我实现了一个简单的工作队列,它接收来自多个不同线程的任务。我希望这些任务向它们的源线程返回一个值,但不知道如何做到这一点。我曾考虑过使用future,但没有办法明确设置future的值。我可以使用一个属性,但我不相信这些是线程安全的。
每个任务都是DBRequest的一个实现。实际内容各不相同,但所有活动的结果都是一个字符串。异步线程创建一个DBRequest并将其提交给队列。队列运行任务,该任务生成一个字符串。如何将该字符串返回到创建DBRequest的线程,以及如何使创建者线程等待结果?
public interface DBRequest {
String execute(VdtsSysDB vdtsSysDB, BoardLoad currentLoad);
}
public class DBQueue implements Runnable {
private static DBQueue dbQueue;
private LinkedBlockingQueue<DBRequest> queue = new LinkedBlockingQueue<>();
private VdtsSysDB vdtsSysDB = new VdtsSysDB();
private ReentrantLock lock = new ReentrantLock();
private static final Logger LOG = LoggerFactory.getLogger(DBQueue.class);
private boolean kill = false;
private BoardLoad currentLoad;
private ProgressController progressController;
public static DBQueue getInstance() {
if (dbQueue == null) synchronized (DBQueue.class) {
if (dbQueue == null)
dbQueue = new DBQueue();
}
return dbQueue;
}
private DBQueue() {
}
public ReentrantLock getLock() {
return lock;
}
@Override
public void run() {
LOG.info("Starting DBQueue loop. Kill {}.", kill);
while (!kill) {
DBRequest dbRequest = removeRequest();
if (dbRequest != null) {
lock.lock();
String result = dbRequest.execute(vdtsSysDB, currentLoad);
lock.unlock();
if (progressController != null) Platform.runLater(() ->
progressController.updateDisplay(currentLoad));
}
}
vdtsSysDB.getEntityManager().close();
}
public void addRequest(DBRequest dbRequest) {
try {
queue.add(dbRequest);
LOG.info("Added request.");
} catch (Exception e) {
LOG.error("Can't add element.", e);
}
}
private DBRequest removeRequest() {
DBRequest result = null;
try {
//result = queue.poll(10, TimeUnit.SECONDS);
result = queue.take();
} catch (Exception e) {
LOG.error("Exception.", e);
}
return result;
}
public void killDBQueue() {
kill = true;
LOG.info("Shutting down DBQueue.");
}
public static void start() {
Thread thread = new Thread(DBQueue.getInstance(), "DBQueue Thread");
thread.start();
LOG.info("Starting DBQueue.");
}
public BoardLoad getCurrentLoad() {
if (currentLoad == null)
currentLoad = BoardLoad.getLastOpenLoad(vdtsSysDB);
return currentLoad;
}
public void setCurrentLoad(BoardLoad proposedLoad) {
// We can only have one open load, and by definition, the current load is open. So close it.
if (this.currentLoad != null && !this.currentLoad.equals(proposedLoad)) {
currentLoad.close(vdtsSysDB);
if (proposedLoad != null) {
this.currentLoad = vdtsSysDB.getEntityManager().find(BoardLoad.class, proposedLoad.getId());
} else this.currentLoad = null;
}
}
public ProgressController getProgressController() {
return progressController;
}
public void setProgressController(ProgressController progressController) {
this.progressController = progressController;
}
}
EDIT:我使用这个队列来同步数据库访问,减少了对锁的需要,并确保请求按顺序完成。我不认为有任何其他方法可以实现这种异步请求->同步请求更改。但我很想改变这种信念。
您应该在DBRequest
接口中添加对提交线程的引用,并实现setResult(String result)
(或类似(方法来接收结果。您可以在提交线程run()
方法上实现CountDownLatch
等待(或类似(,以在向队列发送请求时等待设置闩锁,并在setResult
方法中向下发送请求。如果我不清楚,请告诉我,我会详细说明。