From cf1670f9a6541e42f22d58e2de5940e64cb6637e Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Fri, 15 May 2020 06:50:05 +0200
Subject: Implement ad hoc recipe sharing and locking

---
 libbuild2/rule.hxx | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

(limited to 'libbuild2/rule.hxx')

diff --git a/libbuild2/rule.hxx b/libbuild2/rule.hxx
index ca17f2e..79747d5 100644
--- a/libbuild2/rule.hxx
+++ b/libbuild2/rule.hxx
@@ -22,7 +22,7 @@ namespace build2
   //
   // Note: match() is only called once but may not be followed by apply().
   //
-  class rule
+  class LIBBUILD2_SYMEXPORT rule
   {
   public:
     virtual bool
@@ -33,6 +33,9 @@ namespace build2
 
     rule () = default;
 
+    virtual
+    ~rule ();
+
     rule (const rule&) = delete;
     rule& operator= (const rule&) = delete;
   };
@@ -216,11 +219,17 @@ namespace build2
     dump (ostream&, const string&) const override;
 
     adhoc_cxx_rule (string c, const location& l, size_t b)
-      : adhoc_rule (l, b), code (move (c)) {}
+      : adhoc_rule (l, b), code (move (c)), impl (nullptr) {}
+
+    virtual
+    ~adhoc_cxx_rule () override;
 
   public:
-    string                       code;
-    mutable unique_ptr<cxx_rule> impl;
+    // Note that this recipe (rule instance) can be shared between multiple
+    // targets which could all be matched in parallel.
+    //
+    const string              code;
+    mutable atomic<cxx_rule*> impl;
   };
 }
 
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