LocalSocket

LocalSocket

在Unix域名空间创建一个套接字（非服务端）。
　　是对Linux中Socket进行了封装，采用JNI方式调用，实现进程间通信。
　　具体就是Native层Server和Framework层Client之间进行通信，或在各层次中能使用Client/Server模式实现通信。

LocalServerSocket

创建服务器端Unix域套接字，与LocalSocket对应。

LocalSocketImpl

Framework层Socket的实现，通过JNI调用系统socket API。

JNI访问接口：
\frameworks\base\core\jni\android_net_LocalSocketImpl.cpp

socket_create

socket_connect_local

socket_bind_local

socket_listen

增加socket资源

\system\core\rootdir\init.rc中：

　　service installd /system/bin/installd
          class main
          socket installd stream 600 system system

在启动install服务时，就会为install分配socket文件系统资源：dev/socket/installd
Install服务的Socket资源和名称installd绑定起来。
这些都是在开机初始化化init进程中启动service时完成：

        for (si = svc->sockets; si; si = si->next) {
            int socket_type = (
                    !strcmp(si->type, "stream") ? SOCK_STREAM :
                        (!strcmp(si->type, "dgram") ? SOCK_DGRAM : SOCK_SEQPACKET));
            int s = create_socket(si->name, socket_type,
                                  si->perm, si->uid, si->gid);
            if (s >= 0) {
                publish_socket(si->name, s);
            }
        }

native层

native 层中作为server：\frameworks\base\cmds\installd\installd.c

int main(const int argc, const char *argv[]) 
{
    //获取已绑定socket
    lsocket = android_get_control_socket(SOCKET_PATH);

    //监听socket
    listen(lsocket, 5);

    for (;;) {
        //等待客户端建立连接
        s = accept(lsocket, &addr, &alen);
        for (;;) {
                 //接收数据 相当于recv
                 readx(s, buf, count);

                 //执行相关的操作
                execute(s, buf);
        }

        //关闭socket
        close(s);
    }
}             

class FrameworkListener : public SocketListener {
public:
    static const int CMD_ARGS_MAX = 16;
private:
    FrameworkCommandCollection *mCommands;
 
public:
    FrameworkListener(const char *socketName);
    virtual ~FrameworkListener() {}
 
protected:
    void registerCmd(FrameworkCommand *cmd);
    virtual bool onDataAvailable(SocketClient *c);
 
private:
    void dispatchCommand(SocketClient *c, char *data);
};
bool FrameworkListener::onDataAvailable(SocketClient *c) {
    char buffer[255];
    int len;
 
    if ((len = read(c->getSocket(), buffer, sizeof(buffer) -1)) < 0) {
        SLOGE("read() failed (%s)", strerror(errno));
        return errno;
    } else if (!len)
        return false;
 
    int offset = 0;
    int i;
 
    for (i = 0; i < len; i++) {
        if (buffer[i] == '\0') {
            dispatchCommand(c, buffer + offset);
            offset = i + 1;
        }
    }
    return true;
}

framework层

\frameworks\base\services\java\com\android\server\pm\Installer.java

boolean connect() 
{
       //创建socket
       mSocket = new LocalSocket();

       //设置连接地址
       LocalSocketAddress address = new             LocalSocketAddress("installd",
                    LocalSocketAddress.Namespace.RESERVED);

       //建立连接
       mSocket.connect(address);

       //获取数据输入流 可以读数据
       mIn = mSocket.getInputStream();

       //获取数据输出流 可以写数据
       mOut = mSocket.getOutputStream();
}