具体过程
1.ActivityTaskManagerService->ActivityStarter
frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
ActivityTaskManagerService执行startActivity方法最终获取到ActivityStarter，ActivityStarter对启动activity的相关参数进行了赋值，最终执行execute方法
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
public final int startActivity(IApplicationThread caller, String callingPackage,
String callingFeatureId, Intent intent, String resolvedType, IBinder resultTo,
String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo,
Bundle bOptions) {
return startActivityAsUser(caller, callingPackage, callingFeatureId, intent, resolvedType,
resultTo, resultWho, requestCode, startFlags, profilerInfo, bOptions,
UserHandle.getCallingUserId());
}
private int startActivityAsUser(IApplicationThread caller, String callingPackage,
@Nullable String callingFeatureId, Intent intent, String resolvedType,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, Bundle bOptions, int userId, boolean validateIncomingUser) {
//检查callingUid与当前callingPackage是否是用一个应用，如果不是抛出异常
assertPackageMatchesCallingUid(callingPackage);
//判断是否被隔离
enforceNotIsolatedCaller("startActivityAsUser");
//
userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
// TODO: Switch to user app stacks here.
return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
.setCaller(caller)
.setCallingPackage(callingPackage)
.setCallingFeatureId(callingFeatureId)
.setResolvedType(resolvedType)
.setResultTo(resultTo)
.setResultWho(resultWho)
.setRequestCode(requestCode)
.setStartFlags(startFlags)
.setProfilerInfo(profilerInfo)
.setActivityOptions(bOptions)
.setUserId(userId)
.execute();
}
2.ActivityStarter
frameworks/base/services/core/java/com/android/server/wm/ActivityStarter.java
用于解释如何启动Activity和启动Activity的控制器，执行executeRequest
//根据之前提供的请求参数解析必要的信息，执行启动Activity的请求
int execute() {
try {
final LaunchingState launchingState;
synchronized (mService.mGlobalLock) {
final ActivityRecord caller = ActivityRecord.forTokenLocked(mRequest.resultTo);
launchingState = mSupervisor.getActivityMetricsLogger().notifyActivityLaunching(
mRequest.intent, caller);
}
if (mRequest.activityInfo == null) {
mRequest.resolveActivity(mSupervisor);
}
int res;
synchronized (mService.mGlobalLock) {
final boolean globalConfigWillChange = mRequest.globalConfig != null
&& mService.getGlobalConfiguration().diff(mRequest.globalConfig) != 0;
final ActivityStack stack = mRootWindowContainer.getTopDisplayFocusedStack();
if (stack != null) {
stack.mConfigWillChange = globalConfigWillChange;
}
final long origId = Binder.clearCallingIdentity();
res = resolveToHeavyWeightSwitcherIfNeeded();
if (res != START_SUCCESS) {
return res;
}
//这里执行启动activity
res = executeRequest(mRequest);
Binder.restoreCallingIdentity(origId);
if (globalConfigWillChange) {
mService.mAmInternal.enforceCallingPermission(
android.Manifest.permission.CHANGE_CONFIGURATION,
"updateConfiguration()");
if (stack != null) {
stack.mConfigWillChange = false;
}
mService.updateConfigurationLocked(mRequest.globalConfig, null, false);
}
// 通知 ActivityMetricsLogger 已经启动了activity，ActivityMetricsLogger将会等待window绘制和填充结果
mSupervisor.getActivityMetricsLogger().notifyActivityLaunched(launchingState, res,
mLastStartActivityRecord);
return getExternalResult(mRequest.waitResult == null ? res
: waitForResult(res, mLastStartActivityRecord));
}
} finally {
onExecutionComplete();
}
}
//执行启动Activity的请求并开始启动Activity。在这里首先执行一些初步检查，正常情况下将调用startActivityUnchecked->startActivityInner启动Acitivy
private int executeRequest(Request request) {
//一系列的检查...
mLastStartActivityResult = startActivityUnchecked(r, sourceRecord, voiceSession,
request.voiceInteractor, startFlags, true /* doResume */, checkedOptions, inTask,
restrictedBgActivity, intentGrants);
}
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
boolean restrictedBgActivity, NeededUriGrants intentGrants) {
int result = START_CANCELED;
final ActivityStack startedActivityStack;
try {
mService.deferWindowLayout();
result = startActivityInner(r, sourceRecord, voiceSession, voiceInteractor,
startFlags, doResume, options, inTask, restrictedBgActivity, intentGrants);
} finally {
startedActivityStack = handleStartResult(r, result);
mService.continueWindowLayout();
}
postStartActivityProcessing(r, result, startedActivityStack);
return result;
}
//启动Activity并确定Activity是否应添加到现有任务的顶部或向现有Activity传递新的Intent，同时将Activity Task操作到请求的或有效的任务栈显示上。
//该方法只能被startActivityUnchecked调用
int startActivityInner(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, Task inTask,
boolean restrictedBgActivity, NeededUriGrants intentGrants) {
//计算启动Activity的TaskFlag
computeLaunchingTaskFlags();
//计算源任务栈
computeSourceStack();
//设置启动Flag
mIntent.setFlags(mLaunchFlags);
//获取是否有可用的任务栈
final Task reusedTask = getReusableTask();
//判断是否有可用的目标任务栈
final Task targetTask = reusedTask != null ? reusedTask : computeTargetTask();
final boolean newTask = targetTask == null;
mTargetTask = targetTask;
//计算启动参数
computeLaunchParams(r, sourceRecord, targetTask);
//检查是否允许启动
int startResult = isAllowedToStart(r, newTask, targetTask);
if (startResult != START_SUCCESS) {
return startResult;
}
final ActivityRecord targetTaskTop = newTask? null : targetTask.getTopNonFinishingActivity();
if (targetTaskTop != null) {
//有可复用的任务栈,复用此次启动的任务栈
// Recycle the target task for this launch.
startResult = recycleTask(targetTask, targetTaskTop, reusedTask, intentGrants);
if (startResult != START_SUCCESS) {
return startResult;
}
} else {
//需要添加到新的任务栈
mAddingToTask = true;
}
//如果将要启动的Activity和TopActivity相同，检查是否需要只用启动一次
final ActivityStack topStack = mRootWindowContainer.getTopDisplayFocusedStack();
if (topStack != null) {
startResult = deliverToCurrentTopIfNeeded(topStack, intentGrants);
if (startResult != START_SUCCESS) {
return startResult;
}
}
...
if (mDoResume) {
final ActivityRecord topTaskActivity =
mStartActivity.getTask().topRunningActivityLocked();
if (!mTargetStack.isTopActivityFocusable()
|| (topTaskActivity != null && topTaskActivity.isTaskOverlay()
&& mStartActivity != topTaskActivity)) {
mTargetStack.ensureActivitiesVisible(null /* starting */,
0 /* configChanges */, !PRESERVE_WINDOWS);
mTargetStack.getDisplay().mDisplayContent.executeAppTransition();
} else {
if (mTargetStack.isTopActivityFocusable()&& !mRootWindowContainer.isTopDisplayFocusedStack(mTargetStack)) {
mTargetStack.moveToFront("startActivityInner");
}
//resume栈顶的activity
mRootWindowContainer.resumeFocusedStacksTopActivities(mTargetStack, mStartActivity, mOptions);
}
}
}
3.RootWindowContainer
frameworks/base/services/core/java/com/android/server/wm/RootWindowContainer.java
boolean resumeFocusedStacksTopActivities(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
//...
boolean result = false;
if (targetStack != null && (targetStack.isTopStackInDisplayArea()
|| getTopDisplayFocusedStack() == targetStack)) {
result = targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
}
//...
}
4.ActivityStack
frameworks/base/services/core/java/com/android/server/wm/ActivityStack.java
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
if (mInResumeTopActivity) {
return false;
}
boolean result = false;
try {
// 防止递归
mInResumeTopActivity = true;
//
result = resumeTopActivityInnerLocked(prev, options);
//在resume的过程中，对锁屏等特殊情况处理
final ActivityRecord next = topRunningActivity(true /* focusableOnly */);
if (next == null || !next.canTurnScreenOn()) {
checkReadyForSleep();
}
} finally {
mInResumeTopActivity = false;
}
return result;
}
做了非常多的判断，最终走到了mStackSupervisor.startSpecificActivity(next, true, true)来启动Activity
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
if (!mAtmService.isBooting() && !mAtmService.isBooted()) {
return false;
}
// 找到还没finish的且获取到焦点的TopActivity。如果没有焦点，将在下一个获取焦点的任务中唤醒TopActivity
ActivityRecord next = topRunningActivity(true /* focusableOnly */);
//代码好多，做了大量的判断
...
//topActivity是否启动了ApplicationThread，这里我们分析首次启动，所以跳过，直接进入else
if (next.attachedToProcess()) {
...
} else {
// Whoops, need to restart this activity!
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
next.showStartingWindow(null /* prev */, false /* newTask */,
false /* taskSwich */);
}
if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);
}
if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next);
//ActivityStackSupervisor执行startSpecificActivity
mStackSupervisor.startSpecificActivity(next, true, true);
}
return true;
}
5.ActivityStackSupervisor
frameworks/base/services/core/java/com/android/server/wm/ActivityStackSupervisor.java
void startSpecificActivity(ActivityRecord r, boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
final WindowProcessController wpc =
mService.getProcessController(r.processName, r.info.applicationInfo.uid);
boolean knownToBeDead = false;
//如果已经有了ApplicationThread，直接启动Activity
if (wpc != null && wpc.hasThread()) {
try {
realStartActivityLocked(r, wpc, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
knownToBeDead = true;
}
r.notifyUnknownVisibilityLaunchedForKeyguardTransition();
final boolean isTop = andResume && r.isTopRunningActivity();
//启动进程
mService.startProcessAsync(r, knownToBeDead, isTop, isTop ? "top-activity" : "activity");
}
6. ActivityTaskManagerService，准备开始fork APP进程
frameworks/base/services/core/java/com/android/server/wm/ActivityTaskManagerService.java
注意源码中调用了ActivityManagerInternal::startProcess启动App进程，ActivityManagerInternal是系统服务抽象类，ActivityTaskManagerService中通过mAmInternal = LocalServices.getService(ActivityManagerInternal.class)获取到ActivityManagerInternal实现类对象，它的具体实现是ActivityManagerService的内部类LocalService
void startProcessAsync(ActivityRecord activity, boolean knownToBeDead, boolean isTop,
String hostingType) {
try {
if (Trace.isTagEnabled(TRACE_TAG_WINDOW_MANAGER)) {
Trace.traceBegin(TRACE_TAG_WINDOW_MANAGER, "dispatchingStartProcess:"
+ activity.processName);
}
// Post message to start process to avoid possible deadlock of calling into AMS with the
// ATMS lock held.
//注意这里会先创建APP进程
final Message m = PooledLambda.obtainMessage(ActivityManagerInternal::startProcess,
mAmInternal, activity.processName, activity.info.applicationInfo, knownToBeDead,
isTop, hostingType, activity.intent.getComponent());
mH.sendMessage(m);
} finally {
Trace.traceEnd(TRACE_TAG_WINDOW_MANAGER);
}
}
7.fork进程前
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java#LocalService
public final class LocalService extends ActivityManagerInternal {
@Override
public void startProcess(String processName, ApplicationInfo info, boolean knownToBeDead,
boolean isTop, 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, isTop),
ZYGOTE_POLICY_FLAG_LATENCY_SENSITIVE, false /* allowWhileBooting */,
false /* isolated */, true /* keepIfLarge */);
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
HostingRecord hostingRecord, int zygotePolicyFlags, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge) {
return mProcessList.startProcessLocked(processName, info, knownToBeDead, intentFlags,
hostingRecord, zygotePolicyFlags, allowWhileBooting, isolated, 0 /* isolatedUid */,
keepIfLarge, null /* ABI override */, null /* entryPoint */,
null /* entryPointArgs */, null /* crashHandler */);
}
}
frameworks/base/services/core/java/com/android/server/am/ProcessList.java
注意这里startProcessLocked中传入的entryPoint就是后面RuntimeInit中findStaticMain方法参数中的args.startClass
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, HostingRecord hostingRecord,
int zygotePolicyFlags, boolean allowWhileBooting, boolean isolated, int isolatedUid,
boolean keepIfLarge, String abiOverride, String entryPoint, String[] entryPointArgs,
Runnable crashHandler) {
//....
ProcessRecord app;
final boolean success = startProcessLocked(app, hostingRecord, zygotePolicyFlags, abiOverride);
}
final boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,
int zygotePolicyFlags, String abiOverride) {
return startProcessLocked(app, hostingRecord, zygotePolicyFlags,
false /* disableHiddenApiChecks */, false /* disableTestApiChecks */,
false /* mountExtStorageFull */, abiOverride);
}
boolean startProcessLocked(ProcessRecord app, HostingRecord hostingRecord,
int zygotePolicyFlags, boolean disableHiddenApiChecks, boolean disableTestApiChecks,
boolean mountExtStorageFull, String abiOverride) {
final String seInfo = app.info.seInfo
+ (TextUtils.isEmpty(app.info.seInfoUser) ? "" : app.info.seInfoUser);
//启动进程。如果成功返回进程PID，如果失败抛出运行RuntimeException
//注意这里传入的entryPoint就是后面RuntimeInit中findStaticMain方法参数中的args.startClass
final String entryPoint = "android.app.ActivityThread";
...
return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,
runtimeFlags, zygotePolicyFlags, mountExternal, seInfo, requiredAbi,
instructionSet, invokeWith, startTime);
}
boolean startProcessLocked(HostingRecord hostingRecord, String entryPoint, ProcessRecord app,
int uid, int[] gids, int runtimeFlags, int zygotePolicyFlags, int mountExternal,
String seInfo, String requiredAbi, String instructionSet, String invokeWith,
long startTime) {
...
//判断启动进程是否是异步方式
if (mService.mConstants.FLAG_PROCESS_START_ASYNC) {
if (DEBUG_PROCESSES) Slog.i(TAG_PROCESSES,
"Posting procStart msg for " + app.toShortString());
mService.mProcStartHandler.post(() -> handleProcessStart(
app, entryPoint, gids, runtimeFlags, zygotePolicyFlags, mountExternal,
requiredAbi, instructionSet, invokeWith, startSeq));
return true;
} else {
try {
final Process.ProcessStartResult startResult = startProcess(hostingRecord,
entryPoint, app,
uid, gids, runtimeFlags, zygotePolicyFlags, 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 zygotePolicyFlags,
int mountExternal, String seInfo, String requiredAbi, String instructionSet,
String invokeWith, long startTime) {
if (hostingRecord.usesWebviewZygote()) {
//分支1
...
} else if (hostingRecord.usesAppZygote()) {
//分支2
final AppZygote appZygote = createAppZygoteForProcessIfNeeded(app);
// We can't isolate app data and storage data as parent zygote already did that.
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,
/*zygotePolicyFlags=*/ ZYGOTE_POLICY_FLAG_EMPTY, isTopApp,
app.mDisabledCompatChanges, pkgDataInfoMap, whitelistedAppDataInfoMap,
false, false,
new String[]{PROC_START_SEQ_IDENT + app.startSeq});
} else {
//分支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, zygotePolicyFlags,
isTopApp, app.mDisabledCompatChanges, pkgDataInfoMap,
whitelistedAppDataInfoMap, bindMountAppsData, bindMountAppStorageDirs,
new String[]{PROC_START_SEQ_IDENT + app.startSeq});
}
}
}
因为是从launcher启动App，所以发起进程是launcher所在进程，于是走到分支3，最终会调用 Process.start，Process.start内部调用了ZYGOTE_PROCESS.start
frameworks/base/core/java/android/os/Process.java
public static final ZygoteProcess ZYGOTE_PROCESS = new ZygoteProcess();
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,
int zygotePolicyFlags,
boolean isTopApp,
@Nullable long[] disabledCompatChanges,
@Nullable Map<String, Pair<String, Long>>
pkgDataInfoMap,
@Nullable Map<String, Pair<String, Long>>
whitelistedDataInfoMap,
boolean bindMountAppsData,
boolean bindMountAppStorageDirs,
@Nullable String[] zygoteArgs) {
return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, packageName,
zygotePolicyFlags, isTopApp, disabledCompatChanges,
pkgDataInfoMap, whitelistedDataInfoMap, bindMountAppsData,
bindMountAppStorageDirs, zygoteArgs);
}
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,
int zygotePolicyFlags,
boolean isTopApp,
@Nullable long[] disabledCompatChanges,
@Nullable Map<String, Pair<String, Long>>
pkgDataInfoMap,
@Nullable Map<String, Pair<String, Long>>
whitelistedDataInfoMap,
boolean bindMountAppsData,
boolean bindMountAppStorageDirs,
@Nullable String[] zygoteArgs) {
...
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
runtimeFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, /*startChildZygote=*/ false,
packageName, zygotePolicyFlags, isTopApp, disabledCompatChanges,
pkgDataInfoMap, whitelistedDataInfoMap, bindMountAppsData,
bindMountAppStorageDirs, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
}
}
private Process.ProcessStartResult startViaZygote(...)throws ZygoteStartFailedEx {
ArrayList<String> argsForZygote = new ArrayList<>();
argsForZygote.add("--runtime-args");
创建了一个ArrayList，往里面添加了很多进程启动参数
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),
zygotePolicyFlags,
argsForZygote);
}
}
//尝试通过兼容ABI向Zygote进程打通一个socket连接
private ZygoteState openZygoteSocketIfNeeded(String abi) throws ZygoteStartFailedEx {
try {
attemptConnectionToPrimaryZygote();
if (primaryZygoteState.matches(abi)) {
return primaryZygoteState;
}
if (mZygoteSecondarySocketAddress != null) {
// The primary zygote didn't match. Try the secondary.
attemptConnectionToSecondaryZygote();
if (secondaryZygoteState.matches(abi)) {
return secondaryZygoteState;
}
}
} catch (IOException ioe) {
throw new ZygoteStartFailedEx("Error connecting to zygote", ioe);
}
throw new ZygoteStartFailedEx("Unsupported zygote ABI: " + abi);
}
private Process.ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, int zygotePolicyFlags, @NonNull ArrayList<String> args)
throws ZygoteStartFailedEx {
String msgStr = args.size() + "\n" + String.join("\n", args) + "\n";
if (shouldAttemptUsapLaunch(zygotePolicyFlags, 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);
}
private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(
ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {
try {
final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;
final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;
//向zygoteState写入启动参数
zygoteWriter.write(msgStr);
zygoteWriter.flush();
Process.ProcessStartResult result = new Process.ProcessStartResult();
//创建了进程ID
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);
}
}
在Zygote进程启动后，main方法会创建一个ZygoteServer，并调用ZygoteServer对象的runSelectLoop方法，循环等待AMS的请求。
attemptZygoteSendArgsAndGetResult方法将保存在ArrayList中的启动参数写入ZygoteState对象中，通过socket通道向Zygote进程发送启动参数列表，然后进入阻塞等待状态，直到远端ZygoteServer的socket服务端LocalServerSocket读取到启动参数，发送回来新创建的进程pid才返回。
接下来我们分析下Zygote进程中是如何接收到这个socket消息，并看看接收到消息后干了啥
ServerSocket读取消息
com/android/internal/os/ZygoteInit.java
public static void main(String argv[]) {
ZygoteServer zygoteServer = null;
...
zygoteServer = new ZygoteServer(isPrimaryZygote);
Runnable caller;
caller = zygoteServer.runSelectLoop(abiList);
if (caller != null) {
caller.run();
}
}
可以看到，Zygote的main方法中，创建了ZygoteServer对象，ZygoteServer的构造方法中创建了LocalServerSocket，会在runSelectLoop方法中不断读取Socket消息
frameworks/base/core/java/com/android/internal/os/ZygoteServer.java
/**
* Runs the zygote process's select loop. Accepts new connections as
* they happen, and reads commands from connections one spawn-request's
* worth at a time.
*/
Runnable runSelectLoop(String abiList) {
ArrayList<FileDescriptor> socketFDs = new ArrayList<>();
ArrayList<ZygoteConnection> peers = new ArrayList<>();
socketFDs.add(mZygoteSocket.getFileDescriptor());
peers.add(null);
mUsapPoolRefillTriggerTimestamp = INVALID_TIMESTAMP;
//开始无线循环读取socket链接
while (true) {
fetchUsapPoolPolicyPropsWithMinInterval();
mUsapPoolRefillAction = UsapPoolRefillAction.NONE;
int[] usapPipeFDs = null;
StructPollfd[] pollFDs;
if (mUsapPoolEnabled) {
usapPipeFDs = Zygote.getUsapPipeFDs();
pollFDs = new StructPollfd[socketFDs.size() + 1 + usapPipeFDs.length];
} else {
pollFDs = new StructPollfd[socketFDs.size()];
}
int pollIndex = 0;
for (FileDescriptor socketFD : socketFDs) {
pollFDs[pollIndex] = new StructPollfd();
pollFDs[pollIndex].fd = socketFD;
pollFDs[pollIndex].events = (short) POLLIN;
++pollIndex;
}
final int usapPoolEventFDIndex = pollIndex;
....
int pollTimeoutMs;
....
int pollReturnValue;
..
if (pollReturnValue == 0) {
mUsapPoolRefillTriggerTimestamp = INVALID_TIMESTAMP;
mUsapPoolRefillAction = UsapPoolRefillAction.DELAYED;
} else {
boolean usapPoolFDRead = false;
while (--pollIndex >= 0) {
if ((pollFDs[pollIndex].revents & POLLIN) == 0) {
continue;
}
if (pollIndex == 0) {
// Zygote server socket
//建立了socket链接
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 server socket接收到了一个socket消息
try {
ZygoteConnection connection = peers.get(pollIndex);
//执行命令
final Runnable command = connection.processOneCommand(this);
// TODO (chriswailes): Is this extra check necessary?
if (mIsForkChild) {
return command;
} else {
...
//执行结束后关闭连接
if (connection.isClosedByPeer()) {
connection.closeSocket();
peers.remove(pollIndex);
socketFDs.remove(pollIndex);
}
}
} catch (Exception e) {
...
} finally {
mIsForkChild = false;
}
} else {
...
}
}
...
}
if (mUsapPoolRefillAction != UsapPoolRefillAction.NONE) {
....
}
}
}
ZygoteServer接收到消息后，ZygoteConnection调用processOneCommand方法读取并解析到的启动参数
主要做了两件事：
- 调用Native方法fork了一个进程并返回PID
- 解析参数，执行ActivityThread的Main方法
8.开始fork进程
D:\develop\Sdk\sources\android-30\com\android\internal\os\ZygoteConnection.java
Runnable processOneCommand(ZygoteServer zygoteServer) {
String[] args;
try {
//读取启动参数
args = Zygote.readArgumentList(mSocketReader);
} catch (IOException ex) {
throw new IllegalStateException("IOException on command socket", ex);
}
int pid;
FileDescriptor childPipeFd = null;
FileDescriptor serverPipeFd = null;
//这个类对启动参数进行了解析
//几个关键的参数
//parsedArgs.mTargetSdkVersion,
//parsedArgs.mDisabledCompatChanges,
//parsedArgs.mRemainingArgs
ZygoteArguments parsedArgs = new ZygoteArguments(args);
...
Zygote.applyUidSecurityPolicy(parsedArgs, peer);
Zygote.applyInvokeWithSecurityPolicy(parsedArgs, peer);
Zygote.applyDebuggerSystemProperty(parsedArgs);
Zygote.applyInvokeWithSystemProperty(parsedArgs);
int[][] rlimits = null;
if (parsedArgs.mInvokeWith != null) {
try {
FileDescriptor[] pipeFds = Os.pipe2(O_CLOEXEC);
childPipeFd = pipeFds[1];
serverPipeFd = pipeFds[0];
Os.fcntlInt(childPipeFd, F_SETFD, 0);
fdsToIgnore = new int[]{childPipeFd.getInt$(), serverPipeFd.getInt$()};
} catch (ErrnoException errnoEx) {
throw new IllegalStateException("Unable to set up pipe for invoke-with", errnoEx);
}
}
int [] fdsToClose = { -1, -1 };
FileDescriptor fd = mSocket.getFileDescriptor();
if (fd != null) {
fdsToClose[0] = fd.getInt$();
}
fd = zygoteServer.getZygoteSocketFileDescriptor();
if (fd != null) {
fdsToClose[1] = fd.getInt$();
}
//Zygote进程为启动的App fork了一个进程，并返回进程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.mIsTopApp,
parsedArgs.mPkgDataInfoList, parsedArgs.mWhitelistedDataInfoList,
parsedArgs.mBindMountAppDataDirs, parsedArgs.mBindMountAppStorageDirs);
try {
if (pid == 0) {
// in child
zygoteServer.setForkChild();
zygoteServer.closeServerSocket();
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
return handleChildProc(parsedArgs, 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, serverPipeFd);
return null;
}
} finally {
IoUtils.closeQuietly(childPipeFd);
IoUtils.closeQuietly(serverPipeFd);
}
}
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,
boolean isTopApp, String[] pkgDataInfoList, String[] whitelistedDataInfoList,
boolean bindMountAppDataDirs, boolean bindMountAppStorageDirs) {
ZygoteHooks.preFork();
//调用Native方法fork进程
int pid = nativeForkAndSpecialize(
uid, gid, gids, runtimeFlags, rlimits, mountExternal, seInfo, niceName, fdsToClose,
fdsToIgnore, startChildZygote, instructionSet, appDataDir, isTopApp,
pkgDataInfoList, whitelistedDataInfoList, bindMountAppDataDirs,
bindMountAppStorageDirs);
if (pid == 0) {
// Note that this event ends at the end of handleChildProc,
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "PostFork");
// If no GIDs were specified, don't make any permissions changes based on groups.
if (gids != null && gids.length > 0) {
NetworkUtils.setAllowNetworkingForProcess(containsInetGid(gids));
}
}
// Set the Java Language thread priority to the default value for new apps.
Thread.currentThread().setPriority(Thread.NORM_PRIORITY);
ZygoteHooks.postForkCommon();
return pid;
}
private Runnable handleChildProc(ZygoteArguments parsedArgs,
FileDescriptor pipeFd, boolean isZygote) {
/*
* By the time we get here, the native code has closed the two actual Zygote
* socket connections, and substituted /dev/null in their place. The LocalSocket
* objects still need to be closed properly.
*/
//关闭socket链接
closeSocket();
Zygote.setAppProcessName(parsedArgs, TAG);
// End of the postFork event.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
if (parsedArgs.mInvokeWith != null) {
WrapperInit.execApplication(parsedArgs.mInvokeWith,
parsedArgs.mNiceName, parsedArgs.mTargetSdkVersion,
VMRuntime.getCurrentInstructionSet(),
pipeFd, parsedArgs.mRemainingArgs);
// Should not get here.
throw new IllegalStateException("WrapperInit.execApplication unexpectedly returned");
} else {
if (!isZygote) {
//进入到这里（SystemServer也是通过该方法执行SystemServer的main方法）
return ZygoteInit.zygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mDisabledCompatChanges,
parsedArgs.mRemainingArgs, null /* classLoader */);
} else {
return ZygoteInit.childZygoteInit(parsedArgs.mTargetSdkVersion,
parsedArgs.mRemainingArgs, null /* classLoader */);
}
}
}
frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
各种初始化
public static final Runnable zygoteInit(int targetSdkVersion, long[] disabledCompatChanges,
String[] argv, ClassLoader classLoader) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ZygoteInit");
RuntimeInit.redirectLogStreams();
RuntimeInit.commonInit();
ZygoteInit.nativeZygoteInit();//创建binder连接池，方便后续用心
return RuntimeInit.applicationInit(targetSdkVersion, disabledCompatChanges, argv,
classLoader);
}
执行ActivityThread的main方法并执行
frameworks/base/core/java/com/android/internal/os/RuntimeInit.java
找到ActivityThread的main方法并执行
protected static Runnable applicationInit(int targetSdkVersion, long[] disabledCompatChanges,
String[] argv, ClassLoader classLoader) {
nativeSetExitWithoutCleanup(true);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
VMRuntime.getRuntime().setDisabledCompatChanges(disabledCompatChanges);
//这个类对传入的启动参数进行了再一次解析
final Arguments args = new Arguments(argv);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
//此处args.startClass为android.app.ActivityThread
return findStaticMain(args.startClass, args.startArgs, classLoader);
}
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 {
//通过classLoader获取main方法
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);
}
/*
* 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);
}
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 });
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
Throwable cause = ex.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException(ex);
}
}
}
注意这里返回的new MethodAndArgsCaller(m, argv)是一个runnable，经过层层返回，最终在ZygoteInit.main()中执行run
public static void main(String argv[]) {
zygoteServer = new ZygoteServer(isPrimaryZygote);
caller = zygoteServer.runSelectLoop(abiList);
if (caller != null) {
caller.run();
}
}
至此，APP进程创建完毕，ActivityThread的main方法开始执行
