[foreign-memaccess+abi] RFR: 8294986: Possible mismatched acquire/release in binding specializer

[Jorn Vernee]

We acquire sessions of address parameters before a downcall, and release them afterwards. However, if acquire fails with an exception, we still call release in the finally block.

Fixing this is a simple case of switching 2 lines: when acquire fails, we don't store the session in a local, and so the cleanup in the finally block will not call release on it either.

For testing, I doesn't seem possible to make this bug result in an error with the current code. So, I've added an assert to the implementation that checks whether release was called too many times.

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Commit messages:
 - don't release when acquire fails

Changes: https://git.openjdk.org/panama-foreign/pull/739/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=739&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294986
  Stats: 88 lines in 4 files changed: 82 ins; 4 del; 2 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/739.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/739/head:pull/739

PR: https://git.openjdk.org/panama-foreign/pull/739