From 582940c789fd767d9e8c09cb4147d48b596261be Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Sat, 24 Nov 2018 14:43:25 +0200
Subject: Add support for cancellation to make_guard()

---
 libbutl/utility.mxx | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/libbutl/utility.mxx b/libbutl/utility.mxx
index 5d093ad..7fb4173 100644
--- a/libbutl/utility.mxx
+++ b/libbutl/utility.mxx
@@ -293,6 +293,13 @@ LIBBUTL_MODEXPORT namespace butl
   inline reverse_range<T>
   reverse_iterate (T&& x) {return reverse_range<T> (std::forward<T> (x));}
 
+  // Cleanly cast between incompatible function types or dlsym() result
+  // (void*) to a function pointer.
+  //
+  template <typename F, typename P>
+  F
+  function_cast (P*);
+
   // Call a function on destruction.
   //
   template <typename F>
@@ -308,19 +315,15 @@ LIBBUTL_MODEXPORT namespace butl
   template <typename F>
   struct guard_impl
   {
-    guard_impl (F f): f_ (std::move (f)) {}
-    ~guard_impl () {f_ ();}
+    guard_impl (F f): function (std::move (f)), active (true) {}
+    ~guard_impl () {if (active) function ();}
 
-  private:
-    F f_;
-  };
+    void
+    cancel () {active = false;}
 
-  // Cleanly cast between incompatible function types or dlsym() result
-  // (void*) to a function pointer.
-  //
-  template <typename F, typename P>
-  F
-  function_cast (P*);
+    F function;
+    bool active;
+  };
 
   // Call a function if there is an exception.
   //
-- 
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