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by hot_gril 1005 days ago
Python manages to combine the worst parts of high-level and low-level programming when it comes to multithreading. Like it's using multiple OS-level threads with the associated overhead (not greenthreading like in JS), except it's locking to negate actual multiprocessing, but you still have to use mutexes about as much as in C (no event loop like JS), and the whole API feels low-level and convoluted. It's like they tried to abstract things but gave up halfway through.

I like Python in general, but I avoid it for any kind of concurrent programming other than simple fan-out-fan-in.
1 comments
seabrookmx 1005 days ago
JS doesn't have green threads, just a single threaded event loop and context switching via promises or async/await. Green threads implies parallelism implemented in user space (ala. GoLang goroutines or JVM virtual threads).. JS is not parallel only concurrent.
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hot_gril 1005 days ago
Greenthreading implies concurrency, not parallelism, implemented in userspace rather than OS. Two Java/whatever greenthreads atop a single OS thread cannot run in parallel. It's switching contexts (as managed in userspace) during I/O waits, just like the JS event loop. You call Goroutines threenthreading, and some Golang users would disagree, but it is too.

Some environments support "M:N" greenthreading, mapping multiple userspace threads to multiple (but fewer) OS threads that are running in parallel, but that's not a required feature of greenthreading. In this case, the OS is still doing the parallelism.

And Python is not greenthreading because the concurrency comes from the OS, since each Py thread maps 1:1 to an OS thread.

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seabrookmx 1004 days ago
> Two Java/whatever greenthreads atop a single OS thread cannot run in parallel

Well.. yes. Actually that makes sense!

I guess I just never thought of them as green threads in JS because you don't interact with them as an object like you can in other languages.

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hot_gril 1004 days ago
"Greenthreading" is a weird term because it often refers to a very old Java implementation that was removed in 2000. And the Wikipedia article on the term is plain wrong in some ways.
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paulddraper 1005 days ago
JS has green threads.

Green threads imply only concurrency, not parallelism.

(JS also has parallelism, via worker threads, FYI)

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