.  \"ident	"@(#)cls4:man/task/interrupt.3	1.1"
.  \"Copyright (c) 1984 AT&T
.  \"All Rights Reserved        
.  \"THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T
.  \"The copyright notice above does not evidence any           
.  \"actual or intended publication of such source code.
.TH INTERRUPT 3C++ "C++ Task Library" " "
.SH NAME
Interrupt_handler \- signal handling for the C++ task library
.SH SYNOPSIS
\f3
.nf
#include <task.h>

class Interrupt_handler : public object {
	virtual void	interrupt();
public:
			Interrupt_handler(int);
			~Interrupt_handler();
	objtype		o_type();
	int		pending();
};
.fi
\f1
.SH DESCRIPTION
.P
Class \f(CWInterrupt_handler\fP allows \f(CWtask\fPs to wait
for external events in the form of UNIX system signals.
Class \f(CWInterrupt_handler\fP is derived from class \f(CWobject\fP
so that \f(CWtask\fPs can wait for \f(CWInterrupt_handler\fP objects.
Class \f(CWobject\fP is described on the task(3C++) manual page.
.P
The public member functions supplied in the task system class
\f(CWInterrupt_handler\fP are listed and described below.
The following symbols are used:
.RS 10
.TP 4
.B ih
an \f(CWInterrupt_handler\fP object
.TP 4
.B i
an \f(CWint\fP
.TP 4
.B eo
an \f(CWobjtype\fP enumeration
.RE
.TP
.B "Interrupt_handler ih( i );"
Constructs a new \f(CWInterrupt_handler\fP object, \f3ih\fP,
which is to wait for a signal number \f3i\fP.
(See signal(2).)
Once an \f(CWInterrupt_handler\fP object has been established for
a particular signal,
when that signal occurs, the private, virtual
.B interrupt()
function is called at real time.
When it returns, control will resume at the point where the current
\f(CWtask\fP was interrupted.
That is, signals do not cause the current \f(CWtask\fP to be pre-empted.
When the currently running \f(CWtask\fP is suspended,
a special, built-in task, the
.I "interrupt alerter"
will be scheduled.
This \f(CWtask\fP alerts the \f(CWInterrupt_handler\fP
(and any others that have received interrupts since the
.I interrupt alerter
last ran), and thereby makes any \f(CWtask\fPs waiting for
those \f(CWInterrupt_handler\fPs runnable.
As long as any \f(CWInterrupt_handler\fP exists,
the scheduler will wait for an interrupt,
rather than exiting when the
.I run chain
becomes empty.
.TP
.B "void interrupt()
The private virtual function
.B Interrupt_handler::interrupt()
is a null function, but because it is virtual,
the programmer can specify the action to be taken at interrupt time
by defining an
.B interrupt()
function in a class derived from \f(CWInterrupt_handler\fP.
.TP
.B "eo = ih.o_type()"
Returns the class type of the object
(\f(CWobject::INTHANDLER\fP).
.B o_type()
is a virtual function.
.TP
.B "i = ih.pending()"
Returns TRUE except the first time it is called after a signal occurs.
.SH DIAGNOSTICS
See task(3C++).
.SH BUGS
.P
UNIX System V Releases 3.1 and 3.2 (SVR3.1 and SVR3.2) for the Intel 386 machine
will not call a signal handler when the current \f(CWtask\fP is running on
a stack in the free store,
that is, when the current \f(CWtask\fP has a DEDICATED stack.
If you need to use the signal handling mechanisms on that configuration,
you cannot use tasks which have DEDICATED stacks.
In this case, compile the task library with _SHARED_ONLY defined,
which will make SHARED the default mode for \f(CWtasks\fP.
(Note:  it is insufficient to declare all \f(CWtask\fPs as SHARED without
compiling a _SHARED_ONLY version of the task library,
because the internal system \f(CWtask\fP,
the \f2interrupt alerter\fP,
is DEDICATED by default.)
.SH SEE ALSO
TASK.INTRO(3C++), task(3C++), queue(3C++), tasksim(3C++), signal(2)
.br
Stroustrup, B. and Shopiro, J. E.,
"A Set of C++ Classes for Co-routine Style Programming,"
in
.I "AT&T C++ Language System Release 2.0 Library Manual."
.br
Shopiro, J. E.,
"Extending the C++ Task System for Real-Time Control,"
in
.I "AT&T C++ Language System Release 2.0 Library Manual."