Android应用启动源码解析--ActivityThread main()

（一）ActivityThread main是被谁调用的？

(1)开始启动应用

启动应用是由system_service启动的如下，添加"android.app.ActivityThread"参数至ProcessList中．

ActivityManagerService.java

final String entryPoint = "android.app.ActivityThread";

return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,
runtimeFlags, mountExternal, seInfo, requiredAbi, instructionSet, invokeWith,
startTime);

ProcessList.java

 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 {
                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);
        }
    }

(2)ZygoteProcess.java

ZygoteProcess是存在与system_service进程中的，算是系统zygote进程的代理，通过Socket与系统zygote进程进行通信．

startViaZygote会配置启动参数

 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);
        }
    }

(3)ZygoteProcess.java

zygoteSendArgsAndGetResult通过LocalSocket给系统zygote进程发送新应用的请求

 /**
     * 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);
    }

    private Process.ProcessStartResult attemptZygoteSendArgsAndGetResult(
            ZygoteState zygoteState, String msgStr) throws ZygoteStartFailedEx {
        try {
            final BufferedWriter zygoteWriter = zygoteState.mZygoteOutputWriter;
            final DataInputStream zygoteInputStream = zygoteState.mZygoteInputStream;

            zygoteWriter.write(msgStr);
            zygoteWriter.flush();

            // Always read the entire result from the input stream to avoid leaving
            // bytes in the stream for future process starts to accidentally stumble
            // upon.
            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);
        }
    }

Zygote.java文件中对应的

 /**
     * @hide for internal use only.
     */
    public static final String PRIMARY_SOCKET_NAME = "zygote";

    /**
     * @hide for internal use only.
     */
    public static final String SECONDARY_SOCKET_NAME = "zygote_secondary"; 

(4)Zygote

而在系统zegote进程方面，如下图所示（以前android版本的流程，Android Ｑ有所修改但是大致的流程是可以顺着下面找出来的）：

(5)总结

启动应用的时候，AMS会将携带着ActivityThread类名（"android.app.ActivityThread"）的命令通过Socket传递给当前系统zygote进程的SocketService,zygote进程通过FORK方法创建新的进程，此进程就即将成为新应用进程．

新进程是从zygote进程fork出来的，所以刚开始状态和zygote进程状态是一样的，此后就会退出zygote状态，然后通过反射运行ActivityThread的main方法．进而成为真正的应用进程

（二）执行ActivityThread main方法

ActivityThread的执行的第一个方法：

主要工作是配置网络安全，开始looper循环，挂在系统进程system_service．主要是attach方法．

 public static void main(String[] args) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");

        // Install selective syscall interception
        AndroidOs.install();

        // CloseGuard defaults to true and can be quite spammy.  We
        // disable it here, but selectively enable it later (via
        // StrictMode) on debug builds, but using DropBox, not logs.
        CloseGuard.setEnabled(false);

        Environment.initForCurrentUser();

        // Make sure TrustedCertificateStore looks in the right place for CA certificates
        final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
        TrustedCertificateStore.setDefaultUserDirectory(configDir);

        Process.setArgV0("<pre-initialized>");

        Looper.prepareMainLooper();

        // Find the value for {@link #PROC_START_SEQ_IDENT} if provided on the command line.
        // It will be in the format "seq=114"
        long startSeq = 0;
        if (args != null) {
            for (int i = args.length - 1; i >= 0; --i) {
                if (args[i] != null && args[i].startsWith(PROC_START_SEQ_IDENT)) {
                    startSeq = Long.parseLong(
                            args[i].substring(PROC_START_SEQ_IDENT.length()));
                }
            }
        }
        ActivityThread thread = new ActivityThread();
        thread.attach(false, startSeq);

        if (sMainThreadHandler == null) {
            sMainThreadHandler = thread.getHandler();
        }

        if (false) {
            Looper.myLooper().setMessageLogging(new
                    LogPrinter(Log.DEBUG, "ActivityThread"));
        }

        // End of event ActivityThreadMain.
        Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
        Looper.loop();

        throw new RuntimeException("Main thread loop unexpectedly exited");
    }

(1)应用进程的attach方法

attach中使用到了一个ActivityThread的参数：mAppThread，而mAppThread是ApplicationThread，实现了IApplicationThread.Stub，是一个封装之后的binder.

而mAppThread会通过IActivityManager.attachApplication与系统进程system_service通信，系统进程system_service会记录下mAppThread的代理，并会把此代理作为新应用在system_service进程的标志，方便system_service区分不同的应用进程．

 @UnsupportedAppUsage
    private void attach(boolean system, long startSeq) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            final IActivityManager mgr = ActivityManager.getService();
            try {
                mgr.attachApplication(mAppThread, startSeq);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            ActivityTaskManager.getService().releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                            throw e.rethrowFromSystemServer();
                        }
                    }
                }
            });
        } else {
            // Don't set application object here -- if the system crashes,
            // we can't display an alert, we just want to die die die.
            android.ddm.DdmHandleAppName.setAppName("system_process",
                    UserHandle.myUserId());
            try {
                mInstrumentation = new Instrumentation();
                mInstrumentation.basicInit(this);
                ContextImpl context = ContextImpl.createAppContext(
                        this, getSystemContext().mPackageInfo);
                mInitialApplication = context.mPackageInfo.makeApplication(true, null);
                mInitialApplication.onCreate();
            } catch (Exception e) {
                throw new RuntimeException(
                        "Unable to instantiate Application():" + e.toString(), e);
            }
        }

        ViewRootImpl.ConfigChangedCallback configChangedCallback
                = (Configuration globalConfig) -> {
            synchronized (mResourcesManager) {
                // We need to apply this change to the resources immediately, because upon returning
                // the view hierarchy will be informed about it.
                if (mResourcesManager.applyConfigurationToResourcesLocked(globalConfig,
                        null /* compat */)) {
                    updateLocaleListFromAppContext(mInitialApplication.getApplicationContext(),
                            mResourcesManager.getConfiguration().getLocales());

                    // This actually changed the resources! Tell everyone about it.
                    if (mPendingConfiguration == null
                            || mPendingConfiguration.isOtherSeqNewer(globalConfig)) {
                        mPendingConfiguration = globalConfig;
                        sendMessage(H.CONFIGURATION_CHANGED, globalConfig);
                    }
                }
            }
        };
        ViewRootImpl.addConfigCallback(configChangedCallback);
    }

(2)system_service进程中的attachApplication方法

system_service的attachApplication方法也就是ActivityManagerService的attachApplication方法，此方法获取此前应用启动的缓存状态并初始化应用进程状态，之后通过IApplicationThread.bindApplication通知应用端进行真正的正文启动．

@GuardedBy("this")
    private boolean attachApplicationLocked(@NonNull IApplicationThread thread,
            int pid, int callingUid, long startSeq) {

        // 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();
        long bindApplicationTimeMillis;
        if (pid != MY_PID && pid >= 0) {
            synchronized (mPidsSelfLocked) {
                app = mPidsSelfLocked.get(pid);
            }
            if (app != null && (app.startUid != callingUid || app.startSeq != startSeq)) {
                String processName = null;
                final ProcessRecord pending = mProcessList.mPendingStarts.get(startSeq);
                if (pending != null) {
                    processName = pending.processName;
                }
                final String msg = "attachApplicationLocked process:" + processName
                        + " startSeq:" + startSeq
                        + " pid:" + pid
                        + " belongs to another existing app:" + app.processName
                        + " startSeq:" + app.startSeq;
                Slog.wtf(TAG, msg);
                // SafetyNet logging for b/131105245.
                EventLog.writeEvent(0x534e4554, "131105245", app.startUid, msg);
                // If there is already an app occupying that pid that hasn't been cleaned up
                cleanUpApplicationRecordLocked(app, false, false, -1,
                            true /*replacingPid*/);
                mPidsSelfLocked.remove(app);
                app = null;
            }
        } else {
            app = null;
        }

        // It's possible that process called attachApplication before we got a chance to
        // update the internal state.
        if (app == null && startSeq > 0) {
            final ProcessRecord pending = mProcessList.mPendingStarts.get(startSeq);
            if (pending != null && pending.startUid == callingUid && pending.startSeq == startSeq
                    && mProcessList.handleProcessStartedLocked(pending, pid, pending
                            .isUsingWrapper(),
                            startSeq, true)) {
                app = pending;
            }
        }

        if (app == null) {
            Slog.w(TAG, "No pending application record for pid " + pid
                    + " (IApplicationThread " + thread + "); dropping process");
            EventLog.writeEvent(EventLogTags.AM_DROP_PROCESS, pid);
            if (pid > 0 && pid != MY_PID) {
                killProcessQuiet(pid);
                //TODO: killProcessGroup(app.info.uid, pid);
            } else {
                try {
                    thread.scheduleExit();
                } catch (Exception e) {
                    // Ignore exceptions.
                }
            }
            return false;
        }

        // If this application record is still attached to a previous
        // process, clean it up now.
        if (app.thread != null) {
            handleAppDiedLocked(app, true, true);
        }

        // Tell the process all about itself.

        if (DEBUG_ALL) Slog.v(
                TAG, "Binding process pid " + pid + " to record " + app);

        final String processName = app.processName;
        try {
            AppDeathRecipient adr = new AppDeathRecipient(
                    app, pid, thread);
            thread.asBinder().linkToDeath(adr, 0);
            app.deathRecipient = adr;
        } catch (RemoteException e) {
            app.resetPackageList(mProcessStats);
            mProcessList.startProcessLocked(app,
                    new HostingRecord("link fail", processName));
            return false;
        }

        EventLog.writeEvent(EventLogTags.AM_PROC_BOUND, app.userId, app.pid, app.processName);

        app.curAdj = app.setAdj = app.verifiedAdj = ProcessList.INVALID_ADJ;
        app.setCurrentSchedulingGroup(app.setSchedGroup = ProcessList.SCHED_GROUP_DEFAULT);
        app.forcingToImportant = null;
        updateProcessForegroundLocked(app, false, 0, false);
        app.hasShownUi = false;
        app.setDebugging(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);

        boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
        List<ProviderInfo> providers = normalMode ? generateApplicationProvidersLocked(app) : null;

        if (providers != null && checkAppInLaunchingProvidersLocked(app)) {
            Message msg = mHandler.obtainMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG);
            msg.obj = app;
            mHandler.sendMessageDelayed(msg, CONTENT_PROVIDER_PUBLISH_TIMEOUT);
        }

        checkTime(startTime, "attachApplicationLocked: before bindApplication");

        if (!normalMode) {
            Slog.i(TAG, "Launching preboot mode app: " + app);
        }

        if (DEBUG_ALL) Slog.v(
            TAG, "New app record " + app
            + " thread=" + thread.asBinder() + " pid=" + pid);
        final BackupRecord backupTarget = mBackupTargets.get(app.userId);
        try {
            int testMode = ApplicationThreadConstants.DEBUG_OFF;
            if (mDebugApp != null && mDebugApp.equals(processName)) {
                testMode = mWaitForDebugger
                    ? ApplicationThreadConstants.DEBUG_WAIT
                    : ApplicationThreadConstants.DEBUG_ON;
                app.setDebugging(true);
                if (mDebugTransient) {
                    mDebugApp = mOrigDebugApp;
                    mWaitForDebugger = mOrigWaitForDebugger;
                }
            }

            boolean enableTrackAllocation = false;
            if (mTrackAllocationApp != null && mTrackAllocationApp.equals(processName)) {
                enableTrackAllocation = true;
                mTrackAllocationApp = null;
            }

            // If the app is being launched for restore or full backup, set it up specially
            boolean isRestrictedBackupMode = false;
            if (backupTarget != null && backupTarget.appInfo.packageName.equals(processName)) {
                isRestrictedBackupMode = backupTarget.appInfo.uid >= FIRST_APPLICATION_UID
                        && ((backupTarget.backupMode == BackupRecord.RESTORE)
                                || (backupTarget.backupMode == BackupRecord.RESTORE_FULL)
                                || (backupTarget.backupMode == BackupRecord.BACKUP_FULL));
            }

            final ActiveInstrumentation instr = app.getActiveInstrumentation();

            if (instr != null) {
                notifyPackageUse(instr.mClass.getPackageName(),
                                 PackageManager.NOTIFY_PACKAGE_USE_INSTRUMENTATION);
            }
            if (DEBUG_CONFIGURATION) Slog.v(TAG_CONFIGURATION, "Binding proc "
                    + processName + " with config "
                    + app.getWindowProcessController().getConfiguration());
            ApplicationInfo appInfo = instr != null ? instr.mTargetInfo : app.info;
            app.compat = compatibilityInfoForPackage(appInfo);

            ProfilerInfo profilerInfo = null;
            String preBindAgent = null;
            if (mProfileData.getProfileApp() != null
                    && mProfileData.getProfileApp().equals(processName)) {
                mProfileData.setProfileProc(app);
                if (mProfileData.getProfilerInfo() != null) {
                    // Send a profiler info object to the app if either a file is given, or
                    // an agent should be loaded at bind-time.
                    boolean needsInfo = mProfileData.getProfilerInfo().profileFile != null
                            || mProfileData.getProfilerInfo().attachAgentDuringBind;
                    profilerInfo = needsInfo
                            ? new ProfilerInfo(mProfileData.getProfilerInfo()) : null;
                    if (mProfileData.getProfilerInfo().agent != null) {
                        preBindAgent = mProfileData.getProfilerInfo().agent;
                    }
                }
            } else if (instr != null && instr.mProfileFile != null) {
                profilerInfo = new ProfilerInfo(instr.mProfileFile, null, 0, false, false,
                        null, false);
            }
            if (mAppAgentMap != null && mAppAgentMap.containsKey(processName)) {
                // We need to do a debuggable check here. See setAgentApp for why the check is
                // postponed to here.
                if ((app.info.flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0) {
                    String agent = mAppAgentMap.get(processName);
                    // Do not overwrite already requested agent.
                    if (profilerInfo == null) {
                        profilerInfo = new ProfilerInfo(null, null, 0, false, false,
                                mAppAgentMap.get(processName), true);
                    } else if (profilerInfo.agent == null) {
                        profilerInfo = profilerInfo.setAgent(mAppAgentMap.get(processName), true);
                    }
                }
            }

            if (profilerInfo != null && profilerInfo.profileFd != null) {
                profilerInfo.profileFd = profilerInfo.profileFd.dup();
                if (TextUtils.equals(mProfileData.getProfileApp(), processName)
                        && mProfileData.getProfilerInfo() != null) {
                    clearProfilerLocked();
                }
            }

            // We deprecated Build.SERIAL and it is not accessible to
            // Instant Apps and target APIs higher than O MR1. Since access to the serial
            // is now behind a permission we push down the value.
            final String buildSerial = (!appInfo.isInstantApp()
                    && appInfo.targetSdkVersion < Build.VERSION_CODES.P)
                            ? sTheRealBuildSerial : Build.UNKNOWN;

            // Check if this is a secondary process that should be incorporated into some
            // currently active instrumentation.  (Note we do this AFTER all of the profiling
            // stuff above because profiling can currently happen only in the primary
            // instrumentation process.)
            if (mActiveInstrumentation.size() > 0 && instr == null) {
                for (int i = mActiveInstrumentation.size() - 1;
                        i >= 0 && app.getActiveInstrumentation() == null; i--) {
                    ActiveInstrumentation aInstr = mActiveInstrumentation.get(i);
                    if (!aInstr.mFinished && aInstr.mTargetInfo.uid == app.uid) {
                        if (aInstr.mTargetProcesses.length == 0) {
                            // This is the wildcard mode, where every process brought up for
                            // the target instrumentation should be included.
                            if (aInstr.mTargetInfo.packageName.equals(app.info.packageName)) {
                                app.setActiveInstrumentation(aInstr);
                                aInstr.mRunningProcesses.add(app);
                            }
                        } else {
                            for (String proc : aInstr.mTargetProcesses) {
                                if (proc.equals(app.processName)) {
                                    app.setActiveInstrumentation(aInstr);
                                    aInstr.mRunningProcesses.add(app);
                                    break;
                                }
                            }
                        }
                    }
                }
            }

            // If we were asked to attach an agent on startup, do so now, before we're binding
            // application code.
            if (preBindAgent != null) {
                thread.attachAgent(preBindAgent);
            }


            // Figure out whether the app needs to run in autofill compat mode.
            AutofillOptions autofillOptions = null;
            if (UserHandle.getAppId(app.info.uid) >= Process.FIRST_APPLICATION_UID) {
                final AutofillManagerInternal afm = LocalServices.getService(
                        AutofillManagerInternal.class);
                if (afm != null) {
                    autofillOptions = afm.getAutofillOptions(
                            app.info.packageName, app.info.longVersionCode, app.userId);
                }
            }
            ContentCaptureOptions contentCaptureOptions = null;
            if (UserHandle.getAppId(app.info.uid) >= Process.FIRST_APPLICATION_UID) {
                final ContentCaptureManagerInternal ccm =
                        LocalServices.getService(ContentCaptureManagerInternal.class);
                if (ccm != null) {
                    contentCaptureOptions = ccm.getOptionsForPackage(app.userId,
                            app.info.packageName);
                }
            }

            checkTime(startTime, "attachApplicationLocked: immediately before bindApplication");
            bindApplicationTimeMillis = SystemClock.elapsedRealtime();
            mAtmInternal.preBindApplication(app.getWindowProcessController());
            final ActiveInstrumentation instr2 = app.getActiveInstrumentation();
            if (app.isolatedEntryPoint != null) {
                // This is an isolated process which should just call an entry point instead of
                // being bound to an application.
                thread.runIsolatedEntryPoint(app.isolatedEntryPoint, app.isolatedEntryPointArgs);
            } else if (instr2 != null) {
                thread.bindApplication(processName, appInfo, providers,
                        instr2.mClass,
                        profilerInfo, instr2.mArguments,
                        instr2.mWatcher,
                        instr2.mUiAutomationConnection, testMode,
                        mBinderTransactionTrackingEnabled, enableTrackAllocation,
                        isRestrictedBackupMode || !normalMode, app.isPersistent(),
                        new Configuration(app.getWindowProcessController().getConfiguration()),
                        app.compat, getCommonServicesLocked(app.isolated),
                        mCoreSettingsObserver.getCoreSettingsLocked(),
                        buildSerial, autofillOptions, contentCaptureOptions);
            } else {
                thread.bindApplication(processName, appInfo, providers, null, profilerInfo,
                        null, null, null, testMode,
                        mBinderTransactionTrackingEnabled, enableTrackAllocation,
                        isRestrictedBackupMode || !normalMode, app.isPersistent(),
                        new Configuration(app.getWindowProcessController().getConfiguration()),
                        app.compat, getCommonServicesLocked(app.isolated),
                        mCoreSettingsObserver.getCoreSettingsLocked(),
                        buildSerial, autofillOptions, contentCaptureOptions);
            }
            if (profilerInfo != null) {
                profilerInfo.closeFd();
                profilerInfo = null;
            }

            // Make app active after binding application or client may be running requests (e.g
            // starting activities) before it is ready.
            app.makeActive(thread, mProcessStats);
            checkTime(startTime, "attachApplicationLocked: immediately after bindApplication");
            mProcessList.updateLruProcessLocked(app, false, null);
            checkTime(startTime, "attachApplicationLocked: after updateLruProcessLocked");
            app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();
        } catch (Exception e) {
            // todo: Yikes!  What should we do?  For now we will try to
            // start another process, but that could easily get us in
            // an infinite loop of restarting processes...
            Slog.wtf(TAG, "Exception thrown during bind of " + app, e);

            app.resetPackageList(mProcessStats);
            app.unlinkDeathRecipient();
            mProcessList.startProcessLocked(app, new HostingRecord("bind-fail", processName));
            return false;
        }

        // Remove this record from the list of starting applications.
        mPersistentStartingProcesses.remove(app);
        if (DEBUG_PROCESSES && mProcessesOnHold.contains(app)) Slog.v(TAG_PROCESSES,
                "Attach application locked removing on hold: " + app);
        mProcessesOnHold.remove(app);

        boolean badApp = false;
        boolean didSomething = false;

        // See if the top visible activity is waiting to run in this process...
        if (normalMode) {
            try {
                didSomething = mAtmInternal.attachApplication(app.getWindowProcessController());
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
                badApp = true;
            }
        }

        // Find any services that should be running in this process...
        if (!badApp) {
            try {
                didSomething |= mServices.attachApplicationLocked(app, processName);
                checkTime(startTime, "attachApplicationLocked: after mServices.attachApplicationLocked");
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown starting services in " + app, e);
                badApp = true;
            }
        }

        // Check if a next-broadcast receiver is in this process...
        if (!badApp && isPendingBroadcastProcessLocked(pid)) {
            try {
                didSomething |= sendPendingBroadcastsLocked(app);
                checkTime(startTime, "attachApplicationLocked: after sendPendingBroadcastsLocked");
            } catch (Exception e) {
                // If the app died trying to launch the receiver we declare it 'bad'
                Slog.wtf(TAG, "Exception thrown dispatching broadcasts in " + app, e);
                badApp = true;
            }
        }

        // Check whether the next backup agent is in this process...
        if (!badApp && backupTarget != null && backupTarget.app == app) {
            if (DEBUG_BACKUP) Slog.v(TAG_BACKUP,
                    "New app is backup target, launching agent for " + app);
            notifyPackageUse(backupTarget.appInfo.packageName,
                             PackageManager.NOTIFY_PACKAGE_USE_BACKUP);
            try {
                thread.scheduleCreateBackupAgent(backupTarget.appInfo,
                        compatibilityInfoForPackage(backupTarget.appInfo),
                        backupTarget.backupMode, backupTarget.userId);
            } catch (Exception e) {
                Slog.wtf(TAG, "Exception thrown creating backup agent in " + app, e);
                badApp = true;
            }
        }

        if (badApp) {
            app.kill("error during init", true);
            handleAppDiedLocked(app, false, true);
            return false;
        }

        if (!didSomething) {
            updateOomAdjLocked(OomAdjuster.OOM_ADJ_REASON_PROCESS_BEGIN);
            checkTime(startTime, "attachApplicationLocked: after updateOomAdjLocked");
        }

        StatsLog.write(
                StatsLog.PROCESS_START_TIME,
                app.info.uid,
                app.pid,
                app.info.packageName,
                StatsLog.PROCESS_START_TIME__TYPE__COLD,
                app.startTime,
                (int) (bindApplicationTimeMillis - app.startTime),
                (int) (SystemClock.elapsedRealtime() - app.startTime),
                app.hostingRecord.getType(),
                (app.hostingRecord.getName() != null ? app.hostingRecord.getName() : ""));
        return true;
    }

总结

ActivityThread main是从zygote子进程进化到应用进程的必走之路，是应用启动的基石．其为应用createContext,loadapk,create3rdApplication,getResoure,https等之后的操作打好了基础，也联通了应用与system_service，为之后的四大组件的创建做好基础．

本文地址：https://blog.csdn.net/qq_26825819/article/details/107913879