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第19周—Android的线程和线程池

2018-05-26  本文已影响67人  AR7_

一、线程

主线程

子线程

ANR异常

二、Android中的线程形态

Thread

AsyncTask

HandlerThread

    
    public void run() {
        mTid = Process.myTid();
        Looper.prepare();
        synchronized (this) {
            mLooper = Looper.myLooper();
            notifyAll();
        }
        Process.setThreadPriority(mPriority);
        onLooperPrepared();
        Looper.loop();
        mTid = -1;
    }

IntentService

    @Override
    public void onCreate() {
        // TODO: It would be nice to have an option to hold a partial wakelock
        // during processing, and to have a static startService(Context, Intent)
        // method that would launch the service & hand off a wakelock.

        super.onCreate();
        HandlerThread thread = new HandlerThread("IntentService[" + mName + "]");
        thread.start();

        mServiceLooper = thread.getLooper();
        mServiceHandler = new ServiceHandler(mServiceLooper);
    }

   @Override
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {
        onStart(intent, startId);
        return mRedelivery ? START_REDELIVER_INTENT : START_NOT_STICKY;
    }

    @Override
    public void onStart(@Nullable Intent intent, int startId) {
        Message msg = mServiceHandler.obtainMessage();
        msg.arg1 = startId;
        msg.obj = intent;
        mServiceHandler.sendMessage(msg);
    }

    private final class ServiceHandler extends Handler {
        public ServiceHandler(Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
            onHandleIntent((Intent)msg.obj);
            stopSelf(msg.arg1);
        }
    }

IntentService的onHandlerIntent方法是一个抽象方法，它需要我们在子类中实现，它的作用从Intent参数中区分具体的任务并执行这些任务。如果目前只存在一个后台任务，那么onHandleIntent方法执行完这个任务后，stopSelf(int startId)就会直接停止服务。如果目前存在多个后台任务，那么当onHandleIntent方法执行完最后一个任务时，stopSelf(int startId)才会直接停止服务。另外，由于每执行一个后台任务就必须启动一次IntentService，而IntentService内部则通过消息的方式向HandlerThread请求执行任务，Handler中的Looper是顺序处理消息的，这就意味着IntentService也是顺序执行后台任务的，当有多个后台任务同时存在时，这些后台任务会按照外界发起的顺序排队执行。

    public class LocaIntentService extends IntentService {

        private static final String TAG = "LocalIntentService";

        /**
         * Creates an IntentService.  Invoked by your subclass's constructor.
         *
         * @param name Used to name the worker thread, important only for debugging.
         */
        public LocaIntentService(String name) {
            super(name);
        }

        @Override
        protected void onHandleIntent(@Nullable Intent intent) {
            String action = intent.getStringExtra("task_action");
            Log.d(TAG, "receive task：" + action);
            SystemClock.sleep(3000);
            if ("com.ryq.action.TASK1".equals(action)) {
                Log.d(TAG, "handle task：" + action);
            }
        }

        @Override
        public void onDestroy() {
            Log.d(TAG, "service destroyed.");
            super.onDestroy();
            
        }
    }

这里对LocalIntentService的实现做一下简单的说明，在onHandleIntent方法中会从参数中解析出后台任务的标识，即task_action字段所代表的内容，然后根据不同的任务标识来执行具体的后台任务，这里为了简单起见，直接通过SystemClock.sleep(3000)来休眠3000毫秒从而模拟一种耗时的后台任务，另外为了验证IntentService的停止时机，这里在onDestroy()中打印了一句日志，LocalIntentService实现完成了以后，就可以在外界请求执行后台任务，在下面的代码中先后发起了3个后台任务的请求：

       Intent service = new Intent(this, LocaIntentService.class);
        service.putExtra("task_action", "com.ryq.action.TASK1");
        startService(service);
        service.putExtra("task_action", "com.ryg.action.TASK2");
        startService(service);
        service.putExtra("task_action", "com.ryg.action.TASK3");
        startService(service);

三、Android中的线程池

线程池的优点有3点：

ThreadPoolExecutor

    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory)
corePoolSize
maximumPoolSize
keepAliveTime
unit
workQueue
threadFactory
RejectedExecutionHandler handler。
ThreadPoolExecutor执行任务时大致遵循如下规则：
    private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();
    // We want at least 2 threads and at most 4 threads in the core pool,
    // preferring to have 1 less than the CPU count to avoid saturating
    // the CPU with background work
    private static final int CORE_POOL_SIZE = Math.max(2, Math.min(CPU_COUNT - 1, 4));
    private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1;
    private static final int KEEP_ALIVE_SECONDS = 30;

    private static final ThreadFactory sThreadFactory = new ThreadFactory() {
        private final AtomicInteger mCount = new AtomicInteger(1);

        public Thread newThread(Runnable r) {
            return new Thread(r, "AsyncTask #" + mCount.getAndIncrement());
        }
    };

    private static final BlockingQueue<Runnable> sPoolWorkQueue =
            new LinkedBlockingQueue<Runnable>(128);

    /**
     * An {@link Executor} that can be used to execute tasks in parallel.
     */
    public static final Executor THREAD_POOL_EXECUTOR;

    static {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,
                sPoolWorkQueue, sThreadFactory);
        threadPoolExecutor.allowCoreThreadTimeOut(true);
        THREAD_POOL_EXECUTOR = threadPoolExecutor;
    }

线程池的分类

FixedThreadPool
    public static ExecutorService newFixedThreadPool(int nThreads){
        return new ThreadPoolExecutor(nThreads, nThreads,
                0L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<Runnable>());
    
        }
CachedThreadPool
        public static ExecutorService newCachedThreadPool() {
            return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                    60L, TimeUnit.SECONDS,
                    new SynchronousQueue<Runnable>());
        }
ScheduledThreadPool
    public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
        return new ScheduledThreadPoolExecutor(corePoolSize);
    }

    public ScheduledThreadPoolExecutor(int corePoolSize) {
        super(corePoolSize,Integer.MAX_VALUE,0,NANOSECONDS,new DelayedWorkQueue());
    }
SingleThreadExecutor
        
public static ExecutorService newSingleThreadExecutor() {
    return new FinalizableDelegatedExecutorService(
            new ThreadPoolExecutor(
                    1,
                    1,
                    0L,
                    TimeUnit.MILLISECONDS,
                    new LinkedBlockingQueue<Runnable>())
    );
    );
}
系统预置的4种线程池的典型使用方法，如下所示：
                
        Runnable command = new Runnable() {
               @Override
               public void run() {
                    SystemClock.sleep(2000);  
               }
                    
        };

        ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
        fixedThreadPool.execute(command);

        ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
        cachedThreadPool.execute(command);

        ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(4);
        //2000ms后执行command
        scheduledThreadPool.schedule(command, 2000, TimeUnit.MILLISECONDS);
        //延迟10ms后，每隔1000ms执行一次command
        scheduledThreadPool.scheduleAtFixedRate(command, 10, 1000, TimeUnit.MILLISECONDS);

        ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
        singleThreadExecutor.execute(command);
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