"

 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'

	 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.

"

!

version

    ^ '$Header: /cvs/stx/stx/libbasic/Signal.st,v 1.29 1995-11-11 15:26:50 cg Exp $'

!

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).

"

! !

!Signal class methodsFor:'initialization'!

initialize 

    "setup the signal used to handle unhandled signals"

    NoHandlerSignal isNil ifTrue:[

	NoHandlerSignal := ErrorSignal newSignalMayProceed:true.

	NoHandlerSignal nameClass:self message:#noHandlerSignal.

	NoHandlerSignal notifierString:'unhandled exception'.

    ]

! !

!Signal class methodsFor:'instance creation'!

new

    "return a new signal"

    ^ (self basicNew) notifierString:'signal'

! !

!Signal class methodsFor:'Signal constants'!

noHandlerSignal

    "return the signal used to handle unhandled signals"

    ^ NoHandlerSignal

! !

!Signal methodsFor:'instance creation'!

newSignalMayProceed:aBoolean

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

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

    |newSignal|

    newSignal := (self copy) mayProceed:aBoolean.

    newSignal parent:self.

    ^ newSignal

!

newSignal

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

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

    ^ (self copy) parent:self

! !

!Signal methodsFor:'copying'!

deepCopy

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

    ^ self deepCopyError

! !

!Signal methodsFor:'accessing'!

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

!

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

!

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

!

parent:aSignal 

    "set the parent-signal of the receiver."

    parent := aSignal

!

parent

    "return the parent-signal of the receiver"

    ^ parent

!

notifierString:aString

    "set the notifier string"

    notifierString := aString

!

notifierString

    "return the notifier string"

    ^ notifierString

!

errorString

    "return the notifier string"

    ^ notifierString

!

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

!

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

! !

!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:'save evaluation'!

handle:handleBlock do:aBlock

    "evaluate the argument, aBlock.

     If the receiver-signal is raised during evaluation,

     evaluate the handleBlock passing it an Exception argument.

     The handler may decide how to react to the signal by sending

     a corresponding message to the exception (see there).

     If the signal is not raised, return the value of evaluating

     aBlock."

     ^ aBlock value  "the real logic is in raise/Exception"

      "

       Object messageNotUnderstoodSignal handle:[:ex |

	  'oops' printNL.

	  ex return

       ] do:[

	  123 size open   

       ]

      "

      "

       |num|

       num := 0.

       Number divisionByZeroSignal handle:[:ex |

	  'oops' printNL.

	  ex return

       ] do:[

	  123 / num   

       ]

      "

!

handle:handleBlock from:anObject do:aBlock

    "evaluate the argument, aBlock.

     If the receiver-signal is raised during evaluation,

     and the exception originated from anObject,

     evaluate the handleBlock passing it an Exception argument.

     The handler may decide how to react to the signal by sending

     a corresponding message to the exception (see there).

     If the signal is not raised, return the value of evaluating

     aBlock."

     ^ aBlock value  "the real logic is in raise/Exception"

      "

       the first open will be cought; the second not:

       |o1 o2|

       o1 := 123.

       o2 := nil.

       Object messageNotUnderstoodSignal 

	   handle:

		[:ex |

		    'oops' printNL.

		    ex proceed

		] 

	   from:o1

	   do:

		[

		    o1 open.

		    o2 open

		]

      "

!

catch:aBlock

     "evaluate the argument, aBlock.

      If the receiver-signal is raised during evaluation, abort

      the evaluation and return true; otherwise return false. 

      This is the catch & throw mechanism found in other languages,

      where the returned value indicates if an exception occured."

      |raiseOccurred|

      raiseOccurred := false.

      self handle:[:ex | raiseOccurred := true. ex return] do:aBlock.

      ^ raiseOccurred

      "

       Object messageNotUnderstoodSignal catch:[

	  123 size open   

       ]

      "

!

ignoreIn:aBlock

     "evaluate the argument, aBlock.

      Ignore the receiver-signal during evaluation - i.e. simply

      continue. 

      This makes only sense for some signals, such as UserInterrupt

      or AbortSignal, because continuing after an exception without any cleanup

      often leads to followup-errors."

      ^ self handle:[:ex | ex proceed] do:aBlock.

      "

       Object messageNotUnderstoodSignal ignoreIn:[

	  123 size open   

       ]

      "

! !

!Signal methodsFor:'queries'!

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

!

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

!

isSignal

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

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

    ^ true

!

isQuerySignal

    ^ false

!

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 cought 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 sel|

    con := aContext.

    [con notNil] whileTrue:[

	(((sel := con selector) == #handle:do:) 

	or:[sel == #handle:from:do:]) ifTrue:[

	    "

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

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

	    "

	    (con receiver accepts:self) ifTrue:[

		"found a handler context"

		^ true

	    ].

	].

	con := con sender

    ].

    ^ false

! !

!Signal methodsFor:'private'!

errorStringFor:template

    "used when raising with a given error string; if the given

     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."

    (template startsWith:' ') ifTrue:[

	^ notifierString , template

    ].

    (template endsWith:' ') ifTrue:[

	^ template , notifierString

    ].

    ^ template

! !

!Signal methodsFor:'raising'!

raise

    "raise a signal - create an Exception object

     and call the handler with this as argument.

     The signals notifierString is used as errorString."

    ^ (Exception  

	      signal:self

	      parameter:nil 

	      errorString:notifierString

	      suspendedContext:thisContext sender) raise.

!

raiseErrorString:aString

    "raise a signal - create an Exception object

     and call the handler with this as argument.

     The argument is used as errorString."

    ^ (Exception  

	      signal:self

	      parameter:nil 

	      errorString:(self errorStringFor:aString)

	      suspendedContext:thisContext sender) raise.

!

raiseFrom:something

    "raise a signal - create an Exception object with aParameter