trace_on

Purpose

     Checks whether trace channel is enabled.

Library

     Run-time Services Library (librts.a)

Syntax

     int trace_on (chanmask)
     unsigned long chanmask;

Description

     The  trace_on subroutine  queries  the application  trace
     device driver to determine  whether a given trace channel
     is  enabled.   trace_on allows  a  program  to avoid  the
     unnecessary overhead of setting up the trace message when
     its trace channel is disabled.   trace_on is a C run-time
     subroutine and  should be  used by  application programs,
     but not by device drivers.

     The  chanmask parameter  is a  mask with  the bit  corre-
     sponding to the channel number  set.  It can be formed by
     the  expression  "(1 << 31 - "channum")".  User  programs
     can  use only  channel number  31, which  means that  the
     value of chanmask must be "1" for user programs.

     Making repeated calls to the trace device driver involves
     significant overhead, so call trace_on only once:  either
     at the start of processing or just before the first trace
     point in the program.

     If  the application  trace device  driver is  not already
     open, trace_on opens it.

     Upon  successful completion,  trace_on returns  1 if  the
     channel is enabled, or 0  if the channel is disabled.  If
     the trace_on  subroutine fails,  a message is  written to
     the standard error output, and a value of -1 is returned.

File

     /dev/appltrace

Related Information

     In this book:  "trcunix," and "trace."

     The  discussion of  trsave in  Device Driver  Development
     Guide.

     The trace command in AIX Operating System Commands Refer-
     ence.

     The discussion of trace  in AIX Operating System Program-
     ming Tools and Interfaces.