added preemptive callback control

reinstalled flow control

src/ca/CASG.cpp

@@ -89,6 +89,7 @@ int CASG::block ( double timeout )
     if ( p ) {
         return ECA_EVDISALLOW;
     }
+
     threadPrivateSet (cacRecursionLock, &cacRecursionLock);
 
     cur_time = osiTime::getCurrent ();
@@ -98,6 +99,8 @@ int CASG::block ( double timeout )
     beg_time = cur_time;
     delay = 0.0;
 
+    this->client.enableCallbackPreemption ();
+
     status = ECA_NORMAL;
     while ( 1 ) {
         this->mutex.lock ();
@@ -135,9 +138,6 @@ int CASG::block ( double timeout )
             break;
         }
 
-        /*
-         * wait for asynch notification
-         */
         this->sem.wait ( remaining );
 
         /*
@@ -148,6 +148,8 @@ int CASG::block ( double timeout )
         delay = cur_time - beg_time;
     }
 
+    this->client.disableCallbackPreemption ();
+
     threadPrivateSet (cacRecursionLock, NULL);
 
     return status;