Android Zygote介绍

1. 介绍

Zygote是Android系统创建新进程的核心进程，负责启动Dalvik虚拟机，加载一些必要的系统资源和系统类，启动system_server进程，随后进入等待处理app应用请求

Zygote涉及的主要代码如下

frameworks/base/cmds/app_process/App_main.cpp
frameworks/base/core/jni/AndroidRuntime.cpp

frameworks/base/core/java/com/android/internal/os/
  - Zygote.java
  - ZygoteInit.java
  - ZygoteServer.java
  - ZygoteConnection.java

2. 启动

Zygote进程由init启动，在笔者开发板上是以app_process64为主模式，app_process为辅

# /vendor/default.prop
ro.zygote=zygote64_32

# /init.rc
import /init.${ro.zygote}.rc
on zygote-start && property:ro.crypto.state=...
    # A/B update verifier that marks a successful boot.
    exec_start update_verifier_nonencrypted
    start netd
    start zygote
    start zygote_secondary

# /init.zygote64_32.rc
service zygote /system/bin/app_process64 -Xzygote /system/bin --zygote --start-system-server --socket-name=zygote
    class main
    priority -20
    user root
    group root readproc reserved_disk
    socket zygote stream 660 root system
    onrestart write /sys/android_power/request_state wake
    onrestart write /sys/power/state on
    onrestart restart audioserver
    onrestart restart cameraserver
    onrestart restart media
    onrestart restart netd
    onrestart restart wificond
    writepid /dev/cpuset/foreground/tasks

service zygote_secondary /system/bin/app_process32 -Xzygote /system/bin --zygote --socket-name=zygote_secondary --enable-lazy-preload
    class main
    priority -20
    user root
    group root readproc reserved_disk
    socket zygote_secondary stream 660 root system
    onrestart restart zygote
    writepid /dev/cpuset/foreground/tasks

属性 ro.zygote 的值包括zygote32、zygote64、zygote32_64、zygote64_32，对应区别如下：
- init.zygote32.rc：zygote进程对应的执行程序是app_process(纯32bit模式)
- init.zygote64.rc：zygote进程对应的执行程序是app_process64(纯64bit模式)
- init.zygote32_64.rc：启动两个zygote进程，对应的执行程序分别是app_process32(主模式)、app_process64
- init.zygote64_32.rc：启动两个zygote进程，对应的执行程序分别是app_process64(主模式)、app_process32

3. app_process

下面主要分析app_process

https://www.ctolib.com/topics-105450.html

https://www.jianshu.com/p/ab9b83a77af6

https://www.cnblogs.com/pepsimaxin/p/9448874.html

https://blog.csdn.net/kai_zone/article/details/81637315