Improve the way contextvars.Context is copied

Author: Adam Hrbac

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/ContextvarsModuleBuiltins.java

@@ -78,9 +78,7 @@ public abstract static class GetDefaultEncodingNode extends PythonBuiltinNode {
         @Specialization
         protected Object copyCtx() {
             PythonContext.PythonThreadState threadState = getContext().getThreadState(getLanguage());
-            PContextVarsContext ret = factory().createContextVarsContext();
-            ret.contextVarValues = threadState.getContextVarsContext().contextVarValues;
-            return ret;
+            return factory().copyContextVarsContext(threadState.getContextVarsContext());
         }
     }
 

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/contextvars/PContextVarsContext.java

@@ -48,7 +48,7 @@
 import com.oracle.truffle.api.object.Shape;
 
 public class PContextVarsContext extends PythonBuiltinObject {
-    public Hamt contextVarValues = new Hamt();
+    Hamt contextVarValues;
     private PContextVarsContext previousContext = null;
 
     public void enter(PythonContext.PythonThreadState threadState) {
@@ -68,6 +68,16 @@ public void leave(PythonContext.PythonThreadState threadState) {
     }
 
     public PContextVarsContext(Object cls, Shape instanceShape) {
+        this(new Hamt(), cls, instanceShape);
+    }
+
+    public PContextVarsContext(PContextVarsContext original, Object cls, Shape instanceShape) {
+        this(original.contextVarValues, cls, instanceShape);
+    }
+
+    private PContextVarsContext(Hamt contextVarValues, Object cls, Shape instanceShape) {
         super(cls, instanceShape);
+        this.contextVarValues = contextVarValues;
+
     }
 }

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/object/PythonObjectFactory.java

@@ -1452,6 +1452,10 @@ public final PContextVarsContext createContextVarsContext() {
         return trace(new PContextVarsContext(PythonBuiltinClassType.ContextVarsContext, getShape(PythonBuiltinClassType.ContextVarsContext)));
     }
 
+    public final PContextVarsContext copyContextVarsContext(PContextVarsContext original) {
+        return trace(new PContextVarsContext(original, PythonBuiltinClassType.ContextVarsContext, getShape(PythonBuiltinClassType.ContextVarsContext)));
+    }
+
     public final PContextVarsToken createContextVarsToken(PContextVar var, Object oldValue) {
         return trace(new PContextVarsToken(var, oldValue == null ? PContextVarsToken.MISSING : oldValue, PythonBuiltinClassType.ContextVarsToken, getShape(PythonBuiltinClassType.ContextVarsToken)));
     }