ZMQ_BACKLOG socket option added.

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

doc/zmq_getsockopt.txt

@@ -239,6 +239,19 @@ Default value:: 100
 Applicable socket types:: all
 
 
+ZMQ_BACKLOG: Retrieve maximum length of the queue of pending connections
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_RECONNECT' option shall retrieve maximum size of the
+pending connection backlog for connection-based transports. For details
+refer to your operating system documentation for the 'listen' function.
+
+[horizontal]
+Option value type:: int
+Option value unit:: connections
+Default value:: 100
+Applicable socket types:: all
+
+
 ZMQ_FD: Retrieve file descriptor associated with the socket
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_FD' option shall retrieve file descriptor associated with the 0MQ

doc/zmq_setsockopt.txt

@@ -245,6 +245,19 @@ Default value:: 100
 Applicable socket types:: all
 
 
+ZMQ_BACKLOG: Set maximum length of the queue of pending connections
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_RECONNECT' option shall be set to specify maximum size of the
+pending connection backlog for connection-based transports. For details
+refer to your operating system documentation for the 'listen' function.
+
+[horizontal]
+Option value type:: int
+Option value unit:: connections
+Default value:: 100
+Applicable socket types:: all
+
+
 RETURN VALUE
 ------------
 The _zmq_setsockopt()_ function shall return zero if successful. Otherwise it

include/zmq.h

@@ -193,6 +193,7 @@ ZMQ_EXPORT int zmq_term (void *context);
 #define ZMQ_TYPE 16
 #define ZMQ_LINGER 17
 #define ZMQ_RECONNECT_IVL 18
+#define ZMQ_BACKLOG 19
 
 /*  Send/recv options.                                                        */
 #define ZMQ_NOBLOCK 1

src/config.hpp

@@ -85,10 +85,6 @@ namespace zmq
         //  possible latencies.
         clock_precision = 1000000,
 
-        //  Maximal number of non-accepted connections that can be held by
-        //  TCP listener object.
-        tcp_connection_backlog = 100,
-
         //  Maximum transport data unit size for PGM (TPDU).
         pgm_max_tpdu = 1500
     };

src/options.cpp

@@ -36,6 +36,7 @@ zmq::options_t::options_t () :
     type (-1),
     linger (-1),
     reconnect_ivl (100),
+    backlog (100),
     requires_in (false),
     requires_out (false),
     immediate_connect (true)
@@ -150,6 +151,15 @@ int zmq::options_t::setsockopt (int option_, const void *optval_,
         }
         reconnect_ivl = *((int*) optval_);
         return 0;
+
+    case ZMQ_BACKLOG:
+        if (optvallen_ != sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        backlog = *((int*) optval_);
+        return 0;
+
     }
 
     errno = EINVAL;
@@ -269,6 +279,15 @@ int zmq::options_t::getsockopt (int option_, void *optval_, size_t *optvallen_)
         *optvallen_ = sizeof (int);
         return 0;
 
+    case ZMQ_BACKLOG:
+        if (*optvallen_ < sizeof (int)) {
+            errno = EINVAL;
+            return -1;
+        }
+        *((int*) optval_) = backlog;
+        *optvallen_ = sizeof (int);
+        return 0;
+
     }
 
     errno = EINVAL;

src/options.hpp

@@ -60,6 +60,9 @@ namespace zmq
         //  Interval between attempts to reconnect, in milliseconds.
         int reconnect_ivl;
 
+        //  Maximum backlog for pending connections.
+        int backlog;
+
         //  These options are never set by the user directly. Instead they are
         //  provided by the specific socket type.
         bool requires_in;

src/tcp_listener.cpp

@@ -42,7 +42,8 @@ zmq::tcp_listener_t::~tcp_listener_t ()
         close ();
 }
 
-int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_)
+int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_,
+    int backlog_)
 {
     //  IPC protocol is not supported on Windows platform.
     if (strcmp (protocol_, "tcp") != 0 ) {
@@ -81,7 +82,7 @@ int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_)
     }
 
     //  Listen for incomming connections.
-    rc = listen (s, 1);
+    rc = listen (s, backlog_);
     if (rc == SOCKET_ERROR) {
         wsa_error_to_errno ();
         return -1;
@@ -161,7 +162,8 @@ zmq::tcp_listener_t::~tcp_listener_t ()
         close ();
 }
 
-int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_)
+int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_,
+    int backlog_)
 {
     if (strcmp (protocol_, "tcp") == 0 ) {
 
@@ -201,7 +203,7 @@ int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_)
         }
 
         //  Listen for incomming connections.
-        rc = listen (s, tcp_connection_backlog);
+        rc = listen (s, backlog_);
         if (rc != 0) {
             close ();
             return -1;
@@ -241,7 +243,7 @@ int zmq::tcp_listener_t::set_address (const char *protocol_, const char *addr_)
         }
 
         //  Listen for incomming connections.
-        rc = listen (s, tcp_connection_backlog);
+        rc = listen (s, backlog_);
         if (rc != 0) {
             close ();
             return -1;

src/tcp_listener.hpp

@@ -36,7 +36,8 @@ namespace zmq
         ~tcp_listener_t ();
 
         //  Start listening on the interface.
-        int set_address (const char *protocol_, const char *addr_);
+        int set_address (const char *protocol_, const char *addr_,
+            int backlog_);
 
         //  Close the listening socket.
         int close ();

src/zmq_listener.cpp

@@ -38,7 +38,7 @@ zmq::zmq_listener_t::~zmq_listener_t ()
 
 int zmq::zmq_listener_t::set_address (const char *protocol_, const char *addr_)
 {
-     return tcp_listener.set_address (protocol_, addr_);
+     return tcp_listener.set_address (protocol_, addr_, options.backlog);
 }
 
 void zmq::zmq_listener_t::process_plug ()