merge revision(s) b3d62a77d928eff01268ca7fa1c1c0966702926d: [Backport #17803]

	[ruby/zlib] Synchronize access to zstream to prevent segfault in
	 multithreaded use

	I'm not sure whether this handles all multithreaded use cases,
	but this handles the example that crashes almost immediately
	and does 10,000,000 total deflates using 100 separate threads.

	To prevent the tests from taking forever, the committed test
	for this uses only 10,000 deflates across 10 separate threads,
	which still causes a segfault in the previous implementation
	almost immediately.

	Fixes [Bug #17803]

	https://github.com/ruby/zlib/commit/4b1023b3f2
	---
	 ext/zlib/zlib.c        | 33 ++++++++++++++++++++++++++-
	 test/zlib/test_zlib.rb | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++
	 2 files changed, 93 insertions(+), 1 deletion(-)

1 files changed, 61 insertions, 0 deletions

diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index a51a00d329..a5fc9056c8 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -4,6 +4,7 @@ require 'test/unit'
 require 'stringio'
 require 'tempfile'
 require 'tmpdir'
+require 'securerandom'
 
 begin
   require 'zlib'
@@ -503,6 +504,66 @@ if defined? Zlib
       assert_raise(Zlib::StreamError) { z.set_dictionary("foo") }
       z.close
     end
+
+    def test_multithread_deflate
+      zd = Zlib::Deflate.new
+
+      s = "x" * 10000
+      (0...10).map do |x|
+        Thread.new do
+          1000.times { zd.deflate(s) }
+        end
+      end.each do |th|
+        th.join
+      end
+    ensure
+      zd&.finish
+      zd&.close
+    end
+
+    def test_multithread_inflate
+      zi = Zlib::Inflate.new
+
+      s = Zlib.deflate("x" * 10000)
+      (0...10).map do |x|
+        Thread.new do
+          1000.times { zi.inflate(s) }
+        end
+      end.each do |th|
+        th.join
+      end
+    ensure
+      zi&.finish
+      zi&.close
+    end
+
+    def test_recursive_deflate
+      zd = Zlib::Deflate.new
+
+      s = SecureRandom.random_bytes(1024**2)
+      assert_raise(Zlib::BufError) do
+        zd.deflate(s) do
+          zd.deflate(s)
+        end
+      end
+    ensure
+      zd&.finish
+      zd&.close
+    end
+
+    def test_recursive_inflate
+      zi = Zlib::Inflate.new
+
+      s = Zlib.deflate(SecureRandom.random_bytes(1024**2))
+
+      assert_raise(Zlib::DataError) do
+        zi.inflate(s) do
+          zi.inflate(s)
+        end
+      end
+    ensure
+      zi&.close
+    end
   end
 
   class TestZlibGzipFile < Test::Unit::TestCase