Fix issue 335

By assigning a SECURITY_DESCRIPTOR to the event we gain the ability to
share it between service and console programs. We also added
EVENT_MODIFY_STATE as a requirement to OpenEvent so we can SetEvent later
in the method.

src/signaler.cpp

@@ -233,6 +233,14 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
     return 0;
 
 #elif defined ZMQ_HAVE_WINDOWS
+    SECURITY_DESCRIPTOR sd = {0};
+    SECURITY_ATTRIBUTES sa = {0};
+
+    InitializeSecurityDescriptor(&sd, SECURITY_DESCRIPTOR_REVISION);
+    SetSecurityDescriptorDacl(&sd, TRUE, 0, FALSE);
+
+    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
+    sa.lpSecurityDescriptor = &sd;
 
     //  This function has to be in a system-wide critical section so that
     //  two instances of the library don't accidentally create signaler
@@ -241,9 +249,9 @@ int zmq::signaler_t::make_fdpair (fd_t *r_, fd_t *w_)
     //  Note that if the event object already exists, the CreateEvent requests
     //  EVENT_ALL_ACCESS access right. If this fails, we try to open
     //  the event object asking for SYNCHRONIZE access only.
-    HANDLE sync = CreateEvent (NULL, FALSE, TRUE, TEXT ("zmq-signaler-port-sync"));
+    HANDLE sync = CreateEvent (&sa, FALSE, TRUE, TEXT ("zmq-signaler-port-sync"));
     if (sync == NULL && GetLastError () == ERROR_ACCESS_DENIED)
-      sync = OpenEvent (SYNCHRONIZE, FALSE, TEXT ("zmq-signaler-port-sync"));
+      sync = OpenEvent (SYNCHRONIZE | EVENT_MODIFY_STATE, FALSE, TEXT ("zmq-signaler-port-sync"));
 
     win_assert (sync != NULL);