DOCSP-26368: FAQ entry for state should be open exception

[ccho-mongodb]

Pull Request Info

PR Reviewing Guidelines

JIRA - https://jira.mongodb.org/browse/DOCSP-26368
Staging - https://docs-mongodbcom-staging.corp.mongodb.com/java/docsworker-xlarge/DOCSP-26368-FAQ-illegalstateexception/faq/#how-do-i-prevent-the--illegalstateexception--state-should-be--open--error-

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[rustagir]

just a few things!

[rustagir]

Suggestion: make the question more oriented around the user

Suggested change

	Why does the application throw "IllegalStateException: state should be: open"?
	Why did I receive an "IllegalStateException: state should be: open" error?

[ccho-mongodb]

Thanks, I reworded since "receive" doesn't seem like a common action to describe exceptions.

[rustagir]

Question: Does the client close the connections or does the application close the connections? It could be helpful to clarify the wording here.

Suggested change

	You may encounter this exception if you call an operation on a ``MongoClient``
	instance that closed its connections to MongoDB. The connections could be
	You may encounter this exception if you call an operation on a ``MongoClient``
	instance with a closed connection to MongoDB. The connections could be

[ccho-mongodb]

I'm not sure I understand the question since they both are responsible for the closing of the connection depending on perspective. An application must call the code to instruct the client to close. The client must close the connection when that method is called. Could you clarify what you meant?

[rustagir]

I think I meant to ask whether there were times when a client closes a connection on its own, without the application containing/calling the close method. In any case, i think you can keep the wording as is

[ccho-mongodb]

From what I understand, the client, which I'm assuming is MongoClient, can open and close connections based on load and network state (see How Does Connection Pooling Work in the Java Driver), but when you call an operation, whether a direct one such as ListDatabaseNames() or indirectly such as by calling find() on a MongoCollection, the MongoClient queues it up for the next available connection.

However, if you call close() on the instance, or perhaps another process signals for it to close its connections, it transitions into a state that is no longer "open" and does not accept any further operations.

[rustagir]

Suggested change

	instance that closed its connections to MongoDB. The connections could be
	closed due to one of the following conditions:
	instance that closed its connections to MongoDB. The connections could be
	closed for one of the following reasons:

[rustagir]

Issue: end full sentence list items with periods

Suggested change

	- The ``close()`` method was called on that ``MongoClient`` instance
	- You previously called the ``close()`` method on the ``MongoClient`` instance.

[rustagir]

Suggested change

	- The ``MongoClient`` instance is out of scope
	- The ``MongoClient`` instance is out of scope.

[rustagir]

Suggested change

	- The framework your application uses to manage your MongoDB operations, such
	as Spring Boot, has closed the connection automatically.
	- The framework your application uses to manage your MongoDB operations, such
	as Spring Boot, automatically closed the connection.

Also suggestion: link to something related to Spring Boot

[rustagir]

lgtm!

[jyemin]

I don't understand what the difference is between the first and second bullet. The only way to "close the connection" is to call the close method on the MongoClient. The difference only seems to be where the close is happening (how close/far it is from the code that is getting the exception, whether in the same thread or a different thread.

Also, it's not possible for another process to directly close a MongoClient. It would have to happen indirectly through communication through a socket, or some signal, etc.

Also, it may be the

[ccho-mongodb]

I see. I assumed that this response was referring to an executor service operating on a pool of threads. Would you prefer I remove this list item to avoid any confusion? Is there any info you'd like to add? Thanks!

[jyemin]

Yes, please remove. You could point out that often MongoClient instances are singletons that are accessible by multiple threads, and so the code which closes the MongoClient may be distant from the code receiving the exception, perhaps in another thread of execution.

[jyemin]

MongoClient doesn't use the singleton pattern itself. It's just that frameworks are often configured to manage these instances as singletons.