diff --git a/src/ca/tcpiiu.cpp b/src/ca/tcpiiu.cpp
index 23cc218e0..61dca3ca6 100644
--- a/src/ca/tcpiiu.cpp
+++ b/src/ca/tcpiiu.cpp
@@ -318,7 +318,7 @@ void tcpRecvThread::run ()
                 }
             }
             else {
-                this->iiu.blockUntilBytesArePendingInOS();
+                this->iiu.blockUntilBytesArePendingInOS ();
                 nBytesIn = 0u;
                 if ( this->iiu.state != tcpiiu::iiucs_connected &&
                     this->iiu.state != tcpiiu::iiucs_clean_shutdown ) {
@@ -381,6 +381,7 @@ void tcpRecvThread::run ()
 
                 nBytesIn = pComBuf->fillFromWire ( this->iiu );
             }
+            this->iiu.cacRef.signalRecvThreadActivity ();
         }
 
         if ( pComBuf ) {
@@ -1329,7 +1330,9 @@ int tcpiiu::printf ( const char *pformat, ... )
 // this is called virtually
 void tcpiiu::flushRequest ()
 {
-    this->sendThreadFlushEvent.signal ();
+    if ( this->sendQue.occupiedBytes() > 0 ) {
+        this->sendThreadFlushEvent.signal ();
+    }
 }
 
 void tcpiiu::blockUntilBytesArePendingInOS ()
diff --git a/src/ca/udpiiu.cpp b/src/ca/udpiiu.cpp
index 5a9f5987c..da9f83d88 100644
--- a/src/ca/udpiiu.cpp
+++ b/src/ca/udpiiu.cpp
@@ -340,6 +340,7 @@ void udpRecvThread::run ()
 
     do {
         this->iiu.recvMsg ( this->cbMutex );
+        this->iiu.cacRef.signalRecvThreadActivity ();
     } while ( ! this->iiu.shutdownCmd );
 
     {
diff --git a/src/ca/udpiiu.h b/src/ca/udpiiu.h
index 883c6cad6..c063c75d6 100644
--- a/src/ca/udpiiu.h
+++ b/src/ca/udpiiu.h
@@ -98,6 +98,7 @@ public:
     bool pushDatagramMsg ( const caHdr &hdr, const void *pExt, ca_uint16_t extsize);
     void shutdown ();
     double roundTripDelayEstimate () const;
+    void fdMaskSet ( fd_set & mask ) const;
 
     // exceptions
     class noSocket {};
@@ -221,5 +222,10 @@ inline double udpiiu::roundTripDelayEstimate () const
     return this->rtteMean;
 }
 
+inline void udpiiu::fdMaskSet ( fd_set & mask ) const
+{
+    FD_SET ( this->sock, & mask );
+}
+
 #endif // udpiiuh
 
diff --git a/src/ca/virtualCircuit.h b/src/ca/virtualCircuit.h
index 91cf42ad4..ba3648b4f 100644
--- a/src/ca/virtualCircuit.h
+++ b/src/ca/virtualCircuit.h
@@ -133,6 +133,8 @@ public:
 
     bool bytesArePendingInOS () const;
 
+    void fdMaskSet ( fd_set & ) const;
+
 private:
     hostNameCache hostNameCacheInstance;
     tcpRecvThread recvThread;
@@ -247,6 +249,11 @@ inline unsigned tcpiiu::channelCount ()
     return this->channelList.count ();
 }
 
+inline void tcpiiu::fdMaskSet ( fd_set & mask ) const
+{
+    FD_SET ( this->sock, & mask );
+}
+
 inline void tcpRecvThread::interruptSocketRecv ()
 {
     epicsThreadId threadId = this->thread.getId ();