*注:基于Android11源码
ServiceManager进程是在init进程创建的，所以我们从init进程的main(）开始分析：
// 文件路径： system/core/init/main.cpp
int main(int argc, char** argv) {
...
if (!strcmp(argv[1], "second_stage")) { //TODO 根据条件会走到这个分支
return SecondStageMain(argc, argv);
}
}
int SecondStageMain(int argc, char** argv) {
...
//用来存放解析出的内容
ActionManager& am = ActionManager::GetInstance();
ServiceList& sm = ServiceList::GetInstance();
//在这个方法中会对 /system/core/rootdir/init.rc 脚本文件文件进行解析
LoadBootScripts(am, sm);
//循环处理init.rc脚本中的command命令，处理完就进入等待
while (true) {
if (!(prop_waiter_state.MightBeWaiting() || Service::is_exec_service_running()))
{
//内部遍历执行每个action中携带的command对应的执行函数
am.ExecuteOneCommand();
}
}
}
static void LoadBootScripts(ActionManager& action_manager, ServiceList& service_list) {
//创建解析器
Parser parser = CreateParser(action_manager, service_list);
std::string bootscript = GetProperty("ro.boot.init_rc", "");
if (bootscript.empty()) {
//解析init.rc ,这个是手机设备上的路径，和源码中system/core/init/init.rc是一个文件
parser.ParseConfig("/system/etc/init/hw/init.rc");
if (!parser.ParseConfig("/system/etc/init")) {
late_import_paths.emplace_back("/system/etc/init");
}
// late_import is available only in Q and earlier release. As we don't
// have system_ext in those versions, skip late_import for system_ext.
parser.ParseConfig("/system_ext/etc/init");
if (!parser.ParseConfig("/product/etc/init")) {
late_import_paths.emplace_back("/product/etc/init");
}
if (!parser.ParseConfig("/odm/etc/init")) {
late_import_paths.emplace_back("/odm/etc/init");
}
if (!parser.ParseConfig("/vendor/etc/init")) {
late_import_paths.emplace_back("/vendor/etc/init");
}
} else {
parser.ParseConfig(bootscript);
}
}
下面是init.rc中启动servicemanager进程相关的部分：
on init
# Start essential services.
start servicemanager #启动servicemanager进程
start hwservicemanager
start vndservicemanager
有关servicemanager进程启动的细节配置被放在了 frameworks\native\cmds\servicemanager\servicemanager.rc
#此脚本文件描述了启动servicemanager进程时的一些细节
#service用于通知init进程创建名为servicemanager的进程，这个进程执行程序的路径是/system/bin/servicemanager
#在手机系统中是能找到这个文件的
service servicemanager /system/bin/servicemanager
class core animation
#表明此进程是以system身份运行的
user system
group system readproc
#说明servicemanager是系统中的关键服务，关键服务是不会退出的，若退出系统则会重启，系统重启则会重启
#以下onrestart修饰的进程，也可以说明这些进程是依赖于servicemanager进程的
critical
onrestart restart healthd
onrestart restart zygote
onrestart restart audioserver
onrestart restart media
onrestart restart surfaceflinger
onrestart restart inputflinger
onrestart restart drm
onrestart restart cameraserver
onrestart restart keystore
onrestart restart gatekeeperd
onrestart restart thermalservice
writepid /dev/cpuset/system-background/tasks
shutdown critical
当执行到 start servicemanager 这条命令，就会运行android设备（比如手机）中 /system/bin/servicemanager这个可执行文件，而这个可执行程序就是servicemanager进程，他由 frameworks\native\cmds\servicemanager\main.cpp 文件编译生成的。什么？你不信？打开frameworks\native\cmds\servicemanager\Android.bp,这就是证据：
...
# cc_binary表示编译成一个二进制文件
cc_binary {
name: "servicemanager", #文件名
defaults: ["servicemanager_defaults"],
init_rc: ["servicemanager.rc"], #配置详情
srcs: ["main.cpp"], #要编译的源文件
}
...
这样我们就知道运行servicemanager这个可执行文件就是运行到了frameworks\native\cmds\servicemanager\main.cpp这个文件了。
int main(int argc, char** argv) {
if (argc > 2) {
LOG(FATAL) << "usage: " << argv[0] << " [binder driver]";
}
//此时要使用的binder驱动为 "/dev/binder"，同样这个路径也是android设备上的路径
const char* driver = argc == 2 ? argv[1] : "/dev/binder";
//打开binder驱动文件并将此进程与binder驱动进行内存映射，ProcessState是用来保存进程状态的一个类
sp<ProcessState> ps = ProcessState::initWithDriver(driver); //注释1
//设置最大线程数
ps->setThreadPoolMaxThreadCount(0);
ps->setCallRestriction(ProcessState::CallRestriction::FATAL_IF_NOT_ONEWAY);
//实例化ServiceManager
sp<ServiceManager> manager = new ServiceManager(std::make_unique<Access>());
//将自身作为服务添加
if (!manager->addService("manager", manager, false /*allowIsolated*/, IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT).isOk()) {
LOG(ERROR) << "Could not self register servicemanager";
}
//创建服务端Bbinder对象
IPCThreadState::self()->setTheContextObject(manager); //注释2
//设置称为binder驱动的context manager，称为上下文的管理者
ps->becomeContextManager(nullptr, nullptr);
//通过Looper epoll机制处理binder事务
sp<Looper> looper = Looper::prepare(false /*allowNonCallbacks*/);
//Binder驱动中数据变化的监听
BinderCallback::setupTo(looper); //注释3
ClientCallbackCallback::setupTo(looper, manager);
while(true) {
looper->pollAll(-1);
}
// should not be reached
return EXIT_FAILURE;
}
先看注释1:
//frameworks\native\libs\binder\ProcessState.cpp
sp<ProcessState> ProcessState::initWithDriver(const char* driver)
{
Mutex::Autolock _l(gProcessMutex);
if (gProcess != nullptr) {
// Allow for initWithDriver to be called repeatedly with the same
// driver. 允许使用同一驱动程序重复调用initWithDriver()
if (!strcmp(gProcess->getDriverName().c_str(), driver)) {//若当前ProcessState对象的驱动与传参不同
return gProcess; //直接返回现有的ProcessState对象
}
LOG_ALWAYS_FATAL("ProcessState was already initialized.");
}
if (access(driver, R_OK) == -1) {
ALOGE("Binder driver %s is unavailable. Using /dev/binder instead.", driver);
driver = "/dev/binder";
}
//第一次调用gProcess为空，走这里
gProcess = new ProcessState(driver); //创建新对象
return gProcess;
}
//ProcessState类的构造函数
ProcessState::ProcessState(const char *driver)
: mDriverName(String8(driver)) //以下都是成员变量初始化赋值，设置驱动名
, mDriverFD(open_driver(driver)) //打开驱动文件，拿到驱动文件的文件描述符
, mVMStart(MAP_FAILED)
, mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
, mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
, mExecutingThreadsCount(0)
, mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
, mStarvationStartTimeMs(0)
, mBinderContextCheckFunc(nullptr)
, mBinderContextUserData(nullptr)
, mThreadPoolStarted(false)
, mThreadPoolSeq(1)
, mCallRestriction(CallRestriction::NONE)
{
if (mDriverFD >= 0) { //大于0，说明打开binder驱动成功
// mmap内存映射，提供一块虚拟地址空间来接收事务（即从客户端发送的请求(数据)）。
// BINDER_VM_SIZE 地址空间大小BINDER_VM_SIZE = 1M - 8k
mVMStart = mmap(nullptr, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);
if (mVMStart == MAP_FAILED) {//映射失败
// *sigh*
ALOGE("Using %s failed: unable to mmap transaction memory.\n", mDriverName.c_str());
close(mDriverFD);
mDriverFD = -1;
mDriverName.clear();
}
}
...
}
static int open_driver(const char *driver)
{
//得到驱动的文件描述符
int fd = open(driver, O_RDWR | O_CLOEXEC);
if (fd >= 0) {
int vers = 0;
//binder驱动版本检查
status_t result = ioctl(fd, BINDER_VERSION, &vers);
if (result == -1) {
ALOGE("Binder ioctl to obtain version failed: %s", strerror(errno));
close(fd);
fd = -1;
}
if (result != 0 || vers != BINDER_CURRENT_PROTOCOL_VERSION) {
ALOGE("Binder driver protocol(%d) does not match user space protocol(%d)! ioctl() return value: %d",
vers, BINDER_CURRENT_PROTOCOL_VERSION, result);
close(fd);
fd = -1;
}
size_t maxThreads = DEFAULT_MAX_BINDER_THREADS;
//给驱动设置最大线程数
result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
if (result == -1) {
ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
} else {
ALOGW("Opening '%s' failed: %s\n", driver, strerror(errno));
}
return fd;
}
接下来到注释2部分：
// frameworks\native\libs\binder\IPCThreadState.cpp
//IPCThreadState是线程单例
IPCThreadState* IPCThreadState::self()
{
//不是初次调用的情况，TLS的全称为Thread Local Storage
if (gHaveTLS.load(std::memory_order_acquire)) {
restart:
//初次调用，生成线程私有变量key后
//TLS 表示线程本地存储空间，和java中的ThreadLocal是一个意思
const pthread_key_t k = gTLS;
IPCThreadState* st = (IPCThreadState*)pthread_getspecific(k);
if (st) return st;
//没有的话就实例化一个
return new IPCThreadState;
}
// Racey, heuristic test for simultaneous shutdown.
// IPCThreadState shutdown后不能再获取
if (gShutdown.load(std::memory_order_relaxed)) {
ALOGW("Calling IPCThreadState::self() during shutdown is dangerous, expect a crash.\n");
return nullptr;
}
// 首次获取时gHaveTLS为false，会先走这里
pthread_mutex_lock(&gTLSMutex);
if (!gHaveTLS.load(std::memory_order_relaxed)) {
//创建一个key，作为存放线程本地变量的key
int key_create_value = pthread_key_create(&gTLS, threadDestructor);
if (key_create_value != 0) {
pthread_mutex_unlock(&gTLSMutex);
ALOGW("IPCThreadState::self() unable to create TLS key, expect a crash: %s\n",
strerror(key_create_value));
return nullptr;
}
//创建完毕，gHaveTLS设置为true
gHaveTLS.store(true, std::memory_order_release);
}
pthread_mutex_unlock(&gTLSMutex);
// 回到gHaveTLS为true的case
goto restart;
}
sp<BBinder> the_context_object;
void IPCThreadState::setTheContextObject(sp<BBinder> obj)
{
//赋值给一个BBinder类型的成员变量，即传进来的这个manager就是服务端的BBinder
the_context_object = obj;
}
为了更好的理解ServiceManager这个类，下面是一张它的继承关系图：
下面来到注释3：
static sp<BinderCallback> setupTo(const sp<Looper>& looper) {
sp<BinderCallback> cb = new BinderCallback;
int binder_fd = -1;
//向binder驱动发送BC_ENTER_LOOPER事务请求，并获得binder驱动的文件描述符
IPCThreadState::self()->setupPolling(&binder_fd);
LOG_ALWAYS_FATAL_IF(binder_fd < 0, "Failed to setupPolling: %d", binder_fd);
// Flush after setupPolling(), to make sure the binder driver
// knows about this thread handling commands.
// 检查写缓存是否有可写数据，有的话发给binder驱动
IPCThreadState::self()->flushCommands();
// 监听binder文件描述符
int ret = looper->addFd(binder_fd,
Looper::POLL_CALLBACK,
Looper::EVENT_INPUT,
cb,
nullptr /*data*/);
LOG_ALWAYS_FATAL_IF(ret != 1, "Failed to add binder FD to Looper");
return cb;
}
// 当binder驱动发来消息后，就可以通过次函数接收处理了
int handleEvent(int /* fd */, int /* events */, void* /* data */) override {
//处理消息
IPCThreadState::self()->handlePolledCommands();
return 1; // Continue receiving callbacks.
}
};
servicemanager进程启动过程中，主要做了以下四件事：
1）初始化binder驱动
2）将自身以“manager” 添加到servicemanager中的map集合中
3）注册成为binder驱动的上下问管理者
- 给Looper设置callback,进入无限循环，处理client端发来的请求
总结：
1.ServiceManager是一个独立的进程，由init进程创建，且在创建zygote进程之前被创建。
2.IBinder是什么？它是实现了AIDL接口的实体类，它实现了接口中的所有方法。
标签：系统启动,流程,driver,binder,system,servicemanager,init,fd,ServiceManager From： https://www.cnblogs.com/linhaostudy/p/18301854