8076995: gc/ergonomics/TestDynamicNumberOfGCThreads.java failed with...

8076995: gc/ergonomics/TestDynamicNumberOfGCThreads.java failed with java.lang.RuntimeException: 'new_active_workers' missing from stdout/stderr
Reviewed-by: jmasa, drwhite

src/share/vm/gc_implementation/shared/adaptiveSizePolicy.cpp

@@ -193,8 +193,9 @@ int AdaptiveSizePolicy::calc_active_workers(uintx total_workers,
      (!FLAG_IS_DEFAULT(ParallelGCThreads) && !ForceDynamicNumberOfGCThreads)) {
     new_active_workers = total_workers;
   } else {
+    uintx min_workers = (total_workers == 1) ? 1 : 2;
     new_active_workers = calc_default_active_workers(total_workers,
-                                                     2, /* Minimum number of workers */
+                                                     min_workers,
                                                      active_workers,
                                                      application_workers);
   }

test/TEST.groups

@@ -215,6 +215,7 @@ needs_full_vm_compact1 = \
   runtime/NMT \
   gc/class_unloading/TestCMSClassUnloadingEnabledHWM.java \
   gc/class_unloading/TestG1ClassUnloadingHWM.java \
+  gc/ergonomics/TestDynamicNumberOfGCThreads.java \
   gc/g1/TestRegionAlignment.java \
   gc/g1/TestShrinkToOneRegion.java \
   gc/metaspace/G1AddMetaspaceDependency.java \

test/gc/ergonomics/TestDynamicNumberOfGCThreads.java

@@ -44,14 +44,24 @@ public class TestDynamicNumberOfGCThreads {
   }
 
   private static void verifyDynamicNumberOfGCThreads(OutputAnalyzer output) {
+    output.shouldHaveExitValue(0); // test should run succesfully
     output.shouldContain("new_active_workers");
-    output.shouldHaveExitValue(0);
   }
 
   private static void testDynamicNumberOfGCThreads(String gcFlag) throws Exception {
     // UseDynamicNumberOfGCThreads and TraceDynamicGCThreads enabled
-    ProcessBuilder pb_enabled =
-      ProcessTools.createJavaProcessBuilder("-XX:+" + gcFlag, "-Xmx10M", "-XX:+PrintGCDetails",  "-XX:+UseDynamicNumberOfGCThreads", "-XX:+TraceDynamicGCThreads", GCTest.class.getName());
+    String[] baseArgs = {"-XX:+" + gcFlag, "-Xmx10M", "-XX:+PrintGCDetails",  "-XX:+UseDynamicNumberOfGCThreads", "-XX:+TraceDynamicGCThreads", GCTest.class.getName()};
+
+    // Base test with gc and +UseDynamicNumberOfGCThreads:
+    ProcessBuilder pb_enabled = ProcessTools.createJavaProcessBuilder(baseArgs);
+    verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
+
+    // Ensure it also works on uniprocessors or if user specifies -XX:ParallelGCThreads=1:
+    String[] extraArgs = {"-XX:+UnlockDiagnosticVMOptions", "-XX:+ForceDynamicNumberOfGCThreads", "-XX:ParallelGCThreads=1"};
+    String[] finalArgs = new String[baseArgs.length + extraArgs.length];
+    System.arraycopy(extraArgs, 0, finalArgs, 0,                extraArgs.length);
+    System.arraycopy(baseArgs,  0, finalArgs, extraArgs.length, baseArgs.length);
+    pb_enabled = ProcessTools.createJavaProcessBuilder(finalArgs);
     verifyDynamicNumberOfGCThreads(new OutputAnalyzer(pb_enabled.start()));
   }