11.2.3. zygote进程孵化器
在Android系统中, JavaVM(Java虚拟机) 以及运行系统关键服务的 SystemServer 都是由 Zygote 来创建的，我们称它为孵化器．
它通过 fork 的形式来创建 应用程序进程 和 SystemServer进程 ．
11.2.3.1. zygote启动过程
在 init.rc 脚本中，启动了Zygote进程
on late-init
trigger early-fs
# Mount fstab in init.{$device}.rc by mount_all command. Optional parameter
# '--early' can be specified to skip entries with 'latemount'.
# /system and /vendor must be mounted by the end of the fs stage,
# while /data is optional.
trigger fs
trigger post-fs
# Mount fstab in init.{$device}.rc by mount_all with '--late' parameter
# to only mount entries with 'latemount'. This is needed if '--early' is
# specified in the previous mount_all command on the fs stage.
# With /system mounted and properties form /system + /factory available,
# some services can be started.
trigger late-fs
# Now we can mount /data. File encryption requires keymaster to decrypt
# /data, which in turn can only be loaded when system properties are present.
trigger post-fs-data
# Load persist properties and override properties (if enabled) from /data.
trigger load_persist_props_action
# Should be before netd, but after apex, properties and logging is available.
trigger load_bpf_programs
# Now we can start zygote for devices with file based encryption
# 触发zygote-start
trigger zygote-start
# Remove a file to wake up anything waiting for firmware.
trigger firmware_mounts_complete
trigger early-boot
trigger boot
on zygote-start && property:ro.crypto.state=unencrypted
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start statsd
start netd
# 启动zygote服务
start zygote
start zygote_secondary
init.rc文件中会import init.zygote64.rc文件
# 服务进程名zygote
# 运行的二进制文件是/system/bin/app_process64
# 启动参数是 -Xzygote /system/bin --zygote --start_system-server
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server
class main
priority -20
user root
group root readproc reserved_disk
socket zygote stream 660 root system #创建socket
socket usap_pool_primary stream 660 root system
onrestart exec_background - system system -- /system/bin/vdc volume abort_fuse #当前进程重启时执行的命令
onrestart write /sys/power/state on
onrestart restart audioserver
onrestart restart cameraserver
onrestart restart media
onrestart restart netd
onrestart restart wificond
writepid /dev/cpuset/foreground/tasks #创建子进程时，向/dev/cpuset/foreground/tasks写入pid
start 命令有一个对应的执行函数 do_start() ,定义在 system/core/init/builtins.cpp 中
// Builtin-function-map start
const BuiltinFunctionMap& GetBuiltinFunctionMap() {
constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
// clang-format off
static const BuiltinFunctionMap builtin_functions = {
{"bootchart", {1, 1, {false, do_bootchart}}},
{"chmod", {2, 2, {true, do_chmod}}},
{"chown", {2, 3, {true, do_chown}}},
{"class_reset", {1, 1, {false, do_class_reset}}},
{"class_reset_post_data", {1, 1, {false, do_class_reset_post_data}}},
{"class_restart", {1, 1, {false, do_class_restart}}},
{"class_start", {1, 1, {false, do_class_start}}},
{"class_start_post_data", {1, 1, {false, do_class_start_post_data}}},
{"class_stop", {1, 1, {false, do_class_stop}}},
{"copy", {2, 2, {true, do_copy}}},
{"domainname", {1, 1, {true, do_domainname}}},
{"enable", {1, 1, {false, do_enable}}},
{"exec", {1, kMax, {false, do_exec}}},
{"exec_background", {1, kMax, {false, do_exec_background}}},
{"exec_start", {1, 1, {false, do_exec_start}}},
{"export", {2, 2, {false, do_export}}},
{"hostname", {1, 1, {true, do_hostname}}},
{"ifup", {1, 1, {true, do_ifup}}},
{"init_user0", {0, 0, {false, do_init_user0}}},
{"insmod", {1, kMax, {true, do_insmod}}},
{"installkey", {1, 1, {false, do_installkey}}},
{"interface_restart", {1, 1, {false, do_interface_restart}}},
{"interface_start", {1, 1, {false, do_interface_start}}},
{"interface_stop", {1, 1, {false, do_interface_stop}}},
{"load_persist_props", {0, 0, {false, do_load_persist_props}}},
{"load_system_props", {0, 0, {false, do_load_system_props}}},
{"loglevel", {1, 1, {false, do_loglevel}}},
{"mark_post_data", {0, 0, {false, do_mark_post_data}}},
{"mkdir", {1, 6, {true, do_mkdir}}},
// TODO: Do mount operations in vendor_init.
// mount_all is currently too complex to run in vendor_init as it queues action triggers,
// imports rc scripts, etc. It should be simplified and run in vendor_init context.
// mount and umount are run in the same context as mount_all for symmetry.
{"mount_all", {0, kMax, {false, do_mount_all}}},
{"mount", {3, kMax, {false, do_mount}}},
{"perform_apex_config", {0, 0, {false, do_perform_apex_config}}},
{"umount", {1, 1, {false, do_umount}}},
{"umount_all", {0, 1, {false, do_umount_all}}},
{"update_linker_config", {0, 0, {false, do_update_linker_config}}},
{"readahead", {1, 2, {true, do_readahead}}},
{"remount_userdata", {0, 0, {false, do_remount_userdata}}},
{"restart", {1, 1, {false, do_restart}}},
{"restorecon", {1, kMax, {true, do_restorecon}}},
{"restorecon_recursive", {1, kMax, {true, do_restorecon_recursive}}},
{"rm", {1, 1, {true, do_rm}}},
{"rmdir", {1, 1, {true, do_rmdir}}},
{"setprop", {2, 2, {true, do_setprop}}},
{"setrlimit", {3, 3, {false, do_setrlimit}}},
{"start", {1, 1, {false, do_start}}},
{"stop", {1, 1, {false, do_stop}}},
{"swapon_all", {0, 1, {false, do_swapon_all}}},
{"enter_default_mount_ns", {0, 0, {false, do_enter_default_mount_ns}}},
{"symlink", {2, 2, {true, do_symlink}}},
{"sysclktz", {1, 1, {false, do_sysclktz}}},
{"trigger", {1, 1, {false, do_trigger}}},
{"verity_update_state", {0, 0, {false, do_verity_update_state}}},
{"wait", {1, 2, {true, do_wait}}},
{"wait_for_prop", {2, 2, {false, do_wait_for_prop}}},
{"write", {2, 2, {true, do_write}}},
};
// clang-format on
return builtin_functions;
}
do_start()
static Result<void> do_start(const BuiltinArguments& args) {
Service* svc = ServiceList::GetInstance().FindService(args[1]); //找到zygote service对应信息
if (!svc) return Error() << "service " << args[1] << " not found";
if (auto result = svc->Start(); !result.ok()) { //启动对应的进程
return ErrorIgnoreEnoent() << "Could not start service: " << result.error();
}
return {};
}
do_start() 首先是通过 FindService 去 ServiceList 中遍历，根据名字匹配出对应的 service
Result<void> Service::Start() {
... ...
pid_t pid = -1;
if (namespaces_.flags) {
pid = clone(nullptr, nullptr, namespaces_.flags | SIGCHLD, nullptr);
} else {
pid = fork(); //从init进程中fork出zygote进程
}
... ...
}
11.2.3.2. app_process64
init.zygote64.rc启动文件的地址为 system/bin/app_process64
app_process64 对应的代码定义在 frameworks/base/cmds/app_process/app_main.cpp
在app_main.cpp中主要做的事情就是参数解析，这个函数有两种启动模式
zygote模式,也就是初始化zygote进程，传递的参数有”–start-system-server –socket-name=zygote”, 前者表示启动SystemServer, 后者指定socket的名称application模式，也就是普通应用程序，传递参数有”class名字”以及”class带的参数”
int main(int argc, char* const argv[])
{
//将参数argv放到argv_String字符串中
if (!LOG_NDEBUG) {
String8 argv_String;
for (int i = 0; i < argc; ++i) {
argv_String.append("\"");
argv_String.append(argv[i]);
argv_String.append("\" ");
}
ALOGV("app_process main with argv: %s", argv_String.string());
}
//AppRuntime定义于app_main.cpp中，继承自AndroidRuntime
//就是对Android运行环境的一种抽象，类似于java虚拟机对java程序的作用
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0]
argc--;
argv++;
//这两个参数是java程序需要依赖的jar包，相当于import
const char* spaced_commands[] = { "-cp", "-classpath" };
// Allow "spaced commands" to be succeeded by exactly 1 argument (regardless of -s).
bool known_command = false;
int i;
for (i = 0; i < argc; i++) {
if (known_command == true) {
runtime.addOption(strdup(argv[i]));
// The static analyzer gets upset that we don't ever free the above
// string. Since the allocation is from main, leaking it doesn't seem
// problematic. NOLINTNEXTLINE
ALOGV("app_process main add known option '%s'", argv[i]);
known_command = false;
continue;
}
for (int j = 0;
j < static_cast<int>(sizeof(spaced_commands) / sizeof(spaced_commands[0]));
++j) {
if (strcmp(argv[i], spaced_commands[j]) == 0) {
known_command = true;
ALOGV("app_process main found known command '%s'", argv[i]);
}
}
//如果参数的第一个字符是'-' ,直接跳出循环
//之前传入的第一个参数是-Xzygote,所以执行到就直接跳出了
if (argv[i][0] != '-') {
break;
}
if (argv[i][1] == '-' && argv[i][2] == 0) {
++i; // Skip --.
break;
}
runtime.addOption(strdup(argv[i]));
// The static analyzer gets upset that we don't ever free the above
// string. Since the allocation is from main, leaking it doesn't seem
// problematic. NOLINTNEXTLINE
ALOGV("app_process main add option '%s'", argv[i]);
}
// Parse runtime arguments. Stop at first unrecognized option.
//从这里其实可以看出，通过app_main可以启动zygote, systemserver,以及普通的apk进程
bool zygote = false;
bool startSystemServer = false;
bool application = false;
String8 niceName; //app_process的名称该为zygote
String8 className; //启动apk进程时，对应的类名
//跳过一个参数，之前跳过了-Xzygote,这里继续跳过/system/bin,也就是所谓的"parent dir"
++i; // Skip unused "parent dir" argument.
while (i < argc) {
const char* arg = argv[i++];
if (strcmp(arg, "--zygote") == 0) { //表示是zygote启动模式
zygote = true;
niceName = ZYGOTE_NICE_NAME; //修改名字，zygote64或zygote
} else if (strcmp(arg, "--start-system-server") == 0) { //表示启动system-server
startSystemServer = true;
} else if (strcmp(arg, "--application") == 0) { //表示普通应用程序
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()) { //classname不为空，说明是application启动模式
// 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);
if (!LOG_NDEBUG) {
String8 restOfArgs;
char* const* argv_new = argv + i;
int argc_new = argc - i;
for (int k = 0; k < argc_new; ++k) {
restOfArgs.append("\"");
restOfArgs.append(argv_new[k]);
restOfArgs.append("\" ");
}
ALOGV("Class name = %s, args = %s", className.string(), restOfArgs.string());
}
} else { //zygote启动模式
// We're in zygote mode.
maybeCreateDalvikCache(); //创建Dalvik的缓存目录并定义权限
if (startSystemServer) { //增加start-system-server参数
args.add(String8("start-system-server"));
}
char prop[PROP_VALUE_MAX]; //获取平台对应的abi信息
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); //加入 --abi-list=
// In zygote mode, pass all remaining arguments to the zygote
// main() method.
for (; i < argc; ++i) {
args.add(String8(argv[i]));
}
}
if (!niceName.isEmpty()) { //修改进程别名
runtime.setArgv0(niceName.string(), true /* setProcName */);
}
if (zygote) { //调用Runtime的start函数，启动ZygoteInit
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.");
}
}
由上可知， Zygote 是通过 runtime.start 函数启动，此处的 runtime 是 AppRuntime
AndroidRuntime
由于 AppRuntime 继承自 AndroidRuntime ,且没有重写 start()方法 ,因此 zygote 的流程进入到了 AndroidRuntie.cpp
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
//log输出，环境变换获取
... ...
/* start the virtual machine */
JniInvocation jni_invocation;
jni_invocation.Init(NULL); //初始化JNI,加载libart.so
JNIEnv* env;
//创建虚拟机，启动大多数参数由系统属性决定，最终startVm利用JNI_CreateJavaVm创建出虚拟机
if (startVm(&mJavaVM, &env, zygote, primary_zygote) != 0) {
return;
}
//回调AppRuntime的onVmCreated函数
//对于zygote进程的启动流程而言，无实际操作，表示虚拟创建完成，但里面是空实现
onVmCreated(env);
... ...
char* slashClassName = toSlashClassName(className != NULL ? className : "");
jclass startClass = env->FindClass(slashClassName); //找到class文件
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"); //通过反射找到zygoteInit的main函数
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
env->CallStaticVoidMethod(startClass, startMeth, strArray); //调用zygoteInit的main函数
}
}
}
//frameworks/base/core/jni/AndroidRuntime.cpp
/*
* Register android native functions with the VM.
*/
/*static*/ int AndroidRuntime::startReg(JNIEnv* env)
{
ATRACE_NAME("RegisterAndroidNatives");
/*
* 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.)
*/
//定义Android创建线程的func:: javaCreateThreadEtc，这个函数内部通过linux的clone来创建线程
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.
*/
//创建一个200容量的局部引用作用域，这个局部引用其实就是局部变量
env->PushLocalFrame(200);
//注册JNI函数
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
env->PopLocalFrame(NULL);
return -1;
}
//释放局部引用作用域
env->PopLocalFrame(NULL);
//createJavaThread("fubar", quickTest, (void*) "hello");
return 0;
}
startReg 函数主要通过 register_jni_procs 来注册JNI函数,其中 gRegJNI 是一个全局数组
static const RegJNIRec gRegJNI[] = {
REG_JNI(register_com_android_internal_os_RuntimeInit),
REG_JNI(register_com_android_internal_os_ZygoteInit_nativeZygoteInit),
REG_JNI(register_android_os_SystemClock),
REG_JNI(register_android_util_EventLog),
REG_JNI(register_android_util_Log),
REG_JNI(register_android_util_MemoryIntArray),
REG_JNI(register_android_app_admin_SecurityLog),
REG_JNI(register_android_content_AssetManager),
REG_JNI(register_android_content_StringBlock),
REG_JNI(register_android_content_XmlBlock),
REG_JNI(register_android_content_res_ApkAssets),
REG_JNI(register_android_text_AndroidCharacter),
REG_JNI(register_android_text_Hyphenator),
REG_JNI(register_android_view_InputDevice),
REG_JNI(register_android_view_KeyCharacterMap),
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_os_HidlMemory),
REG_JNI(register_android_os_HidlSupport),
REG_JNI(register_android_os_HwBinder),
REG_JNI(register_android_os_HwBlob),
REG_JNI(register_android_os_HwParcel),
REG_JNI(register_android_os_HwRemoteBinder),
REG_JNI(register_android_os_NativeHandle),
REG_JNI(register_android_os_ServiceManager),
REG_JNI(register_android_os_storage_StorageManager),
REG_JNI(register_android_os_VintfObject),
REG_JNI(register_android_os_VintfRuntimeInfo),
REG_JNI(register_android_service_DataLoaderService),
REG_JNI(register_android_view_DisplayEventReceiver),
REG_JNI(register_android_view_InputApplicationHandle),
REG_JNI(register_android_view_InputWindowHandle),
REG_JNI(register_android_view_Surface),
REG_JNI(register_android_view_SurfaceControl),
REG_JNI(register_android_view_SurfaceSession),
REG_JNI(register_android_view_CompositionSamplingListener),
REG_JNI(register_android_view_TextureView),
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_EGL15),
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_opengl_jni_GLES32),
REG_JNI(register_android_graphics_classes),
REG_JNI(register_android_graphics_BLASTBufferQueue),
REG_JNI(register_android_graphics_GraphicBuffer),
REG_JNI(register_android_graphics_SurfaceTexture),
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_GraphicsEnvironment),
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_LocalSocketImpl),
REG_JNI(register_android_net_NetworkUtils),
REG_JNI(register_android_os_MemoryFile),
REG_JNI(register_android_os_SharedMemory),
REG_JNI(register_android_os_incremental_IncrementalManager),
REG_JNI(register_com_android_internal_content_om_OverlayConfig),
REG_JNI(register_com_android_internal_os_ClassLoaderFactory),
REG_JNI(register_com_android_internal_os_Zygote),
REG_JNI(register_com_android_internal_os_ZygoteInit),
REG_JNI(register_com_android_internal_util_VirtualRefBasePtr),
REG_JNI(register_android_hardware_Camera),
REG_JNI(register_android_hardware_camera2_CameraMetadata),
REG_JNI(register_android_hardware_camera2_legacy_LegacyCameraDevice),
REG_JNI(register_android_hardware_camera2_legacy_PerfMeasurement),
REG_JNI(register_android_hardware_camera2_DngCreator),
REG_JNI(register_android_hardware_display_DisplayManagerGlobal),
REG_JNI(register_android_hardware_HardwareBuffer),
REG_JNI(register_android_hardware_SensorManager),
REG_JNI(register_android_hardware_SerialPort),
REG_JNI(register_android_hardware_UsbDevice),
REG_JNI(register_android_hardware_UsbDeviceConnection),
REG_JNI(register_android_hardware_UsbRequest),
REG_JNI(register_android_hardware_location_ActivityRecognitionHardware),
REG_JNI(register_android_media_AudioDeviceAttributes),
REG_JNI(register_android_media_AudioEffectDescriptor),
REG_JNI(register_android_media_AudioSystem),
REG_JNI(register_android_media_AudioRecord),
REG_JNI(register_android_media_AudioTrack),
REG_JNI(register_android_media_AudioAttributes),
REG_JNI(register_android_media_AudioProductStrategies),
REG_JNI(register_android_media_AudioVolumeGroups),
REG_JNI(register_android_media_AudioVolumeGroupChangeHandler),
REG_JNI(register_android_media_MediaMetrics),
REG_JNI(register_android_media_MicrophoneInfo),
REG_JNI(register_android_media_RemoteDisplay),
REG_JNI(register_android_media_ToneGenerator),
REG_JNI(register_android_media_midi),
REG_JNI(register_android_opengl_classes),
REG_JNI(register_android_server_NetworkManagementSocketTagger),
REG_JNI(register_android_ddm_DdmHandleNativeHeap),
REG_JNI(register_android_backup_BackupDataInput),
REG_JNI(register_android_backup_BackupDataOutput),
REG_JNI(register_android_backup_FileBackupHelperBase),
REG_JNI(register_android_backup_BackupHelperDispatcher),
REG_JNI(register_android_app_backup_FullBackup),
REG_JNI(register_android_app_Activity),
REG_JNI(register_android_app_ActivityThread),
REG_JNI(register_android_app_NativeActivity),
REG_JNI(register_android_util_jar_StrictJarFile),
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),
REG_JNI(register_android_view_MotionEvent),
REG_JNI(register_android_view_PointerIcon),
REG_JNI(register_android_view_VelocityTracker),
REG_JNI(register_android_view_VerifiedKeyEvent),
REG_JNI(register_android_view_VerifiedMotionEvent),
REG_JNI(register_android_content_res_ObbScanner),
REG_JNI(register_android_content_res_Configuration),
REG_JNI(register_android_animation_PropertyValuesHolder),
REG_JNI(register_android_security_Scrypt),
REG_JNI(register_com_android_internal_content_NativeLibraryHelper),
REG_JNI(register_com_android_internal_os_FuseAppLoop),
REG_JNI(register_com_android_internal_os_KernelCpuUidBpfMapReader),
REG_JNI(register_com_android_internal_os_KernelSingleUidTimeReader),
};
注解
在Andorid中，每个进程运行在对应的虚拟机上，因此zygote首先就会负责创建出虚拟机
为了反射调用java代码，必须有对应的JNI函数，因此zygote进行JNI函数的注册
11.2.3.3. ZygoteInit
public class ZygoteInit {
... ...
public static void main(String argv[]) {
//调用native函数，确保当前没有其他线程在运行，主要还是处于安全的考虑
ZygoteHooks.startZygoteNoThreadCreation();
... ...
try {
... ...
boolean startSystemServer = false;
String zygoteSocketName = "zygote";
String abiList = null;
boolean enableLazyPreload = false;
//解析参数，得到上述变量的值
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {
startSystemServer = true;
} else if ("--enable-lazy-preload".equals(argv[i])) {
enableLazyPreload = true;
} else if (argv[i].startsWith(ABI_LIST_ARG)) {
abiList = argv[i].substring(ABI_LIST_ARG.length());
} else if (argv[i].startsWith(SOCKET_NAME_ARG)) {
zygoteSocketName = argv[i].substring(SOCKET_NAME_ARG.length());
} else {
throw new RuntimeException("Unknown command line argument: " + argv[i]);
}
}
... ...
if (!enableLazyPreload) {
bootTimingsTraceLog.traceBegin("ZygotePreload");
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_START,
SystemClock.uptimeMillis());
preload(bootTimingsTraceLog); //默认情况，预加载信息
EventLog.writeEvent(LOG_BOOT_PROGRESS_PRELOAD_END,
SystemClock.uptimeMillis());
bootTimingsTraceLog.traceEnd(); // ZygotePreload
}
//创建zygoteserver对象
zygoteServer = new ZygoteServer(isPrimaryZygote);
if (startSystemServer) {
//启动systemserver
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);
// {@code r == null} in the parent (zygote) process, and {@code r != null} in the
// child (system_server) process.
if (r != null) {
r.run();
return;
}
}
Log.i(TAG, "Accepting command socket connections");
// The select loop returns early in the child process after a fork and
// loops forever in the zygote.
//zygote进程进入无限循环，处理请求
caller = zygoteServer.runSelectLoop(abiList);
}
}
};
Zygote.main 函数除了安全相关的内容外，主要的工作就是注册 server socket, 预加载，启动systemserver以及进入无限循环处理请求消息
//frameworks/base/core/java/android/internal/os/ZygoteInit.java
static void preload(TimingsTraceLog bootTimingsTraceLog) {
Log.d(TAG, "begin preload");
bootTimingsTraceLog.traceBegin("BeginPreload");
beginPreload();
bootTimingsTraceLog.traceEnd(); // BeginPreload
bootTimingsTraceLog.traceBegin("PreloadClasses");
preloadClasses(); //读取文件system/etc/preloaded-classes,然后通过反射加载对应的类
bootTimingsTraceLog.traceEnd(); // PreloadClasses
bootTimingsTraceLog.traceBegin("CacheNonBootClasspathClassLoaders");
cacheNonBootClasspathClassLoaders();
bootTimingsTraceLog.traceEnd(); // CacheNonBootClasspathClassLoaders
bootTimingsTraceLog.traceBegin("PreloadResources");
preloadResources(); //负责加载一些常用的系统资源
bootTimingsTraceLog.traceEnd(); // PreloadResources
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "PreloadAppProcessHALs");
nativePreloadAppProcessHALs();
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
Trace.traceBegin(Trace.TRACE_TAG_DALVIK, "PreloadGraphicsDriver");
maybePreloadGraphicsDriver();
Trace.traceEnd(Trace.TRACE_TAG_DALVIK);
preloadSharedLibraries(); //一些必要库
preloadTextResources(); //语言相关的字符信息
// Ask the WebViewFactory to do any initialization that must run in the zygote process,
// for memory sharing purposes.
WebViewFactory.prepareWebViewInZygote();
endPreload();
warmUpJcaProviders(); //安全相关的
Log.d(TAG, "end preload");
sPreloadComplete = true;
}
为了让系统运行时更加流畅，在zygote启动的时候，调用 preload 进行了一些 预加载操作