Hello..


More precision about Wait-free and Lock-free and about OneFile..

I am a white arab, and i think i am smart like a "genius",
since i have invented many scalable algorithms and there
implementations, and today i will make you understand more:

Look at this new invention of a PhD researcher:

OneFile - The world's first wait-free Software Transactional Memory

http://concurrencyfreaks.blogspot.com/2019/04/onefile-worlds-first-wait-free-software.html

And look carefully at this video about it by its inventor:

Pedro Ramalhete — Wait-free data structures and wait-free transactions

https://www.youtube.com/watch?v=oDfr9w9p8XY

So i think that this invention is not so smart, because
i have just read its source code here:

https://github.com/pramalhe/OneFile/blob/master/stms/OneFileWF.hpp

And it says the following:

Progress condition of the readers transactions: wait-free (bounded by
the number of threads + MAX_READ_TRIES)

and:

The progress condition of the writers transactions: wait-free (bounded
by the number of threads)

1- So as you are noticing it has a weakness and it is the same as the
Lock-free one, and it is that it wastes CPU time on the Progress
condition, so this wasting time is not good for scalability and
it is then not good for parallel programming, because so that it
"generalizes", it has also to work correctly not only for the much more read-mostly but also for other cases where the writes transactions are
of more greater proportion "relative" to the whole of the readers and
writers transactions, so my scalable and fair lock-based read-write
locks are better in this regard, since read about my new invention below
of of the Holy Grail of locks that i will use, and 'you will notice that
it is powerful.

2- Second weakness of the above invention, is that is is a complex
algorithm and this complexity of it is not good, and i think that
lock-based algorithms are much simpler , so they are easy to think about
and to implement.

I have invented a scalable algorithm that is a scalable fast Mutex that
is remarkable and that is the Holy Grail of scalable Locks, it has the following characteristics, read my following thoughts to understand:

About fair and unfair locking..

I have just read the following lead engineer at Amazon:

Highly contended and fair locking in Java

https://brooker.co.za/blog/2012/09/10/locking.html

So as you are noticing that you can use unfair locking that can have
starvation or fair locking that is slower than unfair locking.

I think that Microsoft synchronization objects like the Windows critical section uses unfair locking, but they still can have starvation.

But i think that this not the good way to do, because i am an inventor
and i have invented a scalable Fast Mutex that is much more powerful ,
because with my scalable Fast Mutex you are capable to tune the
"fairness" of the lock, and my Fast Mutex is capable of more than that,
read about it on my following thoughts:

More about research and software development..

I have just looked at the following new video:

Why is coding so hard...

https://www.youtube.com/watch?v=TAAXwrgd1U8

I am understanding this video, but i have to explain my work:

I am not like this techlead in the video above, because i am also an
"inventor" that has invented many scalable algorithms and there
implementions, i am also inventing effective abstractions, i give you an example:

Read the following of the senior research scientist that is called Dave
Dice:

Preemption tolerant MCS locks

https://blogs.oracle.com/dave/preemption-tolerant-mcs-locks

As you are noticing he is trying to invent a new lock that is preemption tolerant, but his lock lacks some important characteristics, this is why
i have just invented a new Fast Mutex that is adaptative and that is
much much better and i think mine is the "best", and i think you will
not find it anywhere, my new scalable Fast Mutex has the following characteristics:

1- Starvation-free
2- Tunable fairness
3- It keeps efficiently and very low its cache coherence traffic
4- Very good fast path performance
5- And it has a good preemption tolerance.
6- It is faster than scalable MCS lock
7- Not prone to convoying.


And about composability of lock-based systems now:

Design your systems to be composable. Among the more galling claims of
the detractors of lock-based systems is the notion that they are somehow uncomposable:

“Locks and condition variables do not support modular programming,”
reads one typically brazen claim, “building large programs by gluing
together smaller programs[:] locks make this impossible.”9 The claim, of course, is incorrect. For evidence one need only point at the
composition of lock-based systems such as databases and operating
systems into larger systems that remain entirely unaware of lower-level locking.

There are two ways to make lock-based systems completely composable, and
each has its own place. First (and most obviously), one can make locking entirely internal to the subsystem. For example, in concurrent operating systems, control never returns to user level with in-kernel locks held;
the locks used to implement the system itself are entirely behind the
system call interface that constitutes the interface to the system. More generally, this model can work whenever a crisp interface exists between software components: as long as control flow is never returned to the
caller with locks held, the subsystem will remain composable.

Second (and perhaps counterintuitively), one can achieve concurrency and composability by having no locks whatsoever. In this case, there must be
no global subsystem state—subsystem state must be captured in
per-instance state, and it must be up to consumers of the subsystem to
assure that they do not access their instance in parallel. By leaving
locking up to the client of the subsystem, the subsystem itself can be
used concurrently by different subsystems and in different contexts. A
concrete example of this is the AVL tree implementation used extensively
in the Solaris kernel. As with any balanced binary tree, the
implementation is sufficiently complex to merit componentization, but by
not having any global state, the implementation may be used concurrently
by disjoint subsystems—the only constraint is that manipulation of a
single AVL tree instance must be serialized.

Read more here:

https://queue.acm.org/detail.cfm?id=1454462

And you have to look here at our DelphiConcurrent and FreepascalConcurrent:

https://sites.google.com/site/scalable68/delphiconcurrent-and-freepascalconcurrent

Thank you,
Amine Moulay Ramdane.

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