zygoteinit.java_Zygote解析

一、Zygote简介

init会创建Zygote进程，SystemServer进程和应用进程都是Zygote(孵化器)fock(复制进程)出来的。所以有必要了解下Zygote的流程。

二、Zygote启动流程

分析Zygote启动首先会调用ZygoteInit的main函数。

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

public static void main(String argv[]) {

......

try {

......

//创建Server Socket

zygoteServer.registerServerSocketFromEnv(socketName);

......

if (startSystemServer) {

//创建启动SystemServer进程

Runnable r = forkSystemServer(abiList, socketName, zygoteServer);

......

}

......

//等待AMS socket连接，请求fork新进程

caller = zygoteServer.runSelectLoop(abiList);

} catch (Throwable ex) {

Log.e(TAG, "System zygote died with exception", ex);

throw ex;

} finally {

zygoteServer.closeServerSocket();

}

......

}

ZygoteInit的main函数主要功能：

1.创建Server Socket

2.创建和启动SystemServer进程

3.等待AMS连接socke和发送创建新进程的请求

2.1创建Server Socket

frameworks/base/core/java/com/android/internal/os/ZygoteServer.java

void registerServerSocketFromEnv(String socketName) {

if (mServerSocket == null) {

......

try {

FileDescriptor fd = new FileDescriptor();

fd.setInt$(fileDesc);

mServerSocket = new LocalServerSocket(fd);//创建服务端的Socket

mCloseSocketFd = true;

} catch (IOException ex) {

throw new RuntimeException(

"Error binding to local socket '" + fileDesc + "'", ex);

}

}

}

创建的LocalServerSocket就是Server端的socket，会在runSelectLoop中调用LocalServerSocket.accept函数等待AMS连接。

2.2启动SystemServer进程

frameworks/base/core/java/com/android/internal/os/ZygoteInit.java

private static Runnable forkSystemServer(String abiList, String socketName,

ZygoteServer zygoteServer) {

......

try {

......

//请求fork System Server进程

pid = Zygote.forkSystemServer(

parsedArgs.uid, parsedArgs.gid,

parsedArgs.gids,

parsedArgs.runtimeFlags,

null,

parsedArgs.permittedCapabilities,

parsedArgs.effectiveCapabilities);

} catch (IllegalArgumentException ex) {

throw new RuntimeException(ex);

}

/* For child process */

if (pid == 0) {

......

//启动SystemServer进程

return handleSystemServerProcess(parsedArgs);

}

return null;

}

2.3fork新进程

runSelectLoop函数开启一个守护线程，等待AMS连接或者求情创建进程

frameworks/base/core/java/com/android/internal/os/ZygoteServer.java

Runnable runSelectLoop(String abiList) {

while (true) {

......

for (int i = pollFds.length - 1; i >= 0; --i) {

......

if (i == 0) {

ZygoteConnection newPeer = acceptCommandPeer(abiList);//等待AMS connect

peers.add(newPeer);

fds.add(newPeer.getFileDesciptor());

} else {

try {

ZygoteConnection connection = peers.get(i);

final Runnable command = connection.processOneCommand(this);//创建新进程

......

}

} catch (Exception e) {

......

} finally {

......

}

}

}

}

}

acceptCommandPeer函数最终会调用LocalServerSocket.accept函数等待AMS连接，当AMS连接成功后会调用processOneCommand函数创建新进程。

private ZygoteConnection acceptCommandPeer(String abiList) {

try {

return createNewConnection(mServerSocket.accept(), abiList);

} catch (IOException ex) {

throw new RuntimeException(

"IOException during accept()", ex);

}

}

frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java

Runnable processOneCommand(ZygoteServer zygoteServer) {

......

//fork 进程

pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,

parsedArgs.runtimeFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,

parsedArgs.niceName, fdsToClose, fdsToIgnore, parsedArgs.startChildZygote,

parsedArgs.instructionSet, parsedArgs.appDataDir);

try {

if (pid == 0) {

// in child

zygoteServer.setForkChild();

zygoteServer.closeServerSocket();

IoUtils.closeQuietly(serverPipeFd);

serverPipeFd = null;

return handleChildProc(parsedArgs, descriptors, childPipeFd,

parsedArgs.startChildZygote);

} else {

// In the parent. A pid < 0 indicates a failure and will be handled in

// handleParentProc.

IoUtils.closeQuietly(childPipeFd);

childPipeFd = null;

handleParentProc(pid, descriptors, serverPipeFd);

return null;

}

} finally {

IoUtils.closeQuietly(childPipeFd);

IoUtils.closeQuietly(serverPipeFd);

}

}

三、时序图

在这里插入图片描述