# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html

# Sets the minimum version of CMake required to build the native library.

cmake_minimum_required(VERSION 3.4.1)

# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.

add_library( # Sets the name of the library.
             native-lib

             # Sets the library as a shared library.
             SHARED

             # Provides a relative path to your source file(s).
             src/main/cpp/native-lib.cpp )

# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.

find_library( # Sets the name of the path variable.
              log-lib

              # Specifies the name of the NDK library that
              # you want CMake to locate.
              log )

# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.

target_link_libraries( # Specifies the target library.
                       native-lib

                       # Links the target library to the log library
                       # included in the NDK.
                       ${log-lib} )

  public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                0L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<Runnable>());
    }

     public static ExecutorService newSingleThreadExecutor() {
        return new FinalizableDelegatedExecutorService
                (new ThreadPoolExecutor(1, 1,
                        0L, TimeUnit.MILLISECONDS,
                        new LinkedBlockingQueue<Runnable>()));
    }

 public static ExecutorService newCachedThreadPool() {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                60L, TimeUnit.SECONDS,
                new SynchronousQueue<Runnable>());
    }

private static final String DESTINATION_ADDRESS = "https://github.com/soulrelay";
OkHttpClient client = new OkHttpClient.Builder().build();
Request request = new Request.Builder()
        .url(DESTINATION_ADDRESS)
        .build();
Response response = client.newCall(request).execute();

private static final String DESTINATION_ADDRESS = "https://github.com/soulrelay";
OkHttpClient client = new OkHttpClient.Builder().build();
Request request = new Request.Builder()
        .url(DESTINATION_ADDRESS)
        .build();
client.newCall(request).enqueue(new Callback() {
    @Override
    public void onFailure(Call call, IOException e) {
    }

    @Override
    public void onResponse(Call call, Response response) throws IOException {
    }
});

// 同步
client.newCall(request).execute()
// 异步
client.newCall(request).enqueue(Callback)

@Override 
public Call newCall(Request request) {
    return new RealCall(this, request);
}

@Override 
public Response execute() throws IOException {
     // 方法检测，execute只能调用1次
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    try {
       // 将RealCall添加到Dispatcher中的同步请求队列中
      client.dispatcher().executed(this);
       // 获取响应的数据
       // Okhttp会对数据（请求流和响应流）进行拦截进行一些额外的处理，
       // 比如失败重连，添加请求头，没网络优先返回缓存数据等等。
       // 这一拦截过程，采用责任链模式来实现的，和Android中的事件传递机制差不多
      Response result = getResponseWithInterceptorChain();
      if (result == null) throw new IOException("Canceled");
      return result;
    } finally {
       // 请求完成或者取消，都会将RealCall从同步请求队列中移除
      client.dispatcher().finished(this);
    }
}

@Override 
public void enqueue(Callback responseCallback) {
    // 和execute一样，enqueue也只能调用1次
    synchronized (this) {
      if (executed) throw new IllegalStateException("Already Executed");
      executed = true;
    }
    // 执行请求
    client.dispatcher().enqueue(new AsyncCall(responseCallback));
}

public abstract class NamedRunnable implements Runnable {
  protected final String name;

  public NamedRunnable(String format, Object... args) {
    this.name = Util.format(format, args);
  }

  @Override public final void run() {
    String oldName = Thread.currentThread().getName();
    Thread.currentThread().setName(name);
    try {
      execute();
    } finally {
      Thread.currentThread().setName(oldName);
    }
  }

  protected abstract void execute();
}

final class AsyncCall extends NamedRunnable {
    // 其他省略，execute方法式真正执行请求
    @Override protected void execute() {
      boolean signalledCallback = false;
      try {
        Response response = getResponseWithInterceptorChain();
        if (retryAndFollowUpInterceptor.isCanceled()) {
          signalledCallback = true;
          responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
        } else {
          signalledCallback = true;
          responseCallback.onResponse(RealCall.this, response);
        }
      } catch (IOException e) {
        if (signalledCallback) {
          // Do not signal the callback twice!
          Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
        } else {
          responseCallback.onFailure(RealCall.this, e);
        }
      } finally {
        client.dispatcher().finished(this);
      }
    }
}

private Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!retryAndFollowUpInterceptor.isForWebSocket()) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(
        retryAndFollowUpInterceptor.isForWebSocket()));

    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }

public final class Dispatcher {
  //最大请求数
  private int maxRequests = 64;
  //相同host最大请求数
  private int maxRequestsPerHost = 5;
  //请求执行，懒加载
  private ExecutorService executorService;
  //就绪状态的异步请求队列
  private final Deque<AsyncCall> readyCalls = new ArrayDeque<>();
  //运行中的异步请求队列
  private final Deque<AsyncCall> runningCalls = new ArrayDeque<>();
  //进行中的同步请求，包括那些尚未完成被取消的请求
  private final Deque<Call> executedCalls = new ArrayDeque<>();

  public Dispatcher(ExecutorService executorService) {
    this.executorService = executorService;
  }

  public Dispatcher() {
  }

  public synchronized ExecutorService getExecutorService() {
    if (executorService == null) {
       //corePoolSize 为 0表示，没有核心线程，所有执行请求的线程，使用完了如果过期了（keepAliveTime）就回收了,
      //maximumPoolSize 无限大的线程池空间
      executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
          new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
    }
    return executorService;
  }

  public synchronized void setMaxRequests(int maxRequests) {
    if (maxRequests < 1) {
      throw new IllegalArgumentException("max < 1: " + maxRequests);
    }
    this.maxRequests = maxRequests;
    promoteCalls();
  }

  public synchronized int getMaxRequests() {
    return maxRequests;
  }

  public synchronized void setMaxRequestsPerHost(int maxRequestsPerHost) {
    if (maxRequestsPerHost < 1) {
      throw new IllegalArgumentException("max < 1: " + maxRequestsPerHost);
    }
    this.maxRequestsPerHost = maxRequestsPerHost;
    promoteCalls();
  }

  public synchronized int getMaxRequestsPerHost() {
    return maxRequestsPerHost;
  }

  synchronized void enqueue(AsyncCall call) {
    if (runningCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {
      runningCalls.add(call);
      getExecutorService().execute(call);
    } else {
      readyCalls.add(call);
    }
  }

  //取消带有tag的所有请求
  public synchronized void cancel(Object tag) {
    for (AsyncCall call : readyCalls) {
      if (Util.equal(tag, call.tag())) {
        call.cancel();
      }
    }

    for (AsyncCall call : runningCalls) {
      if (Util.equal(tag, call.tag())) {
        call.get().canceled = true;
        HttpEngine engine = call.get().engine;
        if (engine != null) engine.cancel();
      }
    }

    for (Call call : executedCalls) {
      if (Util.equal(tag, call.tag())) {
        call.cancel();
      }
    }
  }

  //异步请求结束
  //当该异步请求结束的时候，会调用此方法，
  //用于将运行中的异步请求队列中的该请求移除并调整请求队列
  //此时就绪队列中的请求就可以进入运行中的队列
  synchronized void finished(AsyncCall call) {
    if (!runningCalls.remove(call)) throw new AssertionError("AsyncCall wasn't running!");
    promoteCalls();
  }

  //根据maxRequests和maxRequestsPerHost来调整
  //runningAsyncCalls和readyAsyncCalls
  //使运行中的异步请求不超过两种最大值
  //并且如果队列有空闲，将就绪状态的请求归类为运行中。
  private void promoteCalls() {
    //运行中的异步请求队列的请求数大于最大请求数，那么就没必要去将就绪状态的请求移动到运行中。
    //其实就是说，如果有超过最大请求数的请求正在运行，是不需要将其移出队列的，继续运行完即可
    if (runningCalls.size() >= maxRequests) return;
    //如果就绪的队列为空，那就更没有必要移动了，因为都没有。
    if (readyCalls.isEmpty()) return; 
    //遍历就绪队列
    for (Iterator<AsyncCall> i = readyCalls.iterator(); i.hasNext(); ) {
      //取出一个请求
      AsyncCall call = i.next();
      //如果当前请求对应的host下，没有超过maxRequestsPerHost
      //那么将其从就绪队列中移除，并加入在运行队列。
      if (runningCallsForHost(call) < maxRequestsPerHost) { 
        //移除        
        i.remove();
        //加入运行队列
        runningCalls.add(call);
        //立即执行该请求
        getExecutorService().execute(call);
      }
        //如果运行队列已经到达了最大请求数上限
        //此时如果还有就绪中的请求，也不管了
      if (runningCalls.size() >= maxRequests) return; 
    }
  }

  //对比已有的运行中的请求和当前请求的host
  private int runningCallsForHost(AsyncCall call) {
    int result = 0;
    for (AsyncCall c : runningCalls) {
      if (c.host().equals(call.host())) result++;
    }
    return result;
  }

  synchronized void executed(Call call) {
    executedCalls.add(call);
  }

  //同步请求结束
  //当该同步请求结束的时候，会调用此方法，
  //用于将运行中的同步请求队列中的该请求移除
  synchronized void finished(Call call) {
    if (!executedCalls.remove(call)) throw new AssertionError("Call wasn't in-flight!");
  }

  public synchronized int getRunningCallCount() {
    return runningCalls.size();
  }

  public synchronized int getQueuedCallCount() {
    return readyCalls.size();
  }
}

 public final class Looper {
    private static final String TAG = "Looper";
    // sThreadLocal.get() will return null unless you've called prepare().
    static final ThreadLocal<Looper> sThreadLocal = new ThreadLocal<Looper>();
    
    ....//省略
    }

public class ThreadLocalTest {
    static final String CONSTANT_01 = "CONSTANT_01";
    static final String CONSTANT_02 = "CONSTANT_02";

    public static void main(String[] args) throws InterruptedException {
        ThreadLocal<String> threadLocal = new ThreadLocal<String>();
        threadLocal.set(CONSTANT_01);

        InheritableThreadLocal<String> inheritableThreadLocal = new InheritableThreadLocal<String>();
        inheritableThreadLocal.set(CONSTANT_01);

        Thread thread_1 = new TestThread(threadLocal, inheritableThreadLocal);
        thread_1.setName("thread_01");
        thread_1.start();

        thread_1.join();

        System.out.println("   " + Thread.currentThread().getName() + "  ******************************************");
        System.out.println("   " + Thread.currentThread().getName() + "   \tThreadLocal: " + threadLocal.get());
        System.out.println("   " + Thread.currentThread().getName() + "   \tInheritableThreadLocal: " + inheritableThreadLocal.get());
        System.out.println("   " + Thread.currentThread().getName() + "  ******************************************");
    }
}

class TestThread extends Thread {
    ThreadLocal<String> threadLocal;
    InheritableThreadLocal<String> inheritableThreadLocal;

    public TestThread(ThreadLocal<String> threadLocal, InheritableThreadLocal<String> inheritableThreadLocal) {
        super();
        this.threadLocal = threadLocal;
        this.inheritableThreadLocal = inheritableThreadLocal;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + "******************************************");
        System.out.println(Thread.currentThread().getName() + "\tThreadLocal: " + threadLocal.get());
        System.out.println(Thread.currentThread().getName() + "\tInheritableThreadLocal: " + inheritableThreadLocal.get());
        System.out.println(Thread.currentThread().getName() + "******************************************\n");

        threadLocal.set(ThreadLocalTest.CONSTANT_02);
        inheritableThreadLocal.set(ThreadLocalTest.CONSTANT_02);

        System.out.println(Thread.currentThread().getName() + "*************(Reset Value)****************");
        System.out.println(Thread.currentThread().getName() + "\tThreadLocal: " + threadLocal.get());
        System.out.println(Thread.currentThread().getName() + "\tInheritableThreadLocal: " + inheritableThreadLocal.get());
        System.out.println(Thread.currentThread().getName() + "*************(Reset Value)****************\n");
    }
}

thread_01******************************************
thread_01	ThreadLocal: null
thread_01	InheritableThreadLocal: CONSTANT_01
thread_01******************************************

thread_01*************(Reset Value)****************
thread_01	ThreadLocal: CONSTANT_02
thread_01	InheritableThreadLocal: CONSTANT_02
thread_01*************(Reset Value)****************

   main  ******************************************
   main   	ThreadLocal: CONSTANT_01
   main   	InheritableThreadLocal: CONSTANT_01
   main  ******************************************

    public ThreadLocal() {
    }

    protected T initialValue() {
        return null;
    }

public class TestThreadLocal {
    private static final ThreadLocal<Integer> value = new ThreadLocal<Integer>() {
        @Override
        protected Integer initialValue() {
            return Integer.valueOf(1);
        }
    };
}

   public T get() {
	    //1、首先获取当前线程
        Thread t = Thread.currentThread();
        //2、根据当前线程获取一个map
        ThreadLocalMap map = getMap(t);
        //3、如果获取的map不为空，则在map中以ThreadLocal的引用作为key来在Map中获取对应的Entry e，否则转到5
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            //4、如果e不为null，则返回e.value，否则转到5
            if (e != null)
                return (T)e.value;
        }
        //5、map为空或者e为空，则通过initialValue函数获取初始值value，然后用ThreadLocal的引用和value作为firstKey和firstValue创建一个新的map
        return setInitialValue();
    }

   ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
    }

   private T setInitialValue() {
        T value = initialValue();
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
        return value;
    }
 void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }

 public class Thread implements Runnable {
    ...//省略
    /* ThreadLocal values pertaining to this thread. This map is maintained by the ThreadLocal class. */
    ThreadLocal.ThreadLocalMap threadLocals = null;
    /*
     * InheritableThreadLocal values pertaining to this thread. This map is maintained by the InheritableThreadLocal class.*/
    ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
    ...//省略
}

    public void set(T value) {
        //1、首先获取当前线程
        Thread t = Thread.currentThread();
        //2、根据当前线程获取一个map
        ThreadLocalMap map = getMap(t);
        if (map != null)
        //3、map不为空，则把键值对保存到map中
            map.set(this, value);
        //4、如果map为空（第一次调用的时候map值为null），则去创建一个ThreadLocalMap对象并赋值给map，并把键值对保存到map中。
        else
            createMap(t, value);
    }

 public void remove() {
         ThreadLocalMap m = getMap(Thread.currentThread());
         if (m != null)
             m.remove(this);
     }

static class ThreadLocalMap {
    static class Entry extend WeakReference<ThreadLocal> {
    /** The value associated with this ThreadLocal. */
            Object value;
            Entry(ThreadLocal k, Object v) {
                super(k);
                value = v;
            }
        }
        ...//省略
 }

 private Entry[] table;

     private Entry getEntry(ThreadLocal key) {
            int i = key.threadLocalHashCode & (table.length - 1);
            Entry e = table[i];
            if (e != null && e.get() == key)
                return e;
            else
                return getEntryAfterMiss(key, i, e);
        }

    private Entry getEntryAfterMiss(ThreadLocal key, int i, Entry e) {
            Entry[] tab = table;
            int len = tab.length;

            while (e != null) {
                ThreadLocal k = e.get();
                if (k == key)
                //命中
                    return e;
                if (k == null)
                //如果key值为null，则擦除该位置的Entry
                    expungeStaleEntry(i);
                else
                    i = nextIndex(i, len);
                //继续向下一个位置查询
                e = tab[i];
            }
            return null;
        }

     private void set(ThreadLocal key, Object value) {

            Entry[] tab = table;
            int len = tab.length;
            int i = key.threadLocalHashCode & (len-1);

            for (Entry e = tab[i];
                 e != null;
                 e = tab[i = nextIndex(i, len)]) {
                ThreadLocal k = e.get();

                if (k == key) {
                    e.value = value;
                    return;
                }

                if (k == null) {
                    replaceStaleEntry(key, value, i);
                    return;
                }
            }

            tab[i] = new Entry(key, value);
            int sz = ++size;
            if (!cleanSomeSlots(i, sz) && sz >= threshold)
                rehash();
        }

public class InheritableThreadLocal<T> extends ThreadLocal<T> {
    protected T childValue(T parentValue) {
        return parentValue;
    }
    ThreadLocalMap getMap(Thread t) {
       return t.inheritableThreadLocals;
    }
    void createMap(Thread t, T firstValue) {
        t.inheritableThreadLocals = new ThreadLocalMap(this, firstValue);
    }
}

ndk.dir=/Users/didi/Library/Android/sdk/ndk-bundle
sdk.dir=/Users/didi/Library/Android/sdk

android.useDeprecatedNdk=true

ndk{    
 // 生成的so文件名字，调用C程序的代码中会用到该名字,需要保持一致    
moduleName "algorithm"     
// 输出指定三种平台下的so库
// 还可以添加 'x86_64', 'mips', 'mips64'
abiFilters "armeabi", "armeabi-v7a", "x86" 
}

LOCAL_PATH := $(call my-dir)
 include $(CLEAR_VARS)
LOCAL_MODULE := algorithm
LOCAL_SRC_FILES := /Users/sus/example/JniLab/app/src/main/jni/algorithm.c
 include $(BUILD_SHARED_LIBRARY)

APP_PLATFORM := android-14
APP_ABI :=all //打包出所有cpu平台so文件

public class MainActivity extends AppCompatActivity {

    private static final String TAG = MainActivity.class.getCanonicalName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        android.util.Log.e(TAG, "#onCreate, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());

        new Thread(new Runnable() {
            @Override
            public void run() {
                android.util.Log.e(TAG, "创建AsyncTask的子线程, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                new AsyncTask<Void, Void, String>() {
                    @Override
                    protected void onPreExecute() {
                        android.util.Log.e(TAG, "子线程内初始化AsyncTask #onPreExecute, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                        super.onPreExecute();
                    }

                    @Override
                    protected String doInBackground(Void... params) {
                        android.util.Log.e(TAG, "子线程内初始化AsyncTask #doInBackground, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                        return null;
                    }

                    @Override
                    protected void onPostExecute(String result) {
                        android.util.Log.e(TAG, "子线程内初始化AsyncTask #onPostExecute, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                        super.onPostExecute(result);
                    }
                }.execute((Void) null);
            }
        }).start();

// Caused by: java.util.concurrent.RejectedExecutionException: 
// Task android.os.AsyncTask$3@7c4920 rejected from  
// java.util.concurrent.ThreadPoolExecutor@1f312d9
// [Running, pool size = 17, active threads = 17, queued tasks = 128, completed tasks = 0]

//        for(int i = 0;i<200;i++) {
//            new AsyncTask<Void, Void, Void>() {
//                @Override
//                protected Void doInBackground(Void... params) {
//                    // do something
//                    try {
//                        Thread.sleep(3000);
//                    } catch (InterruptedException e) {
//                        e.printStackTrace();
//                    }
//                    return null;
//                }
//            }.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
//        }

        new AsyncTask<Void, Void, String>() {
            @Override
            protected void onPreExecute() {
                android.util.Log.e(TAG, "主线程内初始化AsyncTask #onPreExecute, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                super.onPreExecute();
            }

            @Override
            protected String doInBackground(Void... params) {
                android.util.Log.e(TAG, "主线程内初始化AsyncTask #doInBackground, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                return null;
            }

            @Override
            protected void onPostExecute(String result) {
                android.util.Log.e(TAG, "主线程内初始化AsyncTask #onPostExecute, " + Thread.currentThread().getName() + "--->" + Thread.currentThread().getId());
                super.onPostExecute(result);
            }
        }.execute((Void) null);
    }
}

public abstract class AsyncTask<Params, Progress, Result> {
    private static final String LOG_TAG = "AsyncTask";

    private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors();
    // 至少需要2个线程，最多需要4个线程在核心池中
    // 可以比CPU数量少一个，避免让所有的CPU都在处理后台工作
    // 这个计算方式不同版本表现不一样，早期是CPU+1
    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;
    
    // 线程创建工厂
    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());
        }
    };

    // 工作队列长度为128
    private static final BlockingQueue<Runnable> sPoolWorkQueue =
            new LinkedBlockingQueue<Runnable>(128);
    // 可以用于并行执行任务的 Executor
    public static final Executor THREAD_POOL_EXECUTOR;
    // THREAD_POOL_EXECUTOR初始化
    static {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS,
                sPoolWorkQueue, sThreadFactory);
        // 核心线程空闲允许超时处理 待遇同非核心线程
        threadPoolExecutor.allowCoreThreadTimeOut(true);
        THREAD_POOL_EXECUTOR = threadPoolExecutor;
    }

    // 串行执行任务的Executor（按顺序每次同时只能执行一个任务）
    // 指定进程全局有效
    public static final Executor SERIAL_EXECUTOR = new SerialExecutor();

    private static final int MESSAGE_POST_RESULT = 0x1;
    private static final int MESSAGE_POST_PROGRESS = 0x2;
    //默认串行执行 而非并行执行
    private static volatile Executor sDefaultExecutor = SERIAL_EXECUTOR;
    private static InternalHandler sHandler;

    private final WorkerRunnable<Params, Result> mWorker;
    private final FutureTask<Result> mFuture;

    private volatile Status mStatus = Status.PENDING;
    
    private final AtomicBoolean mCancelled = new AtomicBoolean();
    private final AtomicBoolean mTaskInvoked = new AtomicBoolean();

    // SERIAL_EXECUTOR也使用THREAD_POOL_EXECUTOR实现的
    // 只不过通过队列mTasks调度实现串行的控制
    private static class SerialExecutor implements Executor {
        final ArrayDeque<Runnable> mTasks = new ArrayDeque<Runnable>();
        Runnable mActive;

        public synchronized void execute(final Runnable r) {
            mTasks.offer(new Runnable() {
                public void run() {
                    try {
                        r.run();
                    } finally {
                        scheduleNext();
                    }
                }
            });
            if (mActive == null) {
                scheduleNext();
            }
        }

        protected synchronized void scheduleNext() {
            if ((mActive = mTasks.poll()) != null) {
                THREAD_POOL_EXECUTOR.execute(mActive);
            }
        }
    }

    public enum Status {
        PENDING,
        RUNNING,
        FINISHED,
    }

    private static Handler getHandler() {
        synchronized (AsyncTask.class) {
            if (sHandler == null) {
                sHandler = new InternalHandler();
            }
            return sHandler;
        }
    }

    /** @hide */
    public static void setDefaultExecutor(Executor exec) {
        sDefaultExecutor = exec;
    }

    // 创建一个异步任务，构造函数必须在UI线程调用
    public AsyncTask() {
        mWorker = new WorkerRunnable<Params, Result>() {
            public Result call() throws Exception {
                mTaskInvoked.set(true);
                Result result = null;
                try {
                    Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
                    //noinspection unchecked
                    result = doInBackground(mParams);
                    Binder.flushPendingCommands();
                } catch (Throwable tr) {
                    mCancelled.set(true);
                    throw tr;
                } finally {
                    postResult(result);
                }
                return result;
            }
        };

        mFuture = new FutureTask<Result>(mWorker) {
            @Override
            protected void done() {
                try {
                    postResultIfNotInvoked(get());
                } catch (InterruptedException e) {
                    android.util.Log.w(LOG_TAG, e);
                } catch (ExecutionException e) {
                    throw new RuntimeException("An error occurred while executing doInBackground()",
                            e.getCause());
                } catch (CancellationException e) {
                    postResultIfNotInvoked(null);
                }
            }
        };
    }

    private void postResultIfNotInvoked(Result result) {
        final boolean wasTaskInvoked = mTaskInvoked.get();
        if (!wasTaskInvoked) {
            postResult(result);
        }
    }

    private Result postResult(Result result) {
        @SuppressWarnings("unchecked")
        Message message = getHandler().obtainMessage(MESSAGE_POST_RESULT,
                new AsyncTaskResult<Result>(this, result));
        message.sendToTarget();
        return result;
    }

    public final Status getStatus() {
        return mStatus;
    }

    @WorkerThread
    protected abstract Result doInBackground(Params... params);

    @MainThread
    protected void onPreExecute() {
    }

    @SuppressWarnings({"UnusedDeclaration"})
    @MainThread
    protected void onPostExecute(Result result) {
    }

    @SuppressWarnings({"UnusedDeclaration"})
    @MainThread
    protected void onProgressUpdate(Progress... values) {
    }

    @SuppressWarnings({"UnusedParameters"})
    @MainThread
    protected void onCancelled(Result result) {
        onCancelled();
    }    
    
    @MainThread
    protected void onCancelled() {
    }

    public final boolean isCancelled() {
        return mCancelled.get();
    }

    public final boolean cancel(boolean mayInterruptIfRunning) {
        mCancelled.set(true);
        return mFuture.cancel(mayInterruptIfRunning);
    }

    public final Result get() throws InterruptedException, ExecutionException {
        return mFuture.get();
    }

    public final Result get(long timeout, TimeUnit unit) throws InterruptedException,
            ExecutionException, TimeoutException {
        return mFuture.get(timeout, unit);
    }
    
     // 基于指定参数执行任务 默认串行执行
    @MainThread
    public final AsyncTask<Params, Progress, Result> execute(Params... params) {
        return executeOnExecutor(sDefaultExecutor, params);
    }
    
    //基于指定参数执行任务，可以自定义Executor，也可以直接使用THREAD_POOL_EXECUTOR
    @MainThread
    public final AsyncTask<Params, Progress, Result> executeOnExecutor(Executor exec,
            Params... params) {
        if (mStatus != Status.PENDING) {
            switch (mStatus) {
                case RUNNING:
                    throw new IllegalStateException("Cannot execute task:"
                            + " the task is already running.");
                case FINISHED:
                    throw new IllegalStateException("Cannot execute task:"
                            + " the task has already been executed "
                            + "(a task can be executed only once)");
            }
        }

        mStatus = Status.RUNNING;

        onPreExecute();

        mWorker.mParams = params;
        exec.execute(mFuture);

        return this;
    }
    
    //简易版 可以直接执行一个Runnable对象
    @MainThread
    public static void execute(Runnable runnable) {
        sDefaultExecutor.execute(runnable);
    }

    @WorkerThread
    protected final void publishProgress(Progress... values) {
        if (!isCancelled()) {
            getHandler().obtainMessage(MESSAGE_POST_PROGRESS,
                    new AsyncTaskResult<Progress>(this, values)).sendToTarget();
        }
    }

    private void finish(Result result) {
        if (isCancelled()) {
            onCancelled(result);
        } else {
            onPostExecute(result);
        }
        mStatus = Status.FINISHED;
    }

    private static class InternalHandler extends Handler {
        public InternalHandler() {
            super(Looper.getMainLooper());
        }

        @SuppressWarnings({"unchecked", "RawUseOfParameterizedType"})
        @Override
        public void handleMessage(Message msg) {
            AsyncTaskResult<?> result = (AsyncTaskResult<?>) msg.obj;
            switch (msg.what) {
                case MESSAGE_POST_RESULT:
                    // There is only one result
                    result.mTask.finish(result.mData[0]);
                    break;
                case MESSAGE_POST_PROGRESS:
                    result.mTask.onProgressUpdate(result.mData);
                    break;
            }
        }
    }

    private static abstract class WorkerRunnable<Params, Result> implements Callable<Result> {
        Params[] mParams;
    }

    @SuppressWarnings({"RawUseOfParameterizedType"})
    private static class AsyncTaskResult<Data> {
        final AsyncTask mTask;
        final Data[] mData;

        AsyncTaskResult(AsyncTask task, Data... data) {
            mTask = task;
            mData = data;
        }
    }
}

if (ContextCompat.checkSelfPermission(context, Manifest.permission.READ_CONTACTS)
     != PackageManager.PERMISSION_GRANTED) {
 // 没有权限，申请权限。
}else{
 // 有权限了，去放肆吧。
}

@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
  switch (requestCode) {
      case MMM: {
          if (grantResults.length > 0
              && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
              // 权限被用户同意，可以去放肆了。
          } else {
              // 权限被用户拒绝了，洗洗睡吧。
          }
          return;
      }
  }
}

if (ContextCompat.checkSelfPermission(this, Manifest.permission.READ_CONTACTS) != PackageManager.PERMISSION_GRANTED) {// 没有权限。
    if (ActivityCompat.shouldShowRequestPermissionRationale(this, Manifest.permission.READ_CONTACTS)) {
            // 用户拒绝过这个权限了，应该提示用户，为什么需要这个权限。
    } else {
        // 申请授权。
        ActivityCompat.requestPermissions(thisActivity, new String[]{Manifest.permission.READ_CONTACTS}, MMM);
    }
}

@Override
public void onRequestPermissionsResult(int requestCode, String permissions[], int[] grantResults) {
    switch (requestCode) {
        case MMM: {
            if (grantResults.length > 0
                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                // 权限被用户同意，可以去放肆了。
            } else {
                // 权限被用户拒绝了，洗洗睡吧。
            }
            return;
        }
    }
}

// 给 ImageView 设置一个 tag
holder.img.setTag(imgUrl);
// 通过 tag 来防止图片错位
if (imageView.getTag() != null && imageView.getTag().equals(imageUrl)) {
    imageView.setImageBitmap(result);
}