2015-05-09 23:21 GMT+02:00 Tudor Girba <tu...@tudorgirba.com>: > I do not think there are many people around here that would think that it > is irrelevant if the Pharo VM can be developed in Pharo or not. Of course, > it is important. > > So, the discussion should not go to challenge this direction, but rather > in you telling us the use cases that you need supported. Please note that I > did not say which exact code and how it should look like. I would be > interested in learning about the use cases you have. I am quite certain > that there are a number of ways to support them and when we work on GT it > would be useful to have your use cases on our table. >
Well I need many lines to explain each point and there are many... I can talk here about a few points. Then I will deal with Esteban for most of them because it is difficult to explain without an interactive discussion. Let me explain the use cases for the Transcript for example. The issues in Pharo are: - The Transcript does not show the stream as it is printed. - The Transcript does not inherit from Stream and thus cannot print with all the methods implemented in Stream. - The Transcript does not allow the user to decorate the text with bold, italic or colors. *Usecase 1: Debug printing methods:* In the VM you have debug printing methods, for example, to print the call stack. These methods are used from the VM simulator, to output the string in the Transcript, and in gdb, to ouput the string in the commandline. The commandline (FileStream stdout in Pharo) and the Squeak Transcript have the same behavior. In Pharo, the Transcript does not inherit from Stream so you can't use the required stream methods to print the debug printing method on the Transcript. In addition, some printing methods print a lot of things and it is important to show the stream as it is printed. For this use-case, we want to keep the smallest difference between the gdb/commadline behavior and the VM simulator/Transcript behavior. If you implement advanced tooling in GT, you therefore need to implement gdb extensions (and lldb extensions because some of us use lldb instead of gdb) and maintain them. I don't think this is a solution. *Usecase 2: CCode generation debugging:* The CCodeGenerator or Slang translator translates Slang code into C code. Sometimes there is a bug. To debug, instead of generating the faulty C method into an external C file, we print only the faulty C method in the Transcript. Again, we want to keep the lowest difference between the real usecase (printing on the C file) and the debug usecase (printing on the Transcript). In Squeak the FileStream and the Transcript are both Stream, everything works as expected. In Pharo the Transcript has not the expected behavior. Again the method can be long, you can have to wait several seconds, so you'd like the transcript to show the stream as you print it. *Usecase 3: VM simulation:* Simulating the VM is quite slow, especially the machine code execution simulation. During the simulation process, the UI is non interactive and shows only every while what the simulator is doing in the Transcript. It is important as sometimes when debugging with a test at each machine code instruction it could take several hours before the UI is interactive again and you want to know what is going on. I don't complain that it takes several hours because the alternatives usually require days of debugging and we can launch the VM simulator overnight. In Pharo this does not work as expected. *Usecase 4: In-image machine-code compilation:* While working in the JIT compiler, sometimes the machine code generated for a bytecoded method is faulty. A common way of debugging it is to print the machine code instructions of the machine code version of the method in the Transcript. It can take a while to print, so it is important to have the Transcript showing the text as it prints. Then, the easiest way of debugging is to look at the machine code and understand what is wrong. For this purpose, we add text decoration to color jump addresses or the instructions where the instruction pointer was when the VM crashed. Then, in squeak, we can easily copy the decorated text to a workspace and generate a new version of the machine code method and compare. In machine code, it is very difficult to do analysis to have more information than just the decompiled text. We add some information while simulating because we know for example the address of specific trampolines, therefore we can print the name of the trampoline when we see that its address is called. Again, sometimes we also have to debug in gdb. In this case, we disassemble the machine code and compare it to the one from in-image compilation, so both printed strings have to be similar (similar text, same chariot returns). Another example is the complexity of the Pharo tools: While developing the VM, I have sometimes a VM partially working or with some plugins not working. In the Squeak image, I can open a workspace on top of this half-working VM and run do-its to see what is working and what is not. In the Pharo image, I can't do anything. You can't open the workspace without opening more advanced tools. I tried to open the Playground, but the first time there was a bug with Traits (Playground use Traits somehow and they were not working due to the new bytecode set not being finished), when that first bug was fixed I could not open it because it crashed simply the VM (I believe it tried to access an external file such as playground-cache). Currently, the Pharo team is trying to build a set of basic tools that have few dependencies to debug a partially working system (that I think you will use to debug glamour while editing it, because you cannot use the glamour inspector if glamour is not working). That would solve this issue. But in no way this point is something that I can do alone to be able to develop the VM in Pharo. This has to be a community effort. And I am saying that because I can't be blamed not to work on the VM in Pharo if to do so I need to spend many months changing Pharo. An example that I believe is a problem in term of the community is the following: I added with Eliot the support for the new bytecode set. Currently, the Squeak image works with the new bytecode set but not the Pharo image. This is because only the Traits are broken, but this is something I could hardly figure out in the Pharo image because nothing is working as the GT tools use Traits. In Squeak I believe there are very few users of Traits so everything worked, and the test suite can reveal that the Traits are broken easily. Currently, the VM process to me is to first make new features work in Squeak, because it is simpler, and then make it work with Pharo, which is more complex. In the last section I discussed how Traits were a problem while implementing the new bytecode set. So what is the long term solution for this issue ? - Will we have a bootstrap process that creates first a Trait-free Kernel and then build the Pharo Kernel out of it ? - Do we forbid people to use Traits in the Pharo Kernel and does that make sense to have Traits in Pharo in this case ? - If we don't do anything, maybe the Traits are only a slight difference with low impact in most cases and it's fine. But maybe there are many small aspects like Traits, such as the Slots the way they were used in GT recently (I don't blame GT or anything, it was just using features in the system that created issues for me), and maybe we reached a point where the complexity between the Pharo kernel and the Squeak kernel is big enough so that a VM developer will first make Squeak works when introducing new features and then deals with the complexity of Pharo ? So, what do we do ? I don't see any simple solution for this issue. And I believe there are people around that see as the only solution for this issue not to have the Pharo VM development process in Pharo because they will see it as a threat to what they want to do with Pharo. Best Doru ! PS: I am still using the GTInspector with additional views on graphs created with Roassal everyday and I still enjoy it. PS2: I am on vacation currently because I was getting crazy looking at machine code all day long, so I may not answer as quick as usually during the next week. Cheers, > Doru > > > > On Sat, May 9, 2015 at 9:31 PM, Clément Bera <bera.clem...@gmail.com> > wrote: > >> >> >> 2015-05-09 20:25 GMT+02:00 stepharo <steph...@free.fr>: >> >>> >>> >>> Le 9/5/15 20:16, Clément Bera a écrit : >>> >>> This whole conversation here shows very well the point that I tried to >>> explain to Stef last week. I'm sorry if the mail is a bit long but I think >>> this discussion has to be done. >>> >>> My whole Smalltalk development life, I have used Pharo and was happy >>> with it. Now I am also working in Cog's JIT compiler and for this specific >>> project, I am working with Squeak. I don't work with Squeak because I don't >>> like Pharo, I told you before, I have worked with Pharo on all my project >>> before, enjoyed it and if it was possible I would use Pharo. I work with >>> Squeak because the VM development tool and development process simply does >>> *not* work in Pharo. This is not only because of VM tools working with the >>> old Morphic not working anymore in Pharo or details like that, it is also >>> due to deeper changes in Pharo. >>> >>> Stef believes it is important that Pharo is able to host development >>> for its own VM. Therefore, I discussed with him and Esteban about a first >>> list of points that are necessary for Pharo to support its VM development >>> in Pharo, which includes this Transcript behavior. >>> >>> As of today, and I am honest here, I believe that what is required for >>> Pharo to support the development process of its VM includes points which >>> goes in the opposite direction than a few points in the Pharo roadmap, that >>> people in the Pharo community will see as a regression, as "an intrusion >>> from the Squeak philosophy into Pharo", or as forbidding the integration of >>> features that breaks the VM development process. Therefore, I believe the >>> Pharo community would disapprove to make such changes and I highly doubt >>> that it is possible to have the development process of the >>> Pharo VM in Pharo. >>> >>> I was thinking that only a few points would be a problem such as the >>> increasing memory footprint of the Pharo image that is going to get worse >>> with the sources that will be included in the image in the future, whereas >>> a VM developer needs a small image (See previous threads in this mailing >>> list where Hilaire complains about that for example). >>> >>> >>> clement can I ask a simple question? >>> why did I ask guille to work on minikernels and bootstrap for his phd >>> instead on a topic where we can publish? >>> - choice A: lack of idea >>> - choice B: .... >>> >> >> I have already stated that you believe that it is important that Pharo is >> able to host development for its own VM. >> >> I am not against what you did and I am very excited with Guille's work. >> >> Pharo is community-driven, so I am not asking the question to you only, >> but to the community. >> >>> >>> >>> However, I didn't think that even simple points like the Transcript >>> behavior discussed here, which looks like to me as a regression and is >>> required for VM development, would be seen as an improvement by a non >>> negligible part of the community. >>> >>> In this mailing-list, the whole Pharo community is present and can see >>> this discussion. So the open questions are: >>> >>> *Do you want to have the development of the Pharo VM in Pharo, or do >>> you want the development of the Pharo VM to remain in Squeak ?* >>> *Do you think a system that is not good enough to handle its own VM >>> development is a good system ?* >>> >>> I am not willing to go against the will of the community because I >>> enjoy community-driven softwares. If the answer is that Pharo should be >>> able to support its own VM development then as I started I will help >>> Esteban and Stef to improve Pharo so that it can support its own VM >>> development. Now, if the answer is that the development of the Pharo VM >>> should remain in Squeak, I will continue developing the VM in Squeak. >>> >>> You are the Pharo community, you are the ones that make Pharo alive >>> and kicking, so you tell me what you think we should do. >>> >>> Clement >>> >>> 2015-05-09 18:23 GMT+02:00 Eliot Miranda <eliot.mira...@gmail.com>: >>> >>>> Hi Ben, >>>> >>>> On May 9, 2015, at 7:41 AM, Ben Coman <b...@openinworld.com> wrote: >>>> >>>> >>>> >>>> On Sat, May 9, 2015 at 10:09 PM, Ben Coman <b...@openinworld.com> wrote: >>>> >>>>> From my limited experience bug hunting, calling #changed: from a >>>>> thread other than the UI thread is a source of evil. There are too many >>>>> assumptions throughout the system that the UI is single threaded. Can >>>>> anyone advise me that is not a proper belief? >>>>> >>>>> Then that implies that a Transcript implementation where #nextPut: >>>>> direct calls #changed: >>>>> is not appropriate for use with multi-threaded applications. In >>>>> Pharo, #changed: is only called from #stepGlobal, which is called from >>>>> doOneCycle:. (This came about as a last minute bug fix before Pharo 3 >>>>> release and maybe could use some cleanup. >>>>> >>>>> Separating the UI from Transcript into its own viewer might be a >>>>> good idea, but actually it would not solve Stef's case since his code >>>>> would >>>>> still be running in the UI thread -- unless the viewer ran in another >>>>> thread, which would have its own complexities. >>>>> >>>>> I think the point about efficiency is significant. The following >>>>> example... >>>>> Time millisecondsToRun: [ 1000 timesRepeat: [ Transcript show: >>>>> 'x' ] ] >>>>> on Squeak 4.5 --> 12749ms >>>>> on Pharo 50029 --> 2ms >>>>> >>>> >>>> As a point of comparison, on VW 8.0 --> 43817ms >>>> and so you might guess, VW 8.0 outputs each 'x' immediately. >>>> cheers -ben >>>> >>>> >>>> Way to go, Squeak! Actually this is disappointing. I'm rather >>>> frustrated with Squeak's slow transcript, and was hoping that VW would >>>> demonstrate it could be faster. Looking at the Squeak implementation I >>>> only see an obvious 30% or so improvement via tuning. Looks like good >>>> performance will take more work :-/ >>>> >>>> >>>> >>>> Eliot (phone) >>>> >>> >>> >>> >> > > > -- > www.tudorgirba.com > > "Every thing has its own flow" >
