Use single port for creating signalers on Windows

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

src/config.hpp

@@ -79,7 +79,11 @@ namespace zmq
         clock_precision = 1000000,
 
         //  Maximum transport data unit size for PGM (TPDU).
-        pgm_max_tpdu = 1500
+        pgm_max_tpdu = 1500,
+
+        //  On some OSes the signaler has to be emulated using a TCP
+        //  connection. In such cases following port is used.
+        signaler_port = 5905
     };
 
 }

src/signaler.cpp

@@ -59,6 +59,7 @@
 #include "signaler.hpp"
 #include "likely.hpp"
 #include "stdint.hpp"
+#include "config.hpp"
 #include "err.hpp"
 #include "fd.hpp"
 #include "ip.hpp"
@@ -233,6 +234,17 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
 
 #elif defined ZMQ_HAVE_WINDOWS
 
+    //  This function has to be in a system-wide critical section so that
+    //  two instances of the library don't accidentally create signaler
+    //  crossing the process boundary.
+    //  We'll use named event object to implement the critical section.
+    HANDLE sync = CreateEvent (NULL, FALSE, FALSE, "zmq-signaler-port-sync");
+    win_assert (sync != NULL);
+
+    //  Enter the critical section.
+    DWORD dwrc = WaitForSingleObject (sync, INFINITE);
+    zmq_assert (dwrc == WAIT_OBJECT_0);
+
     //  Windows has no 'socketpair' function. CreatePipe is no good as pipe
     //  handles cannot be polled on. Here we create the socketpair by hand.
     *w_ = INVALID_SOCKET;
@@ -258,15 +270,10 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
     memset (&addr, 0, sizeof (addr));
     addr.sin_family = AF_INET;
     addr.sin_addr.s_addr = htonl (INADDR_LOOPBACK);
-    addr.sin_port = 0;
+    addr.sin_port = htons (signaler_port);
     rc = bind (listener, (const struct sockaddr*) &addr, sizeof (addr));
     wsa_assert (rc != SOCKET_ERROR);
 
-    //  Retrieve local port listener is bound to (into addr).
-    int addrlen = sizeof (addr);
-    rc = getsockname (listener, (struct sockaddr*) &addr, &addrlen);
-    wsa_assert (rc != SOCKET_ERROR);
-
     //  Listen for incomming connections.
     rc = listen (listener, 1);
     wsa_assert (rc != SOCKET_ERROR);
@@ -292,6 +299,10 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
     rc = closesocket (listener);
     wsa_assert (rc != SOCKET_ERROR);
 
+    //  Exit the critical section.
+    BOOL brc = SetEvent (sync);
+    win_assert (brc != 0);
+
     return 0;
 
 #elif defined ZMQ_HAVE_OPENVMS