remove old GC prevention mechanism which is now replaced by object pinning

Author: javeleon

espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/impl/DebuggerController.java

@@ -711,7 +711,6 @@ private void lockThread(Object thread, boolean forceSuspend, List<Callable<Void>
             }
             checkThreadJobsAndRun(thread);
         }
-        getGCPrevention().releaseActiveWhileSuspended(thread);
         fine(() -> "lock wakeup for thread: " + getThreadName(thread));
     }
 

espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/impl/GCPrevention.java

@@ -22,16 +22,13 @@
  */
 package com.oracle.truffle.espresso.jdwp.impl;
 
-import java.util.ArrayList;
-import java.util.HashMap;
 import java.util.HashSet;
 
 public final class GCPrevention {
 
     // simply hold a strong reference to all objects for which
     // GC should be disabled
     private final HashSet<Object> prevent = new HashSet<>();
-    private final HashMap<Object, ArrayList<Object>> activeWhileSuspended = new HashMap<>();
 
     public void disableGC(Object object) {
         prevent.add(object);
@@ -45,13 +42,4 @@ public void clearAll() {
         prevent.clear();
     }
 
-    public synchronized void setActiveWhileSuspended(Object guestThread, Object obj) {
-        activeWhileSuspended.putIfAbsent(guestThread, new ArrayList<>());
-        activeWhileSuspended.get(guestThread).add(obj);
-    }
-
-    public synchronized void releaseActiveWhileSuspended(Object guestThread) {
-        activeWhileSuspended.remove(guestThread);
-    }
-
 }

espresso/src/com.oracle.truffle.espresso.jdwp/src/com/oracle/truffle/espresso/jdwp/impl/JDWP.java

@@ -1587,7 +1587,7 @@ static CommandResult createReply(Packet packet, JDWPContext context) {
 
                 Object object = context.getIds().fromId((int) objectId);
 
-                if (object == context.getNullObject()) {
+                if (object == null || object == context.getNullObject()) {
                     reply.errorCode(ErrorCodes.INVALID_OBJECT);
                     return new CommandResult(reply);
                 }
@@ -3049,17 +3049,11 @@ private static void writeMethodResult(PacketStream reply, JDWPContext context, T
             reply.writeByte(TagConstants.OBJECT);
             Object guestException = context.getGuestException(result.getException());
             reply.writeLong(context.getIds().getIdAsLong(guestException));
-            if (controller.getThreadSuspension().getSuspensionCount(thread) > 0) {
-                controller.getGCPrevention().setActiveWhileSuspended(thread, guestException);
-            }
         } else {
             Object value = result.getResult();
             if (value != null) {
                 byte tag = context.getTag(value);
                 writeValue(tag, value, reply, true, context);
-                if (controller.getThreadSuspension().getSuspensionCount(thread) > 0) {
-                    controller.getGCPrevention().setActiveWhileSuspended(thread, value);
-                }
             } else { // return value is null
                 reply.writeByte(TagConstants.OBJECT);
                 reply.writeLong(0);