On Mon, 18 Jul 2022 07:40:53 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
> Test appears to pass fine with G1. But it fails with other GCs, for example > Parallel, Shenandoah, etc, it fails: > > > $ CONF=linux-x86_64-server-fastdebug make test > TEST=java/io/ObjectStreamClass/ObjectStreamClassCaching.java > TEST_VM_OPTS="-XX:+UseParallelGC" > > test ObjectStreamClassCaching.testCacheReleaseUnderMemoryPressure(): success > test ObjectStreamClassCaching.testCachingEffectiveness(): failure > java.lang.AssertionError: Cache lost entry although memory was not under > pressure expected [false] but found [true] > at org.testng.Assert.fail(Assert.java:99) > at org.testng.Assert.failNotEquals(Assert.java:1037) > at org.testng.Assert.assertFalse(Assert.java:67) > > > I believe this is because `System.gc()` is not that reliable about what > happens with weak references. As seen with other GCs, they can clear the > weakrefs on Full GC. In fact, the test fails with G1 if we do a second > System.gc() in this test. So the test itself is flaky. The fix is to avoid > doing `System.gc()` altogether in that subtest. The test is still retained to > see that reference is not cleared for a while. > > Additional testing: > - [x] Linux x86_64 fastdebug, affected test with `-XX:+UseSerialGC`, 100 > repetitions > - [x] Linux x86_64 fastdebug, affected test with `-XX:+UseParallelGC`, 100 > repetitions > - [x] Linux x86_64 fastdebug, affected test with `-XX:+UseG1GC`, 100 > repetitions > - [x] Linux x86_64 fastdebug, affected test with `-XX:+UseShenandoahGC`, 100 > repetitions > - [x] Linux x86_64 fastdebug, affected test with `-XX:+UseZGC`, 100 > repetitions I managed to construct/fix test that passes on G1, Shenandoah and ZGC... https://github.com/plevart/jdk/commit/2dbce34d678bee995c808f3bb2a021bcc98b5d01 The combination of JVM options: -Xmx10m -XX:SoftRefLRUPolicyMSPerMB=1 ... makes ZGC and Shenandoah very aggressive and practically causes SoftReferences to be treated equally as WeakReferences. By increasing the max. heap size a bit and using defaults for SoftRefLRUPolicyMSPerMB (I believe 1000 ms/MB for G1 and 200 ms/MB for Shenandoah and ZGC), G1 and Shenandoah were happy with the changed test. For ZGC I also had to make sure that the CacheEffectiveness test is executed as 1st test in VM instance, followed by CacheReleaseUnderMemoryPressure. ------------- PR: https://git.openjdk.org/jdk/pull/9533
