4.11. SigHandler Class
SigHandler is a powerful UNIX signal manager/dispatcher class. It is based on the white paper, published in [DCS97].
4.11.1. DEFINITION
class SigHandler {
public:
virtual int install (int signum_,
EventHandler* new_hand_,
SigAction* new_disp_ = 0,
EventHandler** old_hand_ = 0,
SigAction* old_disp_ = 0);
virtual int remove (int signum_,
EventHandler* eh_ = 0,
SigAction* new_disp_ = 0,
SigAction* old_disp_ = 0);
static void dispatch (int signum_);
EventHandler* handler (int signum_, EventHandler* new_);
EventHandler* handler (int signum_);
};
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SigHandler class plays the role of a centralized signal dispatcher for the running application. It is based on Callback Pattern that overcomes two major difficulties in using UNIX signals with C++ programs:
Lack of encapsulation
Limited functionality in the signal handler
SigHandler class allows to install a EventHandler object in order to manage application's reaction to a UNIX signal. When the registered signal is delivered by the operating system to the running application, handle_signal() method of the registered EventHandler is called to handle the signal.
4.11.2. USAGE
#include <assa/SigHandler.h>
void foo(void)
{
SigHandler sh;
EventHandler eh;
sh.install (SIGHUP, &eh);
// ... go on with the function flow
// ... at some point might be interrupted by SIGNUP
// ... continume with the function flow
sh.remove (SIGHUP, &eh);
}
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In the example above, sh plays the role of a signal manager and signal handler repository. When the SIGHUP signal is delivered to the process, sh dispatches the signal to the application by calling eh.handle_signal(SIGHUP) callback function. of eh.
 | If conventional "C" signal handler was installed prior to calling sh.install(), it would be lost irreversibly. |