"

 COPYRIGHT (c) 1993 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

Object subclass:#Exception

	instanceVariableNames:'signal parameter errorString suspendedContext handlerContext

		rejected originator resumeBlock rejectBlock'

	classVariableNames:'EmergencyHandler RecursiveExceptionSignal'

	poolDictionaries:''

	category:'Kernel-Exceptions'

!

!Exception class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1993 by Claus Gittinger

	      All Rights Reserved

 This software is furnished under a license and may be used

 only in accordance with the terms of that license and with the

 inclusion of the above copyright notice.   This software may not

 be provided or otherwise made available to, or used by, any

 other person.  No title to or ownership of the software is

 hereby transferred.

"

!

documentation

"

    Instances of Exception are passed to a Signal handling block as argument.

    The handler block may perform various actions by sending corresponding messages

    to the exception object. The following actions are possible:

        reject          - dont handle this signal;

                          another handler will be searched for, 

                          upper in the calling hierarchy

        proceed         - return from the Signal>>raise, with nil as value

        proceedWith:val - same, but return val from Signal>>raise

        return          - return from the Signal>>handle:do:, with nil as value

        returnWith:val  - same, but return val from Signal>>handle:do:

                          (this is also the handlers default, 

                           if it falls through; taking the handlerBlocks value

                           as return value)

        restart         - restart the Signal>>handle:do:, after repairing

    Via the Exception object, the handler can also query the state of execution:

    where the Signal was raised, where the handler is, the signal which caused

    the error and the errorString passed when the signal was raised. Also, an optional

    parameter can be passed - the use is signal specific.:

    [instance variables:]

        signal           <Signal>     the signal which caused the exception

        parameter        <Object>     a parameter (if any) which was passed when raising

                                      the signal (only if raised with #raiseWith:aParameter)

        errorString      <String>     an errorString 

                                      (usually the signals own errorString, but sometimes

                                       changed explicitely in #raiseWith:errorString:)

        suspendedContext <Context>    the context in which the raise occured

        handlerContext   <Context>    the context of the handler (if any)

        resumeBlock      <Block>      private to the exception; needed to perform resume action

        rejectBlock      <Block>      private to the exception; needed to perform reject action

    In case of an unhandled signal raise, Exceptions EmergenyHandler will be evaluated. 

    The default emergeny handler will enter the debugger.

    For applications, which do not want Debuggers to come up, other handlers are

    possible.

    For example, to get the typical C++ behavior, use:

        Exception emergencyHandler:[:ex | Smalltalk exitWithCoreDump]

    [Class variables:]

        EmergencyHandler <Block>    this block is evaluated, if no handler was defined

                                    for a signal (i.e. this one is responsible for the

                                    unhandled exception debugger).

                                    Having this being a block allows to globally catch

                                    these errors - even when no enclosing handler-scope

                                    around the erronous code exists.

                                    (as the catch/through does).

        RecursiveExceptionSignal

                         <Signal>   raised when within a handler for some signal,

                                    the same signal is raised again.

    [see also:]

        Context Block

        Object DebugView

    [author:]

        Claus Gittinger

"

! !

!Exception class methodsFor:'initialization'!

initialize 

    "setup the signal used to handle unhandled signals"

    RecursiveExceptionSignal isNil ifTrue:[

	RecursiveExceptionSignal := ErrorSignal newSignalMayProceed:false.

	RecursiveExceptionSignal nameClass:self message:#recursiveExceptionSignal.

	RecursiveExceptionSignal notifierString:'recursive signal raise in handler'

    ]

! !

!Exception class methodsFor:'instance creation'!

signal:aSignal parameter:aParameter errorString:aString suspendedContext:sContext

    "create a new instance and set the fields in preparation for a raise.

     - only to be sent from the signal when raising"

    ^ (self new)

	signal:aSignal 

	parameter:aParameter 

	errorString:aString 

	suspendedContext:sContext 

	originator:(sContext receiver).

!

signal:aSignal parameter:aParameter errorString:aString suspendedContext:sContext originator:origin

    "create a new instance and set the fields in preparation for a raise.

     - only to be sent from the signal when raising"

    ^ (self new)

	signal:aSignal 

	parameter:aParameter 

	errorString:aString 

	suspendedContext:sContext 

	originator:origin.

! !

!Exception class methodsFor:'Signal constants'!

recursiveExceptionSignal

    "return the signal used to handle recursive signals in the handlers"

    ^ RecursiveExceptionSignal

! !

!Exception class methodsFor:'defaults'!

emergencyHandler

    "return the handler used for unhandled exceptions"

    "

     set it up, when called the first time

    "

    EmergencyHandler isNil ifTrue:[

	EmergencyHandler := [:ex |

	    "

	     sending it to the signal allows per-signal specific

	     debuggers to be implemented in the future

	     (for example, segv in primitive code could show things 

	      on the C-level ..)

	    "

	    (ex signal) enterDebuggerWith:ex message:(ex errorString).

	]

    ].

    ^ EmergencyHandler

!

emergencyHandler:aOneArgBlock

    "set the handler used for unhandled exceptions"

    EmergencyHandler := aOneArgBlock

    "ST-80 behavior of first showing a notifier:

     (I prefer to get right into the debugger, though)

     Exception

	emergencyHandler:

	    [:ex | self errorNotify:ex errorString ]

    "

    "automatically aborting current operation, on error:

     (may be useful for end-user apps; make certain, 

      you have abortSignal handlers at appropriate places)

     Exception

	emergencyHandler:

	    [:ex | Object abortSignal raise. ex return. ]

    "

    "finally, traditional language system behavior; dump core ;-)

     Exception

	emergencyHandler:

	    [:ex | Smalltalk exitWithCoreDump. ]

    "

! !

!Exception methodsFor:'accessing'!

errorString 

    "return the errorString passsed with the signal raise

     (or nil, if there was none)"

    ^ errorString

!

handlerContext

    "return the context of the handler"

    ^ handlerContext

!

originator 

    "return the originator passsed with the signal raise

     (or nil, if there was none)"

    ^ originator

!

parameter

    "return the parameter passsed with the signal raise

     (or nil, if there was none)"

    ^ parameter

!

rejected

    "return true, if any other of the exceptions handlers has rejected 

     Uncertain, if this is really interesting to anybody.

     This is only valid during handler execution.

     (i.e. an outer handler can find out, if any other handler has already

     rejected).

     "

    ^ rejected

!

signal

    "return the signal, that caused the exception"

    ^ signal

!

suspendedContext

    "return the context in which the raise occured"

    ^ suspendedContext

!

willProceed

    "return true, if the exception is proceedable"

    ^ resumeBlock notNil

! !

!Exception methodsFor:'handler actions'!

proceed

    "Continue after the raise - the raise returns nil"

    resumeBlock notNil ifTrue:[resumeBlock value:nil]

!

proceedWith:value

    "Continue after the raise - the raise returns value"

    resumeBlock notNil ifTrue:[resumeBlock value:value]

!

reject

    "handler decided not to handle this signal -

     system will look for another handler"

    rejected := true.

    rejectBlock value

!

restart

    "restart the handle:do: - usually after some repair work is done

     in handler"

    handlerContext unwindAndRestart

!

resume

    "Continue after the raise - the raise returns nil"

    resumeBlock notNil ifTrue:[resumeBlock value:nil]

!

resumeWith:value

    "Continue after the raise - the raise returns value"

    resumeBlock notNil ifTrue:[resumeBlock value:value]

!

return

    "Continue after the handle:do: - the handle:do: returns nil"

    handlerContext unwind

!

returnDoing:aBlock

    "Continue after the handle:do: - the handle:do: returns aBlock value"

    handlerContext unwindThenDo:aBlock

!

returnWith:value

    "Continue after the handle:do: - the handle:do: returns value"

    handlerContext unwind:value

! !

!Exception methodsFor:'raising'!

doCallHandler:aHandler

    "call the handler proper - needed an extra method

     to have a separate returnContext for the rejectBlock.

     (which is historical, and actually no longer needed)"

    |val|

    rejectBlock := [^ self]. "this will return on reject"

    val := aHandler value:self.

    "

     handler fall through - is just like a returnWith:blocks-value

    "

    self returnWith:val

!

evaluateHandler

    "search through the context-calling chain for a 'handle:do:'-context 

     to the raising signal a parent of it or a SignalSet which includes 

     the raising signal.

     If found, take the contexts 2nd argument (the handler) and evaluate

     it with the receiver exception as argument.

     If no handler is found, try per signal handler, or

     per process handler (if its the noHandlerSignal).

     Finally fall back to Exceptions emergencyHandler, which is always

     available and enters the debugger."

    |con block noHandlerSignal any msg sel activeHandler conArg1|

    con := thisContext sender.  "the raise-context"

    con := con sender.          "the signal raise context"

    con isRecursive ifTrue:[

        "

         mhmh - an error while in a handler

        "

        ((signal == RecursiveExceptionSignal)

        or:[RecursiveExceptionSignal isNil]) ifTrue:[

            "

             ... either while handling RecursiveExceptionSignal

             or at startup when RecursiveExceptionSignal is not yet

             created -

             - go immediately into the debugger.

            "

            ^ self enterDebuggerWith:self

                             message:'recursive signal raise'

        ].

        ^ RecursiveExceptionSignal 

            raiseRequestWith:self 

                 errorString:('recursive signal raise: ' , errorString)

    ].

    any := false.

    [con notNil] whileTrue:[

        con isBlockContext ifFalse:[

            sel := con selector.

            sel == #doCallHandler: ifTrue:[

                activeHandler := con argAt:1

            ].

            ((sel == #'handle:do:') 

            or:[((sel == #'handle:from:do:') 

                and:[(con argAt:2) == originator])]) ifTrue:[

                "

                 if this is the Signal>>handle:do: context

                 or a SignalSet>>handle:do: context with self in it,

                 call the handler

                "

                (con receiver accepts:signal) ifTrue:[

                    "call the handler"

                    conArg1 := con argAt:1.

                    activeHandler == conArg1 ifTrue:[

"/                        'skip active handler:' print.

"/                        con print. ' ' print. con receiver print.

"/                        ' for ' print. signal printNL

                    ] ifFalse:[

                        handlerContext := con.

                        any := true.

                        self doCallHandler:conArg1.

                        "if the handler rejects, we arrive here"

                        "continue search for another handler"

                    ]

                ].

            ]

        ].

        con := con sender

    ].

    "

     we arrive here, if either no handler was found, or none of the

     handlers did a return (i.e. every handler rejected or fell through).

    "

    "

     try per signal handler

    "

    (block := signal handlerBlock) isNil ifTrue:[

        "/

        "/ if its a querySIgnal, ignore it

        "/

        signal isQuerySignal ifTrue:[^ self].

        "/

        "/ if it is not the NoHandlerSignal, raise it ...

        "/ passing the receiver as parameter.

        "/

        signal ~~ (noHandlerSignal := Signal noHandlerSignal) ifTrue:[

            noHandlerSignal notNil ifTrue:[

                any ifTrue:[

                    msg := 'unhandled (rejected)'

                ] ifFalse:[

                    msg := 'unhandled'

                ].

                ^ noHandlerSignal 

                      raiseRequestWith:self 

                           errorString:(msg , ' exception: ' , errorString)

                                    in:self suspendedContext

            ].

            "/

            "/ mhmh - an error during early startup; noHandlerSignal is

            "/ not yet defined.

            "/

            ^ MiniDebugger enterWithMessage:errorString

        ].

        "

         mhmh - smells like trouble - there is no handler and

         no per-signal handler block.

         Look for either a per-process emergencyHandlerBlock 

         or the global emergencyHandler (from Exception) ...

        "

        Processor notNil ifTrue:[ 

            "care for signal during startup (Processor not yet created)"

            block := Processor activeProcess emergencySignalHandler.

        ].

        block isNil ifTrue:[

            block := Exception emergencyHandler.

            block isNil ifTrue:[

                "care for error during startup (Exception not yet initialized)"

                ^ MiniDebugger enterWithMessage:errorString

            ].

        ].

    ].

    "... and call it"

    ^ block value:self.

!

raise

    "actually raise a nonproceedable exception.

     For now, same as #raiseRequest (always proceedable)."

    resumeBlock := [:value | ^ value].