概述
ActivityManagerService的最后启动了Launcher进程,今天我们来真正分析下桌面的启动流程.
[ActivityManagerService.java]
public void systemReady(final Runnable goingCallback, TimingsTraceLog
traceLog) {
...
//启动Home Activity
//mAtmInternal 对象是ActivityTaskManagerInternal 抽象类 实现类为ATM的LocalServer对象
mAtmInternal.startHomeOnAllDisplays(currentUserId, "systemReady");
...
}
Launcher的启动主要由三部分完成
- SystemServer完成启动Launcher Activity的调用
- Zygote进行Launcher进程的fork操作
- 进入ActivityThread的main()方法,完成最终Launcher的onCreate操作
接下来我们分别从源码部分来分析这个三个启动过程。
ActivityTaskManagerService.java#startHomeOnAllDisplays()
[ActivityTaskManagerService.java#LocalService.class]
final class LocalService extends ActivityTaskManagerInternal {
....................
@Override
public boolean startHomeOnAllDisplays(int userId, String reason) {
synchronized (mGlobalLock) {
return mRootActivityContainer.startHomeOnAllDisplays(userId, reason);
}
}
.................
}
RootActivityContainer.java#startHomeOnDisplay()
boolean startHomeOnDisplay(int userId, String reason, int displayId, boolean allowInstrumenting,
boolean fromHomeKey) {
// Fallback to top focused display if the displayId is invalid.
if (displayId == INVALID_DISPLAY) {
displayId = getTopDisplayFocusedStack().mDisplayId;
}
Intent homeIntent = null;
ActivityInfo aInfo = null;
if (displayId == DEFAULT_DISPLAY) {
//构建一个category为CATEGORY_HOME的Intent,表明是Home Activity
homeIntent = mService.getHomeIntent();
//通过PackageManagerService从系统已安装的列表中,找到一个符合Home Intent的Activity
aInfo = resolveHomeActivity(userId, homeIntent);
} else if (shouldPlaceSecondaryHomeOnDisplay(displayId)) {
Pair<ActivityInfo, Intent> info = resolveSecondaryHomeActivity(userId, displayId);
aInfo = info.first;
homeIntent = info.second;
}
if (aInfo == null || homeIntent == null) {
return false;
}
if (!canStartHomeOnDisplay(aInfo, displayId, allowInstrumenting)) {
return false;
}
// Updates the home component of the intent.
homeIntent.setComponent(new ComponentName(aInfo.applicationInfo.packageName, aInfo.name));
homeIntent.setFlags(homeIntent.getFlags() | FLAG_ACTIVITY_NEW_TASK);
// Updates the extra information of the intent.
if (fromHomeKey) {
homeIntent.putExtra(WindowManagerPolicy.EXTRA_FROM_HOME_KEY, true);
}
// Update the reason for ANR debugging to verify if the user activity is the one that
// actually launched.
final String myReason = reason + ":" + userId + ":" + UserHandle.getUserId(
aInfo.applicationInfo.uid) + ":" + displayId;
//启动Home Activity
mService.getActivityStartController().startHomeActivity(homeIntent, aInfo, myReason,
displayId);
return true;
}
ActivityStartController.java#startHomeActivity()
正在启动Home Activity入口。obtainStarter() 方法返回的是 ActivityStarter 对象,它负责 Activity 的启动,一系列 setXXX() 方法传入启动所需的各种参数,最后的 execute() 是真正的启动逻辑。另外如果home activity处于顶层的resume activity中,则Home Activity 将被初始化,但不会被恢复。并将保持这种状态,直到有东西再次触发它。我们需要进行另一次恢复
void startHomeActivity(Intent intent, ActivityInfo aInfo, String reason, int displayId) {
....
//返回一个 ActivityStarter 对象,它负责 Activity 的启动
//一系列 setXXX() 方法传入启动所需的各种参数,最后的 execute() 是真正的启动逻辑
//最后执行 ActivityStarter的execute方法
mLastHomeActivityStartResult = obtainStarter(intent, "startHomeActivity: " + reason)
.setOutActivity(tmpOutRecord)
.setCallingUid(0)
.setActivityInfo(aInfo)
.setActivityOptions(options.toBundle())
.execute();
mLastHomeActivityStartRecord = tmpOutRecord[0];
final ActivityDisplay display =
mService.mRootActivityContainer.getActivityDisplay(displayId);
final ActivityStack homeStack = display != null ? display.getHomeStack() : null;
if (homeStack != null && homeStack.mInResumeTopActivity) {
//如果home activity 处于顶层的resume activity中,则Home Activity 将被初始化,但不会被恢复(以避免递归恢复),
//并将保持这种状态,直到有东西再次触发它。我们需要进行另一次恢复。
mSupervisor.scheduleResumeTopActivities();
}
}
ActivityStarter.java#execute()
ObtainStarter没有调用setMayWait的方法,因此mRequest.mayWait为false,走startActivity流程
int execute() {
...
if (mRequest.mayWait) {
return startActivityMayWait(...)
} else {
return startActivity(...)
}
...
}
ActivityStarter.java#startActivity()
延时布局,然后通过startActivityUnchecked()来处理启动标记flag,要启动的任务栈,最后恢复布局
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity, boolean restrictedBgActivity) {
...
try {
//延时布局
mService.mWindowManager.deferSurfaceLayout();
//调用 startActivityUnchecked ,一路调用到resumeFocusedStacksTopActivities(),
result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, outActivity, restrictedBgActivity);
} finally {
//恢复布局
mService.mWindowManager.continueSurfaceLayout();
}
...
}
RootActivityContainer.java#resumeFocusedStacksTopActivities
boolean resumeFocusedStacksTopActivities(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
...
//如果秒表栈就是栈顶Activity,启动resumeTopActivityUncheckedLocked()
if (targetStack != null && (targetStack.isTopStackOnDisplay()
|| getTopDisplayFocusedStack() == targetStack)) {
result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
...
if (!resumedOnDisplay) {
// 获取 栈顶的 ActivityRecord
final ActivityStack focusedStack = display.getFocusedStack();
if (focusedStack != null) {
//最终调用startSpecificActivityLocked()
focusedStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
}
}
}
ActivityStackSupervisor.java#startSpecificActivityLocked
发布消息以启动进程,避免在ATM锁保持的情况下调用AMS时可能出现死锁,最终调用到ATM的startProcess()
void startSpecificActivityLocked(ActivityRecord r, boolean andResume, boolean checkConfig) {
...
//发布消息以启动进程,以避免在ATM锁保持的情况下调用AMS时可能出现死锁
//最终调用到AMS的startProcess(),
final Message msg = PooledLambda.obtainMessage(
ActivityManagerInternal::startProcess, mService.mAmInternal, r.processName,
r.info.applicationInfo, knownToBeDead, "activity", r.intent.getComponent());
mService.mH.sendMessage(msg);
...
}
ActivityManagerService.java#startProcess()
一路调用Process.start()最终到ZygoteProcess的attempUsepSendArgsAndGetResult(),用来fork一个新的Launcher进程。
[ActivityManagerService.java#LocalServer.class]
@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) {
//注释1
startProcessLocked(processName, info, knownToBeDead, 0 /* intentFlags */,
new HostingRecord(hostingType, hostingName),
false /* allowWhileBooting */, false /* isolated */,
true /* keepIfLarge */);
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
@GuardedBy("this")
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
HostingRecord hostingRecord, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
//注释2
return mProcessList.startProcessLocked(processName, info, knownToBeDead, intentFlags,
hostingRecord, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
null /* crashHandler */);
}
ProcessList.java#startProcessLocked()
@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) {
............................
checkSlow(startTime, "startProcess: stepping in to startProcess");
final boolean success = startProcessLocked(app, hostingRecord, abiOverride);
checkSlow(startTime, "startProcess: done starting proc!");
return success ? app : null;
}
@GuardedBy("mService")
final boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,
String abiOverride) {
return startProcessLocked(app, hostingRecord,
false /* disableHiddenApiChecks */, false /* mountExtStorageFull */, abiOverride);
}
/**
* @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) {
........................
// Start the process. It will either succeed and return a result containing
// the PID of the new process, or else throw a RuntimeException.
// 1重要
final String entryPoint = "android.app.ActivityThread";
return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,
runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet, invokeWith,
startTime);
} catch (RuntimeException e) {
Slog.e(ActivityManagerService.TAG, "Failure starting process " + app.processName, e);
// Something went very wrong while trying to start this process; one
// common case is when the package is frozen due to an active
// upgrade. To recover, clean up any active bookkeeping related to
// starting this process. (We already invoked this method once when
// the package was initially frozen through KILL_APPLICATION_MSG, so
// it doesn't hurt to use it again.)
mService.forceStopPackageLocked(app.info.packageName, UserHandle.getAppId(app.uid),
false, false, true, false, false, app.userId, "start failure");
return false;
}
}
@GuardedBy("mService")
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) {
app.pendingStart = true;
app.killedByAm = false;
app.removed = false;
app.killed = false;
if (app.startSeq != 0) {
Slog.wtf(TAG, "startProcessLocked processName:" + app.processName
+ " with non-zero startSeq:" + app.startSeq);
}
if (app.pid != 0) {
Slog.wtf(TAG, "startProcessLocked processName:" + app.processName
+ " with non-zero pid:" + app.pid);
}
final long startSeq = app.startSeq = ++mProcStartSeqCounter;
app.setStartParams(uid, hostingRecord, seInfo, startTime);
app.setUsingWrapper(invokeWith != null
|| SystemProperties.get("wrap." + app.processName) != null);
mPendingStarts.put(startSeq, app);
if (mService.mConstants.FLAG_PROCESS_START_ASYNC) {
if (DEBUG_PROCESSES) Slog.i(TAG_PROCESSES,
"Posting procStart msg for " + app.toShortString());
mService.mProcStartHandler.post(() -> {
try {
//注释2
final Process.ProcessStartResult startResult = startProcess(app.hostingRecord,
entryPoint, app, app.startUid, gids, runtimeFlags, mountExternal,
app.seInfo, requiredAbi, instructionSet, invokeWith, app.startTime);
synchronized (mService) {
handleProcessStartedLocked(app, startResult, startSeq);
}
} catch (RuntimeException e) {
synchronized (mService) {
Slog.e(ActivityManagerService.TAG, "Failure starting process "
+ app.processName, e);
mPendingStarts.remove(startSeq);
app.pendingStart = false;
mService.forceStopPackageLocked(app.info.packageName,
UserHandle.getAppId(app.uid),
false, false, true, false, false, app.userId, "start failure");
}
}
});
return true;
} else {
try {
final Process.ProcessStartResult startResult = startProcess(hostingRecord,
entryPoint, app,
uid, gids, runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet,
invokeWith, startTime);
handleProcessStartedLocked(app, startResult.pid, startResult.usingWrapper,
startSeq, false);
} catch (RuntimeException e) {
Slog.e(ActivityManagerService.TAG, "Failure starting process "
+ app.processName, e);
app.pendingStart = false;
mService.forceStopPackageLocked(app.info.packageName, UserHandle.getAppId(app.uid),
false, false, true, false, false, app.userId, "start failure");
}
return app.pid > 0;
}
}
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 {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
app.processName);
checkSlow(startTime, "startProcess: asking zygote to start proc");
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});
} 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});
} else {
//注释3
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});
}
checkSlow(startTime, "startProcess: returned from zygote!");
return startResult;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
注释1处初始化了entryPoint的值为android.app.ActivityThread,这就是我们应用程序的入口,执行这个类的main方法。
Process.java#start()
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) {
//注释1
return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, packageName,
/*useUsapPool=*/ true, zygoteArgs);
}
ZygoteProcess.java#start()
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) {
// TODO (chriswailes): Is there a better place to check this value?
if (fetchUsapPoolEnabledPropWithMinInterval()) {
informZygotesOfUsapPoolStatus();
}
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, /*startChildZygote=*/ false,
packageName, useUsapPool, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}
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<>();
// --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");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_INSTALLER) {
argsForZygote.add("--mount-external-installer");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_LEGACY) {
argsForZygote.add("--mount-external-legacy");
}
argsForZygote.add("--target-sdk-version=" + targetSdkVersion);
// --setgroups is a comma-separated list
if (gids != null && gids.length > 0) {
StringBuilder sb = new StringBuilder();
sb.append("--setgroups=");
int sz = gids.length;
for (int i = 0; i < sz; i++) {
if (i != 0) {
sb.append(',');
}
sb.append(gids[i]);
}
argsForZygote.add(sb.toString());
}
if (niceName != null) {
argsForZygote.add("--nice-name=" + niceName);
}
if (seInfo != null) {
argsForZygote.add("--seinfo=" + seInfo);
}
if (instructionSet != null) {
argsForZygote.add("--instruction-set=" + instructionSet);
}
if (appDataDir != null) {
argsForZygote.add("--app-data-dir=" + appDataDir);
}
if (invokeWith != null) {
argsForZygote.add("--invoke-with");
argsForZygote.add(invokeWith);
}
if (startChildZygote) {
argsForZygote.add("--start-child-zygote");
}
if (packageName != null) {
argsForZygote.add("--package-name=" + packageName);
}
argsForZygote.add(processClass);
if (extraArgs != null) {
Collections.addAll(argsForZygote, extraArgs);
}
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);
}
}
/**
* Sends an argument list to the zygote process, which starts a new child
* and returns the child's pid. Please note: the present implementation
* replaces newlines in the argument list with spaces.
*
* @throws ZygoteStartFailedEx if process start failed for any reason
*/
@GuardedBy("mLock")
private Process.ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, boolean useUsapPool, @NonNull ArrayList<String> args)
throws ZygoteStartFailedEx {
// Throw early if any of the arguments are malformed. This means we can
// avoid writing a partial response to the zygote.
for (String arg : args) {
// Making two indexOf calls here is faster than running a manually fused loop due
// to the fact that indexOf is a optimized intrinsic.
if (arg.indexOf('\n') >= 0) {
throw new ZygoteStartFailedEx("Embedded newlines not allowed");
} else if (arg.indexOf('\r') >= 0) {
throw new ZygoteStartFailedEx("Embedded carriage returns not allowed");
}
}
/*
* See com.android.internal.os.ZygoteArguments.parseArgs()
* Presently the wire format to the zygote process is:
* a) a count of arguments (argc, in essence)
* b) a number of newline-separated argument strings equal to count
*
* After the zygote process reads these it will write the pid of
* the child or -1 on failure, followed by boolean to
* indicate whether a wrapper process was used.
*/
String msgStr = args.size() + "\n" + String.join("\n", args) + "\n";
if (useUsapPool && mUsapPoolEnabled && canAttemptUsap(args)) {
try {
return attemptUsapSendArgsAndGetResult(zygoteState, msgStr);
} 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);
}
ZygoteProcess.java#attemptZygoteSendArgsAndGetResult()
通过Socket连接Zygote进程,把之前组装的msg发给Zygote,其中processClass="android.app.ActivityThread",通过Zygote进程fork出一个新的进程,并执行"android.app.ActivityThread"的main方法。
private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(
ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {
try {
//传入的zygoteState为openZygoteSocketIfNeeded(),里面会通过abi来检查是第一个zygote还是第二个
final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;
final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;
zygoteWriter.write(msgStr); //把应用进程的一些参数写给前面连接的zygote进程,包括前面的processClass ="android.app.ActivityThread"
zygoteWriter.flush(); //进入Zygote进程,处于阻塞状态
//从socket中得到zygote创建的应用pid,赋值给 ProcessStartResult的对象
Process.ProcessStartResult result = new Process.ProcessStartResult();
result.pid = zygoteInputStream.readInt();
result.usingWrapper = zygoteInputStream.readBoolean();
if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
return result;
} catch (IOException ex) {
zygoteState.close();
Log.e(LOG_TAG, "IO Exception while communicating with Zygote - "
+ ex.toString());
throw new ZygoteStartFailedEx(ex);
}
}
第二阶段Zygote fork一个Launcher进程
Zygote的启动过程我们前面有详细讲到过。SystemServer的AMS服务向启动Home Activity发起一个fork请求,Zygote进程通过Linux的fork函数,孵化出一个新的进程。由于Zygote进程在启动时会创建Java虚拟机,因此通过fork而创建的Launcher程序进程可以在内部获取一个Java虚拟机的实例拷贝。fork采用copy-on-write机制,有些类如果不做改变,甚至都不用复制,子进程可以和父进程共享这部分数据,从而省去不少内存的占用。
ZygoteInit.java#main()
Zygote先fork出SystemServer,接着进入循环等待,用来接收Socket发来的消息,用来fork出其他应用进程。比如Launcher
public static void main(String argv[]) {
...
Runnable caller;
....
if (startSystemServer) {
//Zygote Fork出的第一个进程 SystmeServer
Runnable r = forkSystemServer(abiList, zygoteSocketName, zygoteServer);
if (r != null) {
r.run();
return;
}
}
...
//循环等待fork出其他的应用进程,比如Launcher
//最终通过调用processOneCommand()来进行进程的处理
caller = zygoteServer.runSelectLoop(abiList);
...
if (caller != null) {
caller.run(); //执行返回的Runnable对象,进入子进程
}
}
ZygoteConnection.java#processOneCommand()
通过forkAndSpecialize()来fork出Launcher的子进程,并执行handleChildProc,进入子进程的处理
Runnable processOneCommand(ZygoteServer zygoteServer) {
int pid = -1;
...
//Fork子进程,得到一个新的pid
/fork子进程,采用copy on write方式,这里执行一次,会返回两次
///pid=0 表示Zygote fork子进程成功
//pid > 0 表示子进程 的真正的PID
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);
...
if (pid == 0) {
// in child, fork成功,第一次返回的pid = 0
...
return handleChildProc(parsedArgs, descriptors, childPipeFd,
parsedArgs.mStartChildZygote);
} else {
//in parent
...
childPipeFd = null;
handleParentProc(pid, descriptors, serverPipeFd);
return null;
}
}
ZygoteConneciton.java#handleChildProc()
进行子进程的操作,最终获得需要执行的ActivityThread的main()
private Runnable handleChildProc(ZygoteArguments parsedArgs, FileDescriptor[] descriptors,
FileDescriptor pipeFd, boolean isZygote) {
...
if (parsedArgs.mInvokeWith != null) {
...
throw new IllegalStateException("WrapperInit.execApplication unexpectedly returned");
} else {
if (!isZygote) {
// App进程将会调用到这里,执行目标类的main()方法
return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
} else {
return ZygoteInit.childZygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
}
}
}
ZygoteInit进行一些环境的初始化,启动Binder进程等操作
public static final Runnable zygoteInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
RuntimeInit.commonInit(); //初始化运行环境
ZygoteInit.nativeZygoteInit(); //启动Binder线程池
//调用程序入口函数
return RuntimeInit.applicationInit(targetSdkVersion, argv, classLoader);
}
把之前传来的"android.app.ActivityThread"传给findStaticMain:
protected static Runnable applicationInit(int targetSdkVersion, String[] argv,
ClassLoader classLoader) {
...
// startClass: 如果AMS通过socket传递过来的是 ActivityThread
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
通过反射,拿到ActivityThread的main()方法:
protected static Runnable findStaticMain(String className, String[] argv,
ClassLoader classLoader) {
Class<?> cl;
try {
cl = Class.forName(className, true, classLoader);
} 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 });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
return new MethodAndArgsCaller(m, argv);
}
把反射得来的ActivityThread main入口返回给ZygoteInit的main,通过caller.run()进行调用.
第三个阶段,Launcher在自己的进程中进行onCreate等后面的动作
从上面可知,Zygote fork出Launcher的进程,并把接下来的Launcher启动任务交给了ActivityThread来进行,接下来我们可以从ActivityThread main方法来分析Launcher的创建过程。
ActivityThread.java #main()
主线程处理,创建ActivityThread对象,调用attach进行处理,最终进入Looper循环
public static void main(String[] args) {
// 安装选择性的系统调用拦截
AndroidOs.install();
...
//主线程处理
Looper.prepareMainLooper();
...
//之前SystemServer调用attach传入的是true,这里到应用进程传入false就行
ActivityThread thread = new ActivityThread();
thread.attach(false, startSeq);
...
//一直循环,如果退出,说明程序关闭
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
调用ActivityThread的attach进行处理
private void attach(boolean system, long startSeq) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
//应用进程启动,走该流程
...
RuntimeInit.setApplicationObject(mAppThread.asBinder());
//获取AMS的本地代理类
final IActivityManager mgr = ActivityManager.getService();
try {
//通过Binder调用AMS的attachApplication方法
mgr.attachApplication(mAppThread, startSeq);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
...
} else {
//通过system_server启动ActivityThread对象
...
}
// 为 ViewRootImpl 设置配置更新回调,
当系统资源配置(如:系统字体)发生变化时,通知系统配置发生变化
ViewRootImpl.ConfigChangedCallback configChangedCallback
= (Configuration globalConfig) -> {
synchronized (mResourcesManager) {
...
}
};
ViewRootImpl.addConfigCallback(configChangedCallback);
}
ActivityManagerService.java#attachApplicaiton()
清除一些无用的记录,最终调用ActivityStackSupervisor.java的realStartActivityLocked,进行Activity的启动
public final void attachApplication(IApplicationThread thread, long startSeq) {
synchronized (this) {
//通过Binder获取传入的pid信息
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}
public ActivityTaskManagerInternal mAtmInternal;
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid, int callingUid, long startSeq) {
...
//如果当前的Application记录仍然依附到之前的进程中,则清理掉
if (app.thread != null) {
handleAppDiedLocked(app, true, true);
}·
//mProcessesReady这个变量在AMS的 systemReady 中被赋值为true,
//所以这里的normalMode也为true
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
...
//上面说到,这里为true,进入StackSupervisor的attachApplication方法
//去真正启动Activity
if (normalMode) {
...
//调用ATM的attachApplication(),最终层层调用到ActivityStackSupervisor.java的 realStartActivityLocked()
//
didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());
...
}
...
return true;
}
[ActivityTaskManagerService.java # LocalServer.class]
@HotPath(caller = HotPath.PROCESS_CHANGE)
@Override
public boolean attachApplication(WindowProcessController wpc) throws RemoteException {
synchronized (mGlobalLockWithoutBoost) {
return mRootActivityContainer.attachApplication(wpc);
}
}
[RootActivityContainer.java #attachApplicaton()]
boolean attachApplication(WindowProcessController app) throws RemoteException {
final String processName = app.mName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
final ActivityDisplay display = mActivityDisplays.get(displayNdx);
final ActivityStack stack = display.getFocusedStack();
if (stack != null) {
stack.getAllRunningVisibleActivitiesLocked(mTmpActivityList);
final ActivityRecord top = stack.topRunningActivityLocked();
final int size = mTmpActivityList.size();
for (int i = 0; i < size; i++) {
final ActivityRecord activity = mTmpActivityList.get(i);
if (activity.app == null && app.mUid == activity.info.applicationInfo.uid
&& processName.equals(activity.processName)) {
try {
//1
if (mStackSupervisor.realStartActivityLocked(activity, app,
top == activity /* andResume */, true /* checkConfig */)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ top.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisible(null, 0, false /* preserve_windows */);
}
return didSomething;
}
[ActivityStackSupervisor.java#realStartActivityLocked()]
boolean realStartActivityLocked(ActivityRecord r, WindowProcessController proc,
boolean andResume, boolean checkConfig) throws RemoteException {
// 直到所有的 onPause() 执行结束才会去启动新的 activity
if (!mRootActivityContainer.allPausedActivitiesComplete()) {
...
return false;
}
try {
// Create activity launch transaction.
// 添加 LaunchActivityItem
final ClientTransaction clientTransaction = ClientTransaction.obtain(
proc.getThread(), r.appToken);
//LaunchActivityItem.obtain(new Intent(r.intent)作为回调参数
clientTransaction.addCallback(LaunchActivityItem.obtain(new Intent(r.intent),
System.identityHashCode(r), r.info,
// TODO: Have this take the merged configuration instead of separate global
// and override configs.
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, proc.getReportedProcState(),
r.icicle, r.persistentState, results, newIntents,
dc.isNextTransitionForward(), proc.createProfilerInfoIfNeeded(),
r.assistToken));
...
// 设置生命周期状态
final ActivityLifecycleItem lifecycleItem;
if (andResume) {
lifecycleItem = ResumeActivityItem.obtain(dc.isNextTransitionForward());
} else {
lifecycleItem = PauseActivityItem.obtain();
}
clientTransaction.setLifecycleStateRequest(lifecycleItem);
// Schedule transaction.
// 重点关注:调用 ClientLifecycleManager.scheduleTransaction(),得到上面addCallback的LaunchActivityItem的execute()方法
mService.getLifecycleManager().scheduleTransaction(clientTransaction);
} catch (RemoteException e) {
if (r.launchFailed) {
// 第二次启动失败,finish activity
stack.requestFinishActivityLocked(r.appToken, Activity.RESULT_CANCELED, null,
"2nd-crash", false);
return false;
}
// 第一次失败,重启进程并重试
r.launchFailed = true;
proc.removeActivity(r);
throw e;
}
} finally {
endDeferResume();
}
...
return true;
}
TransactionExecutor.java#execute()
执行之前realStartActivityLocked中的clientTransaction.addCallBack
public void execute(ClientTransaction transaction) {
...
// 执行 callBack,参考上面的调用栈,执行回调方法,
//最终调用到ActivityThread的handleLaunchActivity()
executeCallbacks(transaction);
// 执行生命周期状态
executeLifecycleState(transaction);
mPendingActions.clear();
}
ActivityThread.java#handleLaunchActivity()
主要时干了两件事,第一件:初始化WindowManagerGlobal;第二件:调用performLaunchActivity方法
public Activity handleLaunchActivity(ActivityClientRecord r,
PendingTransactionActions pendingActions, Intent customIntent) {
...
//初始化WindowManagerGlobal
WindowManagerGlobal.initialize();
...
//调用performLaunchActivity,来处理Activity
final Activity a = performLaunchActivity(r, customIntent);
..
return a;
ActivityThread.java#perfromLaunchActivity
获取ComponentName,Context,反射创建Activity,设置Activity的一些内容,比如主题等;最终调用callActivityOnCreate()来执行Activity的onCreate方法
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
// 获取 ComponentName
ComponentName component = r.intent.getComponent();
...
// 获取 Context
ContextImpl appContext = createBaseContextForActivity(r);
Activity activity = null;
try {
// 反射创建 Activity
java.lang.ClassLoader cl = appContext.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
} catch (Exception e) {
...
}
try {
// 获取 Application
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
if (activity != null) {
...
//Activity的一些处理
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback,
r.assistToken);
if (customIntent != null) {
activity.mIntent = customIntent;
}
...
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
// 设置主题
activity.setTheme(theme);
}
activity.mCalled = false;
// 执行 onCreate()
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
...
r.activity = activity;
}
//当前状态为ON_CREATE
r.setState(ON_CREATE);
...
} catch (SuperNotCalledException e) {
throw e;
} catch (Exception e) {
...
}
return activity;
}
callActivityOnCreate先执行activity onCreate的预处理,再去调用Activity的onCreate,最终完成Create创建后的内容处理
public void callActivityOnCreate(Activity activity, Bundle icicle,
PersistableBundle persistentState) {
prePerformCreate(activity); //activity onCreate的预处理
activity.performCreate(icicle, persistentState);//执行onCreate()
postPerformCreate(activity); //activity onCreate创建后的一些信息处理
}
performCreate主要调用Activity的onCreate()
final void performCreate(Bundle icicle, PersistableBundle persistentState) {
...
if (persistentState != null) {
onCreate(icicle, persistentState);
} else {
onCreate(icicle);
}
...
}
至此,看到了我们最熟悉的Activity的onCreate(),Launcher的启动完成,Launcher被真正创建起来。
总结
看到onCreate()后,进入到我们最熟悉的Activity的入口,Launcher的启动告一段落。整个Android的启动流程,我们也完整的分析完成。
Launcher的启动经过了三个阶段:
第一个阶段:SystemServer完成启动Launcher Activity的调用。
第二个阶段:Zygote()进行Launcher进程的Fork操作。
第三个阶段:进入ActivityThread的main(),完成最终Launcher的onCreate操作。