Renamings and fixes.

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/GCImpl.java

@@ -1493,7 +1493,7 @@ private CollectionInProgressError() {
 
     private static class CollectionVMOperation extends NativeVMOperation {
         protected CollectionVMOperation() {
-            super("Garbage collection", SystemEffect.CAUSES_SAFEPOINT);
+            super("Garbage collection", SystemEffect.SAFEPOINT);
         }
 
         @Override

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapImpl.java

@@ -171,7 +171,7 @@ static class ObjectVisitorWalkerOperation extends JavaVMOperation implements Aut
         private ObjectVisitor visitor = null;
 
         ObjectVisitorWalkerOperation() {
-            super("ObjectVisitorWalker", SystemEffect.CAUSES_SAFEPOINT);
+            super("ObjectVisitorWalker", SystemEffect.SAFEPOINT);
         }
 
         ObjectVisitorWalkerOperation open(ObjectVisitor value) {

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapVerifierImpl.java

@@ -182,7 +182,7 @@ protected static final class VerifyVMOperation extends JavaVMOperation {
         private boolean result;
 
         VerifyVMOperation(String message, HeapVerifierImpl verifier, HeapVerifier.Occasion occasion) {
-            super("HeapVerification", SystemEffect.CAUSES_SAFEPOINT);
+            super("HeapVerification", SystemEffect.SAFEPOINT);
             this.message = message;
             this.verifier = verifier;
             this.occasion = occasion;

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/MemoryWalkerImpl.java

@@ -57,7 +57,7 @@ protected static final class MemoryWalkerVMOperation extends JavaVMOperation {
         private boolean result;
 
         protected MemoryWalkerVMOperation(MemoryWalker.Visitor memoryVisitor) {
-            super("MemoryWalkerImpl.visitMemory", SystemEffect.CAUSES_SAFEPOINT);
+            super("MemoryWalkerImpl.visitMemory", SystemEffect.SAFEPOINT);
             this.memoryWalkerVisitor = memoryVisitor;
             this.result = false;
         }

substratevm/src/com.oracle.svm.core.graal/src/com/oracle/svm/core/graal/snippets/CEntryPointSnippets.java

@@ -26,7 +26,7 @@
 
 import static com.oracle.svm.core.SubstrateOptions.MultiThreaded;
 import static com.oracle.svm.core.SubstrateOptions.SpawnIsolates;
-import static com.oracle.svm.core.SubstrateOptions.UseDedicatedVMThread;
+import static com.oracle.svm.core.SubstrateOptions.UseDedicatedVMOperationThread;
 import static com.oracle.svm.core.graal.nodes.WriteCurrentVMThreadNode.writeCurrentVMThread;
 import static com.oracle.svm.core.graal.nodes.WriteHeapBaseNode.writeCurrentVMHeapBase;
 import static com.oracle.svm.core.util.VMError.shouldNotReachHere;
@@ -207,8 +207,8 @@ private static int initializeIsolate() {
         if (!success) {
             return CEntryPointErrors.ISOLATE_INITIALIZATION_FAILED;
         }
-        if (UseDedicatedVMThread.getValue()) {
-            VMOperationControl.startVmThread();
+        if (UseDedicatedVMOperationThread.getValue()) {
+            VMOperationControl.startVMOperationThread();
         }
         return CEntryPointErrors.NO_ERROR;
     }
@@ -308,8 +308,8 @@ private static int tearDownIsolate() {
             if (!JavaThreads.singleton().tearDownVM()) {
                 return CEntryPointErrors.UNSPECIFIED;
             }
-            if (UseDedicatedVMThread.getValue()) {
-                VMOperationControl.stopVmThread();
+            if (UseDedicatedVMOperationThread.getValue()) {
+                VMOperationControl.stopVMOperationThread();
             }
             return Isolates.tearDownCurrent();
         } catch (Throwable t) {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/SubstrateOptions.java

@@ -305,14 +305,7 @@ protected void onValueUpdate(EconomicMap<OptionKey<?>, Object> values, String ol
     public static final HostedOptionKey<Boolean> EmitStringEncodingSubstitutions = new HostedOptionKey<>(true);
 
     @Option(help = "Determines if VM operations should be executed in a dedicated thread.", type = OptionType.Debug)//
-    public static final HostedOptionKey<Boolean> UseDedicatedVMThread = new HostedOptionKey<Boolean>(false) {
-        @Override
-        protected void onValueUpdate(EconomicMap<OptionKey<?>, Object> values, Boolean oldValue, Boolean newValue) {
-            if (newValue) {
-                MultiThreaded.update(values, true);
-            }
-        }
-    };
+    public static final HostedOptionKey<Boolean> UseDedicatedVMOperationThread = new HostedOptionKey<>(false);
 
     @Platforms(Platform.HOSTED_ONLY.class)
     public static Predicate<String> makeFilter(String[] definedFilters) {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/deopt/Deoptimizer.java

@@ -594,7 +594,7 @@ private static final class DeoptSourceFrameOperation extends JavaVMOperation {
         private IsolateThread thread;
 
         DeoptSourceFrameOperation(Deoptimizer receiver, CodePointer pc, boolean ignoreNonDeoptimizable, IsolateThread thread) {
-            super("DeoptSourceFrameOperation", SystemEffect.CAUSES_SAFEPOINT);
+            super("DeoptSourceFrameOperation", SystemEffect.SAFEPOINT);
             this.receiver = receiver;
             this.pc = pc;
             this.ignoreNonDeoptimizable = ignoreNonDeoptimizable;

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/GCCause.java

@@ -50,9 +50,11 @@ public class GCCause {
 
     @Platforms(Platform.HOSTED_ONLY.class)
     protected GCCause(String name) {
-        this.id = HostedGCCauseList.size();
-        this.name = name;
-        HostedGCCauseList.add(this);
+        synchronized (HostedGCCauseList) {
+            this.id = HostedGCCauseList.size();
+            this.name = name;
+            HostedGCCauseList.add(this);
+        }
     }
 
     public String getName() {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/JavaLangRefSubstitutions.java

@@ -198,13 +198,13 @@ public Object poll() {
 
     @Substitute
     public Object remove() throws InterruptedException {
-        VMOperation.guaranteeNotInProgress("Calling ReferenceQueue.remove() inside a VMOperation could block the VM thread and cause a deadlock.");
+        VMOperation.guaranteeNotInProgress("Calling ReferenceQueue.remove() inside a VMOperation could block the VM operation thread and cause a deadlock.");
         return ReferenceWrapper.unwrap(feeble.remove());
     }
 
     @Substitute
     public Object remove(long timeoutMillis) throws InterruptedException {
-        VMOperation.guaranteeNotInProgress("Calling ReferenceQueue.remove(long) inside a VMOperation could block the VM thread and cause a deadlock.");
+        VMOperation.guaranteeNotInProgress("Calling ReferenceQueue.remove(long) inside a VMOperation could block the VM operation thread and cause a deadlock.");
         return ReferenceWrapper.unwrap(feeble.remove(timeoutMillis));
     }
 

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/locks/VMMutex.java

@@ -78,7 +78,7 @@ public VMMutex lock() {
      * <li>Thread A calls mutex.lockNoTransition() and acquires the mutex</li>
      * <li>Thread B calls mutex.lockNoTransition() and is blocked</li>
      * <li>Thread A still holds the mutex but needs to trigger a GC. However, the safepoint can't be
-     * initiated as Thread A is still in the Java state but blocked in native code.</li>
+     * initiated as Thread B is still in the Java state but blocked in native code.</li>
      * </ul>
      */
     @Uninterruptible(reason = "Called from uninterruptible code.", callerMustBe = true)

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaThreads.java

@@ -392,7 +392,7 @@ private static boolean waitForTearDown() {
     }
 
     private static boolean isApplicationThread(IsolateThread isolateThread) {
-        return !VMOperationControl.isDedicatedVmThread(isolateThread);
+        return !VMOperationControl.isDedicatedVMOperationThread(isolateThread);
     }
 
     @SuppressFBWarnings(value = "NN", justification = "notifyAll is necessary for Java semantics, no shared state needs to be modified beforehand")
@@ -710,7 +710,7 @@ private static class FetchApplicationThreadsOperation extends JavaVMOperation {
         private final List<Thread> list;
 
         FetchApplicationThreadsOperation(List<Thread> list) {
-            super("FetchApplicationThreads", SystemEffect.DOES_NOT_CAUSE_SAFEPOINT);
+            super("FetchApplicationThreads", SystemEffect.NONE);
             this.list = list;
         }
 
@@ -742,7 +742,7 @@ private static class CountApplicationThreadsOperation extends JavaVMOperation {
         private int count;
 
         CountApplicationThreadsOperation(Log trace, AtomicBoolean printLaggards) {
-            super("VMThreadCounterOperation", SystemEffect.DOES_NOT_CAUSE_SAFEPOINT);
+            super("VMThreadCounterOperation", SystemEffect.NONE);
             this.trace = trace;
             this.printLaggards = printLaggards;
             this.count = 0;

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/JavaVMOperation.java

@@ -35,9 +35,11 @@
  * VM operation on the Java heap is preferable but not always possible.
  *
  * <p>
- * Do <b>NOT</b> create singleton objects that might get enqueued by multiple threads. If
- * {@linkplain SubstrateOptions#UseDedicatedVMThread} is enabled, this can result in race
- * conditions.
+ * {@link JavaVMOperation} objects should be short lived and only enqueued/executed once. It is
+ * possible to reuse {@link JavaVMOperation} objects for multiple executions but it requires extra
+ * care: when a VM operation is enqueued, then it must be guaranteed that it is executed before it
+ * is enqueued again. Otherwise, this could result in various race conditions (especially if
+ * {@linkplain SubstrateOptions#UseDedicatedVMOperationThread} is enabled).
  */
 public abstract class JavaVMOperation extends VMOperation implements VMOperationControl.JavaAllocationFreeQueue.Element<JavaVMOperation> {
     protected IsolateThread queuingThread;
@@ -93,13 +95,13 @@ protected boolean hasWork() {
 
     /** Convenience method for thunks that can be run by allocating a VMOperation. */
     public static void enqueueBlockingSafepoint(String name, Thunk thunk) {
-        ThunkOperation vmOperation = new ThunkOperation(name, SystemEffect.CAUSES_SAFEPOINT, thunk);
+        ThunkOperation vmOperation = new ThunkOperation(name, SystemEffect.SAFEPOINT, thunk);
         vmOperation.enqueue();
     }
 
     /** Convenience method for thunks that can be run by allocating a VMOperation. */
     public static void enqueueBlockingNoSafepoint(String name, Thunk thunk) {
-        ThunkOperation vmOperation = new ThunkOperation(name, SystemEffect.DOES_NOT_CAUSE_SAFEPOINT, thunk);
+        ThunkOperation vmOperation = new ThunkOperation(name, SystemEffect.NONE, thunk);
         vmOperation.enqueue();
     }
 

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/Safepoint.java

@@ -443,8 +443,8 @@ private Master() {
          * Have each of the threads (except myself!) stop at a safepoint.
          *
          * Locking {@linkplain VMThreads#THREAD_MUTEX} in this method is fine because the method is
-         * only executed by the VM thread. Therefore, no other thread can initiate a safepoint and
-         * Java allocations are disabled as well.
+         * only executed by the VM operation thread. Therefore, no other thread can initiate a
+         * safepoint and Java allocations are disabled as well.
          */
         @RestrictHeapAccess(access = RestrictHeapAccess.Access.NO_ALLOCATION, mayBeInlined = true, reason = "The safepoint logic must not allocate.")
         protected boolean freeze(String reason) {

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/thread/VMOperation.java

@@ -53,7 +53,7 @@ public final String getName() {
     }
 
     public final boolean getCausesSafepoint() {
-        return systemEffect == SystemEffect.CAUSES_SAFEPOINT;
+        return systemEffect == SystemEffect.SAFEPOINT;
     }
 
     protected final void execute(NativeVMOperationData data) {
@@ -108,7 +108,11 @@ public static void guaranteeNotInProgress(String message) {
         }
     }
 
-    /** Used to determine if a VMOperation must be executed or if it can be skipped. */
+    /**
+     * Used to determine if a VM operation must be executed or if it can be skipped. Regardless of
+     * the {@linkplain SystemEffect} that was specified for the VM operation, this method might be
+     * called before or after a safepoint was initiated.
+     */
     protected boolean hasWork(@SuppressWarnings("unused") NativeVMOperationData data) {
         return true;
     }
@@ -125,7 +129,7 @@ protected boolean hasWork(@SuppressWarnings("unused") NativeVMOperationData data
     protected abstract void operate(NativeVMOperationData data);
 
     public enum SystemEffect {
-        DOES_NOT_CAUSE_SAFEPOINT,
-        CAUSES_SAFEPOINT
+        NONE,
+        SAFEPOINT
     }
 }