Darwin uses shutdown rather than signals to break out of socket I/O.

src/libCom/osi/os/Darwin/systemCallIntMech.cpp

@@ -0,0 +1,22 @@
+
+/*************************************************************************\
+* Copyright (c) 2002 The University of Chicago, as Operator of Argonne
+*     National Laboratory.
+* Copyright (c) 2002 The Regents of the University of California, as
+*     Operator of Los Alamos National Laboratory.
+* EPICS BASE Versions 3.13.7
+* and higher are distributed subject to a Software License Agreement found
+* in file LICENSE that is included with this distribution. 
+\*************************************************************************/
+/* $Id$ */
+/*
+ *      Author:		Jeff Hill 
+ */
+
+#include "osiSock.h"
+
+enum epicsSocketSystemCallInterruptMechanismQueryInfo 
+        epicsSocketSystemCallInterruptMechanismQuery ()
+{
+    return esscimqi_socketBothShutdownRequired;
+}