1 files changed, 69 insertions, 0 deletions
diff --git a/include/internal/rio_notifier.h b/include/internal/rio_notifier.h
new file mode 100644
index 000000000000..ec2035714f75
--- /dev/null
+++ b/include/internal/rio_notifier.h
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2024-2025 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+#ifndef OSSL_RIO_NOTIFIER_H
+# define OSSL_RIO_NOTIFIER_H
+
+# include "internal/common.h"
+# include "internal/sockets.h"
+
+/*
+ * Pollable Notifier
+ * =================
+ *
+ * RIO_NOTIFIER provides an OS-pollable resource which can be plugged into an
+ * OS's socket polling APIs to allow socket polling calls to be woken
+ * artificially by other threads.
+ */
+# define RIO_NOTIFIER_METHOD_SOCKET      1
+# define RIO_NOTIFIER_METHOD_SOCKETPAIR  2
+
+# if !defined(RIO_NOTIFIER_METHOD)
+#  if defined(OPENSSL_SYS_WINDOWS)
+#   define RIO_NOTIFIER_METHOD          RIO_NOTIFIER_METHOD_SOCKET
+#  elif defined(OPENSSL_SYS_UNIX)
+#   define RIO_NOTIFIER_METHOD          RIO_NOTIFIER_METHOD_SOCKETPAIR
+#  else
+#   define RIO_NOTIFIER_METHOD          RIO_NOTIFIER_METHOD_SOCKET
+#  endif
+# endif
+
+typedef struct rio_notifier_st {
+    int rfd, wfd;
+} RIO_NOTIFIER;
+
+/*
+ * Initialises a RIO_NOTIFIER. Returns 1 on success or 0 on failure.
+ */
+int ossl_rio_notifier_init(RIO_NOTIFIER *nfy);
+
+/*
+ * Cleans up a RIO_NOTIFIER, tearing down any allocated resources.
+ */
+void ossl_rio_notifier_cleanup(RIO_NOTIFIER *nfy);
+
+/*
+ * Signals a RIO_NOTIFIER, waking up any waiting threads.
+ */
+int ossl_rio_notifier_signal(RIO_NOTIFIER *nfy);
+
+/*
+ * Unsignals a RIO_NOTIFIER.
+ */
+int ossl_rio_notifier_unsignal(RIO_NOTIFIER *nfy);
+
+/*
+ * Returns an OS socket handle (FD or Win32 SOCKET) which can be polled for
+ * readability to determine when the notifier has been signalled.
+ */
+static ossl_inline ossl_unused int ossl_rio_notifier_as_fd(RIO_NOTIFIER *nfy)
+{
+    return nfy->rfd;
+}
+
+#endif