"

 COPYRIGHT (c) 1988 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 variableSubclass:#Context

       instanceVariableNames:'flags sender home receiver selector searchClass

			      lineNr retvalTemp handle*'

       classVariableNames:'InvalidReturnSignal'

       poolDictionaries:''

       category:'Kernel-Methods'

!

Context comment:'

COPYRIGHT (c) 1988 by Claus Gittinger

	      All Rights Reserved

'!

!Context class methodsFor:'documentation'!

copyright

"

 COPYRIGHT (c) 1988 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

"

"

!

documentation

"

    Context represents the stack context objects; each message send adds a context

    to a chain, which can be traced back via the sender field. 

    (The actual implementation uses the machines stack for this, building real 

     contexts when needed only).

    For both method- and block-contexts, the layout is the same. 

    For method contexts, the home-field is nil, while for blockcontexts the home-

    field is either the context of its surrounding block (i.e. the context of the

    block, in which the receiving block was created, if its a nested block) or of

    its home method. 

    Contexts of cheap blocks do not have a home context - their home field is 

    also nil.

    Currently, contexts do not contain a reference to the method or block which

    created it - this is not needed for program execution, but could get the debugger

    somewhat into trouble: it has to search the class hierarchy for receiver/selector

    combinations to find the method. This usually works, but fails in case of methods

    which are not anchored in any class - especially leading to problems with wrapper-

    and lazy methods. Also, Method>>valueWithReceiver - type of invocations cannot

    be easily debugged.

    Therefore, the implementation will be changed in the near future, to include a

    field for the method/block, and set it in the VM during program execution.

    (there may be some small performance penalty for this, though).

    instance variables:

	flags       <SmallInteger>          - used by the VM; never touch.

					      contains info about number of args, locals and

					      temporaries.

	sender      <Context>               - the 'calling' context

	home        <Context>               - the context, where this block was created, or nil

	receiver    <Object>                - the receiver of this message

	selector    <Symbol>                - the selector of this message

	searchClass <Class>                 - the class, where the message lookup started

					      (for super sends) or nil, for regular sends.

	lineNr      <SmallInteger>          - the position where the context left off

					      (kind of p-counter)

	retValTemp  nil                     - temporary - always nil, when you see the context

					      (used in the VM as temporary)

	handle      *noObject*              - used by the VM; not accessable, not an object

	<indexed>                           - arguments of the send followed by

					      locals of the method/block followed by

					      temporaries

    WARNING: layout and size known by the compiler and runtime system - do not change.

"

! !

!Context class methodsFor:'initialization'!

initialize

    InvalidReturnSignal isNil ifTrue:[

	Object initialize.

	InvalidReturnSignal := Object errorSignal newSignalMayProceed:true.

	InvalidReturnSignal nameClass:self message:#invalidReturnSignal.

	InvalidReturnSignal notifierString:'invalid return; method cannot return twice'.

    ]

! !

!Context class methodsFor:'signal access'!

invalidReturnSignal

    "return the signal used when a method is tried to be returned twice

     or, when some dead context is unwound or restarted."

    ^ InvalidReturnSignal

! !

!Context class methodsFor:'queries'!

isBuiltInClass

    "this class & subclasses are known by the run-time-system"

    ^ true

! !

!Context methodsFor:'copying'!

deepCopy

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

    ^ self deepCopyError

! !

!Context methodsFor:'testing'!

isContext

    "return true, iff the receiver is a Context, false otherwise"

    ^ true

!

isBlockContext

    "return true, iff the receiver is a BlockContext, false otherwise"

    ^ false

! 

isRecursive

    "return true, if this context is one of a recursive send of the same

     selector and same arguments to the same receiver before. 

     Used to detect recursive errors or recursive printing - for example."

    rec := 0.

    c := self sender.

    [c notNil] whileTrue:[

	((c selector == selector) 

	and:[(c receiver == receiver)]) ifTrue:[

	    "

	     stupid: the current ST/X context does not include

	     the method, but the class, in which the search started ...

	    "

	    (c searchClass whichClassImplements:selector) == (self searchClass whichClassImplements:selector) ifTrue:[

		^ true

	    ]

	].

	c := c sender.

	"

	 this special test was added to get out after a while

	 if the sender chain is corrupt - this gives us at least

	 a chance to find those errors.

	"

	rec := rec + 1.

	rec >= 100000 ifTrue:[

	    'bad context chain' errorPrintNL.

	    ^ true

	]

    ].

    ^ false

! !

!Context methodsFor:'accessing'!

instVarAt:index

    "have to catch instVar access to retVal and handle - they are invalid.

     Notice, that one of the next ST/X versions will get some syntactic

     extension to get this automatically)."

    (index == 8) ifTrue:[^ nil].

    (index == 9) ifTrue:[^ nil].

    ^ super instVarAt:index

!

instVarAt:index put:value

    "have to catch instVar access to retVal and handle - they are invalid.

     Notice, that one of the next ST/X versions will get some syntactic

     extension to get this automatically)."

    (index == 8) ifTrue:[^ nil].

    (index == 9) ifTrue:[^ nil].

    ^ super instVarAt:index put:value

!

methodHome

    "return the method-home - for method contexts this is the receiver"

    ^ self

!

home

    "return the immediate home of the receiver.

     for block contexts, this is the methodcontext, where the block was created,

     for nested block contexts, its the surrounding blocks context.

     for method-contexts this is nil."

    ^ nil "home"

!

method

    "return the method for which the receiver was created.

     To save time during normal execution, this information is not held in the

     context, but computed here on request."

    |c|

    c := self searchClass whichClassImplements:selector.

    c notNil ifTrue:[

	^ c compiledMethodAt:selector

    ].

    ^ nil

!

sender

    "return the sender of the context"

    "this special test is for the very first context (startup-context);

     actually, its cosmetics, to avoid a visible nil>>nil context in the debugger."

"

    (sender isNil or:[sender selector isNil and:[sender sender isNil]]) ifTrue:[^ nil].

"

    ^ sender

!

receiver

    "return the receiver of the context"

    ^ receiver

!

searchClass

    "this is the class where the method-lookup started;

     for normal sends, it is nil (or sometimes the receivers class).

     For supersends, its the superclass of the one, in which the

     caller was defined."

    searchClass notNil ifTrue:[^ searchClass].

    ^ receiver class

!

selector

    "return the selector of the method for which the context was created"

    ^ selector

!

numArgs

    "return the number of arguments to the Block/Method"

%{  /* NOCONTEXT */

    RETURN ( _MKSMALLINT( (_intVal(_INST(flags)) >> __NARG_SHIFT) & __NARG_MASK) );

%}

!

nvars

    "return the number of local variables of the Block/Method"

%{  /* NOCONTEXT */

    RETURN ( _MKSMALLINT( (_intVal(_INST(flags)) >> __NVAR_SHIFT) & __NVAR_MASK) );

%}

!

ntemp

    "return the number of temporary variables of the Block/Method.

     (for debugging only)"

    ^ self size - self numArgs - self nvars

!

args

    "return an array filled with the arguments of this context"

    |newArray n "{ Class: SmallInteger }" |

    n := self numArgs.

    newArray := Array new:n.

    1 to:n do:[:index |

	newArray at:index put:(self at:index)

    ].

    ^ newArray

!

argsAndVars

    "return an array filled with the arguments and variables of this context"

    |newArray mySize "{ Class: SmallInteger }" |

    mySize := self numArgs + self nvars.

    newArray := Array new:mySize.

    1 to:mySize do:[:index |

	newArray at:index put:(self at:index)

    ].

    ^ newArray

!

argAt:n

    "return the n'th argument"

    ^ self at:n

!

argAt:n put:value

    "set the n'th argument - useful when the receiver should be restarted"

    ^ self at:n put:value

!

varAt:n

    "return the n'th local variable"

    ^ self at:(n + self numArgs)

!

varAt:n put:value

    "set the n'th local variable - useful when the receiver should be restarted

     or continued"

    self at:(n + self numArgs) put:value

!

lineNumber

    "this returns the lineNumber within the methods source, where the context was

     interrupted or called another method. (currently, sometimes this information

     is not available - in this case 0 is returned)"

    ^ lineNr

! !

!Context methodsFor:'printing & storing'!

argsDisplayString

    |fullString n "{ Class: SmallInteger }" |

    fullString := ''.

    n := self numArgs.

    1 to:n do:[:index |

	fullString := fullString , (' ' , (self at:index) displayString)

    ].

    ^ fullString

!

printReceiver

    "print the receiver of the context - used for MiniDebugger only"

!

fullPrint

    "print the receiver, selector and args of the context 

     - used for MiniDebuggers walkback print only"

    self printReceiver.

    ' ' print.

    selector print.

    self size ~~ 0 ifTrue: [

	' ' print.

	self argsDisplayString print

    ].

    ' [' print. lineNr print. ']' printNewline

!

receiverPrintString

    "return a string describing the receiver of the context" 

	newString := '(' , receiver printString , ') ' , receiverClassName

    ] ifFalse:[

	newString := receiverClassName

    ].

    selector notNil ifTrue:[

	implementorClass := self searchClass whichClassImplements:selector.

	implementorClass notNil ifTrue: [

		newString := newString , '>>>',

			     implementorClass name printString

	    ]

	] ifFalse:[

		newString := newString , '>>>' , self searchClass name

	    ].

	    newString := newString , '>>>**NONE**'

	]

    ].

    ^ newString

!

printString

    "return a string describing the context" 

    ^ self receiverPrintString , ' ' , self selector printString

!

displayString

    "return a string describing the context - for display in Inspector" 

    ^ self class name , '(' , self printString , ')'

!

printOn:aStream

    "append a printed description of the receiver onto aStream"

    aStream nextPutAll:(self receiverPrintString).

    aStream space.

    self selector printOn:aStream

!

fullPrintAll

    "print a full walkback starting at the receiver

     - for MiniDebugger only"

    |context|

    context := self.

    [context notNil] whileTrue: [

	context fullPrint.

	context := context sender

    ]

! !

!Context methodsFor:'error handling'!

invalidReturn:returnValue

    "this message is sent by the VM, when a methods context

     which has already returned is about to return again.

     (i.e. about to execute a return from an already returned

      method in a block).

    We raise a signal here, to allow catching of that situation."

    "

     in previous versions of ST/X and ST-80, this was no error;