From 08eaf7c5fab7b43f5ff1bbfd4ce1696a30ed802c Mon Sep 17 00:00:00 2001
From: Alan Wu <XrXr@users.noreply.github.com>
Date: Tue, 21 Mar 2023 18:16:33 -0400
Subject: [PATCH] YJIT: Fix deadlock in tests due to pipe capacity

Previously, when there is enough stats that the child process fills up
the pipe capacity, the child process would block, with the parent
process waiting forever as no one is reading to clear up the pipe. The
test timed out in these situations.

Use a separate thread in the parent to read from the pipe to unblock the
child in these situation. EnvUtil also does this for handling stdout and
stderr.

I had the test suite deadlock on a Linux VM.
---
 test/ruby/test_yjit.rb | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/test/ruby/test_yjit.rb b/test/ruby/test_yjit.rb
index 3d354bfc6c..703313f4ab 100644
--- a/test/ruby/test_yjit.rb
+++ b/test/ruby/test_yjit.rb
@@ -1336,13 +1336,24 @@ class TestYJIT < Test::Unit::TestCase
     args << "--yjit-exec-mem-size=#{mem_size}" if mem_size
     args << "-e" << script_shell_encode(script)
     stats_r, stats_w = IO.pipe
+    # Separate thread so we don't deadlock when
+    # the child ruby blocks writing the stats to fd 3
+    stats = ''
+    stats_reader = Thread.new do
+      stats = stats_r.read
+      stats_r.close
+    end
     out, err, status = EnvUtil.invoke_ruby(args,
       '', true, true, timeout: timeout, ios: {3 => stats_w}
     )
     stats_w.close
-    stats = stats_r.read
+    stats_reader.join(timeout)
     stats = Marshal.load(stats) if !stats.empty?
-    stats_r.close
     [status, out, err, stats]
+  ensure
+    stats_reader&.kill
+    stats_reader&.join(timeout)
+    stats_r&.close
+    stats_w&.close
   end
 end