Android12之ServiceManager::addService注册服务的本质(一百五十八)

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1.前言

本篇目的：理解ServiceManager成员函数addService是如何添加服务的。

2.ServiceManager::addService如何添加服务实现

Status ServiceManager::addService(const std::string& name, const sp<IBinder>& binder, bool allowIsolated, int32_t dumpPriority) {
    auto ctx = mAccess->getCallingContext();

    // apps cannot add services
    if (multiuser_get_app_id(ctx.uid) >= AID_APP) {
        return Status::fromExceptionCode(Status::EX_SECURITY);
    }

    if (!mAccess->canAdd(ctx, name)) {
        return Status::fromExceptionCode(Status::EX_SECURITY);
    }

    if (binder == nullptr) {
        return Status::fromExceptionCode(Status::EX_ILLEGAL_ARGUMENT);
    }

    if (!isValidServiceName(name)) {
        LOG(ERROR) << "Invalid service name: " << name;
        return Status::fromExceptionCode(Status::EX_ILLEGAL_ARGUMENT);
    }

#ifndef VENDORSERVICEMANAGER
    if (!meetsDeclarationRequirements(binder, name)) {
        // already logged
        return Status::fromExceptionCode(Status::EX_ILLEGAL_ARGUMENT);
    }
#endif  // !VENDORSERVICEMANAGER

    // implicitly unlinked when the binder is removed
    if (binder->remoteBinder() != nullptr &&
        binder->linkToDeath(sp<ServiceManager>::fromExisting(this)) != OK) {
        LOG(ERROR) << "Could not linkToDeath when adding " << name;
        return Status::fromExceptionCode(Status::EX_ILLEGAL_STATE);
    }

    // Overwrite the old service if it exists
    mNameToService[name] = Service {
        .binder = binder,
        .allowIsolated = allowIsolated,
        .dumpPriority = dumpPriority,
        .debugPid = ctx.debugPid,
    };

    auto it = mNameToRegistrationCallback.find(name);
    if (it != mNameToRegistrationCallback.end()) {
        for (const sp<IServiceCallback>& cb : it->second) {
            mNameToService[name].guaranteeClient = true;
            // permission checked in registerForNotifications
            cb->onRegistration(name, binder);
        }
    }

    return Status::ok();
}

<1>.关键点

mNameToService[name] = Service {
.binder = binder,
.allowIsolated = allowIsolated,
.dumpPriority = dumpPriority,
.debugPid = ctx.debugPid,
};

<2>.注释

其中name表示服务名，binder表示每个服务的实例对象,将他们存放在mNameToService里面，那么mNameToService是什么类型呢？接着往下看

<3>.mNameToService定义

# ServiceManager.h
struct Service {
        sp<IBinder> binder; // not null
        bool allowIsolated;
        int32_t dumpPriority;
        bool hasClients = false; // notifications sent on true -> false.
        bool guaranteeClient = false; // forces the client check to true
        pid_t debugPid = 0; // the process in which this service runs

        // the number of clients of the service, including servicemanager itself
        ssize_t getNodeStrongRefCount();
    };
using ServiceMap = std::map<std::string, Service>;
ServiceMap mNameToService;

  由以上代码可以看到mNameToService的类型是ServiceMap，ServiceMap又是std::map<std::string, Service>的别名，它是一个C++的STL的map容器，第一个参数是key，第二个是value。
  第一个参数的类型是string，第二个是Service类。

<4>.再看mNameToService[name]

mNameToService[name] = Service {
        .binder = binder,
        .allowIsolated = allowIsolated,
        .dumpPriority = dumpPriority,
        .debugPid = ctx.debugPid,
    };
我们再看上边表达式初始化，将类Service的所有成员变量插入到map容器，对应的key就是name，Service的成员变量包括.binder（表示服务类对象）,dumpPriority（表示优先级）。

3.addService应用实例

#include <cstdio>
#include <iostream>
#include <typeinfo>
#include <map>

using namespace std;

class Binder{
};

//struct Service {
class Service {
public:
  Binder *binder;
  bool allowIsolated;
  int32_t dumpPriority;
  bool hasClients = false;
  bool guaranteeClient = false;
  pid_t pid = 0;
  ssize_t getNodeStrongRefCount();
};

//using设置别名:ServiceMap;容器map第一个参数是key,第二个是value;value为Service,Service又是一个类,包含变量和函数.
using ServiceMap = map<string, Service>;
ServiceMap mNameToService;

int main(){

  Binder *binder1 = new Binder;
  string name = "manager";
  mNameToService[name] = Service {
    .binder = binder1,
    .allowIsolated = false,
    .dumpPriority = 20,
    .guaranteeClient = true,
    .pid = 10,
  };

  string name_01 = "camera";
  Binder *binder2 = new Binder;
  mNameToService[name_01] = Service {
    .binder = binder2,
    .allowIsolated = false,
    .dumpPriority = 24,
    .guaranteeClient = false,
    .pid = 11,
  };

  //first:表示key的值;second:表示value的值,即Service.
  for(const auto& pair : mNameToService) {
    printf("xxx-------->line = %d, first_name = %s, priority = %d, pid = %d\n",__LINE__,pair.first.c_str(), pair.second.dumpPriority,pair.second.pid);
  }
}