8259636: Check for buffer backed by shared segment kicks in in unexpected places

[mcimadamore]

When support for shared segment was added, we decided to disable support for buffers derived from shared segment in certain async operations, as there's currently no way to make sure that the memory won't be reclaimed while the IO operation is still taking place.

After looking at the code, it seemed like the best place to put the restriction would be sun.nio.ch.DirectBuffer::address() method, since this method is used in a lot of places just before jumping into some piece of JNI code.

While I still stand by that decision, the Netty team has discovered that this decision also affected operations such as creating slices from byte buffers derived from shared segment - this is caused by the fact that one direct buffer constructor (the one for views and slices) is calling the dreaded DirectBuffer::address method.

The fix is simple: just avoid the method call - which is very easy to do in the case of the buffer constructor: in fact this method just returns the value of the address field inside the Buffer class, so we can always cast to Buffer and then access address field from there.

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Progress

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Issue

• JDK-8259636: Check for buffer backed by shared segment kicks in in unexpected places

Reviewers

• Athijegannathan Sundararajan (@sundararajana - Reviewer) ⚠️ Review applies to b64ff26
• Alan Bateman (@AlanBateman - Reviewer) ⚠️ Review applies to b64ff26
• Chris Hegarty (@ChrisHegarty - Reviewer) ⚠️ Review applies to b64ff26

Download

$ git fetch https://git.openjdk.java.net/jdk16 pull/110/head:pull/110
$ git checkout pull/110

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Webrevs

• 01: Full (fffa34d)
• 00: Full (b64ff26)

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8259636: Check for buffer backed by shared segment kicks in in unexpected places

Reviewed-by: sundar, alanb, chegar

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[mcimadamore]

/integrate

[openjdk]

@mcimadamore Since your change was applied there has been 1 commit pushed to the master branch:

• 5f9cd72: 8259645: Revert JDK-8245956 JavaCompiler still uses File API instead of Path API in a specific case

Your commit was automatically rebased without conflicts.

Pushed as commit 17b4db3.

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