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Subject [GitHub] [zookeeper] xoiss commented on issue #999: ZOOKEEPER-2891: Invalid processing of zookeeper_close for mutli-request
Date Tue, 02 Jul 2019 14:16:44 GMT
xoiss commented on issue #999: ZOOKEEPER-2891: Invalid processing of zookeeper_close for mutli-request
URL: https://github.com/apache/zookeeper/pull/999#issuecomment-507697121
   > add a test to demonstrate the problem and verify that we have fixed it
   I have provided two tests:
   - `testCloseWhileMultiInProgressFromMain`
   - `testCloseWhileMultiInProgressFromCompletion`
   The reason to have namely two tests is about the same as for ZOOKEEPER-2894 (see https://github.com/apache/zookeeper/pull/1000).
So, it's just two subcases of the same problem.
   **Note:** Right now, the first test of two is temporarily disabled because it requires
fixes from ZOOKEEPER-2894. When it's merged, I'll rebase this PR and enable this test.
   Ok, BEFORE this patch both tests fail with `src/zookeeper.c:2033: deserialize_multi: Assertion
'entry' failed` (for the first test, assuming ZOOKEEPER-2894 is already merged, otherwise
it fails with completion lost).
   And after the patch both tests pass successfully (again, for the first test, assuming ZOOKEEPER-2894
is already merged).
   > Can you explain why this is the right point to exit the loop and the method?
   What is the alternative??
   Please, read this: https://issues.apache.org/jira/browse/ZOOKEEPER-2891
   I have revised it again now, and indeed, I don't have more detailed explanation.
   The best is try to reproduce this under debugger. You may use unit-tests published here.
   If you still have questions, please, formulate more specific question, or a use-case (scenario)
that I can reproduce.
   > To my eyes, it is cleaner to have rc_hint == ZOK as a conditional on the while statement
or perhaps a return rc down a few lines where it is set on error.
   If we put `rc_hint == ZOK` directly into the `while`-conditional-expression then we have
to put there also (1) assignment of `entry` and (2) analyzing the value assigned to `entry`
-- i.e., two code lines: `completion_list_t *entry = dequeue_completion(clist);` and `if (entry
== NULL)`. Note also that `entry` is a local variable of the while-loop-body, and C99 does
not allow local variable declarations right in the while-expression.
   So, due to this, it's better to keep things at there original places. I understand that
having additional loop-termination point is not good enough, but sometimes it's a kinda tradeoff.
I wish to keep things as close to the code-before-patch as possible, to minimize the diff.
   > Could we also return immediately from the method is rc_hint is not 0?
   Currently 'yes', because there is nothing between the while-loop-body-end and the final
`return` statement. But there is no lifetime warranty that nothing would be put here between
   Actually, I prefer `break` here because it performs the minimum of the necessary work --
I'm talking about the "Necessity and Sufficiency" -- here `return` is sufficient, but much
more than necessary.

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