Unlink shutdown callback from ref count (#1166)

Co-authored-by: Bret Ambrose <bambrose@amazon.com>

include/aws/common/ref_count.h

@@ -8,11 +8,10 @@
 #include <aws/common/common.h>
 
 #include <aws/common/atomics.h>
+#include <aws/common/shutdown_types.h>
 
 AWS_PUSH_SANE_WARNING_LEVEL
 
-typedef void(aws_simple_completion_callback)(void *);
-
 /*
  * A utility type for making ref-counted types, reminiscent of std::shared_ptr in C++
  */
@@ -22,11 +21,6 @@ struct aws_ref_count {
     aws_simple_completion_callback *on_zero_fn;
 };
 
-struct aws_shutdown_callback_options {
-    aws_simple_completion_callback *shutdown_callback_fn;
-    void *shutdown_callback_user_data;
-};
-
 AWS_EXTERN_C_BEGIN
 
 /**

include/aws/common/shutdown_types.h

@@ -0,0 +1,34 @@
+#ifndef AWS_COMMON_SHUTDOWN_TYPES_H
+#define AWS_COMMON_SHUTDOWN_TYPES_H
+
+/**
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0.
+ */
+
+#include <aws/common/common.h>
+
+AWS_PUSH_SANE_WARNING_LEVEL
+
+typedef void(aws_simple_completion_callback)(void *);
+
+/**
+ * Configuration for a callback to invoke when something has been completely
+ * cleaned up.  Primarily used in async cleanup control flows.
+ */
+struct aws_shutdown_callback_options {
+
+    /**
+     * Function to invoke when the associated object is fully destroyed.
+     */
+    aws_simple_completion_callback *shutdown_callback_fn;
+
+    /**
+     * User data to invoke the shutdown callback with.
+     */
+    void *shutdown_callback_user_data;
+};
+
+AWS_POP_SANE_WARNING_LEVEL
+
+#endif /* AWS_COMMON_SHUTDOWN_TYPES_H */