Apply suggestions from code review

Co-authored-by: Mads R. B. Kristensen <madsbk@gmail.com>

Author: nirandaperera

cpp/include/rapidsmpf/shuffler/finish_counter.hpp

@@ -53,16 +53,6 @@ class FinishCounter {
      * `wait*` methods. And be very careful if acquiring locks. Ideally it should be used
      * to signal a separate thread to do the actual processing (eg. WaitHand).
      *
-     * @note When a callback is registered, it will be identified by the
-     * FinishedCbId returned. So, if a callback needs to be preemptively canceled,
-     * the corresponding identifier needs to be provided.
-     *
-     * @note Every callback will be called as and when each partition is finished. If
-     * there were finished partitions before the callback was registered, the callback
-     * will be called for them immediately by the caller thread. Else, the callback will
-     * be called by the progress thread (Therefore, it will be called
-     * `n_local_partitions_` times in total).
-     *
      * @note Caller needs to be careful when using both callbacks and wait* methods
      * together.
      */

cpp/src/shuffler/finish_counter.cpp

@@ -92,6 +92,7 @@ FinishCounter::FinishCounter(
 )
     : nranks_{nranks},
       finished_callback_{std::forward<FinishedCallback>(finished_callback)} {
+    // Initially, none of the partitions are ready to wait on.
     goalposts_.reserve(local_partitions.size());
     for (auto pid : local_partitions) {
         goalposts_.emplace(pid, PartitionInfo{});