Can no longer invoke Managed_Resource.with when Managed_Resource.finalize was called

Author: JaroslavTulach

distribution/lib/Standard/Base/0.0.0-dev/src/Runtime/Managed_Resource.enso

@@ -58,11 +58,15 @@ type Managed_Resource
        ADVANCED
 
        Executes the provided action on the resource managed by the managed
-       resource object.
+       resource object. The action is only invoked if the managed resource
+       has not yet been finalized.
 
        Arguments:
        - action: The action that will be applied to the resource managed by
          resource.
+       Returns:
+       Value returned from the `action` or `Nothing` if the managed resource
+       was already finalized
     with : (Any -> Any) -> Any
     with self ~action = @Builtin_Method "Managed_Resource.with"
 

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/resource/WithNode.java

@@ -6,7 +6,6 @@
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.runtime.EnsoContext;
-import org.enso.interpreter.runtime.ResourceManager;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
 import org.enso.interpreter.runtime.data.ManagedResource;
 import org.enso.interpreter.runtime.state.State;
@@ -33,12 +32,17 @@ static WithNode build() {
 
   @Specialization
   Object doWith(State state, VirtualFrame frame, ManagedResource self, Object action) {
-    ResourceManager resourceManager = EnsoContext.get(this).getResourceManager();
-    resourceManager.park(self);
-    try {
-      return invokeCallableNode.execute(action, frame, state, new Object[] {self.getResource()});
-    } finally {
-      resourceManager.unpark(self);
+    var ctx = EnsoContext.get(this);
+    var resourceManager = ctx.getResourceManager();
+    if (self.getPhantomReference().refersTo(self)) {
+      resourceManager.park(self);
+      try {
+        return invokeCallableNode.execute(action, frame, state, new Object[] {self.getResource()});
+      } finally {
+        resourceManager.unpark(self);
+      }
+    } else {
+      return ctx.getBuiltins().nothing();
     }
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/runtime/ResourceManager.java

@@ -408,6 +408,7 @@ private Item(
     @CompilerDirectives.TruffleBoundary
     private void finalizeNow(EnsoContext context) {
       try {
+        clear();
         InteropLibrary.getUncached(finalizer).execute(finalizer, underlying);
       } catch (Exception e) {
         context.getErr().println("Exception in finalizer: " + e.getMessage());

engine/runtime/src/main/java/org/enso/interpreter/runtime/data/ManagedResource.java

@@ -1,5 +1,6 @@
 package org.enso.interpreter.runtime.data;
 
+import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.Bind;
 import com.oracle.truffle.api.interop.InteropLibrary;
@@ -12,7 +13,27 @@
 import org.enso.interpreter.runtime.callable.function.Function;
 import org.enso.interpreter.runtime.library.dispatch.TypesLibrary;
 
-/** A runtime representation of a managed resource. */
+/**
+ * An Enso runtime representation of a managed resource.
+ *
+ * <p><b>Instance of this class</b> is convoluted with instances playing various roles:
+ *
+ * <ul>
+ *   <li>this {@link ManagedResource} points to {@code resource}
+ *   <li>this {@link ManagedResource} points to {@link PhantomReference} that is "phantom
+ *       referencing" {@code this}
+ *   <li>the implementation of {@link PhantomReference} is {@code Item} in {@link ResourceManager}
+ *   <li>the {@code Item} <em>"phantom referencing"</em> {@code this} {@link ManagedResource} is
+ *       stored in {@link ResourceManager} {@code pendingItems} collection.
+ *   <li>the {@code Item} has a pointer to the {@code resource} as well
+ *   <li>the {@code Item} has a pointer to the {@code finalizer} function
+ * </ul>
+ *
+ * Once all this braided chunk of objects is eligible for GC because <b>nobody holds pointer to
+ * {@link ManagedResource}</b>, the {@code Item} is put into {@link ResourceManager} {@code
+ * referenceQueue} and process by the intricate machinery of {@link ResourceManager} and its {@code
+ * ProcessItems} processor.
+ */
 @ExportLibrary(InteropLibrary.class)
 @ExportLibrary(TypesLibrary.class)
 @Builtin(pkg = "resource", stdlibName = "Standard.Base.Runtime.Managed_Resource.Managed_Resource")
@@ -97,8 +118,16 @@ Type getType(@Bind("$node") Node node) {
 
   @ExportMessage
   @TruffleBoundary
+  public String toDisplayString(boolean allowSideEffects, @Bind("$node") Node node) {
+    var type = getType(node);
+    return type.getName()
+        + " "
+        + InteropLibrary.getUncached().toDisplayString(resource, allowSideEffects);
+  }
+
+  @ExportMessage.Ignore
   @Override
-  public String toDisplayString(boolean allowSideEffects) {
-    return resource.toString();
+  public Object toDisplayString(boolean allowSideEffects) {
+    throw CompilerDirectives.shouldNotReachHere();
   }
 }

test/Base_Tests/src/Runtime/Managed_Resource_Spec.enso

@@ -2,6 +2,7 @@ from Standard.Base import all
 import Standard.Base.Data.Vector.Builder
 import Standard.Base.Errors.Illegal_State.Illegal_State
 import Standard.Base.Runtime.Managed_Resource.Managed_Resource
+import Standard.Base.Runtime.Ref.Ref
 import project.Runtime.GC_Example
 
 from Standard.Test import all
@@ -68,6 +69,58 @@ add_specs suite_builder = suite_builder.group "Managed_Resource" group_builder->
         if messages.last != "OK" then
             Test.fail (messages.join '\n')
 
+    group_builder.specify "register_with_finalize" <|
+        messages = Vector.build builder->
+            builder.append ""
+
+            create_resource value =
+                # registers new resource
+                Managed_Resource.register (Ref.new value) v->
+                    v.put -1
+                    builder.append "  finalizing:"+v.to_text
+
+            mr = create_resource 42
+
+            builder.append "Allocated: "+mr.to_text
+
+            # operates with its value
+            out = mr.with v->
+                builder.append "  with  :"+v.to_text
+                v.put 7
+                v.modify n->
+                    builder.append "  modify:"+n.to_text
+                    6
+                v
+            builder.append "With finished:"+out.to_text
+
+            # finalizes the resource
+            mr.finalize
+            builder.append "Finalized:"+mr.to_text
+
+            # operation on finalized resource
+            none = mr.with v->
+                # should never be called
+                builder.append "  empty :"+v.to_text
+                "Don't call me!"
+
+            builder.append none.to_text
+            none.is_nothing . should_be_true
+
+        exp_text = """
+
+            Allocated: Managed_Resource 42
+              with  :42
+              modify:7
+            With finished:6
+              finalizing:-1
+            Finalized:Managed_Resource -1
+            Nothing
+
+        msg_text = messages.join '\n'
+
+        if msg_text != exp_text then
+            Test.fail (msg_text)
+
 main filter=Nothing =
     suite = Test.build suite_builder->
         add_specs suite_builder