"

 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:#Signal

	instanceVariableNames:'mayProceed notifierString nameClass message handlerBlock parent'

	classVariableNames:'NoHandlerSignal GenericSignal'

	poolDictionaries:''

	category:'Kernel-Exceptions'

!

!Signal 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

"

    Signal and Exception provide a framework for exception handling.

    A Signal object is usually defined somewhere up in the calling chain

    and associated with some abnormal event. Many signals are also

    created at startup time and reused.

    When the event is raised (by Signal>>raise) the control will be either 

    given to a debugger or - if a handler was defined - to the handler. 

    The handler will get a description of what (and where) happened in an 

    Exception object and can decide how to react on the situation (i.e. 

    proceed, return or restart).

    There is also a companion class called SignalSet, which allows handling

    multiple signals with one handler (for example all arithmetic signals).

    And, finally there is a very special SignalSet which allows catching

    any signal (SignalSet>>anySignal).

    Since there is no official documentation on signal handling (i.e. none

    of the books describes it), this Signal implementation has been modeled

    after what some PD programs seem to expect and what alpha/beta testers told

    me it should look like.

    It may not be perfect and undergo minor changes.

    special:

    In addition to the nested catch & throw mechanism, signals can also be

    used when no such handler scope exists. To support this, signals can be 

    assigned a handlerBlock, which gets evaluated with the exception as argument 

    in case no handler was found (on the stack).

    If no handler was found (i.e. neither a handler context on the stack, nor

    a static handler block), the NoHandlerSignal will be raised instead,

    passing it the original exception in its exception-parameter.

    This NoHandlerSignal can be handled just like any other signal.

    (therefore, it is possible to catch any error by catching NoHandlerSignal.

    When the NoHandler signal is raised, and neither a handler-context, nor 

    a handler block is defined for it, an emergencyHandler(-block) is evaluated.

    This block is either provided by the current process 

    (see Process>>emergencySignalHandler) or as a global default by the Exception

    class (see Exception>>emergencyHandler).

    The default emergencyHandlerBlock (from Exception) will bring up a debugger.

    HandlerBlocks allow a global (if its the EmergencyHandler in Exception)

    or per-process signal handling to be added. Even to code which was never

    planned to handle signals.

    See samples in 'doc/coding' and actual raise code in Exception.

    [Instance variables:]

        mayProceed      <Boolean>       hint for the debugger - program may 

                                        proceed (currently not honored by the

                                        debugger)

        notifierString  <String>        error message to be output 

        nameClass       <Class>         for the printOn-implementation; nameClass

                                        is the class, to which message (below) 

                                        should be sent to create the receiver.

        message         <Symbol>        for the printOn-implementation; message

                                        is the selector, which should be sent to 

                                        nameClass (above) to create the receiver.

        handlerBlock    <Block>         if nonNil, a 1-arg block to be 

                                        evaluated when no handler context is 

                                        found. The block gets the exception

                                        object as argument. This will play the role

                                        of an on-stack handler.

    [Class variables:]

        NoHandlerSignal <Signal>        signal raised when no handler for a signal

                                        was found in raise.

                                        If this one is not handled either,

                                        Exceptions emergencyHandler will be evaluated

                                        instead (or a per-proces handler, if there

                                        is one).

    [author:]

        Claus Gittinger

    [see also:]

        Exception 

        SignalSet QuerySignal

        Object

        (``Exception handling and signals'': programming/exceptions.html)

"

! !

!Signal class methodsFor:'initialization'!

initGenericSignal 

    "setup the parent of all signals."

    GenericSignal isNil ifTrue:[

        GenericSignal := self basicNew notifierString: 'unknown Signal with: '.

        GenericSignal nameClass:self message:#genericSignal.

    ].

    "Modified: 8.10.1997 / 11:58:01 / cg"

!

initialize 

    "setup the signal used to handle unhandled signals"

    GenericSignal isNil ifTrue:[

        self initGenericSignal.

        NoHandlerSignal := ErrorSignal newSignalMayProceed:true.

        NoHandlerSignal nameClass:self message:#noHandlerSignal.

        NoHandlerSignal notifierString:'unhandled exception'.

    ]

    "Modified: 8.10.1997 / 11:48:40 / cg"

! !

!Signal class methodsFor:'instance creation'!

new

    "return a new signal"

    "

     Signal new

    "

    "Modified: 8.10.1997 / 11:51:39 / cg"

! !

!Signal class methodsFor:'Signal constants'!

genericSignal

    "return the generic signal - thats the parent of all signals

     in the system."

    ^ GenericSignal

    "Created: 8.10.1997 / 11:46:28 / cg"

    "Modified: 8.10.1997 / 11:47:08 / cg"

!

noHandlerSignal

    "return the signal used to handle unhandled signals"

    ^ NoHandlerSignal

! !

!Signal methodsFor:'accessing'!

errorString

    "return the notifier string"

    ^ notifierString

!

handlerBlock

    "return the handlerblock - if non-nil, this will be evaluated with the exception 

     object as argument, if no #handle:do: context was found on the stack."

    ^ handlerBlock

!

handlerBlock:aOneArgBlock

    "set the handlerblock - this will be evaluated with the exception 

     object as argument, if no #handle:do: context was found on the stack."

    handlerBlock := aOneArgBlock

!

mayProceed

    "return the signals ability to proceed.

     This flag is (currently) not checked by the system;

     be prepared for changes here, to eventually have nonProceedable

     signals refuse to let you continue execution."

    ^ mayProceed

!

mayProceed:aBoolean

    "set/clear the signals ability to proceed.

     This flag is (currently) not checked by the system;

     be prepared for changes here, to eventually have nonProceedable

     signals refuse to let you continue execution."

    mayProceed := aBoolean

!

nameClass:aClass message:aSelector

    "this sets the class & selector of a method which returns

     that signal - this is simply for documentation purposes -

     see Signal>>printOn: implementation.

     (took me a while to find that one out ;-)"

    nameClass := aClass.

    message := aSelector

!

notifierString

    "return the notifier string"

    ^ notifierString

!

notifierString:aString

    "set the notifier string"

    notifierString := aString

!

parent

    "return the parent-signal of the receiver"

    ^ parent

!

parent:aSignal 

    "set the parent-signal of the receiver."

    parent := aSignal

!

parent:aSignal mayProceed:aBoolean

    "set the parent-signal and the mayProceed flag of the receiver."

    parent isNil ifTrue:[

        parent := aSignal.

        mayProceed := aBoolean.

        ^ self

    ].

    self error:'parent change not allowed'.

    ^ self

    "Modified: 8.10.1997 / 11:56:11 / cg"

! !

!Signal methodsFor:'copying'!

deepCopy

    "raise an error - deepCopy is not allowed for signals"

    ^ self deepCopyError

! !

!Signal methodsFor:'instance creation'!

newSignal

    "create a new signal, using the receiver as a prototype and

     setting the parent of the new signal to the receiver."

    ^ (self class basicNew) parent:self

    "Modified: 8.10.1997 / 11:53:06 / cg"

!

newSignalMayProceed:aBoolean

    "create a new signal, using the receiver as a prototype and

     setting the parent of the new signal to the receiver."

    ^ (self class basicNew) 

        parent:self mayProceed:aBoolean

    "Modified: 8.10.1997 / 11:57:13 / cg"

! !

!Signal methodsFor:'printing'!

printOn:aStream

    "append a printed representation of the receiver on aStream"

    nameClass notNil ifTrue:[

	aStream nextPutAll:nameClass name.

	aStream space.

	aStream nextPutAll:message.

	^ self

    ].

    ^ super printOn:aStream

! !

!Signal methodsFor:'private'!

errorStringFor:errorString with:aParameter

    "used when raising with a given error string and/or parameter; 

     if the errorString starts with a space, it is appended to the receivers

     notifier string; if it ends with a space, it is prepended.

     Otherwise, the errorString is returned.

     If no errorString is given, use the signals default notifierString."

    |t|

    errorString isNil ifTrue:[

        t := notifierString

    ] ifFalse:[

        t := errorString.

        (errorString endsWith:Character space) ifTrue:[

            t := errorString , notifierString

        ] ifFalse:[

            (errorString startsWith:Character space) ifTrue:[

                t := notifierString , errorString

            ]

        ].

    ].

    ^ t.

"/    aParameter isNil ifTrue:[

"/        ^ t

"/    ].

"/

"/    (t startsWith:' ') ifTrue:[

"/        ^ aParameter printString , t

"/    ].

"/    (t endsWith:' ') ifTrue:[

"/        ^ t , aParameter printString

"/    ].

"/    ^ t

    "Modified: 25.3.1997 / 12:12:37 / cg"

! !

!Signal methodsFor:'queries'!

accepts:aSignal

    "return true, if the receiver accepts the argument, aSignal.

     (i.e. the receiver is aSignal or a parent of it). False otherwise."

    |s|

    aSignal isQuerySignal ifTrue:[^ false].

    s := aSignal.

    [s notNil] whileTrue:[

	self == s ifTrue:[^ true].

	s := s parent

    ].

    ^ false

!

inheritsFrom:anotherSignal

    "return true, if the receiver is a child of anotherSignal

     (i.e. if handling anotherSignal also handles the receiver)

     This is almost the same as accepts, but returns false, if

     the receiver is identical to anotherSignal."

    self == anotherSignal ifTrue:[^ false].

    ^ anotherSignal accepts:self

!

isHandled

    "return true, if there is a handler for the receiver signal.

     Raising an unhandled signal will usually lead into the debugger,

     but can be caught globally by setting Exceptions EmergencyHandler."

    ^ self isHandledIn:(thisContext sender).

!

isHandledIn:aContext

    "return true, if there is a handler for the receiver signal in the 

     contextChain starting with aContext."

    |con|

    con := aContext.

    [con notNil] whileTrue:[

        con := con findNextContextWithSelector:#'handle:do:' or:#'handle:from:do:' or:nil.

        con notNil ifTrue:[

            "

             is this is a #handle:do: or a #handle:from:do: context

             with self in it ?

            "

            (con receiver accepts:self) ifTrue:[

                "found a handler context"

                ^ true

            ]

        ]

    ].

    ^ false

    "Modified: 20.1.1997 / 12:45:01 / cg"

!

isQuerySignal

    "return true, if this is a querySignal - always return false here"

    ^ false

    "Modified: 22.4.1996 / 13:45:06 / cg"

!

isSignal

    "return true, if the receiver is some kind of signal;

     true returned here - the method is redefined from Object."

    ^ true

! !

!Signal methodsFor:'raising'!

raise

    "raise a signal nonproceedable

     - notice, ST/X does not (for now) distinguish between proceedable and

       non proceedable exceptions.

     The signals notifierString is used as errorString."

    ^ (Exception  

              signal:self

              parameter:nil 

              errorString:notifierString

              suspendedContext:thisContext sender) raise.

    "Modified: 2.5.1996 / 16:36:23 / cg"

!

raiseErrorString:aString

    "raise a signal nonproceedable.

     - notice, ST/X does not (for now) distinguish between proceedable and

       non proceedable exceptions.

     The argument is used as errorString."

    ^ (Exception  

              signal:self

              parameter:nil 

              errorString:(self errorStringFor:aString with:nil)

              suspendedContext:thisContext sender) raise.

    "Modified: 9.5.1996 / 15:17:59 / cg"

!

raiseErrorString:aString in:aContext

    "raise a signal nonproceedable.

     - notice, ST/X does not (for now) distinguish between proceedable and

       non proceedable exceptions.

     The argument is used as errorString.

     The additional context is passed as the context responsible for the raise,

     allowing a raise to mimicri the exception happened somewhere else."

    ^ (Exception  

              signal:self

              parameter:nil 

              errorString:(self errorStringFor:aString with:nil)

              suspendedContext:aContext) raise.

    "Created: 26.7.1996 / 16:42:32 / cg"

    "Modified: 26.7.1996 / 16:42:47 / cg"

!

raiseFrom:something

    "raise a signal nonproceedable.

     - notice, ST/X does not (for now) distinguish between proceedable and