[GitHub] [daffodil] jadams-tresys commented on a change in pull request #473: Implement variable direction property

[GitBox <gi...@apache.org>]

jadams-tresys commented on a change in pull request #473:
URL: https://github.com/apache/daffodil/pull/473#discussion_r582847166



##########
File path: daffodil-runtime1-unparser/src/main/scala/org/apache/daffodil/processors/unparsers/ExpressionEvaluatingUnparsers.scala
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@@ -77,30 +78,83 @@ final class SetVariableUnparser(
 
 }
 
+final class NewVariableInstanceSuspendableExpression(
+  override val expr: CompiledExpression[AnyRef],
+  override val rd: VariableRuntimeData)
+  extends SuspendableExpression {
+
+  override protected def processExpressionResult(ustate: UState, v: DataValuePrimitive): Unit = {
+    val vi = ustate.variableMap.find(rd.globalQName)
+    Assert.invariant(vi.isDefined)
+    // Reset original variable's state from VariableInProcess
+    vi.get.setState(vi.get.priorState)
+    ustate.variableMap.newVariableInstance(rd, v)
+  }
+
+  override protected def maybeKnownLengthInBits(ustate: UState) = MaybeULong(0)
+}
+
 // When implemented this almost certainly wants to be a combinator
 // Not two separate unparsers.
-class NewVariableInstanceStartUnparser(override val context: RuntimeData)
+class NewVariableInstanceStartUnparser(override val context: VariableRuntimeData)
   extends PrimUnparserNoData {
 
   override lazy val runtimeDependencies = Vector()
 
   override lazy val childProcessors = Vector()
 
   override def unparse(state: UState) = {
-    val vrd = context.asInstanceOf[VariableRuntimeData]
-    state.newVariableInstance(vrd)
+    if (context.maybeDefaultValueExpr.isDefined) {
+      val maybeVar = state.variableMap.find(context.globalQName)
+      Assert.invariant(maybeVar.isDefined)
+
+      // Set the variable's state to VariableInProcess while waiting for the NVI
+      // expression to complete. When the expression completes, this original
+      // variable instance will have its state reset to its original value.
+      maybeVar.get.setState(VariableInProcess)
+      val suspendableExpression = new NewVariableInstanceSuspendableExpression(context.maybeDefaultValueExpr.get, context)
+      suspendableExpression.run(state)

Review comment:
       So I had been trying to get the approach you described to work for quite a while, but kept running into SuspensionDeadlock issues.  Perhaps I wasn't copying things appropriately when the UState gets cloned for suspension.  I'll take another look at it, but this commit was the first thing that I could get to work and handle scoping properly.




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