The issue was observed on a local run in PacketSpaceManagerTest:
org.opentest4j.AssertionFailedError: nextDeadline should not be after 250ms
from now! ==> expected: <false> but was: <true>
at
org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
at
org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
at org.junit.jupiter.api.AssertFalse.failNotFalse(AssertFalse.java:63)
at org.junit.jupiter.api.AssertFalse.assertFalse(AssertFalse.java:36)
at org.junit.jupiter.api.Assertions.assertFalse(Assertions.java:239)
at
PacketSpaceManagerTest$SynchronousTestDriver.run(PacketSpaceManagerTest.java:856)
Investigation suggests that this is caused by a race condition where
`packetSent` was invoked while the transmitter task was running: `packetSent`
will only reschedule the transmitter if there is no deadline, that is, if it
observes that `deadline == Deadline.MAX`; But if `deadline` is already in the
past, which is typically the case when the transmitter task is running, then
there's no guarantee that the transmitter task will actually end up
rescheduling itself with a new deadline. It may not if it thinks there is
nothing pending. The transmitter will then remain unscheduled until something
else happens that causes it to be rescheduled.
In a typical HTTP/3 request/response exchange chances are high that "something
else" will happen, which explains why even if `packetSent` fails to reschedule,
there might not be any observable consequence (outside of
PacketSpaceManagerTest). However, there is no guarantee.
The fix is to always call PacketSpaceManager::reschedule, which will compute a
new prospective deadline which the timer queue can then reliably use to decide
whether the selector should be woken up to take into account the new deadline.
A new testPacketSent() test that deterministically fails without the fix is
added to PacketSpaceManagerTest.
---------
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Interim AI Policy](https://openjdk.org/legal/ai).
-------------
Commit messages:
- Add more test comments
- 8386985: PacketSpaceManagerTest failed with AssertionError; A race condition
may cause packetSent to mistakenly skip rescheduling of the transmitter task
Changes: https://git.openjdk.org/jdk/pull/31662/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=31662&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8386985
Stats: 104 lines in 2 files changed: 75 ins; 22 del; 7 mod
Patch: https://git.openjdk.org/jdk/pull/31662.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/31662/head:pull/31662
PR: https://git.openjdk.org/jdk/pull/31662
