[GitHub] [beam] lukecwik commented on a diff in pull request #24025: [#24024] Stop wrapping light weight functions with Contextful as they add a lot of overhead for functions that are meant to do almost no work.

[GitBox]

lukecwik commented on code in PR #24025:
URL: https://github.com/apache/beam/pull/24025#discussion_r1035252492


##########
sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/FlatMapElements.java:
##########
@@ -137,57 +132,90 @@ public <NewInputT> FlatMapElements<NewInputT, OutputT> 
via(
   @Experimental(Kind.CONTEXTFUL)
   public <NewInputT> FlatMapElements<NewInputT, OutputT> via(
       Contextful<Fn<NewInputT, Iterable<OutputT>>> fn) {
-    return new FlatMapElements<>(
-        fn, fn.getClosure(), TypeDescriptors.inputOf(fn.getClosure()), 
outputType);
+    return new FlatMapElements<>(fn, TypeDescriptors.inputOf(fn.getClosure()), 
outputType);
   }
 
   @Override
   public PCollection<OutputT> expand(PCollection<? extends InputT> input) {
     checkArgument(fn != null, ".via() is required");
-    return input.apply(
-        "FlatMap",
-        ParDo.of(
-                new DoFn<InputT, OutputT>() {
-                  @ProcessElement
-                  public void processElement(ProcessContext c) throws 
Exception {
-                    Iterable<OutputT> res =
-                        fn.getClosure().apply(c.element(), 
Fn.Context.wrapProcessContext(c));
-                    for (OutputT output : res) {
-                      c.output(output);
+    if (fn instanceof Contextful) {

Review Comment:
   Also, I didn't want to wrap with another PTransform that delineated between 
these two options



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