Index: src/backend/libpq/pqcomm.c
===================================================================
RCS file: /projects/cvsroot/pgsql/src/backend/libpq/pqcomm.c,v
retrieving revision 1.191
diff -c -r1.191 pqcomm.c
*** src/backend/libpq/pqcomm.c	3 Mar 2007 19:32:54 -0000	1.191
--- src/backend/libpq/pqcomm.c	14 May 2007 13:52:05 -0000
***************
*** 261,266 ****
--- 261,291 ----
  		snprintf(portNumberStr, sizeof(portNumberStr), "%d", portNumber);
  		service = portNumberStr;
  	}
+ #ifdef WIN32
+ 	/* Win32 doesn't have Unix sockets, but will allow multiple processes
+ 	 * to listen on the same port. This interlock is to prevent that.
+ 	 */
+ 	{
+ 		char mutexName[64];
+ 		HANDLE mutex;
+ 
+ 		sprintf(mutexName,"postgresql.interlock.%i", portNumber);
+ 		mutex = CreateMutex(NULL, FALSE, mutexName);
+ 		if (mutex == NULL)
+ 			ereport(FATAL,
+ 					(errmsg_internal("could not create interlocking mutex: %li",
+ 					GetLastError())));
+ 
+ 		if (GetLastError() == ERROR_ALREADY_EXISTS)
+ 			ereport(FATAL,
+ 					(errcode(ERRCODE_LOCK_FILE_EXISTS),
+ 					 errmsg("interlock mutex \"%s\" already exists", mutexName),
+ 					 errhint("Is another postgres listening on port %i", portNumber)));
+ 
+ 		/* Intentionally leak the handle until process exit, so the mutex
+ 		 * isn't freed. It will be automatically freed when the process exits. */
+ 	}
+ #endif
  
  	ret = pg_getaddrinfo_all(hostName, service, &hint, &addrs);
  	if (ret || !addrs)