Implement flow control for ZMQ_REQ sockets

src/req.cpp

@@ -25,6 +25,7 @@
 
 zmq::req_t::req_t (class app_thread_t *parent_) :
     socket_base_t (parent_),
+    active (0),
     current (0),
     waiting_for_reply (false),
     reply_pipe_active (false),
@@ -45,7 +46,12 @@ void zmq::req_t::xattach_pipes (class reader_t *inpipe_,
     zmq_assert (in_pipes.size () == out_pipes.size ());
 
     in_pipes.push_back (inpipe_);
+    in_pipes.swap (active, in_pipes.size () - 1);
+
     out_pipes.push_back (outpipe_);
+    out_pipes.swap (active, out_pipes.size () - 1);
+
+    active++;
 }
 
 void zmq::req_t::xdetach_inpipe (class reader_t *pipe_)
@@ -61,16 +67,28 @@ void zmq::req_t::xdetach_inpipe (class reader_t *pipe_)
 
     in_pipes_t::size_type index = in_pipes.index (pipe_);
 
-    //  If corresponding outpipe is still in place simply nullify the pointer
-    //  to the inpipe.
+    //  If the corresponding outpipe is still in place nullify the pointer
+    //  to the inpipe ane move both pipes into inactive zone.
     if (out_pipes [index]) {
         in_pipes [index] = NULL;
+        if (index < active) {
+            active--;
+            in_pipes.swap (index, active);
+            out_pipes.swap (index, active);
+            if (current = active)
+                current = 0;
+        }
         return;
     }
 
     //  Now both inpipe and outpipe are detached. Remove them from the lists.
     in_pipes.erase (index);
     out_pipes.erase (index);
+    if (index < active) {
+        active--;
+        if (current == active)
+            current = 0;
+    }
 }
 
 void zmq::req_t::xdetach_outpipe (class writer_t *pipe_)
@@ -80,20 +98,33 @@ void zmq::req_t::xdetach_outpipe (class writer_t *pipe_)
 
     out_pipes_t::size_type index = out_pipes.index (pipe_);
 
-    //  If corresponding inpipe is still in place simply nullify the pointer
-    //  to the outpipe.
+    //  If the corresponding inpipe is still in place nullify the pointer
+    //  to the outpipe and move both pipes into inactive zone.
     if (in_pipes [index]) {
         out_pipes [index] = NULL;
+        if (index < active) {
+            active--;
+            in_pipes.swap (index, active);
+            out_pipes.swap (index, active);
+            if (current == active)
+                current = 0;
+        }
         return;
     }
 
     //  Now both inpipe and outpipe are detached. Remove them from the lists.
     in_pipes.erase (index);
     out_pipes.erase (index);
+    if (index < active) {
+        active--;
+        if (current == active)
+            current = 0;
+    }
 }
 
 void zmq::req_t::xkill (class reader_t *pipe_)
 {
+    zmq_assert (waiting_for_reply);
     zmq_assert (pipe_ == reply_pipe);
 
     reply_pipe_active = false;
@@ -104,13 +135,19 @@ void zmq::req_t::xrevive (class reader_t *pipe_)
     //  TODO: Actually, misbehaving peer can cause this kind of thing.
     //  Handle it decently, presumably kill the offending connection.
     zmq_assert (pipe_ == reply_pipe);
-
     reply_pipe_active = true;
 }
 
 void zmq::req_t::xrevive (class writer_t *pipe_)
 {
-    zmq_not_implemented ();
+    out_pipes_t::size_type index = out_pipes.index (pipe_);
+    zmq_assert (index >= active);
+
+    if (in_pipes [index] != NULL) {
+        in_pipes.swap (index, active);
+        out_pipes.swap (index, active);
+        active++;
+    }
 }
 
 int zmq::req_t::xsetsockopt (int option_, const void *optval_,
@@ -129,24 +166,24 @@ int zmq::req_t::xsend (zmq_msg_t *msg_, int flags_)
         return -1;
     }
 
-    if (out_pipes.empty ()) {
-        errno = EAGAIN;
-        return -1;
-    }
+    while (active > 0) {
+        if (out_pipes [current]->check_write ())
+            break;
 
-    current++;
-    if (current >= out_pipes.size ())
-        current = 0;
-
-    //  TODO: Infinite loop can result here. Integrate the algorithm with
-    //  the active pipes list (i.e. pipe pair that has one pipe missing is
-    //  considered to be inactive.
-    while (!in_pipes [current] || !out_pipes [current]) {
-        current++;
-        if (current >= out_pipes.size ())
+        active--;
+        if (current < active) {
+            in_pipes.swap (current, active);
+            out_pipes.swap (current, active);
+        }
+        else
             current = 0;
     }
 
+    if (active == 0) {
+        errno = EAGAIN;
+        return -1;
+    }
+
     //  Push message to the selected pipe.
     bool written = out_pipes [current]->write (msg_);
     zmq_assert (written);
@@ -164,6 +201,9 @@ int zmq::req_t::xsend (zmq_msg_t *msg_, int flags_)
     int rc = zmq_msg_init (msg_);
     zmq_assert (rc == 0);
 
+    //  Move to the next pipe (load-balancing).
+    current = (current + 1) % active;
+
     return 0;
 }
 
@@ -213,7 +253,23 @@ bool zmq::req_t::xhas_in ()
 
 bool zmq::req_t::xhas_out ()
 {
-    return !waiting_for_reply;
+    if (waiting_for_reply)
+        return false;
+
+    while (active > 0) {
+        if (out_pipes [current]->check_write ())
+            return true;;
+
+        active--;
+        if (current < active) {
+            in_pipes.swap (current, active);
+            out_pipes.swap (current, active);
+        }
+        else
+            current = 0;
+    }
+
+    return false;
 }
 
 

src/req.hpp

@@ -64,6 +64,9 @@ namespace zmq
         typedef yarray_t <class reader_t> in_pipes_t;
         in_pipes_t in_pipes;
 
+        //  Number of active pipes.
+        size_t active;
+
         //  Req_t load-balances the requests - 'current' points to the session
         //  that's processing the request at the moment.
         out_pipes_t::size_type current;