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Comment on Tool for instantiating a C++ template at runtime?

abhibeckert@lemmy.world ⁨8⁩ ⁨months⁩ ago

build a dynamic library with a new instantiation, then dynload it and off we go

I haven’t played around with the internals of C++ myself, but isn’t that a one way thing? Wouldn’t you need to be able to “unload” a query after you’re done with it?

Personally I think child processes are the right approach for this. Launch a new process* for each query and it can (if you choose to go that route) dynamically load in compiled code. Exit when you’re done, and the dynamically loaded code is gone.

(*) On most operating systems launching new process is a bit slow, so you likely wouldn’t want to do that when the query is requested. Instead you’d maintain a pool of processes that are running and ready to receive a query. That’s how HTTP servers are often configured to run. The number of processes “pool” is generally limited by how much memory they need. Is it 1MB per process? 2GB?

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liori@lemm.ee ⁨8⁩ ⁨months⁩ ago

Personally I think child processes are the right approach for this. Launch a new process* for each query and it can (if you choose to go that route) dynamically load in compiled code. Exit when you’re done, and the dynamically loaded code is gone. A side benefit of that is memory leaks are contained, since all memory you allocate is about to be removed anyway.

I’d probably be fine with hundreds or thousands of these hanging in memory. I suspect the generated code for a single query would be in hundreds of kilobytes, maybe a megabyte. But yeah, this is one of those technical details I’d worry about.

Honestly, I wonder if you could just use an actual HTTP server for this? They can handle hundreds or even thousands of simultaneous requests. They can handle requests that complete in a fraction of a millisecond or ones that run for several hours. And they have good tools to catch/deal with code that segfaults, hits an endless loop, attempts to allocate terabytes of swap, etc. HTTP also has wonderful tools to load balance across multiple servers if you do need to scale to massive numbers of requests.

Not sure how a HTTP server would solve the CPU bottleneck of scanning terabytes of data per query?

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