Outstanding requests dropped when requester dies (issue 190)

So far the requests in req/rep pattern were delivered to and processed
by worker even though the original requester was dead. Thus,
the worker processing replies with noone to deliver results to.
This optimisation drops requests in two situations:

1. Queued inbound requests in XREP socket when peer disconnects.
2. Queued outbound requests in XREQ when socket is closed.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/options.cpp

@@ -41,7 +41,9 @@ zmq::options_t::options_t () :
     filter (1),
     rcvtimeo (-1),
     sndtimeo (-1),
-    immediate_connect (true)
+    immediate_connect (true),
+    delay_on_close (true),
+    delay_on_disconnect (true)
 {
 }
 

src/options.hpp

@@ -87,6 +87,14 @@ namespace zmq
         //  is not aware of the peer's identity, however, it is able to send
         //  messages straight away.
         bool immediate_connect;
+
+        //  If true, session reads all the pending messages from the pipe and
+        //  sends them to the network when socket is closed.
+        bool delay_on_close;
+
+        //  If true, socket reads all the messages from the pipe and delivers
+        //  them to the user when the peer terminates.
+        bool delay_on_disconnect;
     };
 
 }

src/pipe.hpp

@@ -34,8 +34,9 @@ namespace zmq
     //  Create a pipepair for bi-directional transfer of messages.
     //  First HWM is for messages passed from first pipe to the second pipe.
     //  Second HWM is for messages passed from second pipe to the first pipe.
-    //  Delay specifies whether the pipe receives all the pending messages
-    //  before terminating or whether it terminates straight away.
+    //  Delay specifies how the pipe behaves when the peer terminates. If true
+    //  pipe receives all the pending messages before terminating, otherwise it
+    //  terminates straight away.
     int pipepair (class object_t *parents_ [2], class pipe_t* pipes_ [2],
         int hwms_ [2], bool delays_ [2]);
 

src/session.cpp

@@ -180,7 +180,7 @@ void zmq::session_t::process_attach (i_engine *engine_,
         object_t *parents [2] = {this, socket};
         pipe_t *pipes [2] = {NULL, NULL};
         int hwms [2] = {options.rcvhwm, options.sndhwm};
-        bool delays [2] = {true, true};
+        bool delays [2] = {options.delay_on_close, options.delay_on_disconnect};
         int rc = pipepair (parents, pipes, hwms, delays);
         errno_assert (rc == 0);
 

src/socket_base.cpp

@@ -426,7 +426,7 @@ int zmq::socket_base_t::connect (const char *addr_)
         object_t *parents [2] = {this, peer.socket};
         pipe_t *pipes [2] = {NULL, NULL};
         int hwms [2] = {sndhwm, rcvhwm};
-        bool delays [2] = {true, true};
+        bool delays [2] = {options.delay_on_disconnect, options.delay_on_close};
         int rc = pipepair (parents, pipes, hwms, delays);
         errno_assert (rc == 0);
 
@@ -462,7 +462,7 @@ int zmq::socket_base_t::connect (const char *addr_)
         object_t *parents [2] = {this, session};
         pipe_t *pipes [2] = {NULL, NULL};
         int hwms [2] = {options.sndhwm, options.rcvhwm};
-        bool delays [2] = {true, true};
+        bool delays [2] = {options.delay_on_disconnect, options.delay_on_close};
         int rc = pipepair (parents, pipes, hwms, delays);
         errno_assert (rc == 0);
 

src/xrep.cpp

@@ -33,6 +33,10 @@ zmq::xrep_t::xrep_t (class ctx_t *parent_, uint32_t tid_) :
 {
     options.type = ZMQ_XREP;
 
+    //  If peer disconnect there's noone to send reply to anyway. We can drop
+    //  all the outstanding requests from that peer.
+    options.delay_on_disconnect = false;
+
     prefetched_msg.init ();
 
     //  Start the peer ID sequence from a random point.

src/xreq.cpp

@@ -26,6 +26,10 @@ zmq::xreq_t::xreq_t (class ctx_t *parent_, uint32_t tid_) :
     socket_base_t (parent_, tid_)
 {
     options.type = ZMQ_XREQ;
+
+    //  If the socket is closing we can drop all the outbound requests. There'll
+    //  be noone to receive the replies anyway.
+    options.delay_on_close = false;
 }
 
 zmq::xreq_t::~xreq_t ()

tests/Makefile.am

@@ -6,7 +6,8 @@ noinst_PROGRAMS = test_pair_inproc \
                   test_reqrep_inproc \
                   test_reqrep_tcp \
                   test_hwm \
-                  test_reqrep_device
+                  test_reqrep_device \
+                  test_reqrep_drop
 
 if !ON_MINGW
 noinst_PROGRAMS += test_shutdown_stress \
@@ -17,13 +18,11 @@ endif
 
 test_pair_inproc_SOURCES = test_pair_inproc.cpp testutil.hpp
 test_pair_tcp_SOURCES = test_pair_tcp.cpp testutil.hpp
-
 test_reqrep_inproc_SOURCES = test_reqrep_inproc.cpp testutil.hpp
 test_reqrep_tcp_SOURCES = test_reqrep_tcp.cpp testutil.hpp
-
 test_hwm_SOURCES = test_hwm.cpp
-
 test_reqrep_device_SOURCES = test_reqrep_device.cpp
+test_reqrep_drop_SOURCES = test_reqrep_drop.cpp
 
 if !ON_MINGW
 test_shutdown_stress_SOURCES = test_shutdown_stress.cpp

tests/test_reqrep_drop.cpp

@@ -0,0 +1,69 @@
+/*
+    Copyright (c) 2007-2011 iMatix Corporation
+    Copyright (c) 2007-2011 Other contributors as noted in the AUTHORS file
+
+    This file is part of 0MQ.
+
+    0MQ is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    0MQ is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <assert.h>
+
+#include "../include/zmq.h"
+#include "../include/zmq_utils.h"
+
+int main (int argc, char *argv [])
+{
+    void *ctx = zmq_init (1);
+    assert (ctx);
+
+    //  Create a server.
+    void *xrep = zmq_socket (ctx, ZMQ_XREP);
+    assert (xrep);
+    int rc = zmq_bind (xrep, "tcp://127.0.0.1:5560");
+    assert (rc == 0);
+
+    //  Create a client.
+    void *xreq = zmq_socket (ctx, ZMQ_XREQ);
+    assert (xreq);
+    rc = zmq_connect (xreq, "tcp://127.0.0.1:5560");
+    assert (rc == 0);
+
+    //  Send requests.
+    rc = zmq_send (xreq, "ABC", 3, 0);
+    assert (rc == 3);
+    rc = zmq_send (xreq, "DEF", 3, 0);
+    assert (rc == 3);
+
+    //  Disconnect client.
+    rc = zmq_close (xreq);
+    assert (rc == 0);
+
+    //  Wait a while for disconnect to happen.
+    zmq_sleep (1);
+
+    //  Try to receive a request -- it should have been discarded.
+    char buff [3];
+    rc = zmq_recv (xrep, buff, 3, ZMQ_DONTWAIT);
+    assert (rc < 0);
+    assert (errno == EAGAIN);
+
+    //  Clean up.
+    rc = zmq_close (xrep);
+    assert (rc == 0);
+    rc = zmq_term (ctx);
+    assert (rc == 0);
+
+    return 0 ;
+}