msg_trace(
-OldValue,
+OnOrOff)
The predicate msg_trace/2
returns the current value of the message-trace
flag (on
or off
) and resets its value. The message-trace flag has
one of the values on
or off
. OldValue is bound to the
previous value of the flag, and the flag is reset to the value of
OnOrOff, which must be either on
or off
. The call
msg_trace(
X,
X)
returns the current value without
changing
it. When the message-trace flag is on, messages to and from the servant are
traced. By executing call_servant(msg_trace(_,on))
,
tracing can be turned on in the servant.