I have a timer I'm testing in camel:
<from uri="timer:testTimer?delay=120000&fixedRate=true&period=120000"/>
<inOnly uri="activemq:getTCdata"/>
I see that the events stack up if something else is going on at that time. I wonder if there is a way to cancel a new timer event if there is one already stacked. While this behavior doesn't get in the way of anything in the flow I have, I'd rather not have stacked timer events all running at once at a lather point. I looked at the camel timer documentation and didn't find anything for this purpose. I know that this is also the behavior of Java's Timer the camel timer is based on. I'd like to check if anyone knows of solutions in camel for this? Thanks in advance.
See the fixedRate option
http://camel.apache.org/timer
Its the option from the JDK timer api, so you can find more detail about it there too. But setting it to true, means new task is only scheduled when the current task completed, so they always run with a fixed X period between them.
Related
As the title says, I would like to send a notification to an endpoint if messages to it start getting throttled, and another message when the throttling stops.
I currently have the following (very basic) route configuration:
from("test-jms:queue:test.queue")
.throttle(2)
.to("file://test");
This configuration throttles messages just fine, but I need a way to let the consumer know that the messages are being throttled.
When the Throttler starts throttling, I would like to send a notification to the 'to' endpoint so those reading the messages know that they are being throttled. I would also like to be able to send another message when the Throttler is no longer throttling, so the consumer knows the messages are up to date.
This doesn't appear to be something the Throttler does. The only way I see of getting a notification when it starts throttling is setting rejectExecution to true, at which point it will throw an exception. The problem is that execution stops at that point, and no more messages are passed through (since an exception was thrown).
My current thoughts are that I will need to create a custom bean/processor/something that performs essentially the same function as the Throttler, but also injects a message when the throttling starts or stops. I don't want to do that unless I really need to, though. Any help is appreciated. Thanks!
No the throttler eip does not support such information (however you may be able to grab some statistics via JMX). A different thought would be to reverse the direction so the consumers signals upstream when they want new messages (this is what reactive systems does).
I assume the above to write to a file is just some example, what consumers are you using in real life, and do they really need to know that some messages are backed up within a short-time period of 1 second because they are throttled? Also since your source is JMS, you can also look at the route throttling policy, where you can suspend/resume the JMS consumer instead of using the throttler EIP.
I'm trying to do one action after the flink job is finished (make some change in DB). I want to do it in the same flink application with no luck.
I found that there is JobStatusListener that is notified in ExecutionGraph about changed state but I cannot find how I can get this ExecutionGraph to register my listener.
I've tried to completely replace ExecutionGraph in my project (yes, bad approach but...) but as soon as it is runtime library it is not called at all in distributed mode, only in local run.
I have next flink application in short:
DataSource.output(RichOutputFormat.class)
ExecutionEnvironment.getExecutionEnvironment().execute()
Can please anybody help?
Using the Cups c api I am able to see the state of a printer (such as paused, printing, jammed ect.) What I am trying to do now is to listen for, or lock against a change in a printer's state. Ultimately I want a live view of a printers state, but I don't want to have a delay loop spamming cups with printer attribute requests.
I have seen many functions and tags in the source code and documentation that hint towards some kind of event system, but I have been unable to figure out how to utilize it. Any help is welcome, even just pointing me towards the right function.
I used this example in my current implementation to get state information. http://cups-dev.easysw.narkive.com/9RO0OBnZ/how-to-get-printer-status-via-cups-api
It ends up this was a very complex question and involved a lot of work to figure out. The only sane way I found to listen for changes was to use the rss notification system. I would advise against attempting to make your own notification module, I wasted a week of my life trying that (I'm not even sure it is possible anymore). Use the Create-Printer-Subscription with a uri like rss://localhost:8000. You will of course need a listener waiting for the xml data.
I put up an a simple debugging tool I made with java/jna here. Select 2 to set up a subscription, you will need to listen for the data yourself though.
Consider a web service, for instance, where user can make an API request to start a task at certain scheduled time. Task definition and scheduled time are persisted in a database.
First approach I came up with is to start a Go timer and wait for the timer to expire in a Goroutine (not blocking the request). This goroutine, after time expiration, will also fire another API request to start executing the task.
Now the problem arises when this service is redeployed. For zero downtime deployment I am using Einhorn with goji. After code reload, obviously both timer goroutine and timer-expiration-handler goroutine dies. Is there any way to recover Go timer after code reload?
Another problem I am struggling with is to allow the user to interrupt the timer (once its started). Go timer has Stop to facilitate this. But since this is a stateless API, when the \interrupt request comes in service doesn't have context of timer channel. And it seems its not possible to marshal the channel (returned from NewTimer) to disk/db.
Its also very well possible that I am not looking at the problem from correct perspective. Any suggestions would be highly appreciated.
One approach that's commonly used is to schedule the task outside your app, for example using crontab or systemd timers.
For example using crontab:
# run every 30 minutes
*/30 * * * * /usr/bin/curl --head http://localhost/cron?key=something-to-verify-local-job >/dev/null 2>&1
Using an external task queue is also a valid option like #Not_a_Golfer mentioned but more complicated.
I have a SL 4.0 app running out of browser with full priviliges. How can I check for updates (CheckAndDownloadUpdateAsync()) every 10 minutes without affecting UI thread. I've tried using the Timer, but the CheckAndDownloadUpdateCompleted doesn't get executed. I think it is erroring out silently.
Thanks in advace...
Never mind, I have solved it by encapsulating the code within a class. I'm not sure what was breaking it, but this works. Maybe the issue was the Timer thread calling an event of the App class or something else, but now the timer calls the a method of the new class and it all works.
Thanks anyway...