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/* Copyright 2014 Adobe Systems Incorporated (http://www.adobe.com/). All Rights Reserved.
This software is licensed as OpenSource, under the Apache License, Version 2.0.
This license is available at: http://opensource.org/licenses/Apache-2.0. */
/*
except.h
*/
/* exception handling */
#ifndef EXCEPT_H
#define EXCEPT_H
#ifndef WINATM
#define WINATM 0
#endif
#include "supportenvironment.h"
#include "supportpublictypes.h"
#if OS == os_mach
#include "supportossyslib.h"
#elif !WINATM
#include <stdlib.h>
#endif
/* #include CANTHAPPEN */ /* To include Abort processing, by reference */
#if defined(USE_CXX_EXCEPTION) && !defined(__cplusplus)
#error("must be compiled as C++ to use C++ exception as error handling")
#endif
#ifndef USE_CXX_EXCEPTION
/* If the macro setjmp_h is defined, it is the #include path to be used
instead of <setjmp.h>
*/
#ifdef setjmp_h
#include setjmp_h
#else /* setjmp_h */
#ifdef VAXC
#include setjmp
#else /* VAXC */
#include <setjmp.h>
#endif /* VAXC */
#endif /* setjmp_h */
#endif
/*
This interface defines a machine-independent exception handling
facility. It depends only on the availability of setjmp and longjmp.
Note that we depend on native setjmp and longjmp facilities; it's
not possible to interpose a veneer due to the way setjmp works.
(In fact, in ANSI C, setjmp is a macro, not a procedure.)
The exception handler is largely defined by a collection of macros
that provide some additional "syntax". A stretch of code that needs
to handle exceptions is written thus:
DURING
statement1;
statement2;
...
HANDLER
statement3
statement4;
...
END_HANDLER
The meaning of this is as follows. Normally, the statements between
DURING and HANDLER are executed. If no exception occurs, the statements
between HANDLER and END_HANDLER are bypassed; execution resumes at the
statement after END_HANDLER.
If an exception is raised while executing the statements between
DURING and HANDLER (including any procedure called from those statements),
execution of those statements is aborted and control passes to the
statements between HANDLER and END_HANDLER. These statements
comprise the "exception handler" for exceptions occurring between
the DURING and the HANDLER.
The exception handler has available to it two local variables,
Exception.Code and Exception.Message, which are the values passed
to the call to RAISE that generated the exception (see below).
These variables have valid contents only between HANDLER and
END_HANDLER.
If the exception handler simply falls off the end (or returns, or
whatever), propagation of the exception ceases. However, if the
exception handler executes RERAISE, the exception is propagated to
the next outer dynamically enclosing occurrence of DURING ... HANDLER.
There are two usual reasons for wanting to handle exceptions:
1. To clean up any local state (e.g., deallocate dynamically allocated
storage), then allow the exception to propagate further. In this
case, the handler should perform its cleanup, then execute RERAISE.
2. To recover from certain exceptions that might occur, then continue
normal execution. In this case, the handler should perform a
"switch" on Exception.Code to determine whether the exception
is one it is prepared to recover from. If so, it should perform
the recovery and just fall through; if not, it should execute
RERAISE to propagate the exception to a higher-level handler.
Note that in an environment with multiple contexts (i.e., multiple
coroutines), each context has its own stack of nested exception
handlers. An exception is raised within the currently executing
context and transfers control to a handler in the same context; the
exception does not propagate across context boundaries.
CAUTIONS:
Due to multi-threading concerns, a global chain of exception buffers
have been removed from DURING ... HANDLER implementation when setjmp/longjmp
is selected as the exception handling mechanism.
Instead, at least one, usually the outer-most exception handler must be
declared with DURING_EX instead of DURING, and its env parameter is respected when
longjmp is used as the exception thrown mechanism under C or USE_CXX_EXCEPTION undefined.
Handlers within HANDLER ... END_HANDLER following DURING (not DURING_EX) are simply ignored.
When C++ exception is used as the implementation, all handlers are respected.
The state of local variables at the time the HANDLER is invoked may
be unpredictable. In particular, a local variable that is modified
between DURING and HANDLER has an unpredictable value between
HANDLER and END_HANDLER. However, a local variable that is set before
DURING and not modified between DURING and HANDLER has a predictable
value.
*/
/* Data structures */
typedef struct _t_Exc_buf {
#ifdef USE_CXX_EXCEPTION
_t_Exc_buf(int code = 0, char *msg = 0) : Message(msg), Code(code) {}
#else
jmp_buf Environ; /* saved environment */
#endif
char *Message; /* Human-readable cause */
int Code; /* Exception code */
} _Exc_Buf;
/* Macros defining the exception handler "syntax":
DURING statements HANDLER statements END_HANDLER
(see the description above)
*/
#ifdef USE_CXX_EXCEPTION
#define DURING_EX(env) DURING
#define DURING \
{ \
_Exc_Buf Exception; \
try {
#define HANDLER \
} \
catch (_Exc_Buf & e) { \
Exception = e;
#define END_HANDLER \
} \
}
#else /* USE_CXX_EXCEPTION */
#define DURING_EX(env) \
{ \
_Exc_Buf Exception; \
_Exc_Buf *_EBP = &env; \
if (!setjmp(env.Environ)) {
#define DURING \
{ \
_Exc_Buf Exception; \
_Exc_Buf *_EBP = &Exception; \
Exception.Code = 0; \
if (1) {
#define HANDLER \
} \
else { \
Exception.Code = _EBP->Code; \
Exception.Message = NULL;
#define END_HANDLER \
} \
}
#endif /* USE_CXX_EXCEPTION */
/* Exported Procedures */
extern procedure os_raise(_Exc_Buf *buf, int Code, char *Message);
/* Initiates an exception; always called via the RAISE macro.
This procedure never returns; instead, the stack is unwound and
control passes to the beginning of the exception handler statements
for the innermost dynamically enclosing occurrence of
DURING ... HANDLER. The Code and Message arguments are passed to
that handler as described above.
It is legal to call os_raise from within a "signal" handler for a
synchronous event such as floating point overflow. It is not reasonable
to do so from within a "signal" handler for an asynchronous event
(e.g., interrupt), since the exception handler's data structures
are not updated atomically with respect to asynchronous events.
If there is no dynamically enclosing exception handler, os_raise
writes an error message to os_stderr and aborts with CantHappen.
*/
#if !defined(USE_CXX_EXCEPTION) && !WINATM && OS != os_windowsNT
#ifndef setjmp
extern int setjmp(jmp_buf buf);
#endif
/* Saves the caller's environment in the buffer (which is an array
type and therefore passed by pointer), then returns the value zero.
It may return again if longjmp is executed subsequently (see below).
*/
/*extern _CRTIMP procedure CDECL longjmp (jmp_buf buf, int value);*/
/* Restores the environment saved by an earlier call to setjmp,
unwinding the stack and causing setjmp to return again with
value as its return value (which must be non-zero).
The procedure that called setjmp must not have returned or
otherwise terminated. The saved environment must be at an earlier
place on the same stack as the call to longjmp (in other words,
it must not be in a different coroutine). It is legal to call
longjmp in a signal handler and to restore an environment
outside the signal handler; longjmp must be able to unwind
the signal cleanly in such a case.
*/
#endif /* !WINATM */
/* In-line Procedures */
#define RAISE os_raise
/* See os_raise above; defined as a macro simply for consistency */
#define RERAISE RAISE(&Exception, Exception.Code, Exception.Message)
/* Called from within an exception handler (between HANDLER and
END_HANDLER), propagates the same exception to the next outer
dynamically enclosing exception handler; does not return.
*/
#define ecComponentPrivBase 256
/* Error codes 256-511 are reserved for any component of the system
to use as it wishes with the restriction that all procedures on
the stack must be procedures from within the component when one
of these errors is raised. These errors are for the private use of
the component and should never be seen by procedures outside the
component.
*/
#endif /* EXCEPT_H */
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