Implement poll() on systems which support it properly.

This eliminates the restriction on maximum socket descriptor number.

src/compat.h

@@ -92,8 +92,15 @@ typedef void* sockopt_arg_type;
 typedef char* sockopt_arg_type;
 #endif
 
+// Note these both should work with the current usage of poll, but best to be safe
+// WIN32 poll is broken https://daniel.haxx.se/blog/2012/10/10/wsapoll-is-broken/
+// __APPLE__ poll is broke https://github.com/bitcoin/bitcoin/pull/14336#issuecomment-437384408
+#if defined(__linux__)
+#define USE_POLL
+#endif
+
 bool static inline IsSelectableSocket(const SOCKET& s) {
-#ifdef WIN32
+#if defined(USE_POLL) || defined(WIN32)
     return true;
 #else
     return (s < FD_SETSIZE);

src/net.cpp

@@ -26,6 +26,10 @@
 #include <fcntl.h>
 #endif
 
+#ifdef USE_POLL
+#include <poll.h>
+#endif
+
 #ifdef USE_UPNP
 #include <miniupnpc/miniupnpc.h>
 #include <miniupnpc/miniwget.h>
@@ -33,6 +37,7 @@
 #include <miniupnpc/upnperrors.h>
 #endif
 
+#include <unordered_map>
 
 #include <math.h>
 
@@ -1307,6 +1312,49 @@ bool CConnman::GenerateSelectSet(std::set<SOCKET> &recv_set, std::set<SOCKET> &s
     return !recv_set.empty() || !send_set.empty() || !error_set.empty();
 }
 
+#ifdef USE_POLL
+void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
+{
+    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));
+        return;
+    }
+
+    std::unordered_map<SOCKET, struct pollfd> pollfds;
+    for (SOCKET socket_id : recv_select_set) {
+        pollfds[socket_id].fd = socket_id;
+        pollfds[socket_id].events |= POLLIN;
+    }
+
+    for (SOCKET socket_id : send_select_set) {
+        pollfds[socket_id].fd = socket_id;
+        pollfds[socket_id].events |= POLLOUT;
+    }
+
+    for (SOCKET socket_id : error_select_set) {
+        pollfds[socket_id].fd = socket_id;
+        // These flags are ignored, but we set them for clarity
+        pollfds[socket_id].events |= POLLERR|POLLHUP;
+    }
+
+    std::vector<struct pollfd> vpollfds;
+    vpollfds.reserve(pollfds.size());
+    for (auto it : pollfds) {
+        vpollfds.push_back(std::move(it.second));
+    }
+
+    if (poll(vpollfds.data(), vpollfds.size(), SELECT_TIMEOUT_MILLISECONDS) < 0) return;
+
+    if (interruptNet) return;
+
+    for (struct pollfd pollfd_entry : vpollfds) {
+        if (pollfd_entry.revents & POLLIN)            recv_set.insert(pollfd_entry.fd);
+        if (pollfd_entry.revents & POLLOUT)           send_set.insert(pollfd_entry.fd);
+        if (pollfd_entry.revents & (POLLERR|POLLHUP)) error_set.insert(pollfd_entry.fd);
+    }
+}
+#else
 void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_set, std::set<SOCKET> &error_set)
 {
     std::set<SOCKET> recv_select_set, send_select_set, error_select_set;
@@ -1380,6 +1428,7 @@ void CConnman::SocketEvents(std::set<SOCKET> &recv_set, std::set<SOCKET> &send_s
         }
     }
 }
+#endif
 
 void CConnman::SocketHandler()
 {

src/netbase.cpp

@@ -21,6 +21,10 @@
 #include <codecvt>
 #endif
 
+#ifdef USE_POLL
+#include <poll.h>
+#endif
+
 #if !defined(MSG_NOSIGNAL)
 #define MSG_NOSIGNAL 0
 #endif
@@ -264,11 +268,19 @@ static IntrRecvError InterruptibleRecv(uint8_t* data, size_t len, int timeout, c
                 if (!IsSelectableSocket(hSocket)) {
                     return IntrRecvError::NetworkError;
                 }
-                struct timeval tval = MillisToTimeval(std::min(endTime - curTime, maxWait));
+                int timeout_ms = std::min(endTime - curTime, maxWait);
+#ifdef USE_POLL
+                struct pollfd pollfd = {};
+                pollfd.fd = hSocket;
+                pollfd.events = POLLIN | POLLOUT;
+                int nRet = poll(&pollfd, 1, timeout_ms);
+#else
+                struct timeval tval = MillisToTimeval(timeout_ms);
                 fd_set fdset;
                 FD_ZERO(&fdset);
                 FD_SET(hSocket, &fdset);
                 int nRet = select(hSocket + 1, &fdset, nullptr, nullptr, &tval);
+#endif
                 if (nRet == SOCKET_ERROR) {
                     return IntrRecvError::NetworkError;
                 }
@@ -499,11 +511,18 @@ bool ConnectSocketDirectly(const CService &addrConnect, const SOCKET& hSocket, i
         // WSAEINVAL is here because some legacy version of winsock uses it
         if (nErr == WSAEINPROGRESS || nErr == WSAEWOULDBLOCK || nErr == WSAEINVAL)
         {
+#ifdef USE_POLL
+            struct pollfd pollfd = {};
+            pollfd.fd = hSocket;
+            pollfd.events = POLLIN | POLLOUT;
+            int nRet = poll(&pollfd, 1, nTimeout);
+#else
             struct timeval timeout = MillisToTimeval(nTimeout);
             fd_set fdset;
             FD_ZERO(&fdset);
             FD_SET(hSocket, &fdset);
             int nRet = select(hSocket + 1, nullptr, &fdset, nullptr, &timeout);
+#endif
             if (nRet == 0)
             {
                 LogPrint(BCLog::NET, "connection to %s timeout\n", addrConnect.ToString());