RFR: 8177968: Add GC stress test TestGCLocker

[Erik Helin]

On 04/12/2017 08:05 AM, Per Liden wrote:
> Hi Erik,
>
> (Re-sending, as Thunderbird crashed on me and it seems that my first
> reply never made it to the list)

Hey Per,

thanks for reviewing! Please see new version at
- inc: http://cr.openjdk.java.net/~ehelin/8177968/00-01/
- full: http://cr.openjdk.java.net/~ehelin/8177968/01/

and comments inline:

> On 2017-04-07 17:48, Erik Helin wrote:
>> Hi all,
>>
>> this patch adds the stress test "TestGCLocker". The test repeatedly
>> calls GCLocker::lock_critical/unlock_critical (via the JNI functions
>> GetPrimitiveArrayCritical/ReleasePrimitiveArrayCritical) while
>> concurrently filling up the old gen. Thea idea is to stress the GCLocker
>> implementation by quickly entering/leaving critical JNI sections while
>> simultaneously allocating objects to fill up the heap in order to
>> provoke a GC.
>>
>> Enhancement:
>> https://bugs.openjdk.java.net/browse/JDK-8177968
>>
>> Patch:
>> http://cr.openjdk.java.net/~ehelin/8177968/00/
>
> I did some test runs and it seems the test only provokes the wanted
> situation in ~20% of the GCs (on my machine at least). Being a stress
> test, I'd like to propose that we remove the sleep() calls to have it
> provoke the situation in ~100% of the GCs.

Thanks for taking the code for a spin!

> --- a/test/gc/stress/gclocker/TestGCLocker.java
> +++ b/test/gc/stress/gclocker/TestGCLocker.java
> @@ -162,7 +153,6 @@
>
>          while (!shouldExit()) {
>              load();
> -            ThreadUtils.sleep(100);
>          }
>      }
>  }
> @@ -175,7 +165,6 @@
>          byte[] array = new byte[1024 * 1024];
>          while (!shouldExit()) {
>              fillWithRandomValues(array);
> -            ThreadUtils.sleep(10);
>          }
>      }
>  }

Great suggestion, will update the patch.

> Also, the filler function only writes to the first byte, which looks
> like a bug. Simple fix:
>
> --- a/test/gc/stress/gclocker/libTestGCLocker.c
> +++ b/test/gc/stress/gclocker/libTestGCLocker.c
> @@ -29,7 +29,7 @@
>    jbyte* p = (*env)->GetPrimitiveArrayCritical(env, arr, NULL);
>    jsize i;
>    for (i = 0; i < size; i++) {
> -      *p = i % 128;
> +    p[i] = i % 128;
>    }
>    (*env)->ReleasePrimitiveArrayCritical(env, arr, p, 0);
>  }

Heh, thanks for noticing this :) Reminds me of:
http://dilbert.com/strip/2001-10-25

> Other than that, looks good!

Thanks!
Erik

> cheers,
> Per
>
>> Testing:
>> - JPRT (to ensure libTestGCLocker.c compiles on all platforms)
>> - make run-test TEST=hotspot/test/gc/stress/gclocker
>>
>> Thanks,
>> Erik