JobScheduler 详解一

前言

最近在调查一个 JobScheduler 的问题，看了不少博客和源码，为了防止撂爪就忘，将自己学习到的东西整理一下。
先给出一个自己写的 demo ：

    private static ComponentName sService = new ComponentName("com.example.mi.myjobtest",            MyJobService.class.getName());    public static void schedule(Context context) {        JobScheduler js = (JobScheduler) context.getSystemService(Context.JOB_SCHEDULER_SERVICE);        JobInfo job = new JobInfo.Builder(JOB_ID, sService)                .setRequiredNetworkType(JobInfo.NETWORK_TYPE_UNMETERED)//网络条件，默认值NETWORK_TYPE_NONE                .setPeriodic(DAY_TIME)//任务执行周期                .setPersisted(true)//设备重启后是否继续执行                .setRequiresCharging(true)//设置是否需要充电                .build();        js.schedule(job);    }

注意：

        /**         * Set whether or not to persist this job across device reboots. This will only have an         * effect if your application holds the permission         * {@link android.Manifest.permission#RECEIVE_BOOT_COMPLETED}. Otherwise an exception will         * be thrown.         * @param isPersisted True to indicate that the job will be written to disk and loaded at         *                    boot.         */        public Builder setPersisted(boolean isPersisted) {            mIsPersisted = isPersisted;            return this;        }

设置此条件需要 holds the permission {@link android.Manifest.permission#RECEIVE_BOOT_COMPLETED}

一、JobScheduler 服务启动

1.1 SystemServer.startOtherServices

SystemServer.java

private void startOtherServices() {  ...  mSystemServiceManager.startService(JobSchedulerService.class);  ...}

其会调用 JobSchedulerService.class 的构造函数

1.2 JobSchedulerService

JobSchedulerService.java

    public JobSchedulerService(Context context) {        super(context);        mControllers = new ArrayList<StateController>();        mControllers.add(ConnectivityController.get(this));        mControllers.add(TimeController.get(this));        mControllers.add(IdleController.get(this));        mControllers.add(BatteryController.get(this));        mControllers.add(AppIdleController.get(this));        // 创建主线程的looper        mHandler = new JobHandler(context.getMainLooper());        // 创建binder服务端        mJobSchedulerStub = new JobSchedulerStub();        mJobs = JobStore.initAndGet(this);    }

创建了5个不同的 StateController，分别添加到 mControllers 中
接下来，整篇文章将以 TimeController 为例进行讲解

1.2.1TimeController

TimeController.java

    /** Singleton. */    private static TimeController mSingleton;    public static synchronized TimeController get(JobSchedulerService jms) {        if (mSingleton == null) {            mSingleton = new TimeController(jms, jms.getContext());        }        return mSingleton;    }    private TimeController(StateChangedListener stateChangedListener, Context context) {        super(stateChangedListener, context);        mDeadlineExpiredAlarmIntent =                PendingIntent.getBroadcast(mContext, 0 /* ignored */,                        new Intent(ACTION_JOB_EXPIRED), 0);        mNextDelayExpiredAlarmIntent =                PendingIntent.getBroadcast(mContext, 0 /* ignored */,                        new Intent(ACTION_JOB_DELAY_EXPIRED), 0);        mNextJobExpiredElapsedMillis = Long.MAX_VALUE;        mNextDelayExpiredElapsedMillis = Long.MAX_VALUE;        // Register BR for these intents.        IntentFilter intentFilter = new IntentFilter(ACTION_JOB_EXPIRED);        intentFilter.addAction(ACTION_JOB_DELAY_EXPIRED);        mContext.registerReceiver(mAlarmExpiredReceiver, intentFilter);    }

1.3 JobStore.initAndGet

JobStore.java

    /** Used by the {@link JobSchedulerService} to instantiate the JobStore. */    static JobStore initAndGet(JobSchedulerService jobManagerService) {        synchronized (sSingletonLock) {            if (sSingleton == null) {                sSingleton = new JobStore(jobManagerService.getContext(),                        Environment.getDataDirectory());            }            return sSingleton;        }    }

1.4 创建 JobStore

JobStore.java

    /**     * Construct the instance of the job store. This results in a blocking read from disk.     */    private JobStore(Context context, File dataDir) {        mContext = context;        mDirtyOperations = 0;        File systemDir = new File(dataDir, "system");        File jobDir = new File(systemDir, "job");        jobDir.mkdirs();        // 创建/data/system/job/jobs.xml        mJobsFile = new AtomicFile(new File(jobDir, "jobs.xml"));        mJobSet = new ArraySet<JobStatus>();        // 从 jobs.xml 中读取 JobMap        readJobMapFromDisk(mJobSet);    }

1.5 xml 解析

1.5.1 ReadJobMapFromDiskRunnable

JobStore.java

    /**     * Runnable that reads list of persisted job from xml. This is run once at start up, so doesn't     * need to go through {@link JobStore#add(com.android.server.job.controllers.JobStatus)}.     */    private class ReadJobMapFromDiskRunnable implements Runnable {        private final ArraySet<JobStatus> jobSet;        ReadJobMapFromDiskRunnable(ArraySet<JobStatus> jobSet) {            this.jobSet = jobSet;        }        @Override        public void run() {            try {                List<JobStatus> jobs;                // mJobsFile 即为 /data/system/job/jobs.xml                FileInputStream fis = mJobsFile.openRead();                synchronized (JobStore.this) {                    // 主要功能执行方法                    jobs = readJobMapImpl(fis);                    if (jobs != null) {                        for (int i=0; i<jobs.size(); i++) {                            this.jobSet.add(jobs.get(i));                        }                    }                }                fis.close();            }            ...        }

“reads list of persisted job from xml” 这里只会读取 setPersisted(true) 的 jobs

1.5.2 xml 示例 (以上面 demo 为例)

<?xml version='1.0' encoding='utf-8' standalone='yes' ?><job-info version="0">...    <job jobid="11111111" package="com.example.mi.myjobtest" class="com.example.mi.myjobtest.MyJobService" uid="10128">        <constraints unmetered="true" charging="true" />        <periodic period="3600000" deadline="1504155742651" delay="1504152142651" />        <extras />    </job>...</job-info>

1.5.3 readJobMapImpl

JobStore.java

        private List<JobStatus> readJobMapImpl(FileInputStream fis)                throws XmlPullParserException, IOException {            XmlPullParser parser = Xml.newPullParser();            parser.setInput(fis, StandardCharsets.UTF_8.name());            ...            String tagName = parser.getName();            if ("job-info".equals(tagName)) {                final List<JobStatus> jobs = new ArrayList<JobStatus>();                // Read in version info.                ...                eventType = parser.next();                do {                    // Read each <job/>                    if (eventType == XmlPullParser.START_TAG) {                        tagName = parser.getName();                        // Start reading job.                        if ("job".equals(tagName)) {                            // 读取 job                            JobStatus persistedJob = restoreJobFromXml(parser);                            if (persistedJob != null) {                                jobs.add(persistedJob);                            }                        }                    }                    eventType = parser.next();                } while (eventType != XmlPullParser.END_DOCUMENT);                return jobs;            }            return null;        }

1.5.4 restoreJobFromXml

JobStore.java

        private JobStatus restoreJobFromXml(XmlPullParser parser) throws XmlPullParserException,                IOException {            JobInfo.Builder jobBuilder;            int uid;            // 解析 job identifier attributes.即 <job jobid="11111111" package="com.example.mi.myjobtest" class="com.example.mi.myjobtest.MyJobService" uid="10128">            jobBuilder = buildBuilderFromXml(parser);            jobBuilder.setPersisted(true);            uid = Integer.valueOf(parser.getAttributeValue(null, "uid"));            int eventType;            // 解析 constraints tag.即 <constraints unmetered="true" charging="true" />            buildConstraintsFromXml(jobBuilder, parser);            // Tuple of (earliest runtime, latest runtime) in elapsed realtime after disk load.            // 解析 deadline="1504155742651" delay="1504152142651" 为 elapsedtime 形式            elapsedRuntimes = buildExecutionTimesFromXml(parser);            final long elapsedNow = SystemClock.elapsedRealtime();            if (XML_TAG_PERIODIC.equals(parser.getName())) {                // 解析 XML_TAG_PERIODIC                ...            } else if (XML_TAG_ONEOFF.equals(parser.getName())) {                // 解析 XML_TAG_ONEOFF                ...            } else {            }            maybeBuildBackoffPolicyFromXml(jobBuilder, parser);            // Read out extras Bundle.            ...            return new JobStatus(                    jobBuilder.build(), uid, elapsedRuntimes.first, elapsedRuntimes.second);        }

1.5.5 buildBuilderFromXml

JobStore.java

        private JobInfo.Builder buildBuilderFromXml(XmlPullParser parser) throws NumberFormatException {            // Pull out required fields from <job> attributes.            // 即解析 <job jobid="11111111" package="com.example.mi.myjobtest" class="com.example.mi.myjobtest.MyJobService" uid="10128"> 此行            int jobId = Integer.valueOf(parser.getAttributeValue(null, "jobid"));            String packageName = parser.getAttributeValue(null, "package");            String className = parser.getAttributeValue(null, "class");            ComponentName cname = new ComponentName(packageName, className);            return new JobInfo.Builder(jobId, cname);        }

1.5.6 创建 JobInfo

JobInfo.java

    private JobInfo(JobInfo.Builder b) {        jobId = b.mJobId;        extras = b.mExtras;        ...//形式与上面相同    }    public static final class Builder {        public Builder(int jobId, ComponentName jobService) {            mJobService = jobService;            mJobId = jobId;        }        public JobInfo build() {            ...            return new JobInfo(this);        }    }

1.5.7 创建 JobStatus

JobStatus.java

    /** How many times this job has failed, used to compute back-off. */    private final int numFailures;    private JobStatus(JobInfo job, int uId, int numFailures) {        this.job = job;        this.uId = uId;        this.name = job.getService().flattenToShortString();        this.tag = "*job*/" + this.name;        this.numFailures = numFailures;    }    public JobStatus(JobInfo job, int uId, long earliestRunTimeElapsedMillis,                      long latestRunTimeElapsedMillis) {        this(job, uId, 0);        this.earliestRunTimeElapsedMillis = earliestRunTimeElapsedMillis;        this.latestRunTimeElapsedMillis = latestRunTimeElapsedMillis;    }

到这里从 jobs.xml 中解析出 JobStatus 并创建出 JobStore 就讲解完了

1.6 JobSchedulerService.onBootPhase

JobSchedulerService.java

public void onBootPhase(int phase) {    if (PHASE_SYSTEM_SERVICES_READY == phase) {        // 500, 注册广播 for package removals and user removals.        final IntentFilter filter = new IntentFilter(Intent.ACTION_PACKAGE_REMOVED);        filter.addDataScheme("package");        getContext().registerReceiverAsUser(                mBroadcastReceiver, UserHandle.ALL, filter, null, null);        final IntentFilter userFilter = new IntentFilter(Intent.ACTION_USER_REMOVED);        userFilter.addAction(PowerManager.ACTION_DEVICE_IDLE_MODE_CHANGED);        getContext().registerReceiverAsUser(                mBroadcastReceiver, UserHandle.ALL, userFilter, null, null);        mPowerManager = (PowerManager)getContext().getSystemService(Context.POWER_SERVICE);    } else if (phase == PHASE_THIRD_PARTY_APPS_CAN_START) {        synchronized (mJobs) {            // 阶段 600            mReadyToRock = true;            mBatteryStats = IBatteryStats.Stub.asInterface(ServiceManager.getService(                    BatteryStats.SERVICE_NAME));            for (int i = 0; i < MAX_JOB_CONTEXTS_COUNT; i++) {                // 创建 JobServiceContext 对象                mActiveServices.add(                        new JobServiceContext(this, mBatteryStats,                                getContext().getMainLooper()));            }            // Attach jobs to their controllers.开始 track jobs            ArraySet<JobStatus> jobs = mJobs.getJobs();            for (int i=0; i<jobs.size(); i++) {                JobStatus job = jobs.valueAt(i);                for (int controller=0; controller<mControllers.size(); controller++) {                    mControllers.get(controller).deviceIdleModeChanged(mDeviceIdleMode);                    mControllers.get(controller).maybeStartTrackingJob(job);                }            }            mHandler.obtainMessage(MSG_CHECK_JOB).sendToTarget();        }    }}

MAX_JOB_CONTEXTS_COUNT = ActivityManager.isLowRamDeviceStatic() ? 1 : 3，对于低内存的设备，则只创建一个创建JobServiceContext对象，否则创建3个该对象

1.7 创建 JobServiceContext

JobServiceContext.java

    JobServiceContext(JobSchedulerService service, IBatteryStats batteryStats, Looper looper) {        this(service.getContext(), batteryStats, service, looper);    }    @VisibleForTesting    JobServiceContext(Context context, IBatteryStats batteryStats,            JobCompletedListener completedListener, Looper looper) {        mContext = context;        mBatteryStats = batteryStats;        mCallbackHandler = new JobServiceHandler(looper);        mCompletedListener = completedListener;        mAvailable = true;    }

此处的 JobServiceHandler 采用的是 system_server 进程的主线程

1.8 小结

• JobSchedulerService.JobHandler 和 JobServiceContext.JobServiceHandler 都运行在 system_server 进程的主线程
• JobSchedulerService 的启动过程主要是：创建了5个不同的 StateController，分别添加到 mControllers 中；从 /data/system/job/jobs.xml 文件中读取每个 JobInfo，再解析成 JobStatus 对象，添加到 JobStore 的成员变量 mJobSet 中；注册广播，绑定 jobs 和 controllers，发送 MSG_CHECK_JOB 开始运转