PGM receiver crash fix (#3226)

Problem: PGM receiver can crash due to race

Solution: do not run in_event until restart_input finishes correctly.
Signed-off-by: answeroo <jiming@yafco.com>

src/pgm_receiver.cpp

@@ -163,6 +163,11 @@ const char *zmq::pgm_receiver_t::get_endpoint () const
 
 void zmq::pgm_receiver_t::in_event ()
 {
+    // If active_tsi is not null, there is a pending restart_input.
+    // Keep the internal state as is so that restart_input would process the right data
+    if (active_tsi) {
+	return;
+    }
     // Read data from the underlying pgm_socket.
     const pgm_tsi_t *tsi = NULL;
 
@@ -176,9 +181,10 @@ void zmq::pgm_receiver_t::in_event ()
     while (true) {
         //  Get new batch of data.
         //  Note the workaround made not to break strict-aliasing rules.
+	
+	insize = 0;
         void *tmp = NULL;
         ssize_t received = pgm_socket.receive (&tmp, &tsi);
-        inpos = (unsigned char *) tmp;
 
         //  No data to process. This may happen if the packet received is
         //  neither ODATA nor ODATA.
@@ -212,6 +218,7 @@ void zmq::pgm_receiver_t::in_event ()
         }
 
         insize = static_cast<size_t> (received);
+        inpos = (unsigned char *) tmp;
 
         //  Read the offset of the fist message in the current packet.
         zmq_assert (insize >= sizeof (uint16_t));