test/jdk/java/lang/management/MemoryMXBean/LowMemoryTest.java

*** 81,93 ****
          final String g1Flag = "-XX:G1HeapRegionSize=1m";
  
          // Runs the test collecting subprocess I/O while it's running.
          traceTest(classMain + ", -XX:+UseSerialGC", nmFlag, lpFlag, "-XX:+UseSerialGC");
          traceTest(classMain + ", -XX:+UseParallelGC", nmFlag, lpFlag, "-XX:+UseParallelGC");
!         traceTest(classMain + ", -XX:+UseG1GC", nmFlag, lpFlag, "-XX:+UseG1GC", g1Flag);
          if (!Compiler.isGraalEnabled()) { // Graal does not support CMS
!             traceTest(classMain + ", -XX:+UseConcMarkSweepGC", nmFlag, lpFlag, "-XX:+UseConcMarkSweepGC");
          }
      }
  
      /*
       * Creating command-line for running subprocess JVM:
--- 81,97 ----
          final String g1Flag = "-XX:G1HeapRegionSize=1m";
  
          // Runs the test collecting subprocess I/O while it's running.
          traceTest(classMain + ", -XX:+UseSerialGC", nmFlag, lpFlag, "-XX:+UseSerialGC");
          traceTest(classMain + ", -XX:+UseParallelGC", nmFlag, lpFlag, "-XX:+UseParallelGC");
!         traceTest(classMain + ", -XX:+UseG1GC -XX:-G1UseLegacyMonitoring", nmFlag, lpFlag,
!                   "-XX:+UseG1GC", "-XX:-G1UseLegacyMonitoring", g1Flag);
!         traceTest(classMain + ", -XX:+UseG1GC -XX:+G1UseLegacyMonitoring", nmFlag, lpFlag,
!                   "-XX:+UseG1GC", "-XX:+G1UseLegacyMonitoring", g1Flag);
          if (!Compiler.isGraalEnabled()) { // Graal does not support CMS
!              traceTest(classMain + ", -XX:+UseConcMarkSweepGC", nmFlag, lpFlag,
!                        "-XX:+UseConcMarkSweepGC");
          }
      }
  
      /*
       * Creating command-line for running subprocess JVM:
*** 230,250 ****
--- 234,276 ----
  
              // Find the Old generation which supports low memory detection
              ListIterator iter = pools.listIterator();
              while (iter.hasNext()) {
                  MemoryPoolMXBean p = (MemoryPoolMXBean) iter.next();
+                 // Only check heap pools that support a usage threshold.
+                 // This is typically only the old generation space
+                 // since the other spaces are expected to get filled up.
                  if (p.getType() == MemoryType.HEAP &&
                      p.isUsageThresholdSupported()) {
+                     // In all collectors except G1, only the old generation supports a
+                     // usage threshold. The G1 legacy mode "G1 Old Gen" also does. In
+                     // G1 default mode, both the old space ("G1 Old Space": it's not
+                     // really a generation in the non-G1 collector sense) and the
+                     // humongous space ("G1 Humongous Space"), support a usage threshold.
+                     // So, the following condition is true for all non-G1 old generations,
+                     // for the G1 legacy old gen, and for the G1 default humongous space.
+                     // It is not true for the G1 default old gen.
+                     //
+                     // We're allocating humongous objects in this test, so the G1 default
+                     // mode "G1 Old Space" occupancy doesn't change, because humongous
+                     // objects are allocated in the "G1 Humongous Space". If we allowed
+                     // the G1 default mode "G1 Old Space", notification would never
+                     // happen because no objects are allocated there.
+                     if (!p.getName().equals("G1 Old Space")) {
                          mpool = p;
                          if (trace) {
                              System.out.println("Selected memory pool for low memory " +
                                                 "detection.");
                              MemoryUtil.printMemoryPool(mpool);
                          }
                          break;
                      }
                  }
+             }
+             if (mpool == null) {
+                 throw new RuntimeException("TEST FAILED: No heap pool found");
+             }
  
              TestListener listener = new TestListener();
              SensorListener l2 = new SensorListener();
              NotificationEmitter emitter = (NotificationEmitter) mm;
              emitter.addNotificationListener(listener, null, null);