Merge pull request #3757 from sigiesec/fix-windows-signaler-regression

Fix windows signaler regression

src/signaler.cpp

@@ -183,10 +183,14 @@ void zmq::signaler_t::send ()
     ssize_t sz = write (_w, &inc, sizeof (inc));
     errno_assert (sz == sizeof (inc));
 #elif defined ZMQ_HAVE_WINDOWS
-    unsigned char dummy = 0;
-    const int nbytes =
-      ::send (_w, reinterpret_cast<char *> (&dummy), sizeof (dummy), 0);
-    wsa_assert (nbytes != SOCKET_ERROR);
+    const char dummy = 0;
+    int nbytes;
+    do {
+        nbytes = ::send (_w, &dummy, sizeof (dummy), 0);
+        wsa_assert (nbytes != SOCKET_ERROR);
+        // wsa_assert does not abort on WSAEWOULDBLOCK. If we get this, we retry.
+    } while (nbytes == SOCKET_ERROR);
+    // Given the small size of dummy (should be 1) expect that send was able to send everything.
     zmq_assert (nbytes == sizeof (dummy));
 #elif defined ZMQ_HAVE_VXWORKS
     unsigned char dummy = 0;