From c4e1a6a2d87522f6e8a3b87815e033b64c3ceda9 Mon Sep 17 00:00:00 2001
From: Kevin Wan <wanjunfeng@gmail.com>
Date: Sat, 1 Feb 2025 00:12:37 +0800
Subject: [PATCH] chore: refactor mapreduce (#4619)

---
 core/mr/mapreduce.go | 166 +++++++++++++++++++++----------------------
 1 file changed, 83 insertions(+), 83 deletions(-)

diff --git a/core/mr/mapreduce.go b/core/mr/mapreduce.go
index a56a82fec..30352441e 100644
--- a/core/mr/mapreduce.go
+++ b/core/mr/mapreduce.go
@@ -142,89 +142,6 @@ func MapReduceChan[T, U, V any](source <-chan T, mapper MapperFunc[T, U], reduce
 	return mapReduceWithPanicChan(source, panicChan, mapper, reducer, opts...)
 }
 
-// mapReduceWithPanicChan maps all elements from source, and reduce the output elements with given reducer.
-func mapReduceWithPanicChan[T, U, V any](source <-chan T, panicChan *onceChan, mapper MapperFunc[T, U],
-	reducer ReducerFunc[U, V], opts ...Option) (val V, err error) {
-	options := buildOptions(opts...)
-	// output is used to write the final result
-	output := make(chan V)
-	defer func() {
-		// reducer can only write once, if more, panic
-		for range output {
-			panic("more than one element written in reducer")
-		}
-	}()
-
-	// collector is used to collect data from mapper, and consume in reducer
-	collector := make(chan U, options.workers)
-	// if done is closed, all mappers and reducer should stop processing
-	done := make(chan struct{})
-	writer := newGuardedWriter(options.ctx, output, done)
-	var closeOnce sync.Once
-	// use atomic type to avoid data race
-	var retErr errorx.AtomicError
-	finish := func() {
-		closeOnce.Do(func() {
-			close(done)
-			close(output)
-		})
-	}
-	cancel := once(func(err error) {
-		if err != nil {
-			retErr.Set(err)
-		} else {
-			retErr.Set(ErrCancelWithNil)
-		}
-
-		drain(source)
-		finish()
-	})
-
-	go func() {
-		defer func() {
-			drain(collector)
-			if r := recover(); r != nil {
-				panicChan.write(r)
-			}
-			finish()
-		}()
-
-		reducer(collector, writer, cancel)
-	}()
-
-	go executeMappers(mapperContext[T, U]{
-		ctx: options.ctx,
-		mapper: func(item T, w Writer[U]) {
-			mapper(item, w, cancel)
-		},
-		source:    source,
-		panicChan: panicChan,
-		collector: collector,
-		doneChan:  done,
-		workers:   options.workers,
-	})
-
-	select {
-	case <-options.ctx.Done():
-		cancel(context.DeadlineExceeded)
-		err = context.DeadlineExceeded
-	case v := <-panicChan.channel:
-		// drain output here, otherwise for loop panic in defer
-		drain(output)
-		panic(v)
-	case v, ok := <-output:
-		if e := retErr.Load(); e != nil {
-			err = e
-		} else if ok {
-			val = v
-		} else {
-			err = ErrReduceNoOutput
-		}
-	}
-
-	return
-}
-
 // MapReduceVoid maps all elements generated from given generate,
 // and reduce the output elements with given reducer.
 func MapReduceVoid[T, U any](generate GenerateFunc[T], mapper MapperFunc[T, U],
@@ -330,6 +247,89 @@ func executeMappers[T, U any](mCtx mapperContext[T, U]) {
 	}
 }
 
+// mapReduceWithPanicChan maps all elements from source, and reduce the output elements with given reducer.
+func mapReduceWithPanicChan[T, U, V any](source <-chan T, panicChan *onceChan, mapper MapperFunc[T, U],
+	reducer ReducerFunc[U, V], opts ...Option) (val V, err error) {
+	options := buildOptions(opts...)
+	// output is used to write the final result
+	output := make(chan V)
+	defer func() {
+		// reducer can only write once, if more, panic
+		for range output {
+			panic("more than one element written in reducer")
+		}
+	}()
+
+	// collector is used to collect data from mapper, and consume in reducer
+	collector := make(chan U, options.workers)
+	// if done is closed, all mappers and reducer should stop processing
+	done := make(chan struct{})
+	writer := newGuardedWriter(options.ctx, output, done)
+	var closeOnce sync.Once
+	// use atomic type to avoid data race
+	var retErr errorx.AtomicError
+	finish := func() {
+		closeOnce.Do(func() {
+			close(done)
+			close(output)
+		})
+	}
+	cancel := once(func(err error) {
+		if err != nil {
+			retErr.Set(err)
+		} else {
+			retErr.Set(ErrCancelWithNil)
+		}
+
+		drain(source)
+		finish()
+	})
+
+	go func() {
+		defer func() {
+			drain(collector)
+			if r := recover(); r != nil {
+				panicChan.write(r)
+			}
+			finish()
+		}()
+
+		reducer(collector, writer, cancel)
+	}()
+
+	go executeMappers(mapperContext[T, U]{
+		ctx: options.ctx,
+		mapper: func(item T, w Writer[U]) {
+			mapper(item, w, cancel)
+		},
+		source:    source,
+		panicChan: panicChan,
+		collector: collector,
+		doneChan:  done,
+		workers:   options.workers,
+	})
+
+	select {
+	case <-options.ctx.Done():
+		cancel(context.DeadlineExceeded)
+		err = context.DeadlineExceeded
+	case v := <-panicChan.channel:
+		// drain output here, otherwise for loop panic in defer
+		drain(output)
+		panic(v)
+	case v, ok := <-output:
+		if e := retErr.Load(); e != nil {
+			err = e
+		} else if ok {
+			val = v
+		} else {
+			err = ErrReduceNoOutput
+		}
+	}
+
+	return
+}
+
 func newOptions() *mapReduceOptions {
 	return &mapReduceOptions{
 		ctx:     context.Background(),