init: add runtime initialisation cookie

CMakeLists.txt

@@ -407,6 +407,8 @@ list (
     hash/wang.hpp
     hash/xxhash.cpp
     hash/xxhash.hpp
+    init.cpp
+    init.hpp
     introspection.cpp
     introspection.hpp
     io.cpp

init.cpp

@@ -0,0 +1,65 @@
+/******************************************************************************
+                              _       _
+                             | |     | |
+                             | | ___ | |__   ___
+                             | |/ _ \| '_ \ / _ \
+                             | | (_) | |_) | (_) |
+                             |_|\___/|_.__/ \___/
+    Copyright:
+        Danny Robson, 2020
+ *****************************************************************************/
+
+#include "init.hpp"
+
+#include "log.hpp"
+
+#include <atomic>
+#include <memory>
+
+using cruft::init::cookie;
+
+
+///////////////////////////////////////////////////////////////////////////////
+namespace {
+    // Stores the various RAII handlers for any registered functionality that
+    // requires it.
+    struct state {
+        state ()
+            : log (cruft::log::setup_level_reflection ())
+        { ; }
+
+        cruft::parse::enumeration::cookie log;
+    };
+
+    std::unique_ptr<state> s_state;
+    std::atomic<int> s_count;
+}
+
+
+//-----------------------------------------------------------------------------
+// Increase the reference count and initialising the requisite functionality if
+// this is the first instance of the class.
+static void up (void)
+{
+    if (int old = s_count++; !old)
+        s_state = std::make_unique<state> ();
+}
+
+
+//-----------------------------------------------------------------------------
+// Decrease the reference count and release any resources if this was the last
+// instance of the class.
+static void down (void)
+{
+    if (int old = --s_count; !old)
+        s_state.reset ();
+}
+
+
+///////////////////////////////////////////////////////////////////////////////
+cookie::cookie () { up (); }
+cookie::cookie (cookie &&) noexcept { up (); }
+cookie::cookie (cookie const&) { up (); }
+cookie& cookie::operator= (cookie &&) noexcept { up (); return *this; }
+cookie& cookie::operator= (cookie const&) { up (); return *this; }
+cookie::~cookie () { down (); }

init.hpp

@@ -0,0 +1,33 @@
+/******************************************************************************
+                              _       _
+                             | |     | |
+                             | | ___ | |__   ___
+                             | |/ _ \| '_ \ / _ \
+                             | | (_) | |_) | (_) |
+                             |_|\___/|_.__/ \___/
+    Copyright:
+        Danny Robson, 2020
+ *****************************************************************************/
+
+#pragma once
+
+
+namespace cruft::init {
+    /// An object that ensures functionality that requires runtime
+    /// registration has been setup, and clears these resources at destruction
+    /// time.
+    ///
+    /// Do not operate on instances of this class at the same time across
+    /// multiple threads. (It is safe to do so if access is has been locked)
+    ///
+    /// In particular, this class ensures that:
+    ///    * log::level_t has been registered for reflection
+    struct cookie {
+        cookie ();
+        cookie (cookie const&);
+        cookie& operator= (cookie const&);
+        cookie (cookie &&) noexcept;
+        cookie& operator= (cookie &&) noexcept;
+        ~cookie ();
+    };
+}