Problem: poller sleeps forever if no events

Solution: Fail with error if no events are active and timeout is infinite

doc/zmq_poller.txt

@@ -256,7 +256,8 @@ At least one of the registered objects is a 'socket' whose associated 0MQ
 'context' was terminated.
 *EFAULT*::
 The provided 'events' was NULL, or 'poller' did not point to a valid poller,
-or there are no registered objects and 'timeout' was negative.
+or there are no registered objects or all event subscriptions are disabled
+and 'timeout' was negative.
 *EINTR*::
 The operation was interrupted by delivery of a signal before any events were
 available.

src/socket_poller.cpp

@@ -548,6 +548,11 @@ int zmq::socket_poller_t::wait (zmq::socket_poller_t::event_t *events_,
     }
 
     if (unlikely (_pollset_size == 0)) {
+        if (timeout_ < 0) {
+            // Fail instead of trying to sleep forever
+            errno = EFAULT;
+            return -1;
+        }
         // We'll report an error (timed out) as if the list was non-empty and
         // no event occurred within the specified timeout. Otherwise the caller
         // needs to check the return value AND the event to avoid using the

tests/test_poller.cpp

@@ -512,6 +512,17 @@ void call_poller_wait_all_empty_with_timeout_fails (void *poller_,
                                zmq_poller_wait_all (poller_, &event, 0, -1));
 }
 
+void call_poller_wait_all_inf_disabled_fails (void *poller_, void *socket_)
+{
+    TEST_ASSERT_SUCCESS_ERRNO (zmq_poller_add (poller_, socket_, NULL, 0));
+
+    zmq_poller_event_t events[1];
+    TEST_ASSERT_FAILURE_ERRNO (EAGAIN,
+                               zmq_poller_wait_all (poller_, events, 1, 0));
+    TEST_ASSERT_FAILURE_ERRNO (EFAULT,
+                               zmq_poller_wait_all (poller_, events, 1, -1));
+}
+
 TEST_CASE_FUNC_PARAM (call_poller_wait_empty_with_timeout_fails,
                       test_with_empty_poller)
 TEST_CASE_FUNC_PARAM (call_poller_wait_empty_without_timeout_fails,
@@ -522,6 +533,8 @@ TEST_CASE_FUNC_PARAM (call_poller_wait_all_empty_without_timeout_fails,
                       test_with_empty_poller)
 TEST_CASE_FUNC_PARAM (call_poller_wait_all_empty_with_timeout_fails,
                       test_with_empty_poller)
+TEST_CASE_FUNC_PARAM (call_poller_wait_all_inf_disabled_fails,
+                      test_with_empty_poller)
 
 void test_poll_basic ()
 {
@@ -695,6 +708,7 @@ int main (void)
     RUN_TEST (test_call_poller_wait_all_empty_negative_count_fails);
     RUN_TEST (test_call_poller_wait_all_empty_without_timeout_fails);
     RUN_TEST (test_call_poller_wait_all_empty_with_timeout_fails);
+    RUN_TEST (test_call_poller_wait_all_inf_disabled_fails);
 
     RUN_TEST (test_call_poller_fd_no_signaler);
     RUN_TEST (test_call_poller_fd);