我正在编写一个使用生产者和消费者线程的应用程序。我需要启动、暂停和取消线程。生产者和消费者共享一个BlockedQueue. 我有一个切换按钮来暂停线程并让它们等待然后再次运行它们。在线程中有标志来指示线程是在等待还是在运行。但是，如果 BlockedQueue 在线程中的某处阻塞，则线程无法到达以检查线程是否应该等待或继续运行。请问我该如何解决？
这是我当前的代码：
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);
}
}
}
如果您有意见可以增强我的代码并使其更健壮，请告诉我！