Android Zygote Startup
Here are some miscellaneous notes on Android startup of the zygote process.
This information is true for eclair, as of August 2010.
Sequence of Zygote startup steps
· init runs the C++ program /system/bin/app_process, and gives the resulting process the name "zygote"
· This is based on the line from init.rc:
service zygote /system/bin/app_process -Xzygote /system/bin --zygote --start-system-server
· app_process executes, and executes a runtime environment for a dalvik class
· app_process usage claims to be:
Usage: app_process [java-options] cmd-dir start-class-name [options]
·
· but you can specify --zygote in place of the start-class-name.
· In the bootup case, --zygote is used
· source for 'app_process is in frameworks/base/cmds/app_process/app_main.cpp
· this is the program to debug when debugging zygote/dalvik itself
· app_process does a 'runtime.start("com.android.internal.os.ZygoteInit", startSystemServer)
· the startSystemServer flag is passed as a parameter on to app_process, to indicate whether to start the system server (duh)
· runtime is an instance of class AppRuntime, which is sub-classed from AndroidRuntime
· AndroidRuntime is the main class for starting the dalvik runtime environment
· source is in frameworks/base/core/jni/AndroidRuntime.cpp
· the start() method starts the virtual machine
· LOG_BOOT_PROGRESS_START is emitted, with systemTime(SYSTEM_TIME_MONOTONIC)
· startVM() is called
· eventually, callStaticVoidMethod() is called, to actually start executing the start class with method "main" in Dalvik code
· com.android.internal.os.ZygoteInit:main() starts executing
· source is at: frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
· the profiler is started
· the Zygote socket is registered (for later communication to start apps)
· classes and resources are preloaded
· if startSystemServer is set, then the system server is started
· the command line to the system server is:
--setuid=1000 --setgid=1000 \
--setgroups=1001,1002,1003,1004,1005,1006,1007,1008,1009,1010,3001,3002,3003 \
--capabilities=130104352,130104352 \
--runtime-init \
--nice-name=system_server \
com.android.server.SystemServer
·
· the class which starts executing is: com.android.server.SystemServer
· a call is made to Zygote.forkSystemServer() to actually start this other process
· zygote runs in "select loop mode", where a single process spins waiting for communication to start subsequent apps
· see runSelectLoopMode()
· new connections are accepted (and put into array "peers")
· the spawn command received over the network is executed by calling the runOnce() method
· source code for this is at: frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
· eventually, a call is made to Zygote.forkAndSpecialize(), which does the actual forking
Sequence of system_server (or SystemServer) startup steps
Source for the SystemServer is in:frameworks/base/services/java/com/android/server/SystemServer.java
in the "ServerThread::run()" method, the following startup occurs:
· LOG_BOOT_PROGRESS_SYSTEM_RUN is emitted
· Lots of critical services are started:
· Entropy Service
· Power Manager
· Activity Manager
· Telephony Registry
· Package Manager
· Account Manager
· Content Manager
· System Content Providers
· Battery Service
· Hardware Service
· Alarm Manager
· Init Watchdog
· Sensor Service
· Window Manager
· Additional services may be started as well:
· Status Bar
· Clipboard Service
· Input Method Service
· NetStat Service
· Connectivity Service
· Accessibility Manager
· Notification Manager
· Mount Service
· Device Storage Monitor
· Location Manager
· Search Service
· Checkin Service
· Wallpaper Service
· Audio Service
· Headset Observer
· Dock Observer
· Backup Service
· AppWidget Service
http://elinux.org/Android_Zygote_Startup
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