Fix a bug in Topology path GC and make it more efficient.

core/Node.cpp

@@ -211,15 +211,16 @@ ZT_ResultCode Node::processBackgroundTasks(
 			try {
 				Vector< SharedPtr< Peer > > allPeers, rootPeers;
 				m_ctx.topology->allPeers(allPeers, rootPeers);
+				std::sort(rootPeers.begin(), rootPeers.end());
 
 				bool online = false;
 				for (Vector< SharedPtr< Peer > >::iterator p(allPeers.begin()); p != allPeers.end(); ++p) {
-					const bool isRoot = std::find(rootPeers.begin(), rootPeers.end(), *p) != rootPeers.end();
+					const bool isRoot = std::binary_search(rootPeers.begin(), rootPeers.end(), *p);
 					(*p)->pulse(m_ctx, cc, isRoot);
 					online |= ((isRoot || rootPeers.empty()) && (*p)->directlyConnected(cc));
 				}
 
-				if (m_online.exchange(online) != online)
+				if (m_online.exchange(online, std::memory_order_relaxed) != online)
 					postEvent(cc.tPtr, online ? ZT_EVENT_ONLINE : ZT_EVENT_OFFLINE);
 
 				ZT_SPEW("ranking roots...");
@@ -346,9 +347,9 @@ struct p_ZT_PeerListPrivate : public ZT_PeerList
 {
 	// Actual containers for the memory, hidden from external users.
 	Vector< ZT_Peer > p_peers;
-	List< Vector< ZT_Path > > p_paths;
-	List< Identity > p_identities;
-	List< Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX > > p_locators;
+	ForwardList< Vector< ZT_Path > > p_paths;
+	ForwardList< Identity > p_identities;
+	ForwardList< Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX > > p_locators;
 };
 
 static void p_peerListFreeFunction(const void *pl)
@@ -381,9 +382,9 @@ ZT_PeerList *Node::peers(const CallContext &cc) const
 			Peer &pp = **pi;
 
 			p.address = pp.address();
-			pl->p_identities.push_back(pp.identity());
-			p.identity = reinterpret_cast<const ZT_Identity *>(&(pl->p_identities.back()));
-			p.fingerprint = &(pl->p_identities.back().fingerprint());
+			pl->p_identities.push_front(pp.identity());
+			p.identity = reinterpret_cast<const ZT_Identity *>(&(pl->p_identities.front()));
+			p.fingerprint = &(pl->p_identities.front().fingerprint());
 			if (pp.remoteVersionKnown()) {
 				p.versionMajor = (int)pp.remoteVersionMajor();
 				p.versionMinor = (int)pp.remoteVersionMinor();
@@ -404,8 +405,8 @@ ZT_PeerList *Node::peers(const CallContext &cc) const
 			Vector< SharedPtr< Path > > ztPaths;
 			pp.getAllPaths(ztPaths);
 			if (ztPaths.empty()) {
-				pl->p_paths.push_back(Vector< ZT_Path >());
-				std::vector< ZT_Path > &apiPaths = pl->p_paths.back();
+				pl->p_paths.push_front(Vector< ZT_Path >());
+				std::vector< ZT_Path > &apiPaths = pl->p_paths.front();
 				apiPaths.resize(ztPaths.size());
 				for (unsigned long i = 0; i < (unsigned long)ztPaths.size(); ++i) {
 					SharedPtr< Path > &ztp = ztPaths[i];
@@ -426,8 +427,8 @@ ZT_PeerList *Node::peers(const CallContext &cc) const
 
 			const SharedPtr< const Locator > loc(pp.locator());
 			if (loc) {
-				pl->p_locators.push_back(Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX >());
-				Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX > &lb = pl->p_locators.back();
+				pl->p_locators.push_front(Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX >());
+				Blob< ZT_LOCATOR_MARSHAL_SIZE_MAX > &lb = pl->p_locators.front();
 				Utils::zero< ZT_LOCATOR_MARSHAL_SIZE_MAX >(lb.data);
 				const int ls = loc->marshal(lb.data);
 				if (ls > 0) {
@@ -611,8 +612,6 @@ void Node::setController(void *networkControllerInstance)
 		m_ctx.localNetworkController->init(m_ctx.identity, this);
 }
 
-// Methods used only within the core ----------------------------------------------------------------------------------
-
 bool Node::shouldUsePathForZeroTierTraffic(void *tPtr, const Identity &id, const int64_t localSocket, const InetAddress &remoteAddress)
 {
 	{

core/SharedPtr.hpp

@@ -116,20 +116,23 @@ public:
 	 * but with the caveat that it only works if there is only one remaining
 	 * SharedPtr to be treated as weak.
 	 *
-	 * @return True if object was in fact deleted OR this pointer was already NULL
+	 * This does not delete the object. It returns it as a naked pointer.
+	 *
+	 * @return Pointer to T if reference count was only one (this shared ptr is left NULL)
 	 */
-	ZT_INLINE bool weakGC()
+	ZT_INLINE T *weakGC()
 	{
 		if (likely(m_ptr != nullptr)) {
 			int one = 1;
-			if (const_cast<std::atomic< int > *>(&(m_ptr->__refCount))->compare_exchange_strong(one, (int)0, std::memory_order_acq_rel)) {
-				delete m_ptr;
+			if (const_cast<std::atomic< int > *>(&(m_ptr->__refCount))->compare_exchange_strong(one, (int)0)) {
+				T *const ptr = m_ptr;
 				m_ptr = nullptr;
-				return true;
+				return ptr;
+			} else {
+				return nullptr;
 			}
-			return false;
 		} else {
-			return true;
+			return nullptr;
 		}
 	}
 
@@ -141,7 +144,7 @@ public:
 	ZT_INLINE int references() noexcept
 	{
 		if (likely(m_ptr != nullptr))
-			return m_ptr->__refCount;
+			return m_ptr->__refCount.load(std::memory_order_relaxed);
 		return 0;
 	}
 

core/Topology.cpp

@@ -61,6 +61,7 @@ void Topology::doPeriodicTasks(const CallContext &cc)
 		for (Vector< SharedPtr< Peer > >::const_iterator r(m_roots.begin()); r != m_roots.end(); ++r)
 			rootLookup.push_back((uintptr_t)r->ptr());
 	}
+	std::sort(rootLookup.begin(), rootLookup.end());
 
 	// Cleaning of peers and paths uses a two pass method to avoid write locking
 	// m_peers or m_paths for any significant amount of time. This avoids pauses
@@ -71,7 +72,7 @@ void Topology::doPeriodicTasks(const CallContext &cc)
 			RWMutex::RLock l1(m_peers_l);
 			for (Map< Address, SharedPtr< Peer > >::iterator i(m_peers.begin()); i != m_peers.end(); ++i) {
 				// TODO: also delete if the peer has not exchanged meaningful communication in a while, such as a network frame or non-trivial control packet.
-				if (((cc.ticks - i->second->lastReceive()) > ZT_PEER_ALIVE_TIMEOUT) && (std::find(rootLookup.begin(), rootLookup.end(), (uintptr_t)(i->second.ptr())) == rootLookup.end()))
+				if (((cc.ticks - i->second->lastReceive()) > ZT_PEER_ALIVE_TIMEOUT) && (!std::binary_search(rootLookup.begin(), rootLookup.end(), reinterpret_cast<uintptr_t>(i->second.ptr()))))
 					toDelete.push_back(i->first);
 			}
 		}
@@ -93,28 +94,28 @@ void Topology::doPeriodicTasks(const CallContext &cc)
 		}
 	}
 
-	// Delete paths that are no longer held by anyone else ("weak reference" type behavior).
-	// First pass: make a list of paths with a reference count of 1 meaning they are likely
-	// orphaned. Second pass: call weakGC() on each of these which does a hard compare/exchange
-	// and delete those that actually are GC'd. Write lock is aquired only briefly on delete
-	// just as with peers.
 	{
-		Vector< Path::Key > possibleDelete;
+		Vector< Path * > toDelete;
 		{
-			RWMutex::RLock l1(m_paths_l);
-			for (Map< Path::Key, SharedPtr< Path > >::iterator i(m_paths.begin()); i != m_paths.end(); ++i) {
-				if (i->second.references() <= 1)
-					possibleDelete.push_back(i->first);
+			RWMutex::Lock l1(m_paths_l);
+			for (Map< Path::Key, SharedPtr< Path > >::iterator i(m_paths.begin()); i != m_paths.end();) {
+				Path *const d = i->second.weakGC();
+				if (likely(d == nullptr)) {
+					++i;
+				} else {
+					m_paths.erase(i++);
+					try {
+						toDelete.push_back(d);
+					} catch (...) {
+						delete d;
+					}
+				}
 			}
 		}
-		if (!possibleDelete.empty()) {
-			ZT_SPEW("garbage collecting (likely) %u orphaned paths", (unsigned int)possibleDelete.size());
-			for (Vector< Path::Key >::const_iterator i(possibleDelete.begin()); i != possibleDelete.end(); ++i) {
-				RWMutex::Lock l1(m_paths_l);
-				Map< Path::Key, SharedPtr< Path > >::iterator p(m_paths.find(*i));
-				if ((p != m_paths.end()) && p->second.weakGC())
-					m_paths.erase(p);
-			}
+		if (!toDelete.empty()) {
+			for (Vector< Path * >::iterator i(toDelete.begin()); i != toDelete.end(); ++i)
+				delete *i;
+			ZT_SPEW("garbage collected %u orphaned paths", (unsigned int)toDelete.size());
 		}
 	}
 }