From d9785635233d94e7a25297584637560605c41c6d Mon Sep 17 00:00:00 2001
From: Kevin Wan <wanjunfeng@gmail.com>
Date: Sat, 27 Aug 2022 22:47:25 +0800
Subject: [PATCH] fix: more accurate panic message on mapreduce (#2311)

---
 core/mr/mapreduce.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/core/mr/mapreduce.go b/core/mr/mapreduce.go
index 5e78e846..1734f7ce 100644
--- a/core/mr/mapreduce.go
+++ b/core/mr/mapreduce.go
@@ -212,6 +212,8 @@ func mapReduceWithPanicChan(source <-chan interface{}, panicChan *onceChan, mapp
 		cancel(context.DeadlineExceeded)
 		return nil, context.DeadlineExceeded
 	case v := <-panicChan.channel:
+		// drain output here, otherwise for loop panic in defer
+		drain(output)
 		panic(v)
 	case v, ok := <-output:
 		if err := retErr.Load(); err != nil {