diff --git a/src/ca/callbackMutex.cpp b/src/ca/callbackMutex.cpp
new file mode 100644
index 000000000..edff6af30
--- /dev/null
+++ b/src/ca/callbackMutex.cpp
@@ -0,0 +1,70 @@
+
+/*  
+ *  $Id$
+ *
+ *                    L O S  A L A M O S
+ *              Los Alamos National Laboratory
+ *               Los Alamos, New Mexico 87545
+ *
+ *  Copyright, 1986, The Regents of the University of California.
+ *
+ *  Author: Jeff Hill
+ */
+
+#define epicsAssertAuthor "Jeff Hill johill@lanl.gov"
+
+#include "cac.h"
+
+callbackMutex::callbackMutex ( bool threadsMayBeBlockingForRecvThreadsToFinishIn ) :
+    recvThreadsPendingCount ( 0u ), 
+    threadsMayBeBlockingForRecvThreadsToFinish ( threadsMayBeBlockingForRecvThreadsToFinishIn )
+{
+}
+
+callbackMutex::~callbackMutex ()
+{
+}
+
+void callbackMutex::lock ()
+{
+    if ( ! this->primaryMutex.tryLock () ) {
+        // the count must be incremented prior to blocking for the lock
+        {
+            epicsGuard < epicsMutex > autoMutex ( this->countMutex );
+            assert ( this->recvThreadsPendingCount < UINT_MAX );
+            this->recvThreadsPendingCount++;
+        }
+        
+        this->primaryMutex.lock ();
+        
+        bool signalRequired;
+        {
+            epicsGuard < epicsMutex > autoMutex ( this->countMutex );
+            assert ( this->recvThreadsPendingCount > 0 );
+            this->recvThreadsPendingCount--;
+            if ( this->recvThreadsPendingCount == 0u &&
+                this->threadsMayBeBlockingForRecvThreadsToFinish ) {
+                signalRequired = true;
+            }
+            else {
+                signalRequired = false;
+            }
+        }
+        
+        if ( signalRequired ) {
+            this->noRecvThreadsPending.signal ();
+        }
+    }
+}
+
+void callbackMutex::unlock ()
+{
+    this->primaryMutex.unlock ();
+}
+
+void callbackMutex::waitUntilNoRecvThreadsPending () 
+{
+    while ( this->recvThreadsPendingCount > 0 ) {
+        this->noRecvThreadsPending.wait ();
+    }
+}