stevedlawrence commented on a change in pull request #473:
URL: https://github.com/apache/incubator-daffodil/pull/473#discussion_r562004598
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File path:
daffodil-runtime1-unparser/src/main/scala/org/apache/daffodil/processors/unparsers/ExpressionEvaluatingUnparsers.scala
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@@ -77,30 +76,52 @@ 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 = {
+ ustate.variableMap.newVariableInstance(rd, v)
+ }
+
+ override protected def maybeKnownLengthInBits(ustate: UState) = MaybeULong(0)
+}
+
Review comment:
One thing to that jumped to my mind, does a setVariable even need to
suspend if the defaultValue is suspending (i.e. the vairables is in the new
VariableSuspended state)? In this case, we'll never use the defaultValue, so
why wait for it to become evaluated if setVariable doesn't need to suspend?
I think the answer here is the defaultValue could access other variables
which changes the state of those variables to read, so it probably is important
to wait for the defaultValue to evaluate, even if it's value will be overwriten
by a setVariable.
Another unrelated thought about how this all needs to work, say we had
something like this:
* NVI variable1, defaultValue = 1
* NVI variable2, defaultValue = "{
/some/future/path/that/requires/suspension + $variable1 }"
* setVariable, variable1 = 2
* element A dfdl:inputValueCalc="{ $variable1 }"
So we create NVI variable1 with an immediate value of defaultValue1. All
good.
Then we create a NVI variable2, but the defaultValue must suspend because it
accesses some future path. In suspending, it clones the UState (including the
current "1" value of variable1). Note that it hasn't read variable1 until the
path comes into existance.
We continue the unparse and evaluate the setVariable and change variable1 to
a value of 2. This is fine because variable1 hasn't been read yet, because NVI
variable2 defaultValue suspended.
Continuing the parse, we evaluate the inputValueCalc and set element A to
variable1, which now has a value of 2.
At some point we unsuspend the defaultValue, and set defalutValue to 1. I
*think* this works because this suspension is working on a cloned UState. But
this uses the 1 value from variable1 because it was cloned. This feels wrong?
And we're done, and it's not clear what the right behavior was.
Note that if variable2 didn' need to suspend (say that long path existed),
then variable1 is immedately read when setting variable2's defaultValue, and so
the setVariable for variable1 should be an SDE.
So it seems we could get two different behaviors depending if defaultValue
suspends or not, and it's not immediately clear to me what the right behavior
is. Hopefully I'm missing something?
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