[Pharo-dev] DebugSession>>activePC:

ducasse stepharo at netcourrier.com
Thu Jan 10 10:59:15 EST 2019

Eliot I would like also two points to this.

- First we asked thomas to write tests about the debugger model and you see if they would be tests about methods we could understand 
that they are used and control what they do. So we should all thank thomas for his energy in this not so easy task.

- Second it would be nice if you could refrain to be systematically negative about what we are doing. I think that our development process
is much better than many others :) It is not perfect because this does not exist. 
I think that we are doing a great job make Smalltalk cool. And yes it may happen that one untested, undocumented method
get lost. I think that we are doing pretty good given the resources we have. 


> On 10 Jan 2019, at 15:11, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> Hi Thomas,
>> On Jan 10, 2019, at 2:24 AM, Thomas Dupriez via Pharo-dev <pharo-dev at 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 context’s 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.

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