multi: implement wait using winsock events

This avoids using a pair of TCP ports to provide wakeup functionality
for every multi instance on Windows, where socketpair() is emulated
using a TCP socket on loopback which could in turn lead to socket
resource exhaustion.

Reviewed-by: Gergely Nagy
Reviewed-by: Marc Hörsken

Closes #5397

lib/multi.c

@@ -374,6 +374,11 @@ struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
   multi->max_concurrent_streams = 100;
   multi->ipv6_works = Curl_ipv6works(NULL);
 
+#ifdef USE_WINSOCK
+  multi->wsa_event = WSACreateEvent();
+  if(multi->wsa_event == WSA_INVALID_EVENT)
+    goto error;
+#else
 #ifdef ENABLE_WAKEUP
   if(Curl_socketpair(AF_UNIX, SOCK_STREAM, 0, multi->wakeup_pair) < 0) {
     multi->wakeup_pair[0] = CURL_SOCKET_BAD;
@@ -386,6 +391,7 @@ struct Curl_multi *Curl_multi_handle(int hashsize, /* socket hash */
     multi->wakeup_pair[0] = CURL_SOCKET_BAD;
     multi->wakeup_pair[1] = CURL_SOCKET_BAD;
   }
+#endif
 #endif
 
   return multi;
@@ -1067,11 +1073,15 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
   unsigned int i;
   unsigned int nfds = 0;
   unsigned int curlfds;
-  bool ufds_malloc = FALSE;
   long timeout_internal;
   int retcode = 0;
+#ifndef USE_WINSOCK
   struct pollfd a_few_on_stack[NUM_POLLS_ON_STACK];
   struct pollfd *ufds = &a_few_on_stack[0];
+  bool ufds_malloc = FALSE;
+#else
+  DEBUGASSERT(multi->wsa_event != WSA_INVALID_EVENT);
+#endif
 
   if(!GOOD_MULTI_HANDLE(multi))
     return CURLM_BAD_HANDLE;
@@ -1117,11 +1127,16 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
   nfds += extra_nfds; /* add the externally provided ones */
 
 #ifdef ENABLE_WAKEUP
+#ifdef USE_WINSOCK
+  if(use_wakeup) {
+#else
   if(use_wakeup && multi->wakeup_pair[0] != CURL_SOCKET_BAD) {
+#endif
     ++nfds;
   }
 #endif
 
+#ifndef USE_WINSOCK
   if(nfds > NUM_POLLS_ON_STACK) {
     /* 'nfds' is a 32 bit value and 'struct pollfd' is typically 8 bytes
        big, so at 2^29 sockets this value might wrap. When a process gets
@@ -1132,7 +1147,9 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
       return CURLM_OUT_OF_MEMORY;
     ufds_malloc = TRUE;
   }
+
   nfds = 0;
+#endif
 
   /* only do the second loop if we found descriptors in the first stage run
      above */
@@ -1145,22 +1162,36 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
 
       for(i = 0; i< MAX_SOCKSPEREASYHANDLE; i++) {
         curl_socket_t s = CURL_SOCKET_BAD;
-
+#ifdef USE_WINSOCK
+        long mask = 0;
+#endif
         if(bitmap & GETSOCK_READSOCK(i)) {
+#ifdef USE_WINSOCK
+          mask |= FD_READ;
+#else
           ufds[nfds].fd = sockbunch[i];
           ufds[nfds].events = POLLIN;
           ++nfds;
+#endif
           s = sockbunch[i];
         }
         if(bitmap & GETSOCK_WRITESOCK(i)) {
+#ifdef USE_WINSOCK
+          mask |= FD_WRITE;
+#else
           ufds[nfds].fd = sockbunch[i];
           ufds[nfds].events = POLLOUT;
           ++nfds;
+#endif
           s = sockbunch[i];
         }
         if(s == CURL_SOCKET_BAD) {
           break;
         }
+#ifdef USE_WINSOCK
+        if(WSAEventSelect(s, multi->wsa_event, mask) != 0)
+          return CURLM_INTERNAL_ERROR;
+#endif
       }
 
       data = data->next; /* check next handle */
@@ -1169,6 +1200,17 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
 
   /* Add external file descriptions from poll-like struct curl_waitfd */
   for(i = 0; i < extra_nfds; i++) {
+#ifdef USE_WINSOCK
+    long events = 0;
+    if(extra_fds[i].events & CURL_WAIT_POLLIN)
+      events |= FD_READ;
+    if(extra_fds[i].events & CURL_WAIT_POLLPRI)
+      events |= FD_OOB;
+    if(extra_fds[i].events & CURL_WAIT_POLLOUT)
+      events |= FD_WRITE;
+    if(WSAEventSelect(extra_fds[i].fd, multi->wsa_event, events) != 0)
+      return CURLM_INTERNAL_ERROR;
+#else
     ufds[nfds].fd = extra_fds[i].fd;
     ufds[nfds].events = 0;
     if(extra_fds[i].events & CURL_WAIT_POLLIN)
@@ -1178,28 +1220,61 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
     if(extra_fds[i].events & CURL_WAIT_POLLOUT)
       ufds[nfds].events |= POLLOUT;
     ++nfds;
+#endif
   }
 
 #ifdef ENABLE_WAKEUP
+#ifndef USE_WINSOCK
   if(use_wakeup && multi->wakeup_pair[0] != CURL_SOCKET_BAD) {
     ufds[nfds].fd = multi->wakeup_pair[0];
     ufds[nfds].events = POLLIN;
     ++nfds;
   }
+#endif
 #endif
 
   if(nfds) {
     int pollrc;
     /* wait... */
+#ifdef USE_WINSOCK
+    DWORD waitrc = WSAWaitForMultipleEvents(1, &multi->wsa_event, FALSE,
+                                            timeout_ms, FALSE);
+    /* WSA_WAIT_EVENT_0 is 0, so waitrc >= WSA_WAIT_EVENT_0 warns */
+    if(waitrc == WSA_WAIT_EVENT_0)
+      pollrc = 1;
+    else
+      pollrc = -1;
+#else
     pollrc = Curl_poll(ufds, nfds, timeout_ms);
+#endif
 
     if(pollrc > 0) {
+#ifdef USE_WINSOCK
+      retcode = 0;
+#else
       retcode = pollrc;
+#endif
       /* copy revents results from the poll to the curl_multi_wait poll
          struct, the bit values of the actual underlying poll() implementation
          may not be the same as the ones in the public libcurl API! */
       for(i = 0; i < extra_nfds; i++) {
         unsigned short mask = 0;
+#ifdef USE_WINSOCK
+        WSANETWORKEVENTS events = {0};
+        if(WSAEnumNetworkEvents(extra_fds[i].fd, multi->wsa_event,
+                                &events) == 0) {
+          if(events.lNetworkEvents & FD_READ)
+            mask |= CURL_WAIT_POLLIN;
+          if(events.lNetworkEvents & FD_WRITE)
+            mask |= CURL_WAIT_POLLOUT;
+          if(events.lNetworkEvents & FD_OOB)
+            mask |= CURL_WAIT_POLLPRI;
+
+          if(events.lNetworkEvents != 0)
+            retcode++;
+        }
+        WSAEventSelect(extra_fds[i].fd, multi->wsa_event, 0);
+#else
         unsigned r = ufds[curlfds + i].revents;
 
         if(r & POLLIN)
@@ -1208,10 +1283,39 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
           mask |= CURL_WAIT_POLLOUT;
         if(r & POLLPRI)
           mask |= CURL_WAIT_POLLPRI;
+#endif
 
         extra_fds[i].revents = mask;
       }
 
+#ifdef USE_WINSOCK
+      /* Count up all our own sockets that had activity,
+         and remove them from the event. */
+      if(curlfds) {
+        data = multi->easyp;
+        while(data) {
+          bitmap = multi_getsock(data, sockbunch);
+
+          for(i = 0; i < MAX_SOCKSPEREASYHANDLE; i++) {
+            if(bitmap & (GETSOCK_READSOCK(i) | GETSOCK_WRITESOCK(i))) {
+              WSANETWORKEVENTS events = {0};
+              if(WSAEnumNetworkEvents(sockbunch[i], multi->wsa_event,
+                                      &events) == 0) {
+                if(events.lNetworkEvents != 0)
+                  retcode++;
+              }
+              WSAEventSelect(sockbunch[i], multi->wsa_event, 0);
+            }
+            else
+              break;
+          }
+
+          data = data->next;
+        }
+      }
+
+      WSAResetEvent(multi->wsa_event);
+#else
 #ifdef ENABLE_WAKEUP
       if(use_wakeup && multi->wakeup_pair[0] != CURL_SOCKET_BAD) {
         if(ufds[curlfds + extra_nfds].revents & POLLIN) {
@@ -1224,10 +1328,8 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
                when there is no more data, breaking the loop. */
             nread = sread(multi->wakeup_pair[0], buf, sizeof(buf));
             if(nread <= 0) {
-#ifndef USE_WINSOCK
               if(nread < 0 && EINTR == SOCKERRNO)
                 continue;
-#endif
               break;
             }
           }
@@ -1235,12 +1337,15 @@ static CURLMcode Curl_multi_wait(struct Curl_multi *multi,
           retcode--;
         }
       }
+#endif
 #endif
     }
   }
 
+#ifndef USE_WINSOCK
   if(ufds_malloc)
     free(ufds);
+#endif
   if(ret)
     *ret = retcode;
   if(!extrawait || nfds)
@@ -1295,6 +1400,10 @@ CURLMcode curl_multi_wakeup(struct Curl_multi *multi)
     return CURLM_BAD_HANDLE;
 
 #ifdef ENABLE_WAKEUP
+#ifdef USE_WINSOCK
+  if(WSASetEvent(multi->wsa_event))
+    return CURLM_OK;
+#else
   /* the wakeup_pair variable is only written during init and cleanup,
      making it safe to access from another thread after the init part
      and before cleanup */
@@ -1327,6 +1436,7 @@ CURLMcode curl_multi_wakeup(struct Curl_multi *multi)
       return CURLM_OK;
     }
   }
+#endif
 #endif
   return CURLM_WAKEUP_FAILURE;
 }
@@ -2485,9 +2595,13 @@ CURLMcode curl_multi_cleanup(struct Curl_multi *multi)
     Curl_hash_destroy(&multi->hostcache);
     Curl_psl_destroy(&multi->psl);
 
+#ifdef USE_WINSOCK
+    WSACloseEvent(multi->wsa_event);
+#else
 #ifdef ENABLE_WAKEUP
     sclose(multi->wakeup_pair[0]);
     sclose(multi->wakeup_pair[1]);
+#endif
 #endif
     free(multi);
 

lib/multihandle.h

@@ -138,9 +138,13 @@ struct Curl_multi {
                                     previous callback */
   unsigned int max_concurrent_streams;
 
+#ifdef USE_WINSOCK
+  WSAEVENT wsa_event; /* winsock event used for waits */
+#else
 #ifdef ENABLE_WAKEUP
   curl_socket_t wakeup_pair[2]; /* socketpair() used for wakeup
                                    0 is used for read, 1 is used for write */
+#endif
 #endif
   /* multiplexing wanted */
   bool multiplexing;