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0 pointsfulafel2y ago0 comments

You could easily have a million threads if you use multi-kb stacks. Million times multi-kb means multi-gb, that's still 3-4 orders of magnitude less than big memory servers/VMs. (and 1 order of magnitude less than a normal laptop)

What do you mean by using a file handle, is this a Windows platform thing? On *ix, threads don't use up file descriptors (but you can still have a million fd's at least on linux for other stuff if you want).

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zmmmmm2y ago

> On *ix, threads don't use up file descriptors

Thanks - this caused me to dig into the specific scenario where creating threads was exhausting file handles in my experience and you are correct - consuming a file handle is indeed not intrinsic to creating a new thread in Linux. It's insanely easy for literally anything you do with the thread to consume a file handle, but of course, that applies to virtual threads as well. Thanks!

thfuran2y ago

But "multi-kb" in this context probably actually means about 1MB.

fulafelOP2y ago

What do you base this on? The stacks and kernel bookkeeping shouldn't use nearly this much at least on linux. Keep in mind that thread stacks have are lazily allocated virtual memory so won't use as much physical memory as the thread stack size setting shows.

If these threads are handling TCP connections and L7 protocol processing on top, you're going to have nontrivial both kernel and userspace memory usage per connection too that may dwarf the thread overhead.

Here's a linux kernel dev (Ingo Molnar) benchmarking Linux in 2002 and starting just shy of 400k threads in 4 GB: https://lkml.iu.edu/hypermail/linux/kernel/0209.2/1153.html - though on a 32 bit systems lots of objects things are 50% the size compared to current 64 bit. But still gives you a ballpark.

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