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Open Client Client-Library/C Reference Manual

Chapter 2 Topics

Callbacks

Signal callbacks

Signal callbacks

A signal callback is called whenever a process receives a signal on a UNIX platform.

On UNIX platforms, Client-Library uses signal-driven I/O to interact with the network. On these platforms, if an application handles signals, it must install the signal handler through Client-Library, even if the signals relate to non-Client-Library work. To install a signal handler, call ct_callback instead of using a system call. A system call to install a signal handler overwrites Client-Library's signal handler. If this occurs, Client-Library's behavior is undefined.

When Client-Library is used in an Open Server gateway, signal handlers should be installed using Server-Library routines.

When Client-Library receives a signal, Client-Library's signal handler:

• Performs any internal Client-Library processing that is required

• Calls the appropriate user-defined signal callback, if any

A signal callback must be defined according to operating system specifications.

An application that defines and installs a signal callback must include the appropriate operating system header file (sys/signal.h on most UNIX platforms).

A signal callback is installed only at the context level.

Signal callbacks are identified by adding the signal number on to the defined constant CS_SIGNAL_CB.

The following routine demonstrates how to install a signal callback:

          /*

           ** INSTALLSIGNALCB

           **

           ** This routine installs a signal callback for the

           ** specified signal

           **

           ** Parameters:

           **      cp   Context handle

           **      signo   Signal number

           **      signalhandler   Signal handler to install

           **

           ** Returns:

           **      CS_SUCCEED   Signal handler was installed

           **                   successfully

           **      CS_FAIL      An error was detected while

           **                   installing the signal handler

           */

           CS_RETCODE  installsignalcb(cp, signo, signalhandler)

           CS_CONTEXT  *cp;

           CS_INT  signo;

           CS_VOID *signalhandler;

           {

                CS_INT       adjustedsigno;

                CS_RETCODE   ret;

               /*

                ** Add the signal number to the CS_SIGNAL_CB 

                ** define to indicate the signal number that this

                ** handler is being installed for.

                */

                adjustedsigno = CS_SIGNAL_CB + signo;

               ret = ct_callback(cp, (CS_CONNECTION *)NULL,

                     CS_SET, adjustedsigno, signalhandler);

               return(ret);

           }