Log when sharing starts with the reason when --shared-objects-debug is passed

Author: eregon

src/main/java/org/truffleruby/RubyContext.java

@@ -262,7 +262,7 @@ public void initialize() {
 
         // Share once everything is loaded
         if (options.SHARED_OBJECTS_ENABLED && options.SHARED_OBJECTS_FORCE) {
-            sharedObjects.startSharing();
+            sharedObjects.startSharing(OptionsCatalog.SHARED_OBJECTS_FORCE.getName() + " being true");
         }
 
         if (isPreInitializing()) {

src/main/java/org/truffleruby/core/thread/ThreadManager.java

@@ -229,7 +229,7 @@ private void setupNativeThreadSupport(TruffleNFIPlatform nfi, NativeConfiguratio
     }
 
     public void initialize(DynamicObject rubyThread, Node currentNode, String info, Supplier<Object> task) {
-        startSharing(rubyThread);
+        startSharing(rubyThread, "creating Ruby Thread " + info);
 
         Layouts.THREAD.setSourceLocation(rubyThread, info);
 
@@ -308,16 +308,16 @@ private static void setException(RubyContext context, DynamicObject thread, Dyna
     }
 
     // Share the Ruby Thread before it can be accessed concurrently, and before it is added to Thread.list
-    public void startSharing(DynamicObject rubyThread) {
+    public void startSharing(DynamicObject rubyThread, String reason) {
         if (context.getOptions().SHARED_OBJECTS_ENABLED) {
             // TODO (eregon, 22 Sept 2017): no need if singleThreaded in isThreadAccessAllowed()
-            context.getSharedObjects().startSharing();
+            context.getSharedObjects().startSharing(reason);
             SharedObjects.writeBarrier(context, rubyThread);
         }
     }
 
     public void startForeignThread(DynamicObject rubyThread, Thread javaThread) {
-        startSharing(rubyThread);
+        startSharing(rubyThread, "creating a foreign thread");
         start(rubyThread, javaThread);
     }
 

src/main/java/org/truffleruby/core/thread/ThreadNodes.java

@@ -276,14 +276,15 @@ public abstract static class ThreadInitializeNode extends PrimitiveArrayArgument
         public DynamicObject initialize(DynamicObject thread, DynamicObject arguments, DynamicObject block,
                 @Cached("of(arguments)") ArrayStrategy strategy,
                 @Cached("strategy.boxedCopyNode()") ArrayOperationNodes.ArrayBoxedCopyNode boxedCopyNode) {
+            final SourceSection sourceSection = Layouts.PROC.getSharedMethodInfo(block).getSourceSection();
+            final String info = getContext().fileLine(sourceSection);
+            final Object[] args = boxedCopyNode.execute(Layouts.ARRAY.getStore(arguments), Layouts.ARRAY.getSize(arguments));
+
             if (getContext().getOptions().SHARED_OBJECTS_ENABLED) {
-                getContext().getThreadManager().startSharing(thread);
+                getContext().getThreadManager().startSharing(thread, "creating Ruby Thread " + info);
                 SharedObjects.shareDeclarationFrame(getContext(), block);
             }
 
-            final Object[] args = boxedCopyNode.execute(Layouts.ARRAY.getStore(arguments), Layouts.ARRAY.getSize(arguments));
-            final SourceSection sourceSection = Layouts.PROC.getSharedMethodInfo(block).getSourceSection();
-            final String info = getContext().fileLine(sourceSection);
             getContext().getThreadManager().initialize(thread, this, info,
                     () -> ProcOperations.rootCall(block, args));
             return nil();

src/main/java/org/truffleruby/language/objects/shared/SharedObjects.java

@@ -37,9 +37,12 @@ public boolean isSharing() {
         return sharing;
     }
 
-    public void startSharing() {
+    public void startSharing(String reason) {
         if (!sharing) {
             sharing = true;
+            if (context.getOptions().SHARED_OBJECTS_DEBUG) {
+                RubyLanguage.LOGGER.info("starting sharing due to " + reason);
+            }
             shareContextRoots(context);
         }
     }