[英]java Timer TimerTask multiple threads
I'm using Timer and TimerTask to long poll for new messages for a chat application. 我正在使用Timer和TimerTask来长时间轮询聊天应用程序的新消息。 I would like to examine two "slightly" different possibilities:
我想研究两种“略微”不同的可能性:
1 : Timer declared as local variable 1:计时器声明为局部变量
public List<MessageBean> getLastMessages(...) {
[...]
Timer timer = new Timer(true); //**Timer declared as local variable**
while (someCondiction) {
MessagesTimerTask returnMessagesTask = new MessagesTimerTask([...]);
timer.schedule(returnMessagesTask, 6000);
synchronized (listMessageBean) {
listMessageBean.wait();
//notify is called in the MessagesTimerTask which extends TimerTask
}
}
}
* Problem: Every time i call the method, i can see that a new thread is created, [Timer-1], [Timer-2], etc.. And in Eclipse Debug window they all seem to be running even after the getLastMessages(..) finishes running and returns a value to the client. * 问题:每次调用方法时,我都会看到创建了一个新线程,[Timer-1],[Timer-2]等。在Eclipse Debug窗口中,即使在getLastMessages之后它们似乎都在运行(..)完成运行并将值返回给客户端。 This may cause a huge problem if the timers are actually using threads, and after few transactions the server will eventually consume all the machine resources.
如果计时器实际上使用线程,这可能会导致巨大的问题,并且在很少的事务之后,服务器最终会消耗所有的机器资源。
2 : Timer declared as local field 2:定时器声明为本地字段
private final Timer timer = new Timer(true); //**Timer declared as local field**
public List<MessageBean> getLastMessages(...) {
[...]
while (someCondiction) {
MessagesTimerTask returnMessagesTask = new MessagesTimerTask([...]);
timer.schedule(returnMessagesTask, 6000);
synchronized (listMessageBean) {
listMessageBean.wait();
//notify is called in the MessagesTimerTask which extends TimerTask
}
}
}
* Problem: every time i call the method, the same thread is used [Thread-1], but i'm not sure if i make two consecutive calls, the latter will cancel/override the former (the class is @Autowired by spring) ? * 问题:每次调用方法时,使用相同的线程[Thread-1],但我不确定是否连续两次调用,后者将取消/覆盖前者(该类是@Autowired by spring )?
Any suggestions ? 有什么建议 ? Thank you.
谢谢。
Here is the source code of the schedule
method: 以下是
schedule
方法的源代码 :
190 public void schedule(TimerTask task, long delay) {
191 if (delay < 0)
192 throw new IllegalArgumentException("Negative delay.");
193 sched(task, System.currentTimeMillis()+delay, 0);
194 }
and the sched
method: 和
sched
方法:
386 private void sched(TimerTask task, long time, long period) {
387 if (time < 0)
388 throw new IllegalArgumentException("Illegal execution time.");
389
390 // Constrain value of period sufficiently to prevent numeric
391 // overflow while still being effectively infinitely large.
392 if (Math.abs(period) > (Long.MAX_VALUE >> 1))
393 period >>= 1;
394
395 synchronized(queue) {
396 if (!thread.newTasksMayBeScheduled)
397 throw new IllegalStateException("Timer already cancelled.");
398
399 synchronized(task.lock) {
400 if (task.state != TimerTask.VIRGIN)
401 throw new IllegalStateException(
402 "Task already scheduled or cancelled");
403 task.nextExecutionTime = time;
404 task.period = period;
405 task.state = TimerTask.SCHEDULED;
406 }
407
408 queue.add(task);
409 if (queue.getMin() == task)
410 queue.notify();
411 }
412 }
From here you can clearly see that a queue is being used to store tasks internally, meaning that later tasks will not overwrite the earlier ones. 从这里可以清楚地看到队列正在用于在内部存储任务,这意味着以后的任务不会覆盖之前的任务。 If you also check the
mainLoop
method in the file, you can see that it takes tasks from the queue one-by-one ordered by their schedule time and executes them. 如果还检查文件中的
mainLoop
方法,则可以看到它按照计划时间逐个从队列中获取任务并执行它们。
So it should not be a problem to schedule multiple tasks on the same Timer
object. 因此,在同一个
Timer
对象上安排多个任务应该不是问题。
As a side-note, consider replacing Timer
with ScheduledThreadPoolExecutor
available since Java 1.5. 作为附注,考虑使用自Java 1.5以来可用的
ScheduledThreadPoolExecutor
替换Timer
。
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