sv2: optimistic send for hot paths

Expose TryOptimisticSend so TemplateProvider can flush send queues
immediately after queuing responses and work updates. This reduces the
latency for frequent message flows while leaving the infrequent
connection-setup messages untouched.

Assisted-by: GitHub Copilot
Assisted-by: OpenAI GPT-5-Codex

Author: Sjors

src/sv2/connman.cpp

@@ -174,6 +174,12 @@ std::pair<size_t, bool> Sv2Connman::SendMessagesAsBytes(Sv2Client& client)
     return {total_sent, expected_more.value_or(false)};
 }
 
+void Sv2Connman::TryOptimisticSend(Sv2Client& client)
+{
+    AssertLockHeld(client.cs_send);
+    SendMessagesAsBytes(client);
+}
+
 void Sv2Connman::EventReadyToSend(NodeId node_id, bool& cancel_recv)
 {
     AssertLockNotHeld(m_clients_mutex);

src/sv2/connman.h

@@ -216,6 +216,13 @@ class Sv2Connman : SockMan
      */
     void ProcessSv2Message(const node::Sv2NetMsg& sv2_header, Sv2Client& client);
 
+    /**
+     * Attempt to flush the send queue immediately, without waiting for the
+     * socket layer to signal readiness. Falls back to the regular send path if
+     * the socket would block.
+     */
+    void TryOptimisticSend(Sv2Client& client) EXCLUSIVE_LOCKS_REQUIRED(client.cs_send);
+
     std::shared_ptr<Sv2Client> GetClientById(NodeId node_id) const EXCLUSIVE_LOCKS_REQUIRED(m_clients_mutex);
 
     using Sv2ClientFn = std::function<void(Sv2Client&)>;

src/sv2/template_provider.cpp

@@ -437,6 +437,7 @@ void Sv2TemplateProvider::RequestTransactionData(Sv2Client& client, node::Sv2Req
                     client.m_id);
     LOCK(client.cs_send);
     client.m_send_messages.emplace_back(request_tx_data_success);
+    m_connman->TryOptimisticSend(client);
 }
 
 void Sv2TemplateProvider::SubmitSolution(node::Sv2SubmitSolutionMsg solution)
@@ -561,8 +562,6 @@ bool Sv2TemplateProvider::SendWork(Sv2Client& client, uint64_t template_id, Bloc
                                         template_id,
                                         future_template};
 
-    // TODO: use optimistic send instead of adding to the queue
-
     LogPrintLevel(BCLog::SV2, BCLog::Level::Debug, "Send 0x71 NewTemplate id=%lu future=%d to client id=%zu\n", template_id, future_template, client.m_id);
     {
         LOCK(client.cs_send);
@@ -573,6 +572,8 @@ bool Sv2TemplateProvider::SendWork(Sv2Client& client, uint64_t template_id, Bloc
             LogPrintLevel(BCLog::SV2, BCLog::Level::Debug, "Send 0x72 SetNewPrevHash to client id=%zu\n", client.m_id);
             client.m_send_messages.emplace_back(new_prev_hash);
         }
+
+        m_connman->TryOptimisticSend(client);
     }
 
     CAmount total_fees{0};