[jdk16] RFR: 8260473: [vector] ZGC: VectorReshape test produces incorrect results with ZGC enabled

[王超]

On Mon, 1 Feb 2021 11:35:13 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

> > compileonly and compilercount=1 will let the VM run slow enough to wait for a gc to be finished.
> 
> That's a strange way to provoke the bug. You could just increase the number of iterations instead.
> 
> But the right way to fix it is to stress ZGC to continuously run in the background while the test case aggressively unboxes vectors in compiled code. `-Xmx256m` helps with that while `-XX:CICompilerCount=1` is irrelevant.

Yes, it's very weird to provoke the bug like this. If CICompilerCount=1 is removed, the test failed 60% roughly on my machine.
And the iteration has already changed from 100 to 1000,  the run time of the test is nearly 30s on release version of jvm.

If I add the following patch, the test always fails on my machine,

diff --git a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
index 1843ec0..959b29a 100644
--- a/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
+++ b/test/hotspot/jtreg/compiler/vectorapi/VectorRebracket128Test.java
@@ -44,7 +44,7 @@ import jdk.internal.vm.annotation.ForceInline;
  * @modules jdk.incubator.vector
  * @modules java.base/jdk.internal.vm.annotation
  * @run testng/othervm -XX:CompileCommand=compileonly,jdk/incubator/vector/ByteVector.fromByteBuffer
- *      -XX:-TieredCompilation -XX:CICompilerCount=1 -XX:+UseZGC -Xbatch -Xmx256m VectorRebracket128Test
+ *      -XX:-TieredCompilation -XX:+UseZGC -Xmx256m VectorRebracket128Test
  */
 
 @Test
@@ -125,6 +125,14 @@ public class VectorRebracket128Test {
     @ForceInline
     static <E,F>
     void testVectorRebracket(VectorSpecies<E> a, VectorSpecies<F> b, byte[] input, byte[] output) {
+        new Thread(() -> {
+            while (true) {
+                try {
+                    System.gc();
+                    Thread.sleep(100);
+                } catch (Exception e) {}
+            }
+        }).start();
         Vector<E> av = a.fromByteArray(input, 0, ByteOrder.nativeOrder());
         int block;
         assert(input.length == output.length);

-------------

PR: https://git.openjdk.java.net/jdk16/pull/139