在前面的文章中已經分析過了init進行rc文件的流程，以及執行rc文件內容的流程
這篇文章主要梳理下init進程是如何一步步啓動zygote進程的。
一，init.rc文件中對於zygote啓動的定義
首先我們看下init.rc文件中對於zygote的相關配置。
# It is recommended to put unnecessary data/ initialization from post-fs-data
# to start-zygote in device's init.rc to unblock zygote start.
on zygote-start && property:ro.crypto.state=unencrypted
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=unsupported
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
on zygote-start && property:ro.crypto.state=encrypted && property:ro.crypto.type=file
# A/B update verifier that marks a successful boot.
exec_start update_verifier_nonencrypted
start netd
start zygote
start zygote_secondary
從這部分代碼中我們可以看到，zygote的啓動是在zygote-start這個事件中啓動，並且ro.crypto.state屬性必須滿足上面的某一項。因爲我使用的機器取消了加密，因此走的是第一個流程。
根據前面的文章Android Q Init進程執行rc文件內容的流程分析我們並沒有看到init.cpp中有設置zygote-start這個事件，因此我們繼續查找這個事件的觸發機制，然後還是在init.rc中發現，這個事件是在on late-init的時候觸發的
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
# Now we can start zygote for devices with file based encryption
trigger zygote-start
# Load persist properties and override properties (if enabled) from /data.
trigger load_persist_props_action
# Remove a file to wake up anything waiting for firmware.
trigger firmware_mounts_complete
trigger early-boot
trigger boot
從上面這些配置中我們可以看出zygote的啓動流程是，init.cpp中配置了late-init事件，然後在執行late-init事件的時候，觸發了zygote-start事件，然後在zygote-start的時候，執行了start zygote以及start zygote_secondary啓動了zygote進程。
二，具體的執行流程分析
根據前面的文章Android Q Init進程執行rc文件內容的流程分析我們已經知道init在執行事件中的每條指令的時候，都會調用指令所對應的具體函數，通過查詢map對象我們知道執行trigger這個指令的函數是do_trigger函數。而傳遞的參數就是zygote-start
const BuiltinFunctionMap::Map& BuiltinFunctionMap::map() const {
constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
// clang-format off
static const Map 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_restart", {1, 1, {false, do_class_restart}}},
{"class_start", {1, 1, {false, do_class_start}}},
{"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}}},
{"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}}},
{"mkdir", {1, 4, {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", {1, kMax, {false, do_mount_all}}},
{"mount", {3, kMax, {false, do_mount}}},
{"umount", {1, 1, {false, do_umount}}},
{"readahead", {1, 2, {true, do_readahead}}},
{"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", {1, 1, {false, do_swapon_all}}},
{"symlink", {2, 2, {true, do_symlink}}},
{"sysclktz", {1, 1, {false, do_sysclktz}}},
{"trigger", {1, 1, {false, do_trigger}}},
{"verity_load_state", {0, 0, {false, do_verity_load_state}}},
{"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;
}
上面是具體的map定義，下面我們就看下do_trigger函數的具體實現。
static Result<Success> do_trigger(const BuiltinArguments& args) {
ActionManager::GetInstance().QueueEventTrigger(args[1]);
return Success();
}
上面可以看出，這個函數的實現非常簡單，就是直接將第二個參數（zygote-start）爲參數調用ActionManager的QueueEventTrigger。
void ActionManager::QueueEventTrigger(const std::string& trigger) {
event_queue_.emplace(trigger);
}
QueueEventTrigger這個函數就是直接使用參數構建action對象，然後添加到event_queue_的待執行列表中，然後這個列表會在後續調用ExecuteOneCommand的時候依次執行。
通過前面的分析，我們知道，在執行late-init的時候，在待執行的列表event_queue_有添加了一個新的事件（zygote-start）那麼在後續的執行的過程中就會執行到zygote-start這個事件。
通過前面的rc文件內容，我們可以知道在on zygote-start && property:ro.crypto.state=unencrypted 中有start zygote，以及start zygote_secondary，因此這裏最終會執行到start zygote的命令，根據前面的map對象，我們可以知道，執行start指令所對應的函數是do_start。因此我們先看下這個函數的實現。
static Result<Success> do_start(const BuiltinArguments& args) {
// 首先根據解析到的參數，從解析的服務列表中查詢對應的服務。
Service* svc = ServiceList::GetInstance().FindService(args[1]);
if (!svc) return Error() << "service " << args[1] << " not found";
if (auto result = svc->Start(); !result) { // 調用查詢到的服務的 start函數啓動對應的服務
return Error() << "Could not start service: " << result.error();
}
return Success();
}
這個函數的實現非常簡單，就是直接從保存的服務列表中，根據服務名稱查詢對應的服務，然後調用其Start函數啓動服務。
下面我們看下這個Start函數的具體實現。
Result<Success> Service::Start() {
bool disabled = (flags_ & (SVC_DISABLED | SVC_RESET));
// Starting a service removes it from the disabled or reset state and
// immediately takes it out of the restarting state if it was in there.
flags_ &= (~(SVC_DISABLED|SVC_RESTARTING|SVC_RESET|SVC_RESTART|SVC_DISABLED_START));
// Running processes require no additional work --- if they're in the
// process of exiting, we've ensured that they will immediately restart
// on exit, unless they are ONESHOT. For ONESHOT service, if it's in
// stopping status, we just set SVC_RESTART flag so it will get restarted
// in Reap().
// 如果當前服務已經開始運行了，直接返回成功
if (flags_ & SVC_RUNNING) {
if ((flags_ & SVC_ONESHOT) && disabled) {
flags_ |= SVC_RESTART;
}
// It is not an error to try to start a service that is already running.
return Success();
}
bool needs_console = (flags_ & SVC_CONSOLE);
if (needs_console) {
if (console_.empty()) {
console_ = default_console;
}
// Make sure that open call succeeds to ensure a console driver is
// properly registered for the device node
int console_fd = open(console_.c_str(), O_RDWR | O_CLOEXEC);
if (console_fd < 0) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Couldn't open console '" << console_ << "'";
}
close(console_fd);
}
struct stat sb;
if (stat(args_[0].c_str(), &sb) == -1) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Cannot find '" << args_[0] << "'";
}
std::string scon;
if (!seclabel_.empty()) {
scon = seclabel_;
} else {
auto result = ComputeContextFromExecutable(args_[0]);
if (!result) {
return result.error();
}
scon = *result;
}
LOG(INFO) << "starting service '" << name_ << "'...";
// 這裏執行fork 來fork出新的進程來運行目標程序
pid_t pid = -1;
if (namespace_flags_) {
pid = clone(nullptr, nullptr, namespace_flags_ | SIGCHLD, nullptr);
} else {
pid = fork();
}
if (pid == 0) { // 子進程中
umask(077);
if (auto result = EnterNamespaces(); !result) {
LOG(FATAL) << "Service '" << name_ << "' could not enter namespaces: " << result.error();
}
if (namespace_flags_ & CLONE_NEWNS) {
if (auto result = SetUpMountNamespace(); !result) {
LOG(FATAL) << "Service '" << name_
<< "' could not set up mount namespace: " << result.error();
}
}
if (namespace_flags_ & CLONE_NEWPID) {
// This will fork again to run an init process inside the PID
// namespace.
if (auto result = SetUpPidNamespace(); !result) {
LOG(FATAL) << "Service '" << name_
<< "' could not set up PID namespace: " << result.error();
}
}
for (const auto& [key, value] : environment_vars_) {
setenv(key.c_str(), value.c_str(), 1);
}
std::for_each(descriptors_.begin(), descriptors_.end(),
std::bind(&DescriptorInfo::CreateAndPublish, std::placeholders::_1, scon));
// See if there were "writepid" instructions to write to files under /dev/cpuset/.
auto cpuset_predicate = [](const std::string& path) {
return StartsWith(path, "/dev/cpuset/");
};
auto iter = std::find_if(writepid_files_.begin(), writepid_files_.end(), cpuset_predicate);
if (iter == writepid_files_.end()) {
// There were no "writepid" instructions for cpusets, check if the system default
// cpuset is specified to be used for the process.
std::string default_cpuset = GetProperty("ro.cpuset.default", "");
if (!default_cpuset.empty()) {
// Make sure the cpuset name starts and ends with '/'.
// A single '/' means the 'root' cpuset.
if (default_cpuset.front() != '/') {
default_cpuset.insert(0, 1, '/');
}
if (default_cpuset.back() != '/') {
default_cpuset.push_back('/');
}
writepid_files_.push_back(
StringPrintf("/dev/cpuset%stasks", default_cpuset.c_str()));
}
}
std::string pid_str = std::to_string(getpid());
for (const auto& file : writepid_files_) {
if (!WriteStringToFile(pid_str, file)) {
PLOG(ERROR) << "couldn't write " << pid_str << " to " << file;
}
}
if (ioprio_class_ != IoSchedClass_NONE) {
if (android_set_ioprio(getpid(), ioprio_class_, ioprio_pri_)) {
PLOG(ERROR) << "failed to set pid " << getpid()
<< " ioprio=" << ioprio_class_ << "," << ioprio_pri_;
}
}
if (needs_console) {
setsid();
OpenConsole();
} else {
ZapStdio();
}
// As requested, set our gid, supplemental gids, uid, context, and
// priority. Aborts on failure.
// 子進程給自己設置參數
SetProcessAttributes();
if (!ExpandArgsAndExecv(args_)) {
PLOG(ERROR) << "cannot execve('" << args_[0] << "')";
}
_exit(127);
}
if (pid < 0) { // 創建進行錯誤
pid_ = 0;
return ErrnoError() << "Failed to fork";
}
if (oom_score_adjust_ != -1000) {
std::string oom_str = std::to_string(oom_score_adjust_);
std::string oom_file = StringPrintf("/proc/%d/oom_score_adj", pid);
if (!WriteStringToFile(oom_str, oom_file)) {
PLOG(ERROR) << "couldn't write oom_score_adj: " << strerror(errno);
}
}
time_started_ = boot_clock::now();
pid_ = pid;
flags_ |= SVC_RUNNING;
start_order_ = next_start_order_++;
process_cgroup_empty_ = false;
errno = -createProcessGroup(uid_, pid_);
if (errno != 0) {
PLOG(ERROR) << "createProcessGroup(" << uid_ << ", " << pid_ << ") failed for service '"
<< name_ << "'";
} else {
if (swappiness_ != -1) {
if (!setProcessGroupSwappiness(uid_, pid_, swappiness_)) {
PLOG(ERROR) << "setProcessGroupSwappiness failed";
}
}
if (soft_limit_in_bytes_ != -1) {
if (!setProcessGroupSoftLimit(uid_, pid_, soft_limit_in_bytes_)) {
PLOG(ERROR) << "setProcessGroupSoftLimit failed";
}
}
if (limit_in_bytes_ != -1) {
if (!setProcessGroupLimit(uid_, pid_, limit_in_bytes_)) {
PLOG(ERROR) << "setProcessGroupLimit failed";
}
}
}
NotifyStateChange("running");
return Success();
}
這個函數比較複雜，我們可以看到函數調用fork創建了新的進程，這裏需要注意的是哪個是子進程，哪個是父進程。
然後在子進程中給zygote設置了各種參數，在子進程的最後調用了ExpandArgsAndExecv進一步處理，下面我們看下這個函數的實現。
static bool ExpandArgsAndExecv(const std::vector<std::string>& args) {
std::vector<std::string> expanded_args;
std::vector<char*> c_strings;
expanded_args.resize(args.size());
c_strings.push_back(const_cast<char*>(args[0].data()));
for (std::size_t i = 1; i < args.size(); ++i) {
if (!expand_props(args[i], &expanded_args[i])) {
LOG(FATAL) << args[0] << ": cannot expand '" << args[i] << "'";
}
c_strings.push_back(expanded_args[i].data());
}
c_strings.push_back(nullptr);
LOG(INFO) << "ExpandArgsAndExecv c_strings[0] = "<< c_strings[0];
// init]init: ExpandArgsAndExecv c_strings[0] = /system/bin/app_process64
// init]init: ExpandArgsAndExecv c_strings[0] = /system/bin/app_process32
// 執行c_strings[0]對應的文件。
// 比如啓動zygote64
return execv(c_strings[0], c_strings.data()) == 0;
}
ExpandArgsAndExecv這個函數的實現比較簡單，就是獲取待執行文件的路徑，然後調用execv執行待執行的具體文件，同時將參數傳遞過去。
至此init中關於zygote的啓動流程就分析完了，從return execv(c_strings[0], c_strings.data()) == 0;起函數的流程就走到了
/system/bin/app_process64這個可執行文件的main函數中。這個就是子進程的處理流程，而init進程在前面pid因爲不是0，因此在不會進入這個函數，在前面的Start函數中就已經退出進行下一輪循環了。
到這裏，代理執行流程就走到了/system/bin/app_process64中，經過搜索我們知道app_process64這個可運行文件的源文件是frameworks/base/cmds/app_process/app_main.cpp，下面我們看下這個文件的實現。
int main(int argc, char* const argv[])
{
// if (!LOG_NDEBUG) {
String8 argv_String;
for (int i = 0; i < argc; ++i) {
argv_String.append("\"");
argv_String.append(argv[i]);
argv_String.append("\" ");
}
ALOGD("app_process main with argv: %s", argv_String.string());
// 下面是啓動的兩個zygote的不同的參數信息
// appproc : app_process main with argv: "/system/bin/app_process32" "-Xzygote" "/system/bin" "--zygote" "--socket-name=zygote_secondary" "--enable-lazy-preload"
// appproc : app_process main with argv: "/system/bin/app_process64" "-Xzygote" "/system/bin" "--zygote" "--start-system-server" "--socket-name=zygote"
// }
AppRuntime runtime(argv[0], computeArgBlockSize(argc, argv));
// Process command line arguments
// ignore argv[0]
argc--;
argv++;
// 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.
//
// As an exception to the above rule, anything in "spaced commands"
// goes to the vm even though it has a space in it.
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
ALOGD("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]);
}
}
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.
bool zygote = false;
bool startSystemServer = false;
bool application = false;
String8 niceName;
String8 className;
// 下面是對參數的解析. 主要獲取前面四個變量的具體值
// 根據前面的參數我們可以知道zygote變量一定是 true，niceName 會根據啓動的參數不同，設置的是不一樣的。
// application 是false className 是空的。startSystemServer 根據具體的參數來決定的。
++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;
}
}
ALOGD("app_process niceName %s", niceName.string());
ALOGD("app_process className %s", className.string());
ALOGD("app_process zygote %d", zygote);
ALOGD("app_process startSystemServer %d", startSystemServer);
ALOGD("app_process application %d", application);
Vector<String8> args;
if (!className.isEmpty()) { // 由於className是空，因此這裏進不去，會走到else分支
// 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 {
// We're in zygote mode.
maybeCreateDalvikCache();
if (startSystemServer) {
args.add(String8("start-system-server"));
}
// 檢查 ro.product.cpu.abilist32 或者 ro.product.cpu.abilist64是否設置，具體檢測那個一，需要根據啓動的具體是32位還是64位來決定
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(), true /* setProcName */);
}
if (zygote) { // 由於前面的參數解析出來的zygote是true，因此這裏會進去
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.");
}
}
上面的diam流程比較簡單，就是解析參數，然後調用runtime.star函數進一步啓動，因爲AppRuntime繼承自AndroidRuntime，因此這個start函數的實現在AndroidRuntime.cpp中，下面看下AndroidRuntime.cpp中對於start函數的實現。
void AndroidRuntime::start(const char* className, const Vector<String8>& options, bool zygote)
{
ALOGD(">>>>>> START %s uid %d <<<<<<\n",className != NULL ? className : "(unknown)", getuid());
static const String8 startSystemServer("start-system-server");
/*
* '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) {
/* 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)));
addBootEvent("boot_progress_start");
}
}
const char* rootDir = getenv("ANDROID_ROOT");
ALOGD("AndroidRuntime::start rootDir = %s ",rootDir);
if (rootDir == NULL) {
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 啓動java虛擬機*/
JniInvocation jni_invocation;
jni_invocation.Init(NULL);
JNIEnv* env;
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
/*
* Register android functions.
* 註冊jni函數
*/
if (startReg(env) < 0) {
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.
* 這裏正式進入java世界，調用ZygoteInit.java 的main函數
*/
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 != NULL ? className : "");
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");
if (startMeth == NULL) {
ALOGE("JavaVM unable to find main() in '%s'\n", className);
/* keep going */
} else {
env->CallStaticVoidMethod(startClass, startMeth, strArray);
#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");
}
這個函數主要做了三件重要的事情，首先是啓動java虛擬機，然後註冊jni函數，之後調用調用ZygoteInit.java 的main函數正式進入java的世界。
接下來的流程就走到了ZygoteInit.java中，這個後續的流程，Android 10的總體流程與Android8.1的流程是一樣的，基本上沒有太大變化。接下來的流程大家可以看下我之前分析Android8.1的文章。