Android11 FallbackHome启动和关闭流程分析

Android 7.0引入了新特性：Direct Boot Mode，设备启动后进入的一个新模式，直到用户解锁（unlock）设备此阶段结束。在这个模式下，系统调用 resolveHomeActivity 找到的是FallbackHome ，而不是我们的桌面应用。所以系统开始启动的是 FallbackHome 这个"桌面"。

03-13 16:58:41.359   431   431 D test10  : ===getDefaultTaskDisplayArea===
03-13 16:58:41.359   431   431 D test10  : comp:null
ResolveInfo:ResolveInfo{b15783 com.android.settings/.FallbackHome p=-1000 m=0x108000}
03-13 16:58:41.361   431   431 D test10  : bestChoice:ResolveInfo{b15783 com.android.settings/.FallbackHome p=-1000 m=0x108000}
03-13 16:58:41.361   431   431 D test10  : aInfo:ActivityInfo{67e5d00 com.android.settings.FallbackHome}

那为什么找到是FallbackHome 呢？FallbackHome 位于 com.android.settings这个包下，看一下主配置文件

//packages\apps\Settings\AndroidManifest.xml
 eebff5 u0 com.android.settings/.FallbackHome t2}
03-13 16:58:41.400   431   431 D test10  : java.lang.Exception
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStackSupervisor.startSpecificActivity(ActivityStackSupervisor.java:979)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStack.resumeTopActivityInnerLocked(ActivityStack.java:1970)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStack.resumeTopActivityUncheckedLocked(ActivityStack.java:1516)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.RootWindowContainer.resumeFocusedStacksTopActivities(RootWindowContainer.java:2311)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStarter.startActivityInner(ActivityStarter.java:1736)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStarter.startActivityUnchecked(ActivityStarter.java:1525)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStarter.executeRequest(ActivityStarter.java:1189)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStarter.execute(ActivityStarter.java:670)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityStartController.startHomeActivity(ActivityStartController.java:207)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.RootWindowContainer.startHomeOnTaskDisplayArea(RootWindowContainer.java:1549)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.RootWindowContainer.startHomeOnDisplay(RootWindowContainer.java:1491)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.RootWindowContainer.startHomeOnDisplay(RootWindowContainer.java:1475)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.RootWindowContainer.startHomeOnAllDisplays(RootWindowContainer.java:1456)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.wm.ActivityTaskManagerService$LocalService.startHomeOnAllDisplays(ActivityTaskManagerService.java:6727)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.am.ActivityManagerService.systemReady(ActivityManagerService.java:9689)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.SystemServer.startOtherServices(SystemServer.java:2257)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.SystemServer.run(SystemServer.java:599)
03-13 16:58:41.400   431   431 D test10  :      at com.android.server.SystemServer.main(SystemServer.java:415)
03-13 16:58:41.400   431   431 D test10  :      at java.lang.reflect.Method.invoke(Native Method)
03-13 16:58:41.400   431   431 D test10  :      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
03-13 16:58:41.400   431   431 D test10  :      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:925)

       
       	//......
        final boolean isTop = andResume && r.isTopRunningActivity();
        mService.startProcessAsync(r, knownToBeDead, isTop, isTop ? "top-activity" : "activity");
    }

		//......
		 // Start the process.  It will either succeed and return a result containing
            // the PID of the new process, or else throw a RuntimeException.
        final String entryPoint = "android.app.ActivityThread";
       return startProcessLocked(hostingRecord, entryPoint, app, uid, gids,
                    runtimeFlags, zygotePolicyFlags, mountExternal, seInfo, requiredAbi,
                    instructionSet, invokeWith, startTime);
}

        return ZYGOTE_PROCESS.start(processClass, niceName, uid, gid, gids,
                    runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, invokeWith, packageName,
                    zygotePolicyFlags, isTopApp, disabledCompatChanges,
                    pkgDataInfoMap, whitelistedDataInfoMap, bindMountAppsData,
  

	//一系列的参数设置，省略......
	
	//这里的processClass为android.app.ActivityThread
	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),
                                              zygotePolicyFlags,
                                              argsForZygote);
        }
}

        try {
            attemptConnectionToPrimaryZygote();
            if (primaryZygoteState.matches(abi)) {
                return primaryZygoteState;
            }
            //......
    }
	
	@GuardedBy("mLock")
    private void attemptConnectionToPrimaryZygote() throws IOException {
        if (primaryZygoteState == null || primaryZygoteState.isClosed()) {
            primaryZygoteState =
                    ZygoteState.connect(mZygoteSocketAddress, mUsapPoolSocketAddress);
            //......
        }
    }

            DataInputStream zygoteInputStream;
            BufferedWriter zygoteOutputWriter;
            final LocalSocket zygoteSessionSocket = new LocalSocket();
            if (zygoteSocketAddress == null) {
                throw new IllegalArgumentException("zygoteSocketAddress can't be null");
            }
            try {
                zygoteSessionSocket.connect(zygoteSocketAddress);
                zygoteInputStream = new DataInputStream(zygoteSessionSocket.getInputStream());
                zygoteOutputWriter =
                        new BufferedWriter(
                                new OutputStreamWriter(zygoteSessionSocket.getOutputStream()),
                                Zygote.SOCKET_BUFFER_SIZE);
            } catch (IOException ex) {
                try {
                    zygoteSessionSocket.close();
                } catch (IOException ignore) { }
                throw ex;
            }
            return new ZygoteState(zygoteSocketAddress, usapSocketAddress,
                                   zygoteSessionSocket, zygoteInputStream, zygoteOutputWriter,
                                   getAbiList(zygoteOutputWriter, zygoteInputStream));
        }

        //......
        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;
            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