From 7348653ff4fc4e9b2dc24943aabdb57179b1c75a Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 3 Sep 2019 12:51:35 +0200
Subject: Ensure that Callback is called only once

Also, make Callback movable but uncopyable.
---
 src/libstore/binary-cache-store.cc | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

(limited to 'src/libstore/binary-cache-store.cc')

diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 4527ee6ba660..e56be625de47 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -249,21 +249,23 @@ void BinaryCacheStore::queryPathInfoUncached(const Path & storePath,
 
     auto narInfoFile = narInfoFileFor(storePath);
 
+    auto callbackPtr = std::make_shared<decltype(callback)>(std::move(callback));
+
     getFile(narInfoFile,
         {[=](std::future<std::shared_ptr<std::string>> fut) {
             try {
                 auto data = fut.get();
 
-                if (!data) return callback(nullptr);
+                if (!data) return (*callbackPtr)(nullptr);
 
                 stats.narInfoRead++;
 
-                callback((std::shared_ptr<ValidPathInfo>)
+                (*callbackPtr)((std::shared_ptr<ValidPathInfo>)
                     std::make_shared<NarInfo>(*this, *data, narInfoFile));
 
                 (void) act; // force Activity into this lambda to ensure it stays alive
             } catch (...) {
-                callback.rethrow();
+                callbackPtr->rethrow();
             }
         }});
 }
-- 
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