IO::Buffer#locked: Release lock even when the block raises (ruby#16180)

IO::Buffer#locked: Release lock even when the block raises/breaks

Previously, `IO::Buffer#locked` leaks the lock when the block raises
an exception, or breaks.

Fixes: [Bug #21882]

Author: Kasumi Hanazuki

io_buffer.c

@@ -1424,6 +1424,17 @@ rb_io_buffer_try_unlock(VALUE self)
     return 0;
 }
 
+static VALUE
+rb_io_buffer_locked_ensure(VALUE self)
+{
+    struct rb_io_buffer *buffer = NULL;
+    TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, buffer);
+
+    buffer->flags &= ~RB_IO_BUFFER_LOCKED;
+
+    return Qnil;
+}
+
 /*
  *  call-seq: locked { ... }
  *
@@ -1466,11 +1477,7 @@ rb_io_buffer_locked(VALUE self)
 
     buffer->flags |= RB_IO_BUFFER_LOCKED;
 
-    VALUE result = rb_yield(self);
-
-    buffer->flags &= ~RB_IO_BUFFER_LOCKED;
-
-    return result;
+    return rb_ensure(rb_yield, self, rb_io_buffer_locked_ensure, self);
 }
 
 /*

test/ruby/test_io_buffer.rb

@@ -930,4 +930,34 @@ def test_integer_endianness_swapping
       assert_equal value, round_trip_value, "#{le_type}/#{be_type}: double-swap should restore original value"
     end
   end
+
+  class Bug21882 < RuntimeError; end
+  def test_locked_exception
+    buf = IO::Buffer.new(10)
+    assert_raise(Bug21882, '#locked should propagate exception') do
+      buf.locked { raise Bug21882 }
+    end
+
+    # should be unlocked now and can be locked again
+    refute_predicate buf, :locked?
+    buf.locked { }
+  end
+
+  def test_locked_break
+    buf = IO::Buffer.new(10)
+    assert_equal :ok, (buf.locked { break :ok })
+
+    # should be unlocked now and can be locked again
+    refute_predicate buf, :locked?
+    buf.locked { }
+  end
+
+  def test_locked_throw
+    buf = IO::Buffer.new(10)
+    assert_equal :ok, (catch(:bug21882) { buf.locked { throw :bug21882, :ok } })
+
+    # should be unlocked now and can be locked again
+    refute_predicate buf, :locked?
+    buf.locked { }
+  end
 end