Is it concurrent or parallel?
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Is it concurrent or parallel? Concurrency and parallelism confuse a lot of new programmers and students of computer science-especially when studying operating systems, high performance computing, threads, and similar systems topics. This video tries to clarify the difference. I hope it helps.
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Welcome! I post videos that help you learn to program and become a more confident software developer. I cover beginner-to-advanced systems topics ranging from network programming, threads, processes, operating systems, embedded systems and others. My goal is to help you get under-the-hood and better understand how computers work and how you can use them to become stronger students and more capable professional developers.
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I tried to keep this in mind “Concurrency is a software mechanism and parallelism is a hardware concern”
thanks
They're both achieved through software
i know this is maybe off-topic, but can you make a video about distributed systems and perhaps MPI ?
Glad to see you putting out more videos!
Keep uploading ... These videos are very insightful !
Well explained... thank you !!!
Hey Jacob, really enjoy your videos, could you make a topic about RISC-V?
Loved this explanation
My interpretation has always been the same. I always think of "parallel processors" which requires more than one core. 🙂
multiprocessor execution surely does not imply parallelism. while I have 16 physical cores, I also have 587 processes running, so the OS will have to resort to scheduling (what you define as concurrency).
Unless only one of the cores is working at each moment, surely you're executing more than one process at the same time, and thus have parallel execution?
This is the way I've learned and understood it as well, granted I've had to double check and google it a few times when I forgot 😁
These diagrams helped me to visualise it better
Concurrency...
_ _
_ _ _
Parallelism :
_ _ _ _ _
_ _ _ _ _
Both of them have "Concurency". First one has ("Concurency" without "Parallelism") and second one has both ("Concurrency" and implicitly "Paralelism"). I do like your representation with the lines :)
Could you do a video on atomics sometime? I've only ever used mutexes for making multithreaded code safe and it seems like it's a bit limiting in certain circumstances
They done it :)
Check the last video «Making variables atomic in C»
You only get real parallelism in multicore bare metal processors and FPGA/ASIC. Everything else is concurrent or concurrently parallel. This is because there is a clear separation of concerns between the OS operation and software you develop on top of OS functionalities.
An example would help me understand this better
Have you seen "Modern C and we can learn from it?" I wonder what you think on that as it's quite different from the usual way you'd use C.
If two completely independent tasks are run in parallel, is that (still) concurrent?
(Referring to the last diagram.)
Hi Jacob,
For the diagram at 3:25 , can an application be parallel and not concurrent? That would contradict the diagram.
"An application can be parallel but not concurrent, which means that it processes multiple sub-tasks of a single task at the same time."
Great question! I think basically that's why threads were created, some tasks have multiple subtask inside so those are what actually interest you, not the big one. So you create threads of execution that run concurrently and ideally in parallel due to multithreaded processors.
Now, i guess if you have multiple cores with multiple threads each, your processes are running in a parallel fashion, with threads running concurrently on each individual thread of the processor. For example, a processor with 2 cores with one thread of execution each can run one thread of one process on one core and another thread of another process on the other core, while threads are executed concurrently waiting for their turn on the core.
can two thread in the same process run in different cores and implement parallism?❤
Ofc they can. Since you wrote "different cores' I assume you have more than 1, else they are not different.
is async computation concurrency?
Yes
@@The-Real-Jack This is incorrect. Asynchrony has nothing to do with concurrency in itself. Asynchrony is merely the absence or privation of synchrony.
It can be both based on the programmer's decision. It can run on a separate hardware thread or it can run on the same thread sequentially.
Async isn't necessarily "true" concurrency in the sense of multithreaded concurrency (though it can be), but even in the case of single threaded async, it allows you to unblock further events and actions while your other instructions continue executing, practically allowing things to happen at the same time, even if they're not technically truely simultaneous. Whether you consider that concurrent or not is mostly semantic.
yes or not, bcause the distributed task don't have to be ran immediately
Thank you so much for your awesome videos.
Would you do some series on Rust.
I hope not. No one should be using it.
How do we get to redefine English words to mean what we want? The definition of ‘concurrent’ says “two or more things happening at the same time.” 10/10 would fail this quiz question and be okay with it.
Indeed. Redefining imprecise natural language to meet our specific needs is kind-of what we tech people do.
@@JacobSorber :(
@@JacobSorbertech language is so bad
Instead of using synonyms to confuse people, why didn't they just call "a single core juggling several processes" what it is: multitasking, as that is what it is called when a person does it. Or does that mean something else entirely in CS?
Do you know what a semaphore is?
I'm downloading a file in my web browser and meanwhile I am watching your CZcams video. Are both happening parallelly or concurrently?
It depends on your hardware and OS. If you're using a modern multicore system then most probably they're running in parallel. Especially since those two processes have nothing to do with each other and are independent.
my summary of this video:
* Concurrency means: overlap in their turning-around period
* Parallelism means: overlap in their actively running time
DO NOT USE THESE DEFINITIONS
this is a REALLY, REALLY bad relationship of names and it causes everyone tangible harm to advocate these names for these concepts. "parallel" and "concurrent" in the context of time are synonymous in the English language, and so using "concurrent" as the name for something discretely different from "parallel" is REALLY, REALLY confusing and semantically misleading. call this concept of rapid OS context switching "scheduling", "round robin", "taking turns", "context switching", "time sharing", "time-slicing", "time-rationing", "focus-swapping", "pseudo-parallism", "virtual parallelism", "interleaving", "task dithering", "sequential sharing", or literally ANYTHING else.
PLEASE stop giving things horrible names. PLEASE. computer science has way too fucking many bad names already. "concurrent" is literally THE word in the English language for when multiple things are happening at the same time. PLEASE do not use that word to refer to something where multiple things are explicitly NOT actually happening at the same time.
this kind of thoughtless, rote repetition of extremely stupid traditions is exactly what's wrong with so much of programming.
Programmers use terms in set X, mathematicians use set Y and "civilians" use set Z, and never the twain shall meet. That's life, get used to it and grow up or get out while you can. Another one that'll trip you up is thinking that terms stay the same for all time, because human beings can and will change the dictionary as often as they can. Go back to the 1950's and you'll more or less be able to have a casual conversation with someone, but go back another 70 years and you might not understand anyone. Something to ponder, if the average is at a specific level, then roughly half, give or take, will be below that average.
TF
Completely agree. Computer Science uses trash language