path: root/utils/Signal.cc

/*
 *	CENA C++ Utilities
 *
 *	by Stephane Chatty
 *
 *	Copyright 1992
 *	Centre d'Etudes de la Navigation Aerienne (CENA)
 *
 *	Signal handling
 *
 *	$Id$
 *	$CurLog$
 */

#include "Signal.h"
#include "List.h"
#ifdef sun
/* This should come from <signal.h>, but no available C++ headers on Suns know about POSIX */
extern "C" {
	typedef int sigset_t;
	struct sigaction {
		void	(*sa_handler)(...);
		sigset_t	sa_mask;
		int	sa_flags;
	};

#	define NSIG 32
#	define SIGHUP  1
#	define SIGINT  2
#	define SIGQUIT 3
#	define SIGILL  4
#	define SIGTRAP 5
#	define SIGIOT  6
#	define SIGABRT 6
#	define SIGEMT  7
#	define SIGFPE  8
#	define SIGKILL 9
#	define SIGBUS  10
#	define SIGSEGV 11
#	define SIGSYS  12
#	define SIGPIPE 13
#	define SIGALRM 14
#	define SIGTERM 15
#	define SIGURG  16
#	define SIGSTOP 17
#	define SIGTSTP 18
#	define SIGCONT 19
#	define SIGCHLD 20
#	define SIGCLD  20
#	define SIGTTIN 21
#	define SIGTTOU 22
#	define SIGIO   23
#	define SIGPOLL SIGIO
#	define SIGXCPU 24
#	define SIGXFSZ 25
#	define SIGVTALRM 26
#	define SIGPROF 27
#	define SIGWINCH 28
#	define SIGLOST 29
#	define SIGUSR1 30
#	define SIGUSR2 31

#	define SIG_DFL	0
#	define SIG_BLOCK	0x0001
#	define SIG_UNBLOCK	0x0002
#	define SIG_SETMASK	0x0004
	int sigaction (int, const struct sigaction*, struct sigaction*);
	int sigemptyset (sigset_t*);
	int sigfillset (sigset_t*);
	int sigaddset (sigset_t*, int);
	int sigprocmask (int, const sigset_t*, sigset_t*);
}
#else
#include <signal.h>
#endif


/*?class CcuBaseSignalHandler
The class \typ{CcuBaseSignalHandler} is provided as a base class for signal handlers.
It comes with a derived class \typ{CcuSignalHandler} that can be used as is, without
any derivation.
A signal handler is created for a specific signal, identified by a numeric value.
The following constants are defined: \var{AllSigs, SigHup, SigInt, SigQuit, SigIll, SigTrap,
SigAbrt, SigEmt, SigFpe, SigKill, SigBus, SigSegv, SigSys, SigPipe, SigAlrm, SigTerm, SigUsr1,
SigUsr2, SigChld, SigVtalrm, SigIo, SigStop, SigTstp, SigCont, SigTtin, SigTtou, SigUrg,}
and \var{SigLost}. The value \var{AllSigs} is not meaningful to signal handlers.

When a signal is received by the program and a signal handler was created for that
signal, its method \fun{Handle} is called. This method should be redefined in derived
classes of \var{CcuBaseSignalHandler}.

Several signal handlers can be created for the same signal. However, only one is
active at a time. A stack of signal handlers is maintained for every signal, so that
the latest created signal handler is the active one, until its destruction. At that time,
the previous signal handler, if there was one, is activated again.
?*/

const int NumSigs = NSIG-1;

const int AllSigs = -1;
const int SigHup = SIGHUP;
const int SigInt = SIGINT;
const int SigQuit = SIGQUIT;
const int SigIll = SIGILL;
const int SigTrap = SIGTRAP;
const int SigAbrt = SIGABRT;
const int SigEmt = SIGEMT;
const int SigFpe = SIGFPE;
const int SigKill = SIGKILL;
const int SigBus = SIGBUS;
const int SigSegv = SIGSEGV;
const int SigSys = SIGSYS;
const int SigPipe = SIGPIPE;
const int SigAlrm = SIGALRM;
const int SigTerm = SIGTERM;
const int SigUsr1 = SIGUSR1;
const int SigUsr2 = SIGUSR2;
const int SigChld = SIGCHLD;
const int SigVtalrm = SIGVTALRM;
const int SigIo = SIGIO;
const int SigStop = SIGSTOP;
const int SigTstp = SIGTSTP;
const int SigCont = SIGCONT;
const int SigTtin = SIGTTIN;
const int SigTtou = SIGTTOU;
const int SigUrg = SIGURG;
const int SigLost = SIGLOST;


CcuList* CcuBaseSignalHandler::HandlerStacks = 0;

/*?hidden?*/
void
CcuBaseSignalHandler :: ClassInit ()
{
	HandlerStacks = new CcuList [NumSigs];
}

/*?
Create a signal handler for the signal \var{sig}.
?*/
CcuBaseSignalHandler :: CcuBaseSignalHandler (int sig)
: Signal (sig)
{
	CcuSignalBlocker b (sig);
	if (!HandlerStacks)
		ClassInit ();
	HandlerStacks [Signal-1].Prepend (this);
	Install ();
}

/*?nodoc?*/
CcuBaseSignalHandler :: ~CcuBaseSignalHandler ()
{
	CcuSignalBlocker b (Signal);
	CcuList& stack = HandlerStacks [Signal-1];
	if (stack.First () == this) {
		stack.RemoveFirst ();
		if (stack.IsEmpty ())
			InstallNone (Signal);
		else
			((CcuBaseSignalHandler*) stack.First ())->Install ();
	} else
		stack.Remove (this, 1);
}

#ifdef DOC
/*?
Get the signal that is handled by this signal handler.
?*/
int
CcuBaseSignalHandler :: GetSignal ()
{
}
#endif	/* DOC */

/*?hidden?*/
void
CcuBaseSignalHandler :: Install ()
{
	struct sigaction act;
	act.sa_handler = (void(*)(...)) DoHandle;
	sigemptyset (&act.sa_mask);
	act.sa_flags = 0;
	sigaction (Signal, &act, 0);
}

/*?hidden?*/
void
CcuBaseSignalHandler :: InstallNone (int sig)
{
	struct sigaction act;
	act.sa_handler = SIG_DFL;
	sigemptyset (&act.sa_mask);
	act.sa_flags = 0;
	sigaction (sig, &act, 0);
}

/*?hidden?*/
void
CcuBaseSignalHandler :: DoHandle (int sig)
{
	CcuBaseSignalHandler* s = (CcuBaseSignalHandler*) HandlerStacks [sig-1].First ();
	if (s)
		s->Handle ();
}

/*?
This virtual function should be redefined in derived classes. It is called
when this handler is the currently active one and a signal is received.
?*/
void
CcuBaseSignalHandler :: Handle ()
{
}

/*?class CcuSignalHandler
The class \typ{CcuSignalHandler} is a derived class of \typ{CcuBaseSignalHandler} that
can be used without deriving a new class.
Each \typ{CcuSignalHandler} holds a pointer to a function which is called when a
signal is received. This function, which is passed to the constructor, must
take an \typ{int} argument and return \typ{void}.
?*/

/*?
Create a signal handler for signal \var{sig}. The function \var{handler} will be
called when a signal is received.
?*/
CcuSignalHandler :: CcuSignalHandler (int sig, void (*handler) (int))
: CcuBaseSignalHandler (sig),
  Handler (handler)
{
}

/*?nodoc?*/
CcuSignalHandler :: ~CcuSignalHandler ()
{
}

/*?hidden?*/
void
CcuSignalHandler :: Handle ()
{
	(*Handler) (Signal);
}

/*?class CcuSignalBlocker
The class \typ{CcuSignalBlocker} provides protection against signals.
When a \typ{CcuSignalBlocker} is created for a signal type, the program will
be protected against such signals during the lifetime of the signal blocker.
Signal blockers are often used as follows:
\begin{ccode}
    void
    sensitive_function ()
    {
        // protect this function against alarms
        CcuSignalBlocker b (SigAlrm);
        ...
    }
\end{ccode}

Some signals, such as \var{SIGKILL}, actually cannot be blocked. Creating
a signal blocker for such a signal is ineffective.
Please note that signal numbers currently cannot be combined. If you wish
to protect a function against two signals, you must create two signal blockers.
However, the special value \var{AllSigs} allows the creation of signal blockers
that protect against all kinds of signals.
?*/

int CcuSignalBlocker::BlockCounts [NumSigs];


/*?
Create a signal blocker for the signal \var{sig}. If \var{sig} is \var{AllSigs},
all signals will be blocked.
?*/
CcuSignalBlocker :: CcuSignalBlocker (int sig)
: Signal (sig)
{
	int all = sig < 1 || sig > NumSigs;
	sigset_t set;
	if (all) {
		sigfillset (&set);
	} else {
		sigemptyset (&set);
		sigaddset (&set, Signal);
	}

	/* inhibit interrupts before registering inhibitions */
	sigprocmask (SIG_BLOCK, &set, 0);

	if (all) {
		for (int s = 0; s < NumSigs; s++)
			BlockCounts [s]++;
	} else {
		BlockCounts [Signal-1]++;
	}
}

/*?nodoc?*/
CcuSignalBlocker :: ~CcuSignalBlocker ()
{
	int all = Signal < 1 || Signal > NumSigs;
	int change = 0;
	sigset_t set;
	sigemptyset (&set);

	if (all) {
		for (int s = 0; s < NumSigs; s++) {
			if (!--BlockCounts [s]) {
				sigaddset (&set, s+1);
				change = 1;
			}
		}
	} else if (!--BlockCounts [Signal-1]) {
		sigaddset (&set, Signal);
		change = 1;
	}

	if (change)
		sigprocmask (SIG_UNBLOCK, &set, 0);
}