A MethodContext ...  Represents the execution of a CompiledMethod in response to a message.

On Wed, Jan 1, 2014 at 2:55 PM, gettimothy <gettimothy@zoho.com> wrote:

 

In Eliot's first example on fixing the reentrancy problem that uses "factorial copy" for the recursion.

I modifed his code:

   | factorial |
        factorial := [:n| n = 1 ifTrue: [1] ifFalse: [(factorial copy value: n - 1) * n]].
        (1 to: 10) collect: factorial copy

into something I could trace out a bit easier.

| factorial fc |
Transcript clear.
factorial := [:n  |
    n = 1
    ifTrue:[   
        Transcript show: ' n=',  (n asString),' ', (thisContext class name), '(',  (thisContext identityHash asString),')' .
        Transcript show: '--sender-->', (thisContext sender) class name, '(',   (thisContext sender) identityHash asString,')'.        
        Transcript show: '--home-->', (thisContext home) class name,  '(', (thisContext home) identityHash asString,')'; cr.                                        
        Transcript show: '++++++++++++++++++++++++++++++++++++++++';cr.                        
         "thisContext explore.    "
        1
    ]
    ifFalse:[    Transcript show: '-----------------------------------------------';cr.
        Transcript show: ' n=',  (n asString),' ', (thisContext class name), '(',  (thisContext identityHash asString),')' .
        Transcript show: '--sender-->', (thisContext sender) class name, '(',   (thisContext sender) identityHash asString,')'.        
        Transcript show: '--home-->', (thisContext home) class name,  '(', (thisContext home) identityHash asString,')'; cr.                                        
        (factorial copy value: n-1) * n
        ]].
Transcript show:' factorial = ' , (factorial class name),'(',factorial identityHash asString,')'.    
Transcript show: '--sender-->', (factorial sender) class name, '(',   (factorial sender) identityHash asString,')'.        
Transcript show: '--home-->', (factorial home) class name,  '(', (factorial home) identityHash asString,')'; cr.    
Transcript show: '^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^';cr.                                        
fc := factorial copy .

Transcript show:' fc = ' , (fc class name),'(',fc identityHash asString,')'.    
Transcript show: '--sender-->', (fc sender) class name, '(',   (fc sender) identityHash asString,')'.        
Transcript show: '--home-->', (fc home) class name,  '(', (fc home) identityHash asString,')'; cr.    
Transcript show: '^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^';cr.    

thisContext inspect.
factorial inspect.
fc inspect.
(1 to: 3) collect: fc

The Transcript output is as follows:

 factorial = BlockContext(694)--sender-->UndefinedObject(3840)--home-->MethodContext(2677)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 fc = BlockContext(3934)--sender-->UndefinedObject(3840)--home-->MethodContext(2677)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 n=1 BlockContext(3934)--sender-->MethodContext(2367)--home-->MethodContext(2677)
++++++++++++++++++++++++++++++++++++++++
-----------------------------------------------
 n=2 BlockContext(3934)--sender-->MethodContext(2367)--home-->MethodContext(2677)
 n=1 BlockContext(1198)--sender-->BlockContext(3934)--home-->MethodContext(2677)
++++++++++++++++++++++++++++++++++++++++
-----------------------------------------------
 n=3 BlockContext(3934)--sender-->MethodContext(2367)--home-->MethodContext(2677)
-----------------------------------------------
 n=2 BlockContext(1684)--sender-->BlockContext(3934)--home-->MethodContext(2677)
 n=1 BlockContext(2780)--sender-->BlockContext(1684)--home-->MethodContext(2677)
++++++++++++++++++++++++++++++++++++++++

Look at the 3'rd line, where n=1.
Why is the sender-->MethodContext(2367) instead of sender-->MethodContext(2677)
What created that new MethodContext?

That would be the activation of Interval>>collect:, which performs the first call of the copied factorial block for each 1 through 3.

collect: aBlock

| nextValue result |

result := self species new: self size.

nextValue := start.

1 to: result size do:

[:i |

result at: i put: (aBlock value: nextValue).

nextValue := nextValue + step].

^ result