直奔主題
首先我們來看看Java的執行緒通訊基礎
//產品
static class ProductObject{
//執行緒操作變數可見
public volatile static String value;
}
//生產者執行緒
static class Producer extends Thread{
Object lock;
public Producer(Object lock) {
this.lock = lock;
}
@Override
public void run() {
//不斷生產產品
while(true){
synchronized (lock) { //互斥鎖
//產品還沒有被消費，等待
if(ProductObject.value != null){
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
//產品已經消費完成，生產新的產品
ProductObject.value = "NO:"+System.currentTimeMillis();
Log.i(TAG,"生產產品："+ProductObject.value);
lock.notify(); //生產完成，通知消費者消費
}
}
}
}
//消費者執行緒
static class Consumer extends Thread{
Object lock;
public Consumer(Object lock) {
this.lock = lock;
}
@Override
public void run() {
while(true){
synchronized (lock) {
//沒有產品可以消費
if(ProductObject.value == null){
//等待，阻塞
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
Log.i(TAG,"消費產品："+ProductObject.value);
ProductObject.value = null;
lock.notify(); //消費完成，通知生產者，繼續生產
}
}
}
}
複製程式碼呼叫:
Object lock = new Object();
new Producer(lock).start();
new Consumer(lock).start();
複製程式碼Log:
這是一些簡單的執行緒通訊基礎，兩個執行緒進行互動的用法。
接下來分析一下 Java中的FutureTask
我們先來看看類圖
//非同步任務
static class Task implements Callable<Integer> {
//返回非同步任務的執行結果
@Override
public Integer call() throws Exception {
int i = 0;
for (; i < 10; i++) {
try {
Thread.sleep(500);
} catch (InterruptedException e) {
e.printStackTrace();
}
Log.i(TAG, Thread.currentThread().getName() + "_" + i);
}
return i;
}
}
複製程式碼初始化執行
Task work = new Task();
FutureTask<Integer> future = new FutureTask<Integer>(work) {
//非同步任務執行完成，回撥
@Override
protected void done() {
try {
Log.i(TAG, "done:" + get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
};
//執行緒池（使用了預定義的配置）
ExecutorService executor = Executors.newCachedThreadPool();
executor.execute(future);
try {
Thread.sleep(1000);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
//取消非同步任務
// future.cancel(true);
try {
//阻塞，等待非同步任務執行完畢
Log.i(TAG, "" + future.get());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
複製程式碼Log：
Future
package java.util.concurrent;
public interface Future<V> {
boolean cancel(boolean mayInterruptIfRunning);
boolean isCancelled();
boolean isDone();
V get() throws InterruptedException, ExecutionException;
V get(long timeout, TimeUnit unit)
throws InterruptedException, ExecutionException, TimeoutException;
}
複製程式碼Runnable
package java.lang;
public interface Runnable {
public abstract void run();
}
複製程式碼RunnableFuture
package java.util.concurrent;
public interface RunnableFuture<V> extends Runnable, Future<V> {
void run();
}
複製程式碼FutureTask
package java.util.concurrent;
import java.util.concurrent.locks.LockSupport;
public class FutureTask<V> implements RunnableFuture<V> {
......以下只擷取部分程式碼
/** The underlying callable; nulled out after running */
private Callable<V> callable;
/** The thread running the callable; CASed during run() */
private volatile Thread runner;
public FutureTask(Callable<V> callable) {
if (callable == null)
throw new NullPointerException();
this.callable = callable;
this.state = NEW; // ensure visibility of callable
}
public boolean cancel(boolean mayInterruptIfRunning) {
if (!(state == NEW &&
U.compareAndSwapInt(this, STATE, NEW,
mayInterruptIfRunning ? INTERRUPTING : CANCELLED)))
return false;
try { // in case call to interrupt throws exception
if (mayInterruptIfRunning) {
try {
Thread t = runner;
if (t != null)
t.interrupt();
} finally { // final state
U.putOrderedInt(this, STATE, INTERRUPTED);
}
}
} finally {
finishCompletion();
}
return true;
}
/**
* @throws CancellationException {@inheritDoc}
*/
public V get() throws InterruptedException, ExecutionException {
int s = state;
if (s <= COMPLETING)
s = awaitDone(false, 0L);
return report(s);
}
protected void done() { }
protected void set(V v) {
if (U.compareAndSwapInt(this, STATE, NEW, COMPLETING)) {
outcome = v;
U.putOrderedInt(this, STATE, NORMAL); // final state
finishCompletion();
}
}
protected void setException(Throwable t) {
if (U.compareAndSwapInt(this, STATE, NEW, COMPLETING)) {
outcome = t;
U.putOrderedInt(this, STATE, EXCEPTIONAL); // final state
finishCompletion();
}
}
public void run() {
if (state != NEW ||
!U.compareAndSwapObject(this, RUNNER, null, Thread.currentThread()))
return;
try {
Callable<V> c = callable;
if (c != null && state == NEW) {
V result;
boolean ran;
try {
result = c.call();
ran = true;
} catch (Throwable ex) {
result = null;
ran = false;
setException(ex);
}
if (ran)
set(result);
}
} finally {
// runner must be non-null until state is settled to
// prevent concurrent calls to run()
runner = null;
// state must be re-read after nulling runner to prevent
// leaked interrupts
int s = state;
if (s >= INTERRUPTING)
handlePossibleCancellationInterrupt(s);
}
}
private void finishCompletion() {
// assert state > COMPLETING;
for (WaitNode q; (q = waiters) != null;) {
if (U.compareAndSwapObject(this, WAITERS, q, null)) {
for (;;) {
Thread t = q.thread;
if (t != null) {
q.thread = null;
LockSupport.unpark(t);
}
WaitNode next = q.next;
if (next == null)
break;
q.next = null; // unlink to help gc
q = next;
}
break;
}
}
done();
callable = null; // to reduce footprint
}
......以上只擷取部分程式碼
}
複製程式碼從上面程式碼可以看出
Java FutureTask 非同步任務操作提供了便利性
1.獲取非同步任務的返回值--> V get()
2.監聽非同步任務的執行完畢-->finishCompletion()-->done()
3.取消非同步任務-->cancel(boolean mayInterruptIfRunning)
從上面的例子，我們可以看到Executors去呼叫這個Future那麼這個Executors又是啥玩意呢？！
像剛才看Future那樣我們點進去看看這個Executors我們可以發現很多東西，然而，其實這個就是鼎鼎大名的 執行緒池 ！ 我們還是先看看類圖
因為實現類方法太多了，還是直接看api文件比較好。
一個任務
static class MyTask implements Runnable {
int i;
public MyTask(int i) {
this.i = i;
}
@Override
public void run() {
Log.i(TAG, Thread.currentThread().getName() + ";i:" + i);
}
}
複製程式碼初始化-->執行執行緒池
int CPU_COUNT = Runtime.getRuntime().availableProcessors(); //可用的CPU個數
Log.i(TAG, "CPU_COUNT-->" + CPU_COUNT);
int CORE_POOL_SIZE = CPU_COUNT + 1; //5(corePoolSize - 池中所儲存的執行緒數，包括空閒執行緒。)
Log.i(TAG, "CORE_POOL_SIZE-->" + CORE_POOL_SIZE);
int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1; //9(maximumPoolSize - 池中允許的最大執行緒數。)
Log.i(TAG, "MAXIMUM_POOL_SIZE-->" + MAXIMUM_POOL_SIZE);
int KEEP_ALIVE = 1;//(keepAliveTime - 當執行緒數大於核心時，此為終止前多餘的空閒執行緒等待新任務的最長時間。)
//任務佇列（128）(workQueue - 執行前用於保持任務的佇列。此佇列僅由保持 execute 方法提交的 Runnable 任務。)
final BlockingQueue<Runnable> sPoolWorkQueue = new LinkedBlockingQueue<Runnable>(128);
//執行緒工廠(threadFactory - 執行程式建立新執行緒時使用的工廠。)
ThreadFactory sThreadFactory = new ThreadFactory() {
private final AtomicInteger mCount = new AtomicInteger(1);
public Thread newThread(Runnable r) {
String name = "Thread #" + mCount.getAndIncrement();
Log.i(TAG, "newThread-->" + name);
return new Thread(r, name);
}
};
//執行緒池
Executor THREAD_POOL_EXECUTOR = new ThreadPoolExecutor(CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE,
//(unit - keepAliveTime 引數的時間單位。)
TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory);
/* 如果執行的執行緒少於 corePoolSize，則 Executor 始終首選新增新的執行緒，而不進行排隊。
如果執行的執行緒等於或多於 corePoolSize，則 Executor 始終首選將請求加入佇列，而不新增新的執行緒。
如果無法將請求加入佇列，則建立新的執行緒，除非建立此執行緒超出 maximumPoolSize，在這種情況下，任務將被拒絕。*/
//執行非同步任務
//如果當前執行緒池中的數量大於corePoolSize，緩衝佇列workQueue已滿，
//並且執行緒池中的數量等於maximumPoolSize，新提交任務由Handler處理。
//RejectedExecutionException
for (int i = 0; i < 200; i++) {
//相當於new AsyncTask().execute();
THREAD_POOL_EXECUTOR.execute(new MyTask(i));
}
複製程式碼Log如下
其實這個就是Android中AsyncTask的原理我們不妨分析一下AsyncTask：
初始化
執行
返回
返回UI執行緒
Progress更新UI
JAVA API 文件：tool.oschina.net/apidocs/api…
Android API文件：tool.oschina.net/apidocs/api…
文章程式碼：github.com/gepriniusce…