Fix mq.notify = nil to unregister notifications

"mq.notify = false" also works now, doing what
"mq.notify = nil" used to do (using SIGEV_NONE).

I was confused by SIGEV_NONE usage vs using a NULL pointer for
the notification passed mq_notify(3).  SIGEV_NONE does not
actually unregister, it registers a no-op notification which
prevents other processes from taking us.

This also fixes the test case to pass under both Linux and
FreeBSD.

2 files changed, 31 insertions, 5 deletions

diff --git a/ext/posix_mq/posix_mq.c b/ext/posix_mq/posix_mq.c
index e64cac3..014927e 100644
--- a/ext/posix_mq/posix_mq.c
+++ b/ext/posix_mq/posix_mq.c
@@ -680,19 +680,32 @@ static int lookup_sig(VALUE sig)
  * to the current process when message is received.
  * If +signal+ is +nil+, it will unregister and disable the notification
  * request to allow other processes to register a request.
+ * If +signal+ is +false+, it will register a no-op notification request
+ * which will prevent other processes from registering a notification.
  * Only one process may have a notification request for a queue
  * at a time, Errno::EBUSY will be raised if there is already
  * a notification request registration for the queue.
+ *
+ * For readers of the mq_notify(3) manpage, passing +false+
+ * is equivalent to SIGEV_NONE, and passing +nil+ is equivalent
+ * of passing a NULL notification pointer to mq_notify(3).
  */
 static VALUE setnotify(VALUE self, VALUE arg)
 {
         struct posix_mq *mq = get(self, 1);
         struct sigevent not;
+        struct sigevent * notification = ¬
         VALUE rv = arg;
 
         not.sigev_notify = SIGEV_SIGNAL;
 
         switch (TYPE(arg)) {
+        case T_FALSE:
+                not.sigev_notify = SIGEV_NONE;
+                break;
+        case T_NIL:
+                notification = NULL;
+                break;
         case T_FIXNUM:
                 not.sigev_signo = NUM2INT(arg);
                 break;
@@ -701,15 +714,12 @@ static VALUE setnotify(VALUE self, VALUE arg)
                 not.sigev_signo = lookup_sig(arg);
                 rv = INT2NUM(not.sigev_signo);
                 break;
-        case T_NIL:
-                not.sigev_notify = SIGEV_NONE;
-                break;
         default:
                 /* maybe support Proc+thread via sigev_notify_function.. */
                 rb_raise(rb_eArgError, "must be a signal or nil");
         }
 
-        if (mq_notify(mq->des, &not) == MQD_INVALID)
+        if (mq_notify(mq->des, notification) == MQD_INVALID)
                 rb_sys_fail("mq_notify");
 
         return rv;
diff --git a/test/test_posix_mq.rb b/test/test_posix_mq.rb
index 00b0f5a..dccc547 100644
--- a/test/test_posix_mq.rb
+++ b/test/test_posix_mq.rb
@@ -136,11 +136,27 @@ class Test_POSIX_MQ < Test::Unit::TestCase
     assert_nil(@mq.notify = nil)
     assert_nothing_raised { @mq.send("hello", 0) }
     assert_nil IO.select([rd], nil, nil, 0.1)
-    assert_raises(Errno::EBUSY) { @mq.notify = :USR1 }
     ensure
       trap(:USR1, orig)
   end
 
+  def test_notify_none
+    @mq = POSIX_MQ.new @path, IO::CREAT|IO::RDWR, 0666
+    assert_nothing_raised { @mq.notify = false }
+    pid = fork do
+      begin
+        @mq.notify = :USR1
+      rescue Errno::EBUSY
+        exit 0
+      rescue => e
+        p e
+      end
+      exit! 1
+    end
+    _, status = Process.waitpid2(pid)
+    assert status.success?, status.inspect
+  end
+
   def test_setattr
     @mq = POSIX_MQ.new @path, IO::CREAT|IO::WRONLY, 0666
     mq_attr = POSIX_MQ::Attr.new(IO::NONBLOCK)