node cache: expire nodes on destructions

Expiring nodes on cache destruction allow to cancel
any remaining request before the dht instance is destructed,
since Node instances might remain alive after the dht instance
is destroyed.

include/opendht/node_cache.h

@@ -37,12 +37,15 @@ struct NodeCache {
      */
     void clearBadNodes(sa_family_t family = 0);
 
+    ~NodeCache();
+
 private:
     class NodeMap : public std::map<InfoHash, std::weak_ptr<Node>> {
     public:
         Sp<Node> getNode(const InfoHash& id);
         Sp<Node> getNode(const InfoHash& id, const SockAddr&, time_point now, bool confirmed, bool client);
         void clearBadNodes();
+        void setExpired();
     };
 
     const NodeMap& cache(sa_family_t af) const { return af == AF_INET ? cache_4 : cache_6; }

src/node_cache.cpp

@@ -20,6 +20,12 @@
 
 namespace dht {
 
+NodeCache::~NodeCache()
+{
+    cache_4.setExpired();
+    cache_6.setExpired();
+}
+
 Sp<Node>
 NodeCache::getNode(const InfoHash& id, sa_family_t family) {
     return cache(family).getNode(id);
@@ -116,4 +122,12 @@ NodeCache::NodeMap::clearBadNodes() {
     }
 }
 
+void
+NodeCache::NodeMap::setExpired() {
+    for (auto& wn : *this)
+        if (auto n = wn.second.lock())
+            n->setExpired();
+    clear();
+}
+
 }