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android Activity启动流程(一)_startactivitymaywait

作者：不正经 | 2024-06-06 08:37:41

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startactivitymaywait

当我们在桌面点击app和app内部启动Activity时都会调用到Activity中的startActivityForResult方法

public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
            @Nullable Bundle options) {
        //开始启动根Activity页面，一般情况mParent都为空，除非类似根Activity为TabActivity
        if (mParent == null) {
            options = transferSpringboardActivityOptions(options);
            //调用Instrumentation中的execStartActivity方法
            Instrumentation.ActivityResult ar =
                mInstrumentation.execStartActivity(
                    this, mMainThread.getApplicationThread(), mToken, this,
                    intent, requestCode, options);
            ...
        } else {
            ...
        }
    }
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startActivityForResult方法中调用了Instrumentation的execStartActivity方法

public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        ...
        try {
           ...
            //通过execStartActivity方法通知ActivityManagerService开启新的Activity
            int result = ActivityManager.getService()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }
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根据ActivityManagerService中方法调用流程，最后会调用startActivityAsUser方法

//ActivityManagerService

    public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId,
            boolean validateIncomingUser) {
        //判断是否是隔离进程，目的目前不清楚，根据异常推断是保证进程安全的
        enforceNotIsolatedCaller("startActivity");
		
        userId = mActivityStartController.checkTargetUser(userId, validateIncomingUser,
                Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");
        ...
        //传入数据，调用ActivityStarter中的execute方法
        return mActivityStartController.obtainStarter(intent, "startActivityAsUser")
                .setCaller(caller)
                .setCallingPackage(callingPackage)
                .setResolvedType(resolvedType)
                .setResultTo(resultTo)
                .setResultWho(resultWho)
                .setRequestCode(requestCode)
                .setStartFlags(startFlags)
                .setProfilerInfo(profilerInfo)
                .setActivityOptions(bOptions)
                .setMayWait(userId)
                .execute();

    }
    
//ActivityStarter

	int execute() {
        try {
            //前面传入数据时调用了setMayWait方法，所以mRequest.mayWait为true
            if (mRequest.mayWait) {
                return startActivityMayWait(mRequest.caller, mRequest.callingUid,
                        mRequest.callingPackage, mRequest.realCallingPid, mRequest.realCallingUid,
                        mRequest.intent, mRequest.resolvedType,
                        mRequest.voiceSession, mRequest.voiceInteractor, mRequest.resultTo,
                        mRequest.resultWho, mRequest.requestCode, mRequest.startFlags,
                        mRequest.profilerInfo, mRequest.waitResult, mRequest.globalConfig,
                        mRequest.activityOptions, mRequest.ignoreTargetSecurity, mRequest.userId,
                        mRequest.inTask, mRequest.reason,
                        mRequest.allowPendingRemoteAnimationRegistryLookup);
            } else {
                return startActivity(mRequest.caller, mRequest.intent, mRequest.ephemeralIntent,
                        mRequest.resolvedType, mRequest.activityInfo, mRequest.resolveInfo,
                        mRequest.voiceSession, mRequest.voiceInteractor, mRequest.resultTo,
                        mRequest.resultWho, mRequest.requestCode, mRequest.callingPid,
                        mRequest.callingUid, mRequest.callingPackage, mRequest.realCallingPid,
                        mRequest.realCallingUid, mRequest.startFlags, mRequest.activityOptions,
                        mRequest.ignoreTargetSecurity, mRequest.componentSpecified,
                        mRequest.outActivity, mRequest.inTask, mRequest.reason,
                        mRequest.allowPendingRemoteAnimationRegistryLookup);
            }
        } finally {
            onExecutionComplete();
        }
    }

	private int startActivityMayWait(IApplicationThread caller, int callingUid,
            String callingPackage, int requestRealCallingPid, int requestRealCallingUid,
            Intent intent, String resolvedType,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            IBinder resultTo, String resultWho, int requestCode, int startFlags,
            ProfilerInfo profilerInfo, WaitResult outResult,
            Configuration globalConfig, SafeActivityOptions options, boolean ignoreTargetSecurity,
            int userId, TaskRecord inTask, String reason,
            boolean allowPendingRemoteAnimationRegistryLookup) {
			...
			//获取进程相关的ActivityInfo信息
        	ActivityInfo aInfo = mSupervisor.resolveActivity(intent, rInfo, startFlags, profilerInfo);
        	//最后调用startActivity
        	synchronized (mService) {
        		...
        		int res = startActivity(caller, intent, ephemeralIntent, resolvedType, aInfo, rInfo,
                    voiceSession, voiceInteractor, resultTo, resultWho, requestCode, callingPid,
                    callingUid, callingPackage, realCallingPid, realCallingUid, startFlags, options,
                    ignoreTargetSecurity, componentSpecified, outRecord, inTask, reason,
                    allowPendingRemoteAnimationRegistryLookup);	
                ...
        	}
   }
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startActivityMayWait方法中调用的startActivity方法跟上面execute方法中的startActivity是同一个方法，目前还没明白startActivityMayWait方法的目的是什么，先往下接着看

	private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
            String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
            String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
            SafeActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
            ActivityRecord[] outActivity, TaskRecord inTask, String reason,
            boolean allowPendingRemoteAnimationRegistryLookup) {

        ...
        mLastStartActivityResult = startActivity(caller, intent, ephemeralIntent, resolvedType,
                aInfo, rInfo, voiceSession, voiceInteractor, resultTo, resultWho, requestCode,
                callingPid, callingUid, callingPackage, realCallingPid, realCallingUid, startFlags,
                options, ignoreTargetSecurity, componentSpecified, mLastStartActivityRecord,
                inTask, allowPendingRemoteAnimationRegistryLookup);
		...
        return getExternalResult(mLastStartActivityResult);
    }

	private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
            String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
            String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
            SafeActivityOptions options,
            boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
            TaskRecord inTask, boolean allowPendingRemoteAnimationRegistryLookup) {
        //提前从选项中取出可选的临时安装程序包
        final Bundle verificationBundle
                = options != null ? options.popAppVerificationBundle() : null;
        ...
            
        //当Activity设置flags为FLAG_ACTIVITY_FORWARD_RESULT时，在这里处理
        final int launchFlags = intent.getFlags();
        if ((launchFlags & Intent.FLAG_ACTIVITY_FORWARD_RESULT) != 0 && sourceRecord != null) {
            // Transfer the result target from the source activity to the new
            // one being started, including any failures.
            if (requestCode >= 0) {
                SafeActivityOptions.abort(options);
                return ActivityManager.START_FORWARD_AND_REQUEST_CONFLICT;
            }
            resultRecord = sourceRecord.resultTo;
            if (resultRecord != null && !resultRecord.isInStackLocked()) {
                resultRecord = null;
            }
            resultWho = sourceRecord.resultWho;
            requestCode = sourceRecord.requestCode;
            sourceRecord.resultTo = null;
            if (resultRecord != null) {
                resultRecord.removeResultsLocked(sourceRecord, resultWho, requestCode);
            }
            if (sourceRecord.launchedFromUid == callingUid) {
                callingPackage = sourceRecord.launchedFromPackage;
            }
        }
        ...
        return startActivity(r, sourceRecord, voiceSession, voiceInteractor, startFlags,
                true /* doResume */, checkedOptions, inTask, outActivity);
    }
    
    private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
                IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
                int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
                ActivityRecord[] outActivity) {
        int result = START_CANCELED;
        try {
            mService.mWindowManager.deferSurfaceLayout();
            result = startActivityUnchecked(r, sourceRecord, voiceSession, voiceInteractor,
                    startFlags, doResume, options, inTask, outActivity);
        } 
        ...
        return result;
    }
    //注意：此方法只能从{@link startActivity}调用
    private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
            IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
            int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
            ActivityRecord[] outActivity) {
		...
		//不管是走下面那个方法，result 最终都会为START_SUCCESS
        int result = START_SUCCESS;
        if (mStartActivity.resultTo == null && mInTask == null && !mAddingToTask
                && (mLaunchFlags & FLAG_ACTIVITY_NEW_TASK) != 0) {
            //当app的第一个Activity启动时会走这个方法
            newTask = true;
            result = setTaskFromReuseOrCreateNewTask(taskToAffiliate, topStack);
        } else if (mSourceRecord != null) {
        	//当app后续的Activity启动时会走这个方法
            result = setTaskFromSourceRecord();
        } else if (mInTask != null) {
            result = setTaskFromInTask();
        } else {
            setTaskToCurrentTopOrCreateNewTask();
        }
        if (result != START_SUCCESS) {
            return result;
        }
        ...
        mSupervisor.resumeFocusedStackTopActivityLocked(mTargetStack, mStartActivity,
                        mOptions);
      	...
	}
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整体大致就是判断启动Activity权限是否正常，是否安全，还有关于栈的处理，Activity的Flags标签处理，有很多细节我还没有仔细研究，毕竟Activity整体启动流程太过庞大了，现在也只是开了个头，我们先接着往下看，上面调用了ActivityStackSupervisor中的resumeFocusedStackTopActivityLocked方法，然后我们跟着流程走

//ActivityStackSupervisor
	boolean resumeFocusedStackTopActivityLocked() {
        return resumeFocusedStackTopActivityLocked(null, null, null);
    }

    boolean resumeFocusedStackTopActivityLocked(
            ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
		...
        if (targetStack != null && isFocusedStack(targetStack)) {
            return targetStack.resumeTopActivityUncheckedLocked(target, targetOptions);
        }
		...
        return false;
    }
//ActivityStack 
	boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options) {
		...
		result = resumeTopActivityInnerLocked(prev, options);
		...
	}
	private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options) {
		...
		mStackSupervisor.startSpecificActivityLocked(next, true, true);
		...
	}
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这时我们发现又回到ActivityStackSupervisor类了，startSpecificActivityLocked这个方法需要注意一下，是判断app的第一个Activity和后续的Activity的地方

void startSpecificActivityLocked(ActivityRecord r,
            boolean andResume, boolean checkConfig) {
        //获取app信息，并判断app是否已在运行
        ProcessRecord app = mService.getProcessRecordLocked(r.processName,
                r.info.applicationInfo.uid, true);

        getLaunchTimeTracker().setLaunchTime(r);

        if (app != null && app.thread != null) {
            try {
            	//如果app已运行会走这里
                if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
                        || !"android".equals(r.info.packageName)) {
                    app.addPackage(r.info.packageName, r.info.applicationInfo.longVersionCode,
                            mService.mProcessStats);
                }
                realStartActivityLocked(r, app, andResume, checkConfig);
                return;
            } catch (RemoteException e) {
                Slog.w(TAG, "Exception when starting activity "
                        + r.intent.getComponent().flattenToShortString(), e);
            }
        }
		//没有运行会走这个方法去启动
        mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
                "activity", r.intent.getComponent(), false, false, true);
    }
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mService就是ActivityManagerService，兜兜转转又回到了最初的起点AMS

	@GuardedBy("this")
    final ProcessRecord startProcessLocked(String processName,
            ApplicationInfo info, boolean knownToBeDead, int intentFlags,
            String hostingType, ComponentName hostingName, boolean allowWhileBooting,
            boolean isolated, boolean keepIfLarge) {
        return startProcessLocked(processName, info, knownToBeDead, intentFlags, hostingType,
                hostingName, allowWhileBooting, isolated, 0 /* isolatedUid */, keepIfLarge,
                null /* ABI override */, null /* entryPoint */, null /* entryPointArgs */,
                null /* crashHandler */);
    }	
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这里插入讲一下GuardedBy注解,根据查询的资料跟synchronized有关，只有持有对应的对象锁才可以调用，然后接着往下看，根据方法流程，最后会调用startProcess方法

	private ProcessStartResult startProcess(String hostingType, String entryPoint,
            ProcessRecord app, int uid, int[] gids, int runtimeFlags, int mountExternal,
            String seInfo, String requiredAbi, String instructionSet, String invokeWith,
            long startTime) {
        ...
                //通过Process.start方法创建应用进程
                startResult = Process.start(entryPoint,
                        app.processName, uid, uid, gids, runtimeFlags, mountExternal,
                        app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
                        app.info.dataDir, invokeWith,
                        new String[] {PROC_START_SEQ_IDENT + app.startSeq});
        ...
    }
//Process
	public static final ProcessStartResult start(final String processClass,
                                  final String niceName,
                                  int uid, int gid, int[] gids,
                                  int runtimeFlags, int mountExternal,
                                  int targetSdkVersion,
                                  String seInfo,
                                  String abi,
                                  String instructionSet,
                                  String appDataDir,
                                  String invokeWith,
                                  String[] zygoteArgs) {
        return zygoteProcess.start(processClass, niceName, uid, gid, gids,
                    runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
    }
//zygoteProcess
	public final Process.ProcessStartResult start(final String processClass,
                                                  final String niceName,
                                                  int uid, int gid, int[] gids,
                                                  int runtimeFlags, int mountExternal,
                                                  int targetSdkVersion,
                                                  String seInfo,
                                                  String abi,
                                                  String instructionSet,
                                                  String appDataDir,
                                                  String invokeWith,
                                                  String[] zygoteArgs) {
        try {
            return startViaZygote(processClass, niceName, uid, gid, gids,
                    runtimeFlags, mountExternal, targetSdkVersion, seInfo,
                    abi, instructionSet, appDataDir, invokeWith, false /* startChildZygote */,
                    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(final String processClass,
                                                      final String niceName,
                                                      final int uid, final int gid,
                                                      final int[] gids,
                                                      int runtimeFlags, int mountExternal,
                                                      int targetSdkVersion,
                                                      String seInfo,
                                                      String abi,
                                                      String instructionSet,
                                                      String appDataDir,
                                                      String invokeWith,
                                                      boolean startChildZygote,
                                                      String[] extraArgs)
                                                      throws ZygoteStartFailedEx {
        ArrayList<String> argsForZygote = new ArrayList<String>();
		//创建字符串列表argsForZygote，并将启动应用进程的启动参数保存在这个列表中
        // --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");
        }
        argsForZygote.add("--target-sdk-version=" + targetSdkVersion);
        ...
        synchronized(mLock) {
            return zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote);
        }
    }
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根据方法名称openZygoteSocketIfNeeded，可以看出来是创建ZygoteSocket并连接的方法，zygoteSendArgsAndGetResult 是发送信息的方法，将信息发送给Zygote并创建应用进程，这个时候看似结束了，实则还没有，到现在也没有看见我们熟悉的Activity生命周期，因为应用进程是在Zygote创建的，接下来要看一下Zygote相关的内容

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