zygote篇

public static void main(String argv[]) {
    try {
        RuntimeInit.enableDdms(); //开启DDMS功能
        SamplingProfilerIntegration.start();
        boolean startSystemServer = false;
        String socketName = "zygote";
        String abiList = null;
        for (int i = 1; i < argv.length; i++) {
            if ("start-system-server".equals(argv[i])) {
                startSystemServer = 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)) {
                socketName = argv[i].substring(SOCKET_NAME_ARG.length());
            } else {
                throw new RuntimeException("Unknown command line argument: " + argv[i]);
            }
        }
        ...

        registerZygoteSocket(socketName); //为Zygote注册socket
        preload(); // 预加载类和资源
        SamplingProfilerIntegration.writeZygoteSnapshot();
        gcAndFinalize(); //GC操作
        if (startSystemServer) {
            startSystemServer(abiList, socketName);//启动system_server
        }
        runSelectLoop(abiList); //进入循环模式
        closeServerSocket();
    } catch (MethodAndArgsCaller caller) {
        caller.run(); //启动system_server中会讲到。
    } catch (RuntimeException ex) {
        closeServerSocket();
        throw ex;
    }
}

private static void runSelectLoop(String abiList) throws MethodAndArgsCaller {
    ArrayList<FileDescriptor> fds = new ArrayList<FileDescriptor>();
    ArrayList<ZygoteConnection> peers = new ArrayList<ZygoteConnection>();
    //sServerSocket是socket通信中的服务端，即zygote进程。保存到fds[0]
    fds.add(sServerSocket.getFileDescriptor());
    peers.add(null);

    while (true) {
        StructPollfd[] pollFds = new StructPollfd[fds.size()];
        for (int i = 0; i < pollFds.length; ++i) {
            pollFds[i] = new StructPollfd();
            pollFds[i].fd = fds.get(i);
            pollFds[i].events = (short) POLLIN;
        }
        try {
             //处理轮询状态，当pollFds有事件到来则往下执行，否则阻塞在这里
            Os.poll(pollFds, -1);
        } catch (ErrnoException ex) {
            ...
        }
        
        for (int i = pollFds.length - 1; i >= 0; --i) {
            //采用I/O多路复用机制，当接收到客户端发出连接请求 或者数据处理请求到来，则往下执行；
            // 否则进入continue，跳出本次循环。
            if ((pollFds[i].revents & POLLIN) == 0) {
                continue;
            }
            if (i == 0) {
                //即fds[0]，代表的是sServerSocket，则意味着有客户端连接请求；
                // 则创建ZygoteConnection对象,并添加到fds。
                ZygoteConnection newPeer = acceptCommandPeer(abiList);
                peers.add(newPeer);
                fds.add(newPeer.getFileDesciptor()); //添加到fds.
            } else {
                //i>0，则代表通过socket接收来自对端的数据，并执行相应操作
                boolean done = peers.get(i).runOnce();
                if (done) {
                    peers.remove(i);
                    fds.remove(i); //处理完则从fds中移除该文件描述符
                }
            }
        }
    }
}