如何让两个线程等待然后运行，假定他们使用BlockedQueue？ [英] How to make two threads wait then run, given that they use a BlockedQueue?
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问题描述
我在写一个使用生产者和消费者线程的应用程序。我需要开始，暂停和取消，线程。生产者和消费者分享 BlockedQueue 。我有一个切换按钮，暂停线程，让他们等待，然后再次运行它们。在线程中有标志来指示线程是否正在等待或运行。但是如果BlockedQueue在线程中某处被阻塞，那么线程无法到达以检查线程是否应该等待或继续运行。
I'm writing an app that uses producer and consumer threads. I need to start, pause and cancel, the threads. The producer and consumer share a BlockedQueue. I have a toggle button to pause the threads and make them wait and then to run them again. In the threads there are flags to indicate if the threads are waiting or running. However if the BlockedQueue is blocking somewhere in the thread, then the thread can't reach to check if the thread should wait or keep running. How can I solve this please?
这是我目前的代码：
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JToggleButton;
import javax.swing.SwingUtilities;
public class GUIController implements ActionListener, ItemListener {
ExecutorService executor = Executors.newCachedThreadPool();
private final BlockingQueue<Integer> queue = new LinkedBlockingQueue<Integer>(10);
private final List<Integer> holder = new LinkedList<Integer>();
private volatile ApplicationState appState = ApplicationState.CLEAN;
private FakeProducer fakeProducer = new FakeProducer("FakeProducer");
private FakeConsumer fakeConsumer = new FakeConsumer();
//GUI stuff
static JToggleButton startBtn;
//static JToggleButton pauseBtn;
static JButton stopBtn;
static JButton showBtn;
private enum ApplicationState {
CLEAN, RUN, PAUSE
}
private enum ThreadState {
RUNNING, WAITING
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
GUIController guiController = new GUIController();
JFrame frame = new JFrame("GUI Concurrency");
frame.setPreferredSize( new Dimension(400, 200));
frame.setLayout( new FlowLayout() );
frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
startBtn = new JToggleButton("Start");
startBtn.addItemListener(guiController);
stopBtn = new JButton("Cancel");
stopBtn.setEnabled(false);
stopBtn.setActionCommand("Cancel");
stopBtn.addActionListener(guiController);
showBtn = new JButton("Show");
showBtn.setActionCommand("Show");
showBtn.addActionListener(guiController);
frame.getContentPane().add(startBtn);
frame.getContentPane().add(stopBtn);
frame.getContentPane().add(showBtn);
frame.pack();
frame.setVisible(true);
}
@Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
System.out.println(command + " is clicked");
if ( command.equals("Cancel") ) {
startBtn.setText("Start");
appState = ApplicationState.CLEAN;
synchronized (fakeProducer) {
fakeProducer.notify();
}
synchronized (fakeConsumer) {
fakeConsumer.notify();
}
holder.clear();
executor.shutdown();
}
else if ( command.equals("Show") ) {
for ( int i : holder ) {
System.out.println("[" + i + "]");
}
System.out.println();
}
}
class FakeProducer implements Runnable {
private String name;
public ThreadState state;
public FakeProducer(String name) {
this.name = name;
}
@Override
public void run() {
state = ThreadState.RUNNING;
List<Integer> list = new LinkedList<Integer>();
for ( int i = 0; i <= 10000; i++ ) {
list.add(i);
}
/**
* While the application state is run, then keep running.
* But if the state is put to be paused, then the thread waits.
* I want to start running again after putting the application to pause.
* When I click Cancel, then the application stop the thread. Then I start as clean.
*/
for ( int i : list ) {
if ( appState == ApplicationState.RUN ) {
try {
//This line blocks the app if there is no
//space in the queue, so it
//will never reach appState=Pause
queue.put(i);
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
else if (appState == ApplicationState.PAUSE) {
try {
synchronized (this) {
state = ThreadState.WAITING;
wait();
}
} catch (InterruptedException e) {
e.printStackTrace();
//This condition is to not to miss the i_th item when the state
//was PAUSE
if ( appState == ApplicationState.RUN ) {
try {
queue.put(i);
} catch (InterruptedException e1) {
e1.printStackTrace();
}
}
}
}
else if ( appState == ApplicationState.CLEAN ) {
break;
}
}
//This is to let the rest of the app know that the list is finished
//appState = ApplicationState.CLEAN;
}
}
class FakeConsumer implements Runnable {
public ThreadState state;
@Override
public void run() {
state = ThreadState.RUNNING;
while( (appState == ApplicationState.RUN) || (appState == ApplicationState.PAUSE) ) {
if ( appState == ApplicationState.RUN ) {
try {
//If this thing is blocking then it won't see anything i.e
//it won't check appState if Pause
//holder.add( queue.take() );
int value = queue.remove();
holder.add(value);
} catch (NoSuchElementException e) {
//e.printStackTrace();
}
}
else if (appState == ApplicationState.PAUSE) {
try {
synchronized (this) {
state = ThreadState.WAITING;
wait();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
@Override
public void itemStateChanged(ItemEvent e) {
if ( e.getStateChange() == ItemEvent.SELECTED ) {
if ( appState == ApplicationState.CLEAN ) {
System.out.println("Start");
startBtn.setText("Pause");
appState = ApplicationState.RUN;
executor = Executors.newCachedThreadPool();
fakeProducer = new FakeProducer("FakeProducer");
fakeConsumer = new FakeConsumer();
executor.execute( fakeProducer );
executor.execute( fakeConsumer );
executor.shutdown();
stopBtn.setEnabled(false);
}
//Now continue execution
else if ( appState == ApplicationState.PAUSE ) {
startBtn.setEnabled(false);
System.out.println( fakeProducer.state );
System.out.println( fakeConsumer.state );
//Block the app until all threads are waiting
while( fakeProducer.state == ThreadState.RUNNING |
fakeConsumer.state == ThreadState.RUNNING ) {
}
/*
*Once they are really both are waiting, then push them to work again
*/
appState = ApplicationState.RUN;
synchronized (fakeProducer) {
fakeProducer.state = ThreadState.RUNNING;
fakeProducer.notify();
}
synchronized (fakeConsumer) {
fakeConsumer.state = ThreadState.RUNNING;
fakeConsumer.notify();
}
startBtn.setText("Pause");
stopBtn.setEnabled(false);
startBtn.setEnabled(true);
}
}
else {
System.out.println("Pause");
startBtn.setText("Continue");
appState = ApplicationState.PAUSE;
stopBtn.setEnabled(true);
}
}
}
请告诉我！
推荐答案
将某些内容放入队列中，告诉他们退出。
Put something into the queue that tells them to exit.
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