Hi Thomas,
On Jan 11, 2019, at 6:49 AM, Thomas Dupriez <tdupriez@ens-paris-saclay.fr> wrote:
Hi,
Yes, my question was just of the form: "Hey there's this method in DebugSession. What is it doing? What's the intention behind it? Does someone know?". There was no hidden agenda behind it.
@Eliot
After taking another look at this method, there's something I don't understand:
activePC: aContext ^ (self isLatestContext: aContext) ifTrue: [ interruptedContext pc ] ifFalse: [ self previousPC: aContext ]
isLatestContext: checks whether its argument is the suspended context (the context at the top of the stack of the interrupted process). And if that's true, activePC: returns the pc of **interruptedContext**, not of the suspended context. These two contexts are different when the debugger opens on an exception, so this method is potentially returning a pc for another context than its argument...
Ugh, I had missed that. Thanks for pointing that out. It does look like a bug. The Squeak code is very different (much less elegant code written by me in DebuggerMethodMap) but that code does use only one context. So I expect the code should read activePC: aContext ^ (self isLatestContext: aContext) ifTrue: [ aContext pc ] ifFalse: [ self previousPC: aContext ]
Another question I have to improve the comment for this method is: what's the high-level meaning of this concept of "activePC". You gave the formal definition, but what's the point of defining this so to speak? What makes this concept interesting enough to warrant defining it and giving it a name?
Because the active pc is used to derive display feedback in the debugger. In particular it is used to derive source ranges for contexts.
Cheers, Thomas
On 11/01/2019 13:53, Tudor Girba wrote: Hi,
@Eliot: Thanks for the clarifying answer.
I believe you might have jumped to conclusion about the intention of the question. Thomas asked a legitimate question. Without users of a method it is hard to understand its use. It does not necessarily imply that the intention is to remove it, but it does show that someone wants to understand.
As far as I know, Thomas actually wants to write a test to cover that usage. I am sure that you appreciate and encourage that :).
@Thomas: Thanks for this effort!
Cheers, Doru
On Jan 10, 2019, at 3:11 PM, Eliot Miranda <eliot.miranda@gmail.com> wrote:
Hi Thomas,
On Jan 10, 2019, at 2:24 AM, Thomas Dupriez via Pharo-dev <pharo-dev@lists.pharo.org> wrote:
<mime-attachment> in a stack of contexts the active pc is different for the top context. For other than the top context, a contextâs pc will be pointing after the send that created the context above it, so to find the pc of the send one finds the previous pc. For the top context its pc is the active pc.
Typically the debugger is invoked in two different modes, interruption or exception. When interrupted, a process is stopped at the next suspension point (method entry or backward branch) and the top context in the process is the context to be displayed in the debugger. When an exception occurs the exception search machinery will find the signaling context, the context that raised the exception, which will be below the search machinery and the debugger invocation above that. The active pc of the signaling context will be the of for the send of digbsl et al.
So the distinction is important and the utility method is probably useful.
Do you want to remove the method simply because there are no senders in the image?
If so, this is indicative of a serious problem with the Pharo development process. In the summer I ported VMMaker.oscog to Pharo 6. Now as feenk try and build a VMMaker.oscog image on Pharo 7, the system is broken, in part because of depreciations and in part because useful methods (isOptimisedBlock (isOptimizedBlock?) in the Opal compiler) have been removed.
Just because a method is not in the image does not imply it is not in use. It simply means that it is not in use in the base image. As the system gets modularised this issue will only increase. There are lots of collection methods that exist as a library that are not used in the base image and removing them would clearly damage the library for users. This is the case for lots of so-called system code. There are users out there, like those of us in the vm team, who rely on such system code, and it is extremely unsettling and frustrating to have that system code change all the time. If Pharo is to be a useful platform to the vm team it has to be more stable. -- www.feenk.com
âThe smaller and more pervasive the hardware becomes, the more physical the software gets."