Fixed concurrency bug in StartupContext

[Arcane561]

Fixed the issue of parallel addition and reading after. ArrayList is not a concurrency safe collection and subsequent threads may not see the changes. The add streams and read streams are different. And shutdown events can also be added during the application (pg vertex as an example) and this does not happen in the main thread. Please consider the corrections

[geoand]

Thanks for the contribution, but I'd like to know whether you are actually encountered a problem that this change fixes.

My point is that theoretically, sure the addShutdownTask and addLastShutdownTask could be called on any thread, but I am pretty certain that is not the case currently - all tasks are added and run on the main thread.

[Arcane561]

Thanks for the contribution, but I'd like to know whether you are actually encountered a problem that this change fixes.

My point is that theoretically, sure the addShutdownTask and addLastShutdownTask could be called on any thread, but I am pretty certain that is not the case currently - all tasks are added and run on the main thread.

Have a nice day, thank you for reviewing it so quickly. To be honest, I didn't have any problems with this specifically (although I didn't test it in detail). I was developing an extension that would allow you to accurately register the shutdownhandler after all the infrastructure addons have already registered their shutdown handlers (since, for example, I need to leave an entry in the database if the program terminates, but now it turns out that pgpoll closes before the code in the @Shutdown methods is called) and I noticed, that changing the collection and reading when the application is closed occurs in different thread (screenshots are attached below). I have prepared a test project for demonstration.

Repository https://github.com/Arcane561/quarkus-concurrency-example

To run it, you need a postgres database, and you will also need changes to the properties. https://github.com/Arcane561/quarkus-concurrency-example/blob/master/src/main/resources/application.properties

To quickly launch postgres, I provide the following commands

docker run -d -p 127.0.0.1:5432:5432 \      
  --name some-timescaledb-example \
  -e POSTGRES_PASSWORD=example \
  -e POSTGRES_USER=example \
  -e POSTGRES_DB=example \
  timescale/timescaledb:latest-pg14

and then the property needs to be changed to

quarkus.datasource.db-kind=postgresql
quarkus.datasource.username=example
quarkus.datasource.password=example
quarkus.datasource.reactive.url=postgresql://localhost:5432/example

The debager stop points should be placed here: https://github.com/quarkusio/quarkus/blob/67d73901be2901033f1417c9377ae092b679bcb3/core/runtime/src/main/java/io/quarkus/runtime/StartupContext.java#L33

https://github.com/quarkusio/quarkus/blob/67d73901be2901033f1417c9377ae092b679bcb3/core/runtime/src/main/java/io/quarkus/runtime/StartupContext.java#L73

[geoand]

Thanks for the feedback, but unless I am missing something, I don't see what you describe in the code you uploaded.

[Arcane561]

Thanks for the feedback, but unless I am missing something, I don't see what you describe in the code you uploaded.

Good day to you, to eliminate misunderstandings, we are now talking about the code in https://github.com/Arcane561/quarkus-concurrency-example ? if so, then I can clearly see on 2 independent machines how PgPollRecorder adds a Shutdown handler not in the main thread, but in the thread of my ScheduledExecutorService. And also the reading does not take place in the main thread in the shutdown thread. I can describe in more detail the points of how and what to run and to reproduce this behavior

[geoand]

Ah okay, I thought you had added code that adds a shutdown handler.

I'll look into it more soon.

[geoand]

if so, then I can clearly see on 2 independent machines how PgPollRecorder adds a Shutdown handler not in the main thread

I am not seeing this...

[Arcane561]

I am not seeing this...

Just in case, I notify you that it is being PgPollRecorder constructed (and therefore will add a shutdown event) only 2 seconds after the application is launched. This is regulated by this line https://github.com/Arcane561/quarkus-concurrency-example/blob/e28ab236f3362a97137120c9306e42ea902047a5/src/main/java/org/quarkus/ExampleService.java#L24

[geoand]

Never mind my comment above, I see this as well.

[geoand]

Okay, I see why this happens.

It comes down to the fact that your Database bean is "initialized" on your custom executor. If you change your Database bean to @Singleton, that results in the bean actually being initialized eagerly on the main thread.

Given how specific this is and how easily it is to work around it, I am not inclined to introduce the thread safe variants in StartupContext

[Arcane561]

Okay, I see why this happens.

It comes down to the fact that your Database bean is "initialized" on your custom executor. If you change your Database bean to @Singleton, that results in the bean actually being initialized eagerly on the main thread.

Given how specific this is and how easily it is to work around it, I am not inclined to introduce the thread safe variants in StartupContext

Unfortunately, this will not help

[Arcane561]

And I would also like to draw attention to the fact that shutdownthread is not the main thread either.

[geoand]

Unfortunately, this will not help

I tried it and it does :)

[geoand]

It seems that it's indeed not determenistic with @Singleton.

Even so, I want to try everything to avoid changing StartupContext

[Arcane561]

It seems that it's indeed not determenistic with @Singleton.

Even so, I want to try everything to avoid changing StartupContext

I understand you, you can close my pr if you think you can do something better and more convenient for you. It's just that there's a race there right now and it scares me a little bit.

[geoand]

I need to think about it more

[Arcane561]

I need to think about it more

And I have a big request for you, if you decide not to add concurrent collections, then please think about making sure that the @Shutdown methods are always executed first, without exceptions, because now I have to wait until PgPollRecorder is constructed and add my shutdown handler with the completion event

[geoand]

Right, I need to see why that happens

[Arcane561]

@geoand Good day to you. Is there any news? If I can help you in any way, please let me know.

[geoand]

👋

I haven't had any time for it unfortunately

[Arcane561]

@geoand Have a nice day. Have you not been able to watch it?

[geoand]

Hi,

I have not, no time.

Since I doubt I will have to look at this any time soon, maybe @mkouba can have a look and decide if we want to go down the route of your PR (which admitedly can't cause any harm other a potentially tiny slowdown)

[Arcane561]

Hi,

I have not, no time.

Since I doubt I will have to look at this any time soon, maybe @mkouba can have a look and decide if we want to go down the route of your PR (which admitedly can't cause any harm other a potentially tiny slowdown)

Thank you very much for the answer, sorry to interrupt (

[geoand]

Not a problem :)

[mkouba]

Hi,

I have not, no time.

Since I doubt I will have to look at this any time soon, maybe @mkouba can have a look and decide if we want to go down the route of your PR (which admitedly can't cause any harm other a potentially tiny slowdown)

Well, given the fact that the list of shutdown tasks can be modified in a recorder method and there's no guarantee that it will be modified on the main thread I think that we should use a thread-safe structure here. I'm not so sure about ConcurrentLinkedDeque though. Collections.synchronizedList(List<T>) might be a more "straightforward" replacement?

[Arcane561]

Good day to you mkouba. I used ConcurrentLinkedDeque for several reasons. The first is non-blocking addition and the second is that you don't have to reverse the list when reading handlers. I decided as an experiment to call the service in rest controller . And I found out that the handler is also added not in the main thread, but in threads serving the server (in vertx it is vertx poll threads, and in blocking it is executor).

non blocking rest point:

blocking rest point:

[Arcane561]

@mkouba Have a nice day. Could you tell me who I should work with on this pr now?

[Arcane561]

Good day to you @geoand , sorry if I am distracting could you please give feedback on what we will do about the problem...

[geoand]

Let's wait for @mkouba's feedback

[Arcane561]

@mkouba Corrected, please check back when you have time.

[Arcane561]

@mkouba Corrected, please check back when you have time.