Remove race condition from XPUB/SUB test in test_blocking()

tests/test_hwm_pubsub.cpp

@@ -95,12 +95,21 @@ int test_defaults (int send_hwm_, int msg_cnt_, const char *endpoint)
     return recv_count;
 }
 
-int receive (void *socket_)
+int receive (void *socket_, int *is_termination)
 {
     int recv_count = 0;
+    *is_termination = 0;
+
     // Now receive all sent messages
-    while (0 == zmq_recv (socket_, NULL, 0, 0)) {
+    char buffer[255];
+    int len;
+    while ((len = zmq_recv (socket_, buffer, sizeof (buffer), 0)) >= 0) {
         ++recv_count;
+
+        if (len == 3 && strncmp (buffer, "end", len) == 0) {
+            *is_termination = 1;
+            return recv_count;
+        }
     }
 
     return recv_count;
@@ -141,19 +150,36 @@ int test_blocking (int send_hwm_, int msg_cnt_, const char *endpoint)
     // Send until we block
     int send_count = 0;
     int recv_count = 0;
+    int blocked_count = 0;
+    int is_termination = 0;
     while (send_count < msg_cnt_) {
         const int rc = zmq_send (pub_socket, NULL, 0, ZMQ_DONTWAIT);
         if (rc == 0) {
             ++send_count;
         } else if (-1 == rc) {
             // if the PUB socket blocks due to HWM, errno should be EAGAIN:
+            blocked_count++;
             TEST_ASSERT_EQUAL_INT (EAGAIN, errno);
-            recv_count += receive (sub_socket);
+            recv_count += receive (sub_socket, &is_termination);
         }
     }
 
-    msleep (2 * SETTLE_TIME); // required for TCP transport
-    recv_count += receive (sub_socket);
+    // if send_hwm_ < msg_cnt_, we should block at least once:
+    TEST_ASSERT (blocked_count > 0);
+
+    // dequeue SUB socket again, to make sure XPUB has space to send the termination message
+    recv_count += receive (sub_socket, &is_termination);
+
+    // send termination message
+    send_string_expect_success (pub_socket, "end", 0);
+
+    // now block on the SUB side till we get the termination message
+    while (is_termination == 0)
+        recv_count += receive (sub_socket, &is_termination);
+
+    // remove termination message from the count:
+    recv_count--;
+
     TEST_ASSERT_EQUAL_INT (send_count, recv_count);
 
     // Clean up