之前从网上找到的一张activity启动流程图,步骤画的比较全,不过有创建应用进程的地方有两个点没表现出来,本文又根据代码简单的捋了一下这个地方。
AMS创建应用进程时,在startProcessLocked方法中通过Process.start方法创建进程:
// Start the process. It will either succeed and return a result containing
// the PID of the new process, or else throw a RuntimeException.
boolean isActivityProcess = (entryPoint == null);
if (entryPoint == null) entryPoint = "android.app.ActivityThread";
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
app.processName);
checkTime(startTime, "startProcess: asking zygote to start proc");
ProcessStartResult startResult;
if (hostingType.equals("webview_service")) {
startResult = startWebView(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, null, entryPointArgs);
} else {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, entryPointArgs);
}
并将创建的进程PID和对应的app对象保存起来,并发了一个延时判断消息,表明应用段进程中的初始化必须在此时间内完成:
synchronized (mPidsSelfLocked) {
this.mPidsSelfLocked.put(startResult.pid, app);
if (isActivityProcess) {
Message msg = mHandler.obtainMessage(PROC_START_TIMEOUT_MSG);
msg.obj = app;
mHandler.sendMessageDelayed(msg, startResult.usingWrapper
? PROC_START_TIMEOUT_WITH_WRAPPER : PROC_START_TIMEOUT);
}
}
我们知道Process.start方法最终会调用到ActivityThread的main方法,在main方法中又调用了attach方法来执行应用进程的初始化,最后执行IactivityManager的attachApplication方法,此方法通过Binder通信调用到AMS的attachApplication方法,该方法继续调用attachApplicationLocked方法,在此方法中:
// Find the application record that is being attached... either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
long startTime = SystemClock.uptimeMillis();
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);
}
} else {
app = null;
}
会查询我们之前保存的PID和app map,通过PID找到app对象,然后给app对象赋上应用端的ApplicationThread等信息,同时remove掉之前的延时判断消息:
app.makeActive(thread, mProcessStats);
app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;
app.curSchedGroup = app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT;
app.forcingToImportant = null;
updateProcessForegroundLocked(app, false, false);
app.hasShownUi = false;
app.debugging = false;
app.cached = false;
app.killedByAm = false;
app.killed = false;
// We carefully use the same state that PackageManager uses for
// filtering, since we use this flag to decide if we need to install
// providers when user is unlocked later
app.unlocked = StorageManager.isUserKeyUnlocked(app.userId);
mHandler.removeMessages(PROC_START_TIMEOUT_MSG, app);
然后调用IApplicationThread的bindApplication方法:
if (app.instr != null) {
thread.bindApplication(processName, appInfo, providers,
app.instr.mClass,
profilerInfo, app.instr.mArguments,
app.instr.mWatcher,
app.instr.mUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial);
} else {
thread.bindApplication(processName, appInfo, providers, null, profilerInfo,
null, null, null, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(getGlobalConfiguration()), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked(),
buildSerial);
}
此方法经过Binder调用后,会执行ActivityThread中ApplicationThread的bindApplication方法,然后继续调用到ActivityThread的handleBindApplication方法,这个方法主要进行了我们应用Applicaton对象的初始化创建以及OnCreate调用等:
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch (Exception e) {
throw new RuntimeException(
"Exception thrown in onCreate() of "
+ data.instrumentationName + ": " + e.toString(), e);
}
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
} finally {
StrictMode.setThreadPolicy(savedPolicy);
}
这个地方完成后就结束了,我们回头看下AMS这边,调用IApplicationThread的bindApplication方法后面是怎么走的:
// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
上面这段代码的意思是,看看有没有activity还等着进程创建完启动呢?ActivityStackSupervisor的attachApplicationLocked这个函数很小,我们进来看一眼:
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
}
return didSomething;
}
ActivityRecord hr = stack.topRunningActivityLocked(); 这个地方与 hr 对应的Activity就是要被启动的Activity组件,后面判断了下这个hr的uid还有processName和当前进程是否一致,一致就调用realStartActivityLocked方法去启动了,后面就是Activity启动的流程了,我们就不再赘述了。
最后附上在网上找的一个activity启动流程图,画的比较详细: