From ad0a1df23aeab46def7bdbdc994465ff9e4988c9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Carl=20Ho=CC=88rberg?= <carl.hoerberg@gmail.com>
Date: Wed, 28 Mar 2018 12:59:27 +0200
Subject: [PATCH] Enqueue senders in Channel#close

Fixes #5875
---
 spec/std/channel_spec.cr  | 23 +++++++++++++++++++++++
 src/concurrent/channel.cr | 11 +++++++++++
 2 files changed, 34 insertions(+)

diff --git a/spec/std/channel_spec.cr b/spec/std/channel_spec.cr
index c13571aec30e..c68cf19dbdff 100644
--- a/spec/std/channel_spec.cr
+++ b/spec/std/channel_spec.cr
@@ -137,6 +137,29 @@ describe Channel::Unbuffered do
     spawn { ch.send 123 }
     ch.receive?.should eq(123)
   end
+
+  it "wakes up the sender fiber when channel is closed" do
+    ch = Channel::Unbuffered(Nil).new
+    sender_closed = false
+    spawn do
+      ch.send nil
+      ch.send nil
+    rescue Channel::ClosedError
+      sender_closed = true
+    end
+    receiver_closed = false
+    spawn do
+      Fiber.yield
+      ch.receive
+    rescue Channel::ClosedError
+      receiver_closed = true
+    end
+    Fiber.yield
+    ch.close
+    Fiber.yield
+    sender_closed.should be_true
+    receiver_closed.should be_true
+  end
 end
 
 describe Channel::Buffered do
diff --git a/src/concurrent/channel.cr b/src/concurrent/channel.cr
index c3eb1ccfb347..7e5c20857586 100644
--- a/src/concurrent/channel.cr
+++ b/src/concurrent/channel.cr
@@ -30,6 +30,8 @@ abstract class Channel(T)
 
   def close
     @closed = true
+    Scheduler.enqueue @senders
+    @senders.clear
     Scheduler.enqueue @receivers
     @receivers.clear
     nil
@@ -259,6 +261,7 @@ class Channel::Unbuffered(T) < Channel(T)
     @value.tap do
       @has_value = false
       Scheduler.enqueue @sender.not_nil!
+      @sender = nil
     end
   end
 
@@ -269,4 +272,12 @@ class Channel::Unbuffered(T) < Channel(T)
   def full?
     @has_value || @receivers.empty?
   end
+
+  def close
+    super
+    if sender = @sender
+      Scheduler.enqueue sender
+      @sender = nil
+    end
+  end
 end