从而为Java层访问JNI层提供通道
return RegisterMethodsOrDie(
env, kBinderProxyPathName,
gBinderProxyMethods, NELEM(gBinderProxyMethods));
}
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