8198562: (ch) Separate blocking and non-blocking code paths (part 1)

Remi Forax forax at univ-mlv.fr
Fri Feb 23 20:48:07 UTC 2018

----- Mail original -----
> De: "Alan Bateman" <Alan.Bateman at oracle.com>
> À: "nio-dev" <nio-dev at openjdk.java.net>
> Envoyé: Jeudi 22 Février 2018 20:08:41
> Objet: 8198562: (ch) Separate blocking and non-blocking code paths (part 1)

> I mentioned in a thread here earlier this month that I have a number of
> patches to reduce the complexity and overhead of supporting async close
> and interrupt in the selectable channel implementations.  All combined,
> there are a lot of changes but are easy to split into a series of
> smaller patches that are easier to test and review.
> The patch here changes the SocketChannel and ServerSocketChannel
> implementations so that channels configured non-blocking don't set the
> hook for Thread.interrupt or don't track the threads potentially
> blocking in I/O operations. The blocking case is improved too by
> reducing, at least for the SocketChannel implementation, the locking
> around the blocking calls. All the locking is consistent now, something
> that will be clearer once the changes to DatagramChannel and the Pipe.*
> implementations are discussed.
> Simplification of the read/write/accept/connect/finishConnect methods
> means that the implCloseSelectableChannel has to handle both the
> blocking and non-blocking cases but it's not too complicated.
> The socket adaptors have also changed so that they do timed operations
> (Socket setSoTimeout and friends) with the channel configured blocking.
> This it to avoid an explosion of scenarios (and complexity) that arises
> when trying to be both blocking and non-blocking at the same time.
> In terms of compatibility, there are two behavioral changes:
> 1. If a thread's interrupt status is set and it invokes an I/O method on
> a channel configured non-blocking then the channel will not be closed.
> The original specification was vague on this point as it focused on
> threads blocking in I/O operations. Several people have complained
> bitterly over the years about the existing behavior so they will welcome
> this change. I haven't found anything yet that depends on long standing
> behavior but we will need to track this in a CSR anyway.

I agree with the people that have complained bitterly, i've seen several ugly half broken workarounds because of this undocumented behavior.
I'm happy to see this bug been fixed !

> 2. configureBlocking will now block if there are pending I/O operations.
> The spec has always stated that it may block so it should not be a
> surprise but there may be some cases where code attempts to change a
> channel to non-blocking while another thread is doing on a blocking I/O
> operation on the channel. This method now coordinates with channel
> closing, something that has never been right in the implementation.
> The webrev with the patch is here:
>    http://cr.openjdk.java.net/~alanb/8198562/webrev/
> -Alan


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