Invoke select/poll with 0 timeout in case we know that there is work

dashpay · Apr 17, 2020 · e97495e · e97495e
1 parent 9c2cd80
commit e97495e
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Showing 2 changed files with 25 additions and 7 deletions.
diff --git a/src/net.cpp b/src/net.cpp
@@ -1425,11 +1425,11 @@ bool CConnman::GenerateSelectSet(std::set<SOCKET> &recv_set, std::set<SOCKET> &s
 }
 
 #ifdef USE_POLL
-void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
+void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set, bool fOnlyPoll)
 {
     std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
     if (!GenerateSelectSet(recv_select_set, send_select_set, error_select_set)) {
-        interruptNet.sleep_for(std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS));
+        if (!fOnlyPoll) interruptNet.sleep_for(std::chrono::milliseconds(SELECT_TIMEOUT_MILLISECONDS));
         return;
     }
 
@@ -1457,7 +1457,7 @@ void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_s
     }
 
     wakeupSelectNeeded = true;
-    int r = poll(vpollfds.data(), vpollfds.size(), SELECT_TIMEOUT_MILLISECONDS);
+    int r = poll(vpollfds.data(), vpollfds.size(), fOnlyPoll ? 0 : SELECT_TIMEOUT_MILLISECONDS);
     wakeupSelectNeeded = false;
     if (r < 0) {
         return;
@@ -1472,7 +1472,7 @@ void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_s
     }
 }
 #else
-void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
+void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set, bool fOnlyPoll)
 {
     std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
     if (!GenerateSelectSet(recv_select_set, send_select_set, error_select_set)) {
@@ -1485,7 +1485,7 @@ void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_s
     //
     struct timeval timeout;
     timeout.tv_sec  = 0;
-    timeout.tv_usec = SELECT_TIMEOUT_MILLISECONDS * 1000; // frequency to poll pnode->vSend
+    timeout.tv_usec = fOnlyPoll ? 0 : SELECT_TIMEOUT_MILLISECONDS * 1000; // frequency to poll pnode->vSend
 
     fd_set fdsetRecv;
     fd_set fdsetSend;
@@ -1550,8 +1550,26 @@ void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_s
 
 void CConnman::SocketHandler()
 {
+    bool fOnlyPoll = false;
+    {
+        // check if we have work to do and thus should avoid waiting for events
+        LOCK2(cs_vNodes, cs_mapNodesWithDataToSend);
+        if (!mapReceivableNodes.empty()) {
+            fOnlyPoll = true;
+        } else if (!mapSendableNodes.empty() && !mapNodesWithDataToSend.empty()) {
+            // we must check if at least one of the nodes with pending messages is also sendable, as otherwise a single
+            // node would be able to make the network thread busy with polling
+            for (auto& p : mapNodesWithDataToSend) {
+                if (mapSendableNodes.count(p.first)) {
+                    fOnlyPoll = true;
+                    break;
+                }
+            }
+        }
+    }
+
     std::set<SOCKET> recv_set, send_set, error_set;
-    SocketEvents(recv_set, send_set, error_set);
+    SocketEvents(recv_set, send_set, error_set, fOnlyPoll);
 
 #ifdef USE_WAKEUP_PIPE
     // drain the wakeup pipe

diff --git a/src/net.h b/src/net.h
@@ -481,7 +481,7 @@ friend class CNode;
     void NotifyNumConnectionsChanged();
     void InactivityCheck(CNode *pnode);
     bool GenerateSelectSet(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set);
-    void SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set);
+    void SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set, bool fOnlyPoll);
     void SocketHandler();
     void ThreadSocketHandler();
     void ThreadDNSAddressSeed();