quartz：防止jobs.xml中的作业的并发实例 [英] quartz: preventing concurrent instances of a job in jobs.xml

问题描述

这应该很容易。我使用Quartz在Apache Tomcat 6.0.18下运行，我有一个工作

我想做的是，如果作业仍在运行，当下一个触发时间滚动，我不想开始一个新的工作，所以我可以让老实例完成。

是否有办法在工作中指定。如果没有，是否有一种方式，我可以共享访问内存中的单例在我的应用程序的

< /www.quartz-scheduler.org/docs/api/org/quartz/Job.htmlrel =nofollow noreferrer> Job 实现（就是通过 JobExecutionContext ？）所以我可以自己处理并发？ （并检测上一个实例是否正在运行）

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更新： docs，这里有一些我正在考虑的方法，但是不知道如何让他们工作，或有问题。

1. 使用 StatefulJob 。这防止并发访问...但我不知道如果我使用它会发生什么其他副作用，我想避免以下情况：

   
   
   

   假设触发时间将是每分钟，即触发＃0 =在时间0，触发＃1 = 60000msec，＃2 = 120000，＃3 = 180000等，并且在时间0的触发器＃0触发我的工作，这需要130000msec。使用纯作业，当作业触发器＃0仍在运行时，将执行触发器＃1和＃2。使用StatefulJob，这将按顺序执行触发器＃1和＃2，在＃0在130000完成后立即执行。我不想要，我想＃1和＃2不运行，并且运行作业的下一个触发器发生在＃3（180000毫秒）。所以我还是要用StatefulJob做其他事情，让它以我想要的方式工作，所以我没有看到使用它的优势。



2. p>使用 TriggerListener 从vetoJobExecution返回true （）。
   
   
   

   虽然实现接口看起来很简单，但我必须找出如何以声明方式设置一个TriggerListener实例。 找不到xml文件的文档。




3. 使用我的实现Job的类拥有的 static 共享线程安全对象（例如信号量或其他）。

   
   
   

   我不喜欢通过Tomcat / Quartz下的 static 关键字使用单例的想法，不知道是否有side效果。




4. 实现我自己的触发，它扩展了 SimpleTrigger ，并且包含可以运行其自己的TriggerListener的共享状态。

   
   
   

   同样，我不知道如何设置XML文件来使用此触发器，而不是标准< trigger>< simple> ...< / simple> / trigger>







解决方案Quartz工作唤醒你可以做：

  JobDetail existingJobDetail = sched.getJobDetail（jobName，jobGroup）; 
 if（existingJobDetail！= null）{
 List< JobExecutionContext> currentExecutingJobs =（List< JobExecutionContext>）sched.getCurrentlyExecutingJobs（）; 
 for（JobExecutionContext jec：currentlyExecutingJobs）{
 if（existingJobDetail.equals（jec.getJobDetail（）））{
 //字符串message = jobName +已经在运行。 
 //log.info(message）; 
 // throw new JobExecutionException（message，false）; 
} 
} 
 //sched.deleteJob(jobName，jobGroup）;如果要删除计划但不是当前运行的作业
} 
  

This should be really easy. I'm using Quartz running under Apache Tomcat 6.0.18, and I have a jobs.xml file which sets up my scheduled job that runs every minute.

What I would like to do, is if the job is still running when the next trigger time rolls around, I don't want to start a new job, so I can let the old instance complete.

Is there a way to specify this in jobs.xml (prevent concurrent instances)?

If not, is there a way I can share access to an in-memory singleton within my application's Job implementation (is this through the JobExecutionContext?) so I can handle the concurrency myself? (and detect if a previous instance is running)

---

update: After floundering around in the docs, here's a couple of approaches I am considering, but either don't know how to get them to work, or there are problems.

1. Use StatefulJob. This prevents concurrent access... but I'm not sure what other side-effects would occur if I use it, also I want to avoid the following situation:

   Suppose trigger times would be every minute, i.e. trigger#0 = at time 0, trigger #1 = 60000msec, #2 = 120000, #3 = 180000, etc. and the trigger#0 at time 0 fires my job which takes 130000msec. With a plain Job, this would execute triggers #1 and #2 while job trigger #0 is still running. With a StatefulJob, this would execute triggers #1 and #2 in order, immediately after #0 finishes at 130000. I don't want that, I want #1 and #2 not to run and the next trigger that runs a job should take place at #3 (180000msec). So I still have to do something else with StatefulJob to get it to work the way I want, so I don't see much of an advantage to using it.

2. Use a TriggerListener to return true from vetoJobExecution().

   Although implementing the interface seems straightforward, I have to figure out how to setup one instance of a TriggerListener declaratively. Can't find the docs for the xml file.

3. Use a static shared thread-safe object (e.g. a semaphore or whatever) owned by my class that implements Job.

   I don't like the idea of using singletons via the static keyword under Tomcat/Quartz, not sure if there are side effects. Also I really don't want them to be true singletons, just something that is associated with a particular job definition.

4. Implement my own Trigger which extends SimpleTrigger and contains shared state that could run its own TriggerListener.

   Again, I don't know how to setup the XML file to use this trigger rather than the standard <trigger><simple>...</simple></trigger>.

解决方案

when your Quartz job wakes up you can do:

JobDetail existingJobDetail = sched.getJobDetail(jobName, jobGroup);
    if (existingJobDetail != null) {
        List<JobExecutionContext> currentlyExecutingJobs = (List<JobExecutionContext>) sched.getCurrentlyExecutingJobs();
        for (JobExecutionContext jec : currentlyExecutingJobs) {
            if(existingJobDetail.equals(jec.getJobDetail())) {
                //String message = jobName + " is already running.";
                //log.info(message);
                //throw new JobExecutionException(message,false);
            }
        }
        //sched.deleteJob(jobName, jobGroup); if you want to delete the scheduled but not-currently-running job
    }

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