Problem: socket poller shutdown asserts when context is terminating

Solution: do not call getsockopt to query thread-safety of a socket

src/socket_base.cpp

@@ -102,6 +102,11 @@ bool zmq::socket_base_t::check_tag ()
     return tag == 0xbaddecaf;
 }
 
+bool zmq::socket_base_t::is_thread_safe () const
+{
+    return thread_safe;
+}
+
 zmq::socket_base_t *zmq::socket_base_t::create (int type_,
                                                 class ctx_t *parent_,
                                                 uint32_t tid_,

src/socket_base.hpp

@@ -67,6 +67,9 @@ class socket_base_t : public own_t,
     //  Returns false if object is not a socket.
     bool check_tag ();
 
+    //  Returns whether the socket is thread-safe.
+    bool is_thread_safe () const;
+
     //  Create a socket of a specified type.
     static socket_base_t *
     create (int type_, zmq::ctx_t *parent_, uint32_t tid_, int sid_);

src/socket_poller.cpp

@@ -33,13 +33,8 @@
 
 static bool is_thread_safe (zmq::socket_base_t &socket)
 {
-    int thread_safe;
-    size_t thread_safe_size = sizeof (int);
-
-    int rc =
-      socket.getsockopt (ZMQ_THREAD_SAFE, &thread_safe, &thread_safe_size);
-    zmq_assert (rc == 0);
-    return thread_safe;
+    // do not use getsockopt here, since that would fail during context termination
+    return socket.is_thread_safe ();
 }
 
 zmq::socket_poller_t::socket_poller_t () :