Android开发
深入理解Android之应用程序进程启动流程(Android 10)
本文主要是介绍深入理解Android之应用程序进程启动流程(Android 10)，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！
在上一篇文章深入理解Android 之 Activity启动流程中，应用程序根Activity的启动过程通过系统源码梳理了一遍，其中还有一个细节便是Android每个应用都是都是一个应用进程，而应用进程不会凭空产生，本文则通过系统源码继续探究Android应用程序进程启动流程（文中源码基于Android 10 ）。
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首先照例还是先看一个脑图，在自己大脑中能产生初步印象
ActivityManagerService请求Zygote启动应用程序进程
AMS处理启动应用程序基本数据
- 上一篇文章第二小节分析中提到了ActivityStackSupervisor的startSpecificActivityLocked的方法
frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
// Activity应用程序进程是否已经准备好
final WindowProcessController wpc =
mService.getProcessController(r.processName, r.info.applicationInfo.uid);
boolean knownToBeDead = false;
if (wpc != null && wpc.hasThread()) { //1
try {
realStartActivityLocked(r, wpc, andResume, checkConfig); //2
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
.......
}
.......
try {
.......
// Post message to start process to avoid possible deadlock of calling into AMS with the
// ATMS lock held. Hnadler发消息 避免死锁
final Message msg = PooledLambda.obtainMessage(
ActivityManagerInternal::startProcess, mService.mAmInternal, r.processName,
r.info.applicationInfo, knownToBeDead, "activity", r.intent.getComponent());//3
mService.mH.sendMessage(msg);
}
........
}
复制代码- 由以前源码注释1和2如果应用程序进程已经存在，则继续启动Activity逻辑，否则来到注释3出，我们看到关键部分ActivityManagerInternal::startProcess，"::"是Java 8 新增特性，相当于调用了ActivityManagerInternal的startProcess方法，而ActivityManagerInternal（frameworks/base/core/java/android/app/ActivityManagerInternal.java）是一个抽象类，它是Activity管理器本地服务接口，它的实现为AMS的内部类LocalService，它注册在AMS启动的过程，通过LocalServices（frameworks/base/core/java/com/android/server/LocalServices.java）注册，此类的使用方式与ServiceManager相似，不同之处在于，此处注册的服务不是Binder对象，并且只能在同一进程（SystemServer进程）中使用。也就是说ActivityManagerInternal实现类LocalService是SystemServer进程的本地服务Service，通过本地服务注册到LocalServices中，而AMS也是运行在SystemServer进程，则可以直接使用LocalService。所以注释3处调用了LocalService的startProcess方法
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@Override
public void startProcess(String processName, ApplicationInfo info,
boolean knownToBeDead, String hostingType, ComponentName hostingName) {
try {
if (Trace.isTagEnabled(Trace.TRACE_TAG_ACTIVITY_MANAGER)) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "startProcess:"
+ processName);
}
synchronized (ActivityManagerService.this) {
startProcessLocked(processName, info, knownToBeDead, 0 /* intentFlags */,
new HostingRecord(hostingType, hostingName),
false /* allowWhileBooting */, false /* isolated */,
true /* keepIfLarge */);//
}
}
.......
}
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
HostingRecord hostingRecord, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return mProcessList.startProcessLocked(processName, info, knownToBeDead, intentFlags,
hostingRecord, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */); //2
}
复制代码- 由以上源码注释1处调用了startProcessLocked方法，由注释2处则调用了 ProcessList的 startProcessLocked方法，ProcessList是处理Activity进程的管理类，接着往下看
frameworks/base/services/core/java/com/android/server/am/ProcessList.java
@GuardedBy("mService")
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, HostingRecord hostingRecord,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler) {
long startTime = SystemClock.elapsedRealtime();
ProcessRecord app;
..........
if (app == null) {
checkSlow(startTime, "startProcess: creating new process record");
app = newProcessRecordLocked(info, processName, isolated, isolatedUid, hostingRecord);//1
if (app == null) {
Slog.w(TAG, "Failed making new process record for "
+ processName + "/" + info.uid + " isolated=" + isolated);
return null;
}
app.crashHandler = crashHandler;
app.isolatedEntryPoint = entryPoint;
app.isolatedEntryPointArgs = entryPointArgs;
checkSlow(startTime, "startProcess: done creating new process record");
}
.....
final boolean success = startProcessLocked(app, hostingRecord, abiOverride);//2
checkSlow(startTime, "startProcess: done starting proc!");
return success ? app : null;
}
复制代码- 由以上代码，注释1处创建了ProcessRecord对象，它保存了当前正在运行的特定进程的完整信息，也就是需要启动的应用程序进程，接着注释2继续调用startProcessLocked方法
frameworks/base/services/core/java/com/android/server/am/ProcessList.java
/**
* @return {@code true} if process start is successful, false otherwise.
* @param app
* @param hostingRecord
* @param disableHiddenApiChecks
* @param abiOverride
*/
@GuardedBy("mService")
boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,
boolean disableHiddenApiChecks, boolean mountExtStorageFull,
String abiOverride) {
try {
....
int uid = app.uid;//1
int[] gids = null;
int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;
if (!app.isolated) {
......
/*
*添加共享的应用程序和配置文件GID，以便应用程序可以共享 某些资源（如共享库）并访问用户范围的资源
*/
if (ArrayUtils.isEmpty(permGids)) {
gids = new int[3];
} else {
gids = new int[permGids.length + 3];
System.arraycopy(permGids, 0, gids, 3, permGids.length);
}
gids[0] = UserHandle.getSharedAppGid(UserHandle.getAppId(uid));
gids[1] = UserHandle.getCacheAppGid(UserHandle.getAppId(uid));
gids[2] = UserHandle.getUserGid(UserHandle.getUserId(uid)); //2
.......
}
......
final String entryPoint = "android.app.ActivityThread";//3
return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,
runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet, invokeWith,
startTime);//4
} catch (RuntimeException e) {
.......
}
}
boolean startProcessLocked(HostingRecord hostingRecord,
String entryPoint,
ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
.......
if (mService.mConstants.FLAG_PROCESS_START_ASYNC) {
if (DEBUG_PROCESSES) Slog.i(TAG_PROCESSES,
"Posting procStart msg for " + app.toShortString());
mService.mProcStartHandler.post(() -> {
try {
final Process.ProcessStartResult startResult = startProcess(app.hostingRecord,
entryPoint, app, app.startUid, gids, runtimeFlags, mountExternal,
app.seInfo, requiredAbi, instructionSet, invokeWith, app.startTime);//5
synchronized (mService) {
handleProcessStartedLocked(app, startResult, startSeq);
}
} catch (RuntimeException e) {
.....
});
return true;
} else {
try {
final Process.ProcessStartResult startResult = startProcess(hostingRecord,
entryPoint, app,
uid, gids, runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet,
invokeWith, startTime);//6
handleProcessStartedLocked(app, startResult.pid, startResult.usingWrapper,
startSeq, false);
} catch (RuntimeException e) {
........
}
return app.pid > 0;
}
}
复制代码- 由以上代码注释1处获取了应用程序的用户id，注释2出获取了用户组ID，为应用程序进程提供用户组资源访问权限，注释3处给entryPoint赋值为android.app.ActivityThread，先记住这个值，后续分析还会继续提起它；注释4处接着调用了startProcessLocked方法，在该方法中注释5和6最终都是调用了ProcessList类的startProcess方法，接着往下看
frameworks/base/services/core/java/com/android/server/am/ProcessList.java
/**
* The currently running application zygotes.
*/
final ProcessMap<AppZygote> mAppZygotes = new ProcessMap<AppZygote>();
/**
* The processes that are forked off an application zygote.
*/
final ArrayMap<AppZygote, ArrayList<ProcessRecord>> mAppZygoteProcesses =
new ArrayMap<AppZygote, ArrayList<ProcessRecord>>();
private Process.ProcessStartResult startProcess(HostingRecord hostingRecord, String entryPoint,
ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
try {
.......
final Process.ProcessStartResult startResult;
if (hostingRecord.usesWebviewZygote()) {
startResult = startWebView(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null, app.info.packageName,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});//1
} else if (hostingRecord.usesAppZygote()) {
final AppZygote appZygote = createAppZygoteForProcessIfNeeded(app);
startResult = appZygote.getProcess().start(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null, app.info.packageName,
/*useUsapPool=*/ false,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});//2
} else {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, runtimeFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, app.info.packageName,
new String[] {PROC_START_SEQ_IDENT + app.startSeq});//3
}
....
return startResult;
}
......
}
复制代码- 由以上代码，startProcess方法会根据当前启动的是什么进程处理不同的逻辑，注释1是启动webview进程，注释2处理用户AppZygote，而注释3处才是出路新创建的应用程序进程，也就是调用了Process类的start方法，Process是 用于管理操作系统进程的工具类，接着看它的start方法
Process 处理启动参数到Zygote进程
frameworks/base/core/java/android/os/Process.java
/**
* State associated with the zygote process.
* @hide
*/
public static final ZygoteProcess ZYGOTE_PROCESS = new ZygoteProcess(); //1
public static ProcessStartResult start(@NonNull final String processClass,
@Nullable final String niceName,
int uid, int gid, @Nullable int[] gids,
int runtimeFlags,
int mountExternal,
int targetSdkVersion,
@Nullable String seInfo,
@NonNull String abi,
@Nullable String instructionSet,
@Nullable String appDataDir,
@Nullable String invokeWith,
@Nullable String packageName,
@Nullable String[] zygoteArgs) {
return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, packageName,
/*useUsapPool=*/ true, zygoteArgs);//2
}
复制代码- 由以上代码，结合注释1和注释2则调用了ZygoteProcess类的start方法，ZygoteProcess保持与Zygote 的通信状态。 此类负责对Zygote 打开套接字，并代表Porcess启动进程。接着看到ZygoteProcess类的start方法
frameworks/base/core/java/android/os/ZygoteProcess.java
public final Process.ProcessStartResult start(@NonNull final String processClass,
final String niceName,
int uid, int gid, @Nullable int[] gids,
int runtimeFlags, int mountExternal,
int targetSdkVersion,
@Nullable String seInfo,
@NonNull String abi,
@Nullable String instructionSet,
@Nullable String appDataDir,
@Nullable String invokeWith,
@Nullable String packageName,
boolean useUsapPool,
@Nullable String[] zygoteArgs) {
.....
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, /*startChildZygote=*/ false,
packageName, useUsapPool, zygoteArgs);//1
}
.....
}
复制代码- 由以上代码注释1，又调用了ZygoteProcess类的start方法，接着往下看
frameworks/base/core/java/android/os/ZygoteProcess.java
private Process.ProcessStartResult startViaZygote(@NonNull final String processClass,
@Nullable final String niceName,
final int uid, final int gid,
@Nullable final int[] gids,
int runtimeFlags, int mountExternal,
int targetSdkVersion,
@Nullable String seInfo,
@NonNull String abi,
@Nullable String instructionSet,
@Nullable String appDataDir,
@Nullable String invokeWith,
boolean startChildZygote,
@Nullable String packageName,
boolean useUsapPool,
@Nullable String[] extraArgs)
throws ZygoteStartFailedEx {
ArrayList<String> argsForZygote = new ArrayList<>();//1
// --runtime-args, --setuid=, --setgid=,
// and --setgroups= must go first
argsForZygote.add("--runtime-args");
argsForZygote.add("--setuid=" + uid);
argsForZygote.add("--setgid=" + gid);
argsForZygote.add("--runtime-flags=" + runtimeFlags);
if (mountExternal == Zygote.MOUNT_EXTERNAL_DEFAULT) {
argsForZygote.add("--mount-external-default");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_READ) {
argsForZygote.add("--mount-external-read");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_WRITE) {
argsForZygote.add("--mount-external-write");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_FULL) {
argsForZygote.add("--mount-external-full");
}
.......
synchronized(mLock) {
// The USAP pool can not be used if the application will not use the systems graphics
// driver. If that driver is requested use the Zygote application start path.
return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi),
useUsapPool,
argsForZygote);//2
}
}
复制代码- 由以上代码，注释1处创建了一个集合argsForZygote用来保存启动应用程序进程参数，接着又调用了zygoteSendArgsAndGetResult方法，而该方法第一个参数又调用了openZygoteSocketIfNeeded方法
frameworks/base/core/java/android/os/ZygoteProcess.java
private Process.ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, boolean useUsapPool, @NonNull ArrayList<String> args)
throws ZygoteStartFailedEx {
.......
if (useUsapPool && mUsapPoolEnabled && canAttemptUsap(args)) {
try {
return attemptUsapSendArgsAndGetResult(zygoteState, msgStr);//1
} catch (IOException ex) {
// If there was an IOException using the USAP pool we will log the error and
// attempt to start the process through the Zygote.
Log.e(LOG_TAG, "IO Exception while communicating with USAP pool - "
+ ex.getMessage());
}
}
return attemptZygoteSendArgsAndGetResult(zygoteState, msgStr);//2
}
private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
try {
attemptConnectionToPrimaryZygote();//3
if (primaryZygoteState.matches(abi)) {
return primaryZygoteState;
}
if (mZygoteSecondarySocketAddress != null) {
// The primary zygote didn't match. Try the secondary.
attemptConnectionToSecondaryZygote();//4
if (secondaryZygoteState.matches(abi)) {
return secondaryZygoteState;
}
}
} catch (IOException ioe) {
throw new ZygoteStartFailedEx("Error connecting to zygote", ioe);
}
throw new ZygoteStartFailedEx("Unsupported zygote ABI: " + abi);
}
复制代码- 由以上代码，注释1处和注释2都传入了zygoteState，它代表的是ZygoteState类，它是ZygoteProcess静态内部类，保存了与 Zygote 进行通信的状态，而它的返回是由openZygoteSocketIfNeeded方法处理的，所以看到注释3和注释4分别调用了attemptConnectionToPrimaryZygote方法和attemptConnectionToSecondaryZygote方法，这和Zygote进程启动加载的配置文件有关，这里就不展开了，两个方法逻辑基本相同，直接看到其中一个attemptConnectionToPrimaryZygote方法
frameworks/base/core/java/android/os/ZygoteProcess.java
/**
* Creates a ZygoteState for the primary zygote if it doesn't exist or has been disconnected.
*/
@GuardedBy("mLock")
private void attemptConnectionToPrimaryZygote() throws IOException {
if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
primaryZygoteState =
ZygoteState.connect(mZygoteSocketAddress, mUsapPoolSocketAddress);//1
maybeSetApiBlacklistExemptions(primaryZygoteState, false);
maybeSetHiddenApiAccessLogSampleRate(primaryZygoteState);
maybeSetHiddenApiAccessStatslogSampleRate(primaryZygoteState);
}
}
复制代码- 由注释1调用ZygoteState的connect方法来打开Socket连接，mZygoteSocketAddress则是名称为zygote的 Socket 服务
ActivityManagerService请求Zygote启动应用程序进程时序图
- 本小节最后还是通过时序图来对上面的步骤进行回顾
Zygote启动应用程序进程
- 经过上一小节分析，AMS最终是通过Socket方式进程间通信请求到了Zygote进程。Zygote英文为受精卵的意思，它启动过程创建了Android 虚拟机，其他应用程序进程则通过fork复制Zygote来创建应用程序进程，比如AMS服务所在的SystemServer进程，关于Zygote进程进程的启动过程细节又是另一部分内容了，本文则先只分析应用程序进程启动的过程，接下来从ZygoteInit的main方法开始
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
@UnsupportedAppUsage
public static void main(String argv[]) {
.....
Runnable caller;//1
try {
........
boolean startSystemServer = false;//2
String zygoteSocketName = "zygote";//3
String abiList = null;
boolean enableLazyPreload = false;
for (int i = 1; i < argv.length; i++) {
if ("start-system-server".equals(argv[i])) {//4
startSystemServer = true;
}
.......
}
final boolean isPrimaryZygote = zygoteSocketName.equals(Zygote.PRIMARY_SOCKET_NAME);
......
Zygote.initNativeState(isPrimaryZygote);//5
.....
zygoteServer = new ZygoteServer(isPrimaryZygote);//6
if (startSystemServer) {
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer); //7
}
// The select loop returns early in the child process after a fork and
// loops forever in the zygote.
caller = zygoteServer.runSelectLoop(abiList);//8
}
.......
// We're in the child process and have exited the select loop. Proceed to execute the
// command.
if (caller != null) {
caller.run(); //9
}
}
复制代码由以上是缩短精简的ZygoteInit的main方法，注释1处创建了一个Runnable类型的请求对象代表此次请求Zygote获取应用进程的对象；结合注释2、4和7如果是Android系统启动过程，则会启动核心进程SystemServer，否则是启动其他应用程序进程，注释3出设置Socket连接名称为zygote，注释5出则初始化了Zygote的状态环境，包括支持套接字的环境，安全环境等,同时也包括Socket连接的名称为zygote；注释6创建了ZygoteServer对象，它可以理解为Zygote支持Socket进程通信的服务端，而在注释8的 runSelectLoop 方法则是Zygote进程等待接收AMS请求启动应用程序进程的关键方法，注释9先放着，接着往下看
frameworks/base/core/java/com/android/internal/os/ZygoteServer.java
Runnable runSelectLoop(String abiList) {
......
while (true) {
while (--pollIndex >= 0) {
if ((pollFDs[pollIndex].revents & POLLIN) == 0) {
continue;
}
if (pollIndex == 0) {
// Zygote server socket
ZygoteConnection newPeer = acceptCommandPeer(abiList);
peers.add(newPeer);
socketFDs.add(newPeer.getFileDescriptor());
} else if (pollIndex < usapPoolEventFDIndex) {
// Session socket accepted from the Zygote server socket 从Zygote服务器套接字接受会话套接字
try {
ZygoteConnection connection = peers.get(pollIndex);
final Runnable command = connection.processOneCommand(this); //1
......
return command;
}
.......
}
复制代码- 由以上代码，通过一个死循环等待接收请求，注释1处则调用了ZygoteConnection的processOneCommand方法，接着往下看
获取应用程序进程
frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
/**
* Reads one start command from the command socket. If successful, a child is forked and a
* {@code Runnable} that calls the childs main method (or equivalent) is returned in the child
* process. {@code null} is always returned in the parent process (the zygote).
*
* If the client closes the socket, an {@code EOF} condition is set, which callers can test
* for by calling {@code ZygoteConnection.isClosedByPeer}.
*/
Runnable processOneCommand(ZygoteServer zygoteServer) {
String args[];
ZygoteArguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
args = Zygote.readArgumentList(mSocketReader);//1
....
}
......
pid = Zygote.forkAndSpecialize(parsedArgs.mUid, parsedArgs.mGid, parsedArgs.mGids,
parsedArgs.mRuntimeFlags, rlimits, parsedArgs.mMountExternal, parsedArgs.mSeInfo,
parsedArgs.mNiceName, fdsToClose, fdsToIgnore, parsedArgs.mStartChildZygote,
parsedArgs.mInstructionSet, parsedArgs.mAppDataDir, parsedArgs.mTargetSdkVersion); //2
try {
if (pid == 0) { //3
// in child
zygoteServer.setForkChild();
zygoteServer.closeServerSocket();
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
return handleChildProc(parsedArgs, descriptors, childPipeFd,
parsedArgs.mStartChildZygote);
} 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;
}
}
......
}
复制代码- 由以上代码注释1处获取了启动应用程序进程的参数，看到注释2处，直接调用了Zygote类的forkAndSpecialize方法
frameworks/base/core/java/com/android/internal/os/Zygote.java
/**
* Forks a new VM instance. The current VM must have been started
* @return 0 if this is the child, pid of the child
* if this is the parent, or -1 on error.
*/
public static int forkAndSpecialize(int uid, int gid, int[] gids, int runtimeFlags,
int[][] rlimits, int mountExternal, String seInfo, String niceName, int[] fdsToClose,
int[] fdsToIgnore, boolean startChildZygote, String instructionSet, String appDataDir,
int targetSdkVersion) {
ZygoteHooks.preFork();
// Resets nice priority for zygote process.
resetNicePriority();
int pid = nativeForkAndSpecialize(
uid, gid, gids, runtimeFlags, rlimits, mountExternal, seInfo, niceName, fdsToClose,
fdsToIgnore, startChildZygote, instructionSet, appDataDir);//1
return pid;
}
复制代码- 由以上代码注释1处，通过Native方法nativeForkAndSpecialize与底层通信复制fork出应用即将要启动的应用程序进程，本文则关注大致流程，底层Native实现则不再继续展开，有兴趣朋友可以继续跟进frameworks/base/core/jni/com_android_internal_os_Zygote.cpp查看。根据forkAndSpecialize方法的注释也可以明白，该方法返回0则为child，也就是应用程序进程，-1则为父进程，所以这里再次回到ZygoteConnection的processOneCommand方法，启动的是应用程序进程，则在注释3出pid=0 此时已经处于应用程序进程了，接着继续调用ZygoteConnection的 handleChildProc方法
frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
private Runnable handleChildProc(ZygoteArguments parsedArgs, FileDescriptor[] descriptors,
FileDescriptor pipeFd, boolean isZygote) {
..........
} else {
if (!isZygote) {
return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */); //1
} else {
return ZygoteInit.childZygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
}
}
}
复制代码- 由以上源码，启动的是应用程序进程则会走到注释1处调用ZygoteInit类的zygoteInit方法
创建应用程序的ActivityThread
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
if (RuntimeInit.DEBUG) {
Slog.d(RuntimeInit.TAG, "RuntimeInit: Starting application from zygote");
}
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams();
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit();//1
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader); //2
}
复制代码- 由以上源码，注释1出的Native方法会创建当前应用程序进程的Binder线程池，则当前应用程序就拥有了Binder通信的能力，注释2处接着调用了RuntimeInit的applicationInit方法
frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
......
final Arguments args = new Arguments(argv); //1
......
return findStaticMain(args.startClass, args.startArgs, classLoader);2
}
复制代码- 由以上代码，注释1处处理AMS请求中传递过来的参数，这其中就包括android.app.ActivityThread，也就是注释2处args.startClass代表的值，接着继续看findStaticMain方法
frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
protected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
Class<?> cl;
try {
cl = Class.forName(className, true, classLoader);//1
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });//2
}
......
/*
* This throw gets caught in ZygoteInit.main(), which responds
* by invoking the exception's run() method. This arrangement
* clears up all the stack frames that were required in setting
* up the process.
*/
return new MethodAndArgsCaller(m, argv);
}
复制代码- 由以上代码，注释1处反射获取了android.app.ActivityThread，也就是应用程序进程的ActivityThread，注释2处获取了ActivityThread的main方法，然后返回了Runnable对象为MethodAndArgsCaller
frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
/**
* Helper class which holds a method and arguments and can call them. This is used as part of
* a trampoline to get rid of the initial process setup stack frames.
*/
static class MethodAndArgsCaller implements Runnable {
/** method to call */
private final Method mMethod;
/** argument array */
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod = method;
mArgs = args;
}
public void run() {
try {
mMethod.invoke(null, new Object[] { mArgs }); //1
}
...
}
}
复制代码- 由以上代码，注释1处代表应用程序进程ActivityThread的main方法，结合本小节开头的从ZygoteInit的main方法的注释9，目前已经处于应用程序进程，则会调用Runnable类型caller的run方法，也就是MethodAndArgsCaller的run方法，由以上代码注释1处，则会调用ActivityThread的main方法，而ActivityThread作为每个应程序主线程的管理类，到此，应用程序进程启动完成，接着上一篇文章，当ATMS与应用程序Binder通信通过IApplicationThread为ActivityThread的内部类，然后调用ActivityThread的performLaunchActivity方法来启动Activity。
Zygote启动应用程序进程时序图
- 本小节最后还是通过时序图来对上面的步骤进行回顾
总结
启动过程涉及的进程
- 结合上一篇文章深入理解Android 之 Activity启动流程，总结出如下应用程序进程启动涉及的几个进程间调用的关系图
最后
- 通过以上源码的理解，其中还有很多细节等待我们探索，所以“Read The Fucking Source Code”，怀着敬畏的心继续前进。如果文章中有写得不对的地方，欢迎在留言区留言大家一起讨论，共同学习进步。如果觉得我的文章给予你帮助，也请给我一个喜欢和关注。
参考
- 书籍《Android 进阶解密》
- Android源码地址
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