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/*

    		 Crown Copyright (c) 1997

    This TenDRA(r) Computer Program is subject to Copyright

    owned by the United Kingdom Secretary of State for Defence

    acting through the Defence Evaluation and Research Agency

    (DERA).  It is made available to Recipients with a

    royalty-free licence for its use, reproduction, transfer

    to other parties and amendment for any purpose not excluding

    product development provided that any such use et cetera

    shall be deemed to be acceptance of the following conditions:-

        (1) Its Recipients shall ensure that this Notice is

        reproduced upon any copies or amended versions of it;

        (2) Any amended version of it shall be clearly marked to

        show both the nature of and the organisation responsible

        for the relevant amendment or amendments;

        (3) Its onward transfer from a recipient to another

        party shall be deemed to be that party's acceptance of

        these conditions;

        (4) DERA gives no warranty or assurance as to its

        quality or suitability for any purpose and DERA accepts

        no liability whatsoever in relation to any use to which

        it may be put.

*/

/**** exception.h --- Exception handling.

 *

 ** Author: Steve Folkes <smf@hermes.mod.uk>

 *

 **** Commentary:

 *

 ***=== INTRODUCTION =========================================================

 *

 * This file specifies the interface to an exception handling facility.  The

 * facility is built on top of the ANSI C non-local exit mechanism (``setjmp''

 * and ``longjmp''), and should be used in preference to it.  The mechanism is

 * implemented as a set of macros.

 *

 * This file requires that two external functions are provided:

 *

 *	extern void			E_exception_unhandled

 *			(ExceptionP, CStringP, unsigned);

 *	extern void			E_exception_corrupt_handler

 *			(CStringP, unsigned);

 *

 * The first of these functions will be called if there is an unhandled

 * exception.  The exception will be given as an argument, along with the name

 * of the file, and the line within that file that the exception was thrown

 * from.  The second function will be called if a corrupt exception handler

 * stack is detected.  It will be called with the file name, and line number

 * where the corrupt handler was established.  Neither of these functions

 * should return.  If either function raises an exception, the program will

 * abort.

 *

 * If the ``PO_EXCEPTION_STACK_DIRECTION'' macro is defined, then an attempt

 * is made to detect corrupt exception handler stacks (almost certainly due to

 * missing or excessive calls to the ``UNHANDLE'' macro).  If the macro is

 * defined to be less than zero, it is assumed that the (system) stack grows

 * downwards; if it defined to be greater than zero, then it is assumed that

 * the (system) stack grows upwards; if it is defined to be zero, then a

 * weaker check that doesn't use the stack direction is used.

 *

 ***=== TYPES ================================================================

 *

 ** Type:	ExceptionP

 ** Repr:	<private>

 *

 * This is the type of an exception.  Exceptions are initialised using the

 * ``EXCEPTION'' macro (see later).  Once initialised, the exception should

 * not be changed.

 *

 ** Type:	ThrowDataT

 ** Type:	ThrowDataP

 ** Repr:	<private>

 *

 * This type is used internally to store data about the exception being

 * thrown.

 *

 ** Type:	HandlerT

 ** Type:	HandlerP

 ** Repr:	<private>

 *

 * This type is used internally to store data about the exception handler

 * stack.

 *

 ***=== FUNCTIONS ============================================================

 *

 ** Function:	CStringP		exception_name

 *			(ExceptionP exception)

 *

 * This function returns the name of the specified exception.  The return

 * value should not be modified or deallocated.

 *

 ***=== MACROS ===============================================================

 *

 ** Macro:	EXCEPTION (name)

 *

 * This macro is used to initialise an exception, e.g.:

 *

 *	ExceptionP XX_exception = EXCEPTION ("an exception");

 *

 * This creates an exception object called ``XX_exception''.  The string used

 * as an argument to the ``EXCEPTION'' macro is a description of the

 * exception.  This string is used as a message to be printed when an

 * exception is thrown but not handled.  It can also be accessed through the

 * ``exception_name'' function.  The string should be different for each

 * exception (the string content should be different as well, as some

 * compilers put strings with the same content into the same memory location,

 * and the address of the string is used to make the exception unique).

 *

 * Exceptions should only be defined in global scope. Exceptions with

 * automatic scope may cause problems if they are not handled within their

 * scope.

 *

 ** Macro:	THROW (exception)

 *

 * This macro raises an exception.  The specified exception is thrown, and

 * control passes to the innermost exception handler.  If there are no

 * exception handlers, a message is printed and the program is aborted.

 *

 ** Macro:	THROW_VALUE (exception, value)

 *

 * This macro raises an exception.  The specified exception is thrown, and

 * control passes to the innermost exception handler.  If there are no

 * exception handlers, a message is printed and the program is aborted.

 * Unlike the ``THROW'' macro, this macro also passes a value to the exception

 * handler.  The value should be a pointer to a non-function object.  The

 * object pointed to should not be automatically allocated (unless it is

 * guaranteed to be caught within its scope).

 *

 ** Macro:	HANDLE

 ** Macro:	WITH

 ** Macro:	END_HANDLE

 *

 * These macros are used to handle an exception. They should be used as in the

 * following example:

 *

 *	HANDLE

 *		normal code - possible variable corruption here

 *	WITH

 *		exception handler code

 *	END_HANDLE

 *

 * The ``HANDLE'' macro begins an exception handler construct.  This should be

 * followed by the normal code to be executed.  The ``WITH'' macro begins the

 * exception handler region.  This macro is followed by the code to handle the

 * exception.  The ``END_HANDLE'' macro terminates the exception handler

 * construct.

 *

 * If any part of the construct is omitted, the code will not compile, or the

 * exception handler stack will become corrupted at run time.

 *

 * The exception handler is removed by the ``WITH'' macro, so throwing another

 * exception in the exception handler region (between the ``WITH'' macro and

 * the ``END_HANDLE'' macro) will cause the next error handler to be invoked.

 *

 * When an exception is caught, it is possible that some of the variables in

 * scope will not contain the correct value.  It is best to declare any

 * variables you wish to use inside an exception handler as ``volatile''.

 * This program assumes that what the ANSI C library specifiaction says about

 * ``setjmp'' and ``longjmp'' holds, so only non-volatile automatic variables

 * in the indicated region should become corrupted.

 *

 ** Macro:	EXCEPTION_EXCEPTION ()

 *

 * This macro returns the current exception.  It should only be used within

 * the exception handler region (between the ``WITH'' and ``END_HANDLE''

 * macros).

 *

 ** Macro:	EXCEPTION_VALUE ()

 *

 * This macro returns the data that was thrown with the current exception.  It

 * should only be used within the exception handler region (between the

 * ``WITH'' and ``END_HANDLE'' macros).

 *

 ** Macro:	EXCEPTION_LINE ()

 *

 * This macro returns the line from which the current exception was thrown.

 * It should only be used within the exception handler region (between the

 * ``WITH'' and ``END_HANDLE'' macros).

 *

 ** Macro:	EXCEPTION_FILE ()

 *

 * This macro returns the file from which the current exception was thrown.

 * It should only be used within the exception handler region (between the

 * ``WITH'' and ``END_HANDLE'' macros).

 *

 ** Macro:	RETHROW ()

 *

 * This macro should only be used in the exception handler region (between the

 * ``WITH'' and ``END_HANDLE'' macros), and causes the current exception to be

 * rethrown (to be caught by the next outermost exception handler).

 *

 ** Macro:	UNHANDLE

 *

 * This macro MUST be used before using a ``goto'' or ``return'' that would

 * cause the normal code region (between the ``HANDLE'' and ``WITH'' macros)

 * to be exited (otherwise the exception handler stack will become corrupt at

 * run time).

 *

 **** Change Log:

 * $Log: exception.h,v $

 * Revision 1.1.1.1  1998/01/17  15:57:45  release

 * First version to be checked into rolling release.

 *

 * Revision 1.2  1994/12/12  11:45:34  smf

 * Performing changes for 'CR94_178.sid+tld-update' - bringing in line with

 * OSSG C Coding Standards.

 *

 * Revision 1.1.1.1  1994/07/25  16:06:10  smf

 * Initial import of os-interface shared files.

 *

**/

/****************************************************************************/

#ifndef H_EXCEPTION

#define H_EXCEPTION

#include "os-interface.h"

/*--------------------------------------------------------------------------*/

typedef CStringP		ExceptionP;

typedef struct {

    CStringP			exception;

    GenericP			data;

    unsigned			line;

    CStringP			file;

} ThrowDataT, *ThrowDataP;

typedef struct HandlerT {

#ifdef PO_EXCEPTION_STACK_DIRECTION

    unsigned			magic_start;

    CStringP			file;

    unsigned			line;

#endif /* defined (PO_EXCEPTION_STACK_DIRECTION) */

    struct HandlerT	       *next;

    jmp_buf			buffer;

#ifdef PO_EXCEPTION_STACK_DIRECTION

    unsigned			magic_end;

#endif /* defined (PO_EXCEPTION_STACK_DIRECTION) */

} HandlerT, *HandlerP;

/*--------------------------------------------------------------------------*/

extern	CStringP		exception_name(ExceptionP);

/*--------------------------------------------------------------------------*/

extern HandlerP			X__exception_handler_stack;

extern ThrowDataT		X__exception_throw_data;

extern NoReturnT		X__exception_throw(void);

/*--------------------------------------------------------------------------*/

#define EXCEPTION(name)name

#define THROW(exc)\

{X__exception_throw_data.exception = (exc); \

 X__exception_throw_data.data      = NIL(GenericP); \

 X__exception_throw_data.line      = __LINE__; \

 X__exception_throw_data.file      = __FILE__; \

 X__exception_throw();}

#define THROW_VALUE(exc,val)\

{X__exception_throw_data.exception = (exc); \

 X__exception_throw_data.data      = ((GenericP)(val)); \

 X__exception_throw_data.line      = __LINE__; \

 X__exception_throw_data.file      = __FILE__; \

 X__exception_throw();}

#ifdef PO_EXCEPTION_STACK_DIRECTION

#define X__EXCEPTION_MAGIC(0x1234)

#define HANDLE \

{HandlerT X___exception_handler; \

 X___exception_handler.magic_start = X__EXCEPTION_MAGIC; \

 X___exception_handler.file        = __FILE__; \

 X___exception_handler.line        = __LINE__; \

 X___exception_handler.next        = X__exception_handler_stack; \

 X___exception_handler.magic_end   = X__EXCEPTION_MAGIC; \

 X__exception_handler_stack        = &X___exception_handler; \

 if (!setjmp(X___exception_handler.buffer)) {

#else

#define HANDLE \

{HandlerT X___exception_handler; \

 X___exception_handler.next = X__exception_handler_stack; \

 X__exception_handler_stack = &X___exception_handler; \

 if (!setjmp(X___exception_handler.buffer)) {

#endif /* defined (PO_EXCEPTION_STACK_DIRECTION) */

#define WITH \

     X__exception_handler_stack = X___exception_handler.next; \

 } else { \

     X__exception_handler_stack = X___exception_handler.next; {

#define END_HANDLE }}}

#define EXCEPTION_EXCEPTION()\

X__exception_throw_data.exception

#define EXCEPTION_VALUE()\

X__exception_throw_data.data

#define EXCEPTION_LINE()\

X__exception_throw_data.line

#define EXCEPTION_FILE()\

X__exception_throw_data.file

#define RETHROW()\

X__exception_throw();

#define UNHANDLE X__exception_handler_stack = X___exception_handler.next;

#endif /* !defined (H_EXCEPTION) */