Remove unused Platform.GC code (#8115)

* Remove unused Platform.GC code; add warning about accessing JMX too early
* temporarily turn off DDProf due to PROF-11066

Author: mcculls

dd-smoke-tests/java9-modules/src/test/groovy/datadog/smoketest/Java9ModulesSmokeTest.groovy

@@ -15,6 +15,9 @@ class Java9ModulesSmokeTest extends AbstractSmokeTest {
     List<String> command = new ArrayList<>()
     command.add(imageDir + "/bin/java")
     command.addAll(defaultJavaProperties)
+    // temporarily turn off DDProf due to PROF-11066
+    command.removeAll { it.startsWith("-Ddd.profiling.ddprof.enabled") }
+    command.add("-Ddd.profiling.ddprof.enabled=false")
     command.addAll((String[]) ["-m", "datadog.smoketest.moduleapp/datadog.smoketest.moduleapp.ModuleApplication"])
     ProcessBuilder processBuilder = new ProcessBuilder(command)
     processBuilder.directory(new File(buildDirectory))

internal-api/build.gradle

@@ -27,7 +27,6 @@ minimumInstructionCoverage = 0.8
 excludedClassesCoverage += [
   "datadog.trace.api.EndpointTracker",
   "datadog.trace.api.Platform",
-  "datadog.trace.api.Platform.GC",
   "datadog.trace.api.StatsDClient",
   "datadog.trace.api.NoOpStatsDClient",
   "datadog.trace.api.TraceSegment.NoOp",

internal-api/src/main/java/datadog/trace/api/Platform.java

@@ -1,61 +1,27 @@
 package datadog.trace.api;
 
-import java.lang.management.GarbageCollectorMXBean;
-import java.lang.management.ManagementFactory;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Locale;
 
+/**
+ * This class is used early on during premain; it must not touch features like JMX or JUL in case
+ * they trigger early loading/binding.
+ */
 public final class Platform {
   // A helper class to capture whether the executable is a native image or not.
   // This class needs to be iniatlized at build only during the AOT compilation and build.
   private static class Captured {
     public static final boolean isNativeImage = checkForNativeImageBuilder();
   }
 
-  public enum GC {
-    SERIAL("marksweep"),
-    PARALLEL("ps"),
-    CMS("concurrentmarksweep"),
-    G1("g1"),
-    SHENANDOAH("shenandoah"),
-    Z("z"),
-    UNKNOWN("");
-
-    private final String identifierPrefix;
-
-    GC(String identifierPrefix) {
-      this.identifierPrefix = identifierPrefix;
-    }
-
-    static GC current() {
-      for (GarbageCollectorMXBean mxBean : ManagementFactory.getGarbageCollectorMXBeans()) {
-        if (mxBean.isValid()) {
-          String name = mxBean.getName().toLowerCase(Locale.ROOT);
-          for (GC gc : GC.values()) {
-            if (gc != UNKNOWN && name.startsWith(gc.identifierPrefix)) {
-              return gc;
-            }
-          }
-        }
-      }
-      return UNKNOWN;
-    }
-  }
-
   private static final Version JAVA_VERSION = parseJavaVersion(System.getProperty("java.version"));
   private static final JvmRuntime RUNTIME = new JvmRuntime();
 
-  private static final GC GARBAGE_COLLECTOR = GC.current();
-
   private static final boolean HAS_JFR = checkForJfr();
   private static final boolean IS_NATIVE_IMAGE_BUILDER = checkForNativeImageBuilder();
   private static final boolean IS_NATIVE_IMAGE = Captured.isNativeImage;
 
-  public static GC activeGarbageCollector() {
-    return GARBAGE_COLLECTOR;
-  }
-
   public static boolean hasJfr() {
     return HAS_JFR;
   }