I want to make a function to restart any process without reference to Process Key from the start event. The Code is following:
engine.runtimeService.restartProcessInstances(processDefinitionId)
.processInstanceIds("processInstanceId")
.execute()
While running this code I get an error: Restart instructions cannot be empty. So I add called method startAfterActivity
engine.runtimeService.restartProcessInstances(processDefinitionId)
.processInstanceIds("processInstanceId")
.startAfterActivity("StartEvent_Foo")
.execute()
But now I'm supposed to guarantee that start event of every process is called "StartEvent_Foo".
Is it possible to restart a process instance without setting instruction?
Related
I have a Sidekiq job that runs every 4 minutes.
This job checks if the current code block is being executed before executing the code again
process = ProcessTime.where("name = 'ad_queue_process'").first
# Return if job is running
return if process.is_running == true
If Sidekiq restarts midway through the code block, code that updates the status of the job never runs
# Done running, update the process times and allow it to be ran again
process.update_attributes(is_running: false, last_execution_time: Time.now)
Which leads the the Job never running unless i run an update statement to set is_running = false
Is there any way to execute code before Sidekiq is restarted?
Update:
Thanks to #Aaron, and following our discussion (comments below), the ensure block (which is executed by the forked worker-threads) can only be ran for a few unguaranteed milliseconds before the main-thread forcefully terminates these worker-threads, in order for the main-thread to do some "cleanup" up the exception stack, in order to avoid getting SIGKILL-ed by Heroku. Therefore, make sure that your ensure code should be really fast!
TL;DR:
def perform(*args)
# your code here
ensure
process.update_attributes(is_running: false, last_execution_time: Time.now)
end
The ensure above is always called regardless if the method "succeeded" or an Exception is raised. I tested this: see this repl code, and click "Run"
In other words, this is always called even on a SignalException, even if the signal is SIGTERM (gracefully shutdown signal), but ONLY EXCEPT on SIGKILL (force unrescueable shutdown). You can verify this behaviour by checking my repl code, and then change Process.kill('TERM', Process.pid) to Process.kill('KILL', Process.pid), and then click "run" again (you'll notice that the puts won't be called)
Looking at Heroku docs, I quote:
When Heroku is going to shut down a dyno (for a restart or a new deploy, etc.), it first sends a SIGTERM signal to the processes in the dyno.
After Heroku sends SIGTERM to your application, it will wait a few seconds and then send SIGKILL to force it to shut down, even if it has not finished cleaning up. In this example, the ensure block does not get called at all, the program simply exits
... which means that the ensure block will be called because it's a SIGTERM and not a SIGKILL, only except if the shutting down takes a looong time, which may due to (some reasons I could think of ATM):
Something inside your perform code (or any ruby code in the stack; even gems) that also rescued the SignalException, or even rescued the root Exception class because SignalException is a subclass of Exception) but takes a long time cleaning up (i.e. cleaning up connections to DB or something, or I/O stuff that hangs your application)
Or, your own ensure block above takes a looong time. I.E when doing the process.update_attributes(...), for some reason the DB temporary hangs / network delay or timeout, then that update might not succeed at all! and will ran out of time, of which from my quote above, after a few seconds after the SIGTERM, the application will be forced to be stopped by Heroku sending a SIGKILL.
... which all means that my solution is still not fully reliable, but should work under normal situations
Handle sidekiq shutdown exception
class SomeWorker
include Sidekiq::Worker
sidekiq_options queue: :default
def perform(params)
...
rescue Sidekiq::Shutdown
SomeWorker.perform_async(params)
end
end
(I am paraphrasing question asked by Rich Harris in the "Stuff I wish I'd known sooner about service workers" gist.)
If I have code in my service worker that runs outside an event handler, when does it run?
And, closely related to that, what is the difference between putting inside an install handler and putting it outside an event handler entirely?
In general, code that's outside any event handler, in the "top-level" of the service worker's global scope, will run each and every time the service worker thread(/process) is started up. The service worker thread may start (and stop) at arbitrary times, and it's not tied to the lifetime of the web pages it controlled.
(Starting/stopping the service worker thread frequently is a performance/battery optimization, and ensures that, e.g., just because you browse to a page that has registered a service worker, you won't get an extra idle thread spinning in the background.)
The flip side of that is that every time the service worker thread is stopped, any existing global state is destroyed. So while you can make certain optimizations, like storing an open IndexedDB connection in global state in the hopes of sharing it across multiple events, you need to be prepared to re-initialize them if the thread had been killed in between event handler invocations.
Closely related to this question is a misconception I've seen about the install event handler. I have seen some developers use the install handler to initialize global state that they then rely on in other event handlers, like fetch. This is dangerous, and will likely lead to bugs in production. The install handler fires once per version of a service worker, and is normally best used for tasks that are tied to service worker versioning—like caching new or updated resources that are needed by that version. After the install handler has completed successfully, a given version of a service worker will be considered "installed", and the install handler won't be triggered again when the service worker starts up to handle, e.g., a fetch or message event.
So, if there is global state that needs to be initialized prior to handling, e.g., a fetch event, you can do that in the top-level service worker global scope (optionally waiting on a promise to resolve inside the fetch event handler to ensure that any asynchronous operations have completed). Do not rely on the install handler to set up global scope!
Here's an example that illustrates some of these points:
// Assume this code lives in service-worker.js
// This is top-level code, outside of an event handler.
// You can use it to manage global state.
// _db will cache an open IndexedDB connection.
let _db;
const dbPromise = () => {
if (_db) {
return Promise.resolve(_db);
}
// Assume we're using some Promise-friendly IndexedDB wrapper.
// E.g., https://www.npmjs.com/package/idb
return idb.open('my-db', 1, upgradeDB => {
return upgradeDB.createObjectStore('key-val');
}).then(db => {
_db = db;
return db;
});
};
self.addEventListener('install', event => {
// `install` is fired once per version of service-worker.js.
// Do **not** use it to manage global state!
// You can use it to, e.g., cache resources using the Cache Storage API.
});
self.addEventListener('fetch', event => {
event.respondWith(
// Wait on dbPromise to resolve. If _db is already set, because the
// service worker hasn't been killed in between event handlers, the promise
// will resolve right away and the open connection will be reused.
// Otherwise, if the global state was reset, then a new IndexedDB
// connection will be opened.
dbPromise().then(db => {
// Do something with IndexedDB, and eventually return a `Response`.
});
);
});
I have a wxLua Gui app that has a "Run" button. Depending on selected options, Run can take a long time, so I would like to implement a "Cancel" button/feature. But it looks like everything in wxLua is working on one Gui thread, and once you hit Run, pressing Cancel does nothing, the Run always goes to completion.
Cancel basically sets a variable to true, and the running process regularly checks that variable. But the Cancel button press event never happens while Running.
I have never used co-routines; if the Run process regularly yields to a "Cancel check" process, will the Cancel event happen then?
Or is there another way?
(the following assumes that by "Run" you mean a long running operation in the same process and not running an external process using wxExecute or wxProcess.)
"Cancel" event is not triggered because by executing your Run logic you have not given a chance to the UI to handle the click event.
To avoid blocking the UI you need to do something like this. When you click Run button create a co-routine around the function you want to run:
coro = coroutine.create(myLongRunningFunction)
Your Run event is completed at this point. Then in EVT_IDLE event you will be resuming this coroutine as long as it's not complete. It will look something like this:
if coro then -- only if there is a coroutine to work on
local ok, res = coroutine.resume(coro, additional, parameters)
-- your function either yielded or returned
-- you may check ok to see if there was an error
-- res can tell you how far you are in the process
-- coro can return multiple values (just give them as parameters to yield)
if coroutine.status(coro) == 'dead' then -- finished or stopped with error
coro = nil
-- do whatever you need to do knowing the process is completed
end
end
You will probably need to request more IDLE event for as long as your process is not finished as some operating systems will not trigger IDLE events unless there is some other event triggered. Assuming your handler has event parameter, you can do event:RequestMore(true) to ask for more IDLE events (RequestMore).
Your long-running process will need to call coroutine.yield() at the right time (not too short as you will be wasting time to switch back and forth and not too long for users to notice delays in the UI); you probably need to experiment with this, but something timer-based with 100ms or so between calls may work.
You can check for Cancel values either in your IDLE event handler or in the long-running function as you do now. The logic I described will give your application UI a chance to process Cancel event as you expect.
I don't use WXWidgets, but the way I implement cancel buttons in my lua scripts which use IUP is to have a cancel flag, which is set when the button is pressed and the progress display is checked for during the run.
Usage is like this
ProgressDisplay.Start('This is my progress box',100)
for i=1,100 do
ProgressDisplay.SetMessage(i.." %")
fhSleep(50,40) -- Emulate performing the task
ProgressDisplay.Step(1)
if ProgressDisplay.Cancel() then
break
end
end
ProgressDisplay.Reset()
ProgressDisplay.Close()
If you want to see the definition for the ProgressDisplay see:
http://www.fhug.org.uk/wiki/doku.php?id=plugins:code_snippets:progress_bar
this is my question:
I have a group of gen_servers which are started without name and that during the init function use pg2:join(group, self()). Until here it works fine.
I used in terminate function pg2:leave(group, self()). but if I kill one of the pids retrieved using pg2:get_members(group). the pid of the killed process in still in the list given by pg2:get_members(group).
I tried to use the leave function by mean of a gen_server call and in this case it works fine.
Can you tell me what is wrong?
Thanks
it was a problem on erlang version.
We need to Start a thread into a service application we developed.
We did in the OnExecute event, and it failed, and later we did in the OnStart event, and it failed again. Maybe we have to do something else to start the thread.
The line of code we only have to type is MonitorThread.Start;
Where and how we can to start the thread??
Thanks.
On the face of it, starting a thread in a service is no different from starting a thread in any other kind of application. Simply instantiate the thread object and let it run. If you created the object in a suspended state, then call Start on it (or, in versions earlier than 2010, Resume).
MonitorThread := TMonitorThread.Create;
MonitorThread.Start; // or MonitorThread.Resume
If that doesn't work, then you need to take a closer look at exactly what doesn't work. Examine exception messages and return codes. Use the debugger to narrow things down.
If it's possible, I advise you to not create the thread suspended. Instead, just provide the object all the parameters it needs in its constructor. Let it initialize itself, and it will start running just before the constructor returns to the caller. No need for additional thread management outside the thread object.