ZMQ_RECONNECT_IVL_MAX socket option added

It allows for exponential back-off strategy when reconnecting.

Signed-off-by: Thijs Terlouw <thijsterlouw@gmail.com>

AUTHORS

@@ -54,6 +54,7 @@ Tamara Kustarova <kustarova.tamara@gmail.com>
 Taras Shpot <taras.shpot@eleks.com>
 Tero Marttila <terom@fixme.fi>
 Terry Wilson <terry@logivox.net>
+Thijs Terlouw <thijsterlouw@gmail.com>
 Toralf Wittner <toralf.wittner@gmail.com>
 Vitaly Mayatskikh <v.mayatskih@gmail.com>
 

doc/zmq_getsockopt.txt

@@ -261,10 +261,11 @@ Option value unit:: milliseconds
 Default value:: -1 (infinite)
 Applicable socket types:: all
 
+
 ZMQ_RECONNECT_IVL: Retrieve reconnection interval
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The 'ZMQ_RECONNECT_IVL' option shall retrieve the reconnection interval for the
-specified 'socket'.  The reconnection interval is the maximum period 0MQ shall
+The 'ZMQ_RECONNECT_IVL' option shall retrieve the initial reconnection interval
+for the specified 'socket'.  The reconnection interval is the period 0MQ shall
 wait between attempts to reconnect disconnected peers when using
 connection-oriented transports.
 
@@ -278,6 +279,24 @@ Default value:: 100
 Applicable socket types:: all, only for connection-oriented transports
 
 
+ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_RECONNECT_IVL_MAX' option shall retrieve the maximum reconnection 
+interval for the specified 'socket'.  This is the maximum period 0MQ shall wait 
+between attempts to reconnect. On each reconnect attempt, the previous interval 
+shall be doubled untill ZMQ_RECONNECT_IVL_MAX is reached. This allows for 
+exponential backoff strategy. Default value means no exponential backoff is 
+performed and reconnect interval calculations are only based on ZMQ_RECONNECT_IVL.
+
+NOTE:  Values less than ZMQ_RECONNECT_IVL will be ignored.
+
+[horizontal]
+Option value type:: int
+Option value unit:: milliseconds
+Default value:: 0 (only use ZMQ_RECONNECT_IVL)
+Applicable socket types:: all, only for connection-oriented transport
+
+
 ZMQ_BACKLOG: Retrieve maximum length of the queue of outstanding connections
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_BACKLOG' option shall retrieve the maximum length of the queue of

doc/zmq_setsockopt.txt

@@ -272,9 +272,9 @@ Applicable socket types:: all
 
 ZMQ_RECONNECT_IVL: Set reconnection interval
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-The 'ZMQ_RECONNECT_IVL' option shall set the reconnection interval for the
-specified 'socket'.  The reconnection interval is the maximum period 0MQ shall
-wait between attempts to reconnect disconnected peers when using
+The 'ZMQ_RECONNECT_IVL' option shall set the initial reconnection interval for
+the specified 'socket'.  The reconnection interval is the period 0MQ
+shall wait between attempts to reconnect disconnected peers when using
 connection-oriented transports.
 
 NOTE: The reconnection interval may be randomized by 0MQ to prevent
@@ -287,6 +287,24 @@ Default value:: 100
 Applicable socket types:: all, only for connection-oriented transports
 
 
+ZMQ_RECONNECT_IVL_MAX: Set maximum reconnection interval
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_RECONNECT_IVL_MAX' option shall set the maximum reconnection interval 
+for the specified 'socket'.  This is the maximum period 0MQ shall wait between
+attempts to reconnect. On each reconnect attempt, the previous interval shall be
+doubled untill ZMQ_RECONNECT_IVL_MAX is reached. This allows for exponential
+backoff strategy. Default value means no exponential backoff is performed and
+reconnect interval calculations are only based on ZMQ_RECONNECT_IVL.
+
+NOTE:  Values less than ZMQ_RECONNECT_IVL will be ignored.
+
+[horizontal]
+Option value type:: int
+Option value unit:: milliseconds
+Default value:: 0 (only use ZMQ_RECONNECT_IVL)
+Applicable socket types:: all, only for connection-oriented transports
+
+
 ZMQ_BACKLOG: Set maximum length of the queue of outstanding connections
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_BACKLOG' option shall set the maximum length of the queue of

include/zmq.h

@@ -203,6 +203,7 @@ ZMQ_EXPORT int zmq_term (void *context);
 #define ZMQ_RECONNECT_IVL 18
 #define ZMQ_BACKLOG 19
 #define ZMQ_RECOVERY_IVL_MSEC 20   /*  opt. recovery time, reconcile in 3.x   */
+#define ZMQ_RECONNECT_IVL_MAX 21
     
 /*  Send/recv options.                                                        */
 #define ZMQ_NOBLOCK 1

src/options.cpp

@@ -37,6 +37,7 @@ zmq::options_t::options_t () :
     type (-1),
     linger (-1),
     reconnect_ivl (100),
+    reconnect_ivl_max (0),
     backlog (100),
     requires_in (false),
     requires_out (false),
@@ -161,6 +162,18 @@ int zmq::options_t::setsockopt (int option_, const void *optval_,
         reconnect_ivl = *((int*) optval_);
         return 0;
 
+    case ZMQ_RECONNECT_IVL_MAX:
+        if (optvallen_ != sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        if (*((int*) optval_) < 0) {
+            errno = EINVAL;
+            return -1;
+        }
+        reconnect_ivl_max = *((int*) optval_);
+        return 0;
+
     case ZMQ_BACKLOG:
         if (optvallen_ != sizeof (int)) {
             errno = EINVAL;
@@ -297,6 +310,15 @@ int zmq::options_t::getsockopt (int option_, void *optval_, size_t *optvallen_)
         *optvallen_ = sizeof (int);
         return 0;
 
+    case ZMQ_RECONNECT_IVL_MAX:
+        if (*optvallen_ < sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        *((int*) optval_) = reconnect_ivl_max;
+        *optvallen_ = sizeof (int);
+        return 0;
+
     case ZMQ_BACKLOG:
         if (*optvallen_ < sizeof (int)) {
             errno = EINVAL;

src/options.hpp

@@ -59,8 +59,12 @@ namespace zmq
         //  Linger time, in milliseconds.
         int linger;
 
-        //  Interval between attempts to reconnect, in milliseconds.
+        //  Minimum interval between attempts to reconnect, in milliseconds.
+        //  Default 100ms
         int reconnect_ivl;
+        //  Maximum interval between attempts to reconnect, in milliseconds.
+        //  Default 0 (unused)
+        int reconnect_ivl_max;
 
         //  Maximum backlog for pending connections.
         int backlog;

src/zmq_connecter.cpp

@@ -40,7 +40,8 @@ zmq::zmq_connecter_t::zmq_connecter_t (class io_thread_t *io_thread_,
     io_object_t (io_thread_),
     handle_valid (false),
     wait (wait_before_connect),
-    session (session_)
+    session (session_),
+    current_reconnect_ivl(options.reconnect_ivl)
 {
     int rc = tcp_connecter.set_address (protocol_, address_);
     zmq_assert (rc == 0);
@@ -54,21 +55,10 @@ zmq::zmq_connecter_t::~zmq_connecter_t ()
         rm_fd (handle);
 }
 
-int zmq::zmq_connecter_t::get_reconnect_ivl ()
-{
-#if defined ZMQ_HAVE_WINDOWS
-    return (options.reconnect_ivl + (((int) GetCurrentProcessId () * 13)
-        % options.reconnect_ivl));
-#else
-    return (options.reconnect_ivl + (((int) getpid () * 13)
-        % options.reconnect_ivl));
-#endif
-}
-
 void zmq::zmq_connecter_t::process_plug ()
 {
     if (wait)
-        add_timer (get_reconnect_ivl (), reconnect_timer_id);
+        add_reconnect_timer();
     else
         start_connecting ();
 }
@@ -91,7 +81,7 @@ void zmq::zmq_connecter_t::out_event ()
     if (fd == retired_fd) {
         tcp_connecter.close ();
         wait = true;
-        add_timer (get_reconnect_ivl (), reconnect_timer_id);
+        add_reconnect_timer();
         return;
     }
 
@@ -140,5 +130,36 @@ void zmq::zmq_connecter_t::start_connecting ()
 
     //  Handle any other error condition by eventual reconnect.
     wait = true;
-    add_timer (get_reconnect_ivl (), reconnect_timer_id);
+    add_reconnect_timer();
+}
+
+void zmq::zmq_connecter_t::add_reconnect_timer()
+{
+    add_timer (get_new_reconnect_ivl(), reconnect_timer_id);
+}
+
+int zmq::zmq_connecter_t::get_new_reconnect_ivl ()
+{
+#if defined ZMQ_HAVE_WINDOWS
+    int pid = (int) GetCurrentProcessId ();
+#else
+    int pid = (int) getpid ();
+#endif
+
+    //  The new interval is the current interval + random value.
+    int this_interval = current_reconnect_ivl +
+        ((pid * 13) % options.reconnect_ivl);
+
+    //  Only change the current reconnect interval  if the maximum reconnect
+    //  interval was set and if it's larger than the reconnect interval.
+    if (options.reconnect_ivl_max > 0 && 
+        options.reconnect_ivl_max > options.reconnect_ivl) {
+
+        //  Calculate the next interval
+        current_reconnect_ivl = current_reconnect_ivl * 2;
+        if(current_reconnect_ivl >= options.reconnect_ivl_max) {
+            current_reconnect_ivl = options.reconnect_ivl_max;
+        }   
+    }
+    return this_interval;
 }

src/zmq_connecter.hpp

@@ -55,8 +55,13 @@ namespace zmq
         //  Internal function to start the actual connection establishment.
         void start_connecting ();
 
-        //  Internal function to return the reconnect backoff delay.
-        int get_reconnect_ivl ();
+        //  Internal function to add a reconnect timer
+        void add_reconnect_timer();
+
+        //  Internal function to return a reconnect backoff delay.
+        //  Will modify the current_reconnect_ivl used for next call
+        //  Returns the currently used interval
+        int get_new_reconnect_ivl ();
 
         //  Actual connecting socket.
         tcp_connecter_t tcp_connecter;
@@ -74,6 +79,9 @@ namespace zmq
         //  Reference to the session we belong to.
         class session_t *session;
 
+        //  Current reconnect ivl, updated for backoff strategy
+        int current_reconnect_ivl;
+
         zmq_connecter_t (const zmq_connecter_t&);
         const zmq_connecter_t &operator = (const zmq_connecter_t&);
     };