O(1) fair-queueing in XREP implemented

Up to now the complexity of fair-queueing in XREP was O(n).
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/pipe.cpp

@@ -63,7 +63,8 @@ zmq::pipe_t::pipe_t (object_t *parent_, upipe_t *inpipe_, upipe_t *outpipe_,
     peer (NULL),
     sink (NULL),
     state (active),
-    delay (delay_)
+    delay (delay_),
+    pipe_id (0)
 {
 }
 
@@ -85,6 +86,16 @@ void zmq::pipe_t::set_event_sink (i_pipe_events *sink_)
     sink = sink_;
 }
 
+void zmq::pipe_t::set_pipe_id (uint32_t id_)
+{
+    pipe_id = id_;
+}
+
+uint32_t zmq::pipe_t::get_pipe_id ()
+{
+    return pipe_id;
+}
+
 bool zmq::pipe_t::check_read ()
 {
     if (unlikely (!in_active || (state != active && state != pending)))

src/pipe.hpp

@@ -25,6 +25,7 @@
 #include "ypipe.hpp"
 #include "config.hpp"
 #include "object.hpp"
+#include "stdint.hpp"
 #include "array.hpp"
 
 namespace zmq
@@ -67,6 +68,10 @@ namespace zmq
         //  Specifies the object to send events to.
         void set_event_sink (i_pipe_events *sink_);
 
+        //  Pipe endpoint can store an opaque ID to be used by its clients.
+        void set_pipe_id (uint32_t id_);
+        uint32_t get_pipe_id ();
+
         //  Returns true if there is at least one message to read in the pipe.
         bool check_read ();
 
@@ -176,6 +181,9 @@ namespace zmq
         //  asks us to.
         bool delay;
 
+        //  Opaque ID. To be used by the clients, not the pipe itself.
+        uint32_t pipe_id;
+
         //  Returns true if the message is delimiter; false otherwise.
         static bool is_delimiter (msg_t &msg_);
 

src/xrep.cpp

@@ -26,7 +26,6 @@
 
 zmq::xrep_t::xrep_t (class ctx_t *parent_, uint32_t tid_) :
     socket_base_t (parent_, tid_),
-    current_in (0),
     prefetched (false),
     more_in (false),
     current_out (NULL),
@@ -34,14 +33,16 @@ zmq::xrep_t::xrep_t (class ctx_t *parent_, uint32_t tid_) :
 {
     options.type = ZMQ_XREP;
 
+    prefetched_msg.init ();
+
     //  Start the peer ID sequence from a random point.
     generate_random (&next_peer_id, sizeof (next_peer_id));
 }
 
 zmq::xrep_t::~xrep_t ()
 {
-    zmq_assert (inpipes.empty ());
     zmq_assert (outpipes.empty ());
+    prefetched_msg.close ();
 }
 
 void zmq::xrep_t::xattach_pipe (pipe_t *pipe_, const blob_t &peer_identity_)
@@ -68,8 +69,8 @@ void zmq::xrep_t::xattach_pipe (pipe_t *pipe_, const blob_t &peer_identity_)
     zmq_assert (ok);
 
     //  Add the pipe to the list of inbound pipes.
-    inpipe_t inpipe = {pipe_, next_peer_id, true};
-    inpipes.push_back (inpipe);
+    pipe_->set_pipe_id (next_peer_id);
+    fq.attach (pipe_);
 
     //  Advance next peer ID so that if new connection is dropped shortly after
     //  its creation we don't accidentally get two subsequent peers with
@@ -79,20 +80,8 @@ void zmq::xrep_t::xattach_pipe (pipe_t *pipe_, const blob_t &peer_identity_)
 
 void zmq::xrep_t::xterminated (pipe_t *pipe_)
 {
-    for (inpipes_t::iterator it = inpipes.begin (); it != inpipes.end ();
-          ++it) {
-        if (it->pipe == pipe_) {
-            if ((inpipes_t::size_type) (it - inpipes.begin ()) < current_in)
-                current_in--;
-            inpipes.erase (it);
-            if (current_in >= inpipes.size ())
-                current_in = 0;
-            goto clean_outpipes;
-        }
-    }
-    zmq_assert (false);
+    fq.terminated (pipe_);
 
-clean_outpipes:
     for (outpipes_t::iterator it = outpipes.begin ();
           it != outpipes.end (); ++it) {
         if (it->second.pipe == pipe_) {
@@ -107,15 +96,7 @@ clean_outpipes:
 
 void zmq::xrep_t::xread_activated (pipe_t *pipe_)
 {
-    for (inpipes_t::iterator it = inpipes.begin (); it != inpipes.end ();
-          ++it) {
-        if (it->pipe == pipe_) {
-            zmq_assert (!it->active);
-            it->active = true;
-            return;
-        }
-    }
-    zmq_assert (false);
+    fq.activated (pipe_);
 }
 
 void zmq::xrep_t::xwrite_activated (pipe_t *pipe_)
@@ -212,55 +193,30 @@ int zmq::xrep_t::xrecv (msg_t *msg_, int flags_)
         return 0;
     }
 
-    //  Deallocate old content of the message.
-    int rc = msg_->close ();
-    errno_assert (rc == 0);
+    //  Get next message part.
+    pipe_t *pipe;
+    int rc = fq.recvpipe (msg_, flags_, &pipe);
+    if (rc != 0)
+        return -1;
 
-    //  If we are in the middle of reading a message, just grab next part of it.
+    //  If we are in the middle of reading a message, just return the next part.
     if (more_in) {
-        zmq_assert (inpipes [current_in].active);
-        bool fetched = inpipes [current_in].pipe->read (msg_);
-        zmq_assert (fetched);
         more_in = msg_->flags () & (msg_t::more | msg_t::label);
-        if (!more_in) {
-            current_in++;
-            if (current_in >= inpipes.size ())
-                current_in = 0;
-        }
         return 0;
     }
-
-    //  Round-robin over the pipes to get the next message.
-    for (inpipes_t::size_type count = inpipes.size (); count != 0; count--) {
-
-        //  Try to fetch new message.
-        if (inpipes [current_in].active)
-            prefetched = inpipes [current_in].pipe->read (&prefetched_msg);
-
-        //  If we have a message, create a prefix and return it to the caller.
-        if (prefetched) {
-            int rc = msg_->init_size (4);
-            errno_assert (rc == 0);
-            put_uint32 ((unsigned char*) msg_->data (),
-                inpipes [current_in].peer_id);
-            msg_->set_flags (msg_t::label);
-            return 0;
-        }
-
-        //  If me don't have a message, mark the pipe as passive and
-        //  move to next pipe.
-        inpipes [current_in].active = false;
-        current_in++;
-        if (current_in >= inpipes.size ())
-            current_in = 0;
-    }
-
-    //  No message is available. Initialise the output parameter
-    //  to be a 0-byte message.
-    rc = msg_->init ();
+ 
+    //  We are at the beginning of a new message. Move the message part we
+    //  have to the prefetched and return the ID of the peer instead.
+    rc = prefetched_msg.move (*msg_);
+    errno_assert (rc == 0);
+    prefetched = true;
+    rc = msg_->close ();
     errno_assert (rc == 0);
-    errno = EAGAIN;
-    return -1;
+    rc = msg_->init_size (4);
+    errno_assert (rc == 0);
+    put_uint32 ((unsigned char*) msg_->data (), pipe->get_pipe_id ());
+    msg_->set_flags (msg_t::label);
+    return 0;
 }
 
 int zmq::xrep_t::rollback (void)
@@ -275,28 +231,9 @@ int zmq::xrep_t::rollback (void)
 
 bool zmq::xrep_t::xhas_in ()
 {
-    //  There are subsequent parts of the partly-read message available.
-    if (prefetched || more_in)
+    if (prefetched)
         return true;
-
-    //  Note that messing with current doesn't break the fairness of fair
-    //  queueing algorithm. If there are no messages available current will
-    //  get back to its original value. Otherwise it'll point to the first
-    //  pipe holding messages, skipping only pipes with no messages available.
-    for (inpipes_t::size_type count = inpipes.size (); count != 0; count--) {
-        if (inpipes [current_in].active &&
-              inpipes [current_in].pipe->check_read ())
-            return true;
-
-        //  If me don't have a message, mark the pipe as passive and
-        //  move to next pipe.
-        inpipes [current_in].active = false;
-        current_in++;
-        if (current_in >= inpipes.size ())
-            current_in = 0;
-    }
-
-    return false;
+    return fq.has_in ();
 }
 
 bool zmq::xrep_t::xhas_out ()

src/xrep.hpp

@@ -22,11 +22,11 @@
 #define __ZMQ_XREP_HPP_INCLUDED__
 
 #include <map>
-#include <vector>
 
 #include "socket_base.hpp"
 #include "stdint.hpp"
 #include "msg.hpp"
+#include "fq.hpp"
 
 namespace zmq
 {
@@ -58,19 +58,8 @@ namespace zmq
 
     private:
 
-        struct inpipe_t
-        {
-            class pipe_t *pipe;
-            uint32_t peer_id;
-            bool active;
-        };
-
-        //  Inbound pipes with the names of corresponging peers.
-        typedef std::vector <inpipe_t> inpipes_t;
-        inpipes_t inpipes;
-
-        //  The pipe we are currently reading from.
-        inpipes_t::size_type current_in;
+        //  Fair queueing object for inbound pipes.
+        fq_t fq;
 
         //  Have we prefetched a message.
         bool prefetched;