net_processing: indicate more work to do when orphans are ready to reconsider

When PR#15644 made orphan processing interruptible, it also introduced a
potential 100ms delay between processing of the first and second newly
reconsiderable orphan, because it didn't check if the orphan work set
was non-empty after invoking ProcessMessage(). This adds that check, so
that ProcessMessages() will return true if there are orphans to process,
usually avoiding the 100ms delay in CConnman::ThreadMessageHandler().

src/net_processing.cpp

@@ -4902,6 +4902,12 @@ bool PeerManagerImpl::ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt
             LOCK(peer->m_getdata_requests_mutex);
             if (!peer->m_getdata_requests.empty()) fMoreWork = true;
         }
+        // Does this peer has an orphan ready to reconsider?
+        // (Note: we may have provided a parent for an orphan provided
+        //  by another peer that was already processed; in that case,
+        //  the extra work may not be noticed, possibly resulting in an
+        //  unnecessary 100ms delay)
+        if (m_orphanage.HaveTxToReconsider(peer->m_id)) fMoreWork = true;
     } catch (const std::exception& e) {
         LogPrint(BCLog::NET, "%s(%s, %u bytes): Exception '%s' (%s) caught\n", __func__, SanitizeString(msg.m_type), msg.m_message_size, e.what(), typeid(e).name());
     } catch (...) {

src/txorphanage.cpp

@@ -194,6 +194,18 @@ CTransactionRef TxOrphanage::GetTxToReconsider(NodeId peer)
     return nullptr;
 }
 
+bool TxOrphanage::HaveTxToReconsider(NodeId peer)
+{
+    LOCK(m_mutex);
+
+    auto work_set_it = m_peer_work_set.find(peer);
+    if (work_set_it != m_peer_work_set.end()) {
+        auto& work_set = work_set_it->second;
+        return !work_set.empty();
+    }
+    return false;
+}
+
 void TxOrphanage::EraseForBlock(const CBlock& block)
 {
     LOCK(m_mutex);

src/txorphanage.h

@@ -48,6 +48,9 @@ public:
     /** Add any orphans that list a particular tx as a parent into the from peer's work set */
     void AddChildrenToWorkSet(const CTransaction& tx) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);;
 
+    /** Does this peer have any work to do? */
+    bool HaveTxToReconsider(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);;
+
     /** Return how many entries exist in the orphange */
     size_t Size() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
     {