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
- see runSelectLoopMode()
- 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
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