/* * dpsexcept.h -- exception handling for the DPS client library * * (c) Copyright 1984-1994 Adobe Systems Incorporated. * All rights reserved. * * Permission to use, copy, modify, distribute, and sublicense this software * and its documentation for any purpose and without fee is hereby granted, * provided that the above copyright notices appear in all copies and that * both those copyright notices and this permission notice appear in * supporting documentation and that the name of Adobe Systems Incorporated * not be used in advertising or publicity pertaining to distribution of the * software without specific, written prior permission. No trademark license * to use the Adobe trademarks is hereby granted. If the Adobe trademark * "Display PostScript"(tm) is used to describe this software, its * functionality or for any other purpose, such use shall be limited to a * statement that this software works in conjunction with the Display * PostScript system. Proper trademark attribution to reflect Adobe's * ownership of the trademark shall be given whenever any such reference to * the Display PostScript system is made. * * ADOBE MAKES NO REPRESENTATIONS ABOUT THE SUITABILITY OF THE SOFTWARE FOR * ANY PURPOSE. IT IS PROVIDED "AS IS" WITHOUT EXPRESS OR IMPLIED WARRANTY. * ADOBE DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NON- INFRINGEMENT OF THIRD PARTY RIGHTS. IN NO EVENT SHALL ADOBE BE LIABLE * TO YOU OR ANY OTHER PARTY FOR ANY SPECIAL, INDIRECT, OR CONSEQUENTIAL * DAMAGES OR ANY DAMAGES WHATSOEVER WHETHER IN AN ACTION OF CONTRACT, * NEGLIGENCE, STRICT LIABILITY OR ANY OTHER ACTION ARISING OUT OF OR IN * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. ADOBE WILL NOT * PROVIDE ANY TRAINING OR OTHER SUPPORT FOR THE SOFTWARE. * * Adobe, PostScript, and Display PostScript are trademarks of Adobe Systems * Incorporated which may be registered in certain jurisdictions * * Author: Adobe Systems Incorporated */ /* $XFree86: xc/include/DPS/dpsexcept.h,v 1.3 2000/06/07 22:02:56 tsi Exp $ */ /* Original version: Jeffrey Mogul, Stanford, 18 February 1983 */ #ifndef DPSEXCEPT_H #define DPSEXCEPT_H /* 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 */ /* 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. It is ILLEGAL to execute a statement between DURING and HANDLER that would transfer control outside of those statements. In particular, "return" is illegal (an unspecified malfunction will occur). To perform a "return", execute E_RETURN_VOID; to perform a "return(x)", execute E_RETURN(x). This restriction does not apply to the statements between HANDLER and END_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. */ /* Data structures */ typedef struct _Exc_buf_x { struct _Exc_buf_x *Prev; /* exception chain back-pointer */ jmp_buf Environ; /* saved environment */ char *Message; /* Human-readable cause */ int Code; /* Exception code */ } _Exc_Buf; extern _Exc_Buf *_Exc_Header; /* global exception chain header */ /* Macros defining the exception handler "syntax": DURING statements HANDLER statements END_HANDLER (see the description above) */ #define _E_RESTORE _Exc_Header = Exception.Prev #define DURING {_Exc_Buf Exception;\ Exception.Prev=_Exc_Header;\ _Exc_Header= &Exception;\ if (! setjmp(Exception.Environ)) { #define HANDLER _E_RESTORE;} else { #define END_HANDLER }} #define E_RETURN(x) {_E_RESTORE; return(x);} #define E_RTRN_VOID {_E_RESTORE; return;} /* Exported Procedures */ #if defined(__cplusplus) || defined(c_plusplus) extern "C" { #endif extern void DPSRaise(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 DPSRaise 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, DPSRaise writes an error message to os_stderr and aborts with DPSCantHappen. */ extern void DPSCantHappen(void); /* Calls abort. This is used only to handle "impossible" errors; there is no recovery, and DPSCantHappen does not return. */ /* The following two operations are invoked only from the exception handler macros and from the DPSRaise procedure. Note that they are not actually declared here but in <setjmp.h> (or a substitute specified by the macro SETJMP, above). Note that the exception handler facility uses setjmp/longjmp in a stylized way that may not require the full generality of the standard setjmp/longjmp mechanism. In particular, setjmp is never called during execution of a signal handler; thus, the signal mask saved by setjmp can be constant rather than obtained from the operating system on each call. This can have considerable performance consequences. */ #if 0 extern int setjmp(jmp_buf buf); /* 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 void 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 /* 0 */ #if defined(__cplusplus) || defined(c_plusplus) } #endif /* In-line Procedures */ #define RAISE DPSRaise /* See DPSRaise above; defined as a macro simply for consistency */ #define RERAISE RAISE(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. */ /* Error code enumerations By convention, error codes are divided into blocks belonging to different components of the Display PostScript system. Negative error codes and the codes between 0 and 999 (inclusive) are reserved for use by the Display PostScript system. */ #define dps_err_base 1000 #endif /* DPSEXCEPT_H */