Hi,
This patch fixes the deadlock in `TestMemorySession#testAcquireCloseRace`. The
lock-step spin lock is implemented as with `lock` being an `AtomicInteger`:
// Keep the 2 threads operating on the same scope
int k = lock.getAndAdd(1) + 1;
while (k != i * 2) {
Thread.onSpinWait();
k = lock.get();
}
Given the initial condition:
Thread 1: i = 0
Thread 2: i = 0
lock: -2
The `lock` then undergoes the following operations:
Thread 1 Thread 2 lock value
getAndAdd(1) -1
getAndAdd(1) 0 -> Thread 2 then continues its
next iteration, its i value is now 1
getAndAdd(1) 1 -> Thread 2 reaches the next
iteration before thread 1 has a chance to read the value 0
get() 1 -> Thread 1 now cannot proceed
because it missed the value 0
get() 1 -> Thread 2 now cannot proceed
because lock can never reach 2
The solution is to not rely on the exact value of the lock but instead whether
the lock has passed the expected value.
Please take a look, thanks a lot.
-------------
Commit messages:
- use < instead of !=
Changes: https://git.openjdk.org/jdk/pull/21976/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21976&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8343793
Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
Patch: https://git.openjdk.org/jdk/pull/21976.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/21976/head:pull/21976
PR: https://git.openjdk.org/jdk/pull/21976
