Re: Hi [Gsoc-2014 Accepted]

Progress Report:

hello Vlad,

It took me a lot of time to get familiar with the technical concepts and
terminologies about system system programming.

The amount of information was  overwhelming at first but now I do
have a sound knowledge about synchronization primitives - spinlocks,
 condition variables, compare-and-swap, test-and-set. And how to use
them. I also spent time going through each line of xthread.d file and
its now committed in my memory.

Questions .. yes! many.
(I found answers to a lot of the questions I faced mostly related to
OS concepts on the internet itself.)

1.  Is test-and-set faster than compare-and-swap?

2.  In [xthread.d, line 104 ]  its mentioned "raw mutex used for thread
suspension/resume". What does a raw mutex refer to here? Is it any
different from a normal mutex? Does by raw mutex you mean .. simply
a mutex (! mutex/condition variable pair) ?

3.  I came across futex. It's a kernel facility the enables fast
implementations
of mutex in userspace and is used to implement basic locking. Why don't we
incorporate it in achieving locking ? since Pthread Mutex in the latest
Linux
distributions are implemented through Futex logic.

4.  In [xthread.d, line 52 ] I could not understand the 'Create a new
thread'
method's  void* (*startroutine)(void*) argument. Please, also provide me
with a definition of startroutine.

5.  In [xthread.d, line 99,152] what does #define THREADPROC_SIGNATURE do?

6.  In [xthread.d, line 156],  its mentioned 'an
inefficient implementation of
condition variable for win32.'. Why don't we use windows 'Events' instead of
a condition variable, since I read they are like a mutex/condition pair
wrapped
around a boolean.
plus there's also a to-do marked there-  "TODO : make it better."


Shashank


On Sat, Apr 26, 2014 at 12:22 PM, shashank <[email protected]> wrote:

> I apologize for the delayed response. I got occupied with college work
> and also I was unsure what to write to you since you have given me a lot
> of information to study.
>
> Please allow me sometime to go through all this and become familiar with
> it.
> I'll ask question as I face them.
>
>
>
> On Thu, Apr 24, 2014 at 12:18 PM, Vladimir Tzankov <[email protected]>wrote:
>
>> Yep, CAS is for Compare-And-Swap. Bear in mind we should support
>> multiple platforms and compilers. Recent gcc versions have builtin
>> support for atomic ops but we are not using them since other compilers
>> do not support them (e.g. msvc).
>>
>> In xthread.d is platform dependent portability layer - there are
>> mutex, condition variable and spinlock implementations for posix and
>> win32. Note that spinlock is special case of compare-and-swap (just
>> two values 0 or 1).
>>
>> zthread.d contains lisp land synchronization routines - lisp mutex and
>> lisp condition variable (called 'exemption').
>>
>> For hash table implementation you will need both.
>> 1. xthread.d should be extended with CAS (i suggest to extend
>> testandset macros).
>> 2. you will need this CAS + lisp sync object in order to implement the
>> hash table.
>>
>> As an example how to use lisp mutex - see package.d. There are helper
>> macros in lispbibl.d - WITH_LISP_MUTEX_LOCK which ensure proper
>> acquire/release handling in case of non-local exits.
>>
>> Vlad
>>
>> On Wed, Apr 23, 2014 at 6:16 PM, shashank <[email protected]>
>> wrote:
>> > Affirmative.
>> > I will CC all my question to clisp-devel list too.
>> > And I'll try to group together as many questions that I come up
>> > with into a single email, instead of spanning it over multiple emails.
>> >
>> >> Lock free hash table implementation itself is not very hard but
>> >> tricky in the details.
>> > Thanks for clearing this up. I got really worked up since the answer
>> > to a question here on stackoverflow said "Creating lock free structures
>> > is extremely hard and only experts in this field can do it.".
>> >
>> >> Also atomic primitives have to be added to xthread.d (cas in
>> particular).
>> > quick question .. what is cas?
>> >
>> > Also while doing a grep I found zthread.d file.While xthread.d contains
>> > macros
>> > for adding thread support, zthread.d contains the multithreading
>> > implementation (should I look into this too? ).
>> > So is there a top level file where xthread.c is called ?
>> >
>> >
>> >
>> > On Wed, Apr 23, 2014 at 12:02 AM, Vladimir Tzankov <[email protected]>
>> > wrote:
>> >>
>> >> Hey Shashank,
>> >>
>> >> I am glad the proposal was accepted - now it's time for the real work
>> :).
>> >>
>> >> I'll be quite busy in recent weeks and the preferred way of
>> >> communication is via emails. I'll try to respond as quickly as I can
>> >> (but bare in mind there will be some gaps due to travelling). Also CC
>> >> your questions to clisp-devel.
>> >>
>> >> Now it's the time to go over the clisp internals at
>> >> http://clisp.org/impnotes/ (Chapter IV). Play around with clisp code
>> >> base - change some things, run tests, etc. Lock free hash table
>> >> implementation itself is not very hard but tricky in the details.
>> >> Making it compatible with CL standard is harder. Also atomic
>> >> primitives have to be added to xthread.d (cas in particular).
>> >>
>> >> So please spend first week or two in getting comfortable with the
>> >> toolchain, code base and internals. Ask questions.
>> >>
>> >> BR
>> >>   Vlad
>> >>
>> >> On Tue, Apr 22, 2014 at 12:14 AM, shashank <[email protected]>
>> >> wrote:
>> >> > Hi
>> >> >
>> >> > Hey Vlad and Sam, thank you soo much :D
>> >> > And also thank you everyone who is a part of CLISP.
>> >> >
>> >> > I just found out that I got accepted into Google Summer of Code '14
>> to
>> >> > work
>> >> > with GNU and on CLISP. [0]
>> >> >
>> >> > I know I haven't been able to interact more with you guys about the
>> >> > project
>> >> > and in general. But thank for spotting the good in me and accepting
>> me
>> >> > as a
>> >> > part of clisp team.
>> >> > This is Exhilarating feeling for me. I am desperately waiting to
>> learn
>> >> > more
>> >> > & more from you all under your guidance and I commit that I will be a
>> >> > really
>> >> > good student and fun person to work with :)
>> >> >
>> >> > I am glad I'll be hanging out more here.
>> >> > Thanks again
>> >> >
>> >> > Best
>> >> > Shashank
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
>> >> >
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>> >> >
>> >
>> >
>>
>
>

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