jemallocator in cdylib ?

[NotSqrt]

Hello !

I'm working on a lib, and I get a 20% speed up in my tests when using jemallocator instead of the default allocator, with a marginal loss in memory usage.

But I have not found how to use it when building a lib with crate-type = ["cdylib"] and pyo3.
Currently, I get cannot allocate memory in static TLS block when importing the lib from python.
Google did not help me ..

Any tips ?
Thanks a lot !

[gnzlbg]

How are you using jemallocator ? Typically, the #[global_allocator] is something that can only be meaningfully chosen by the final binary, and when compiling a cdylib, that library should work when linked to multiple different binaries, all using different allocators.

[NotSqrt]

For the moment, I just put:

#[global_allocator]
static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;

in my lib.rs.

Which is enough to switch allocators for cargo test.

[NotSqrt]

And I build the python extension based on that example : https://github.com/PyO3/rust-numpy/tree/master/examples/simple-extension

[gnzlbg]

So you probably also need to get the final binary that links to your cdylib to use the same exact version of jemalloc configured in the exact same way. That might be hard to do if the binary that you are using is python which might be using a different allocator.

Hmmm, have you tried generating a staticlib instead of a cdylib ? Pinging: @alexcrichton , they might be able to help or know who else could help. I'm not really sure what happens when you put an allocator in a cdylib - if it gets dynamically linked, it would probably be replaced by the allocator in the final library, and if it gets statically linked, then you can't transfer ownerships of allocations across the cdylib boundary (e.g. you can't allocate memory in the cdylib, and free it in the final binary somewhere else).

[NotSqrt]

Generating a staticlib instead of a cdylib:

setuptools_rust forces cdylib: https://github.com/PyO3/setuptools-rust/blob/v0.10.6/setuptools_rust/build.py#L142
I changed the code to staticlib, but the lib is not picked up by setuptools_rust, because they specifically look for .so files : https://github.com/PyO3/setuptools-rust/blob/v0.10.6/setuptools_rust/build.py#L226

I'm not sure a static lib will be easy to use as a python extension anyway..

[NotSqrt]

the final binary that links to your cdylib

Well, setuptools_rust just copies the .so generated by rustc, and from there, the my_lib.so can be used dynamically from python with:

import my_lib

There's no other binary than python itself..

I'll resume working on it on Monday.

[gnzlbg]

I'm not sure either. Maybe you can try asking in users.rust-lang.org forums ? Other people there might be able to help :)

[NotSqrt]

Thanks, I'll also ask on the pyo3 repo.

[NotSqrt]

jemalloc/jemalloc#937 seems related.

[NotSqrt]

It seems jemallocator = {version = "0.3", features = ["disable_initial_exec_tls"]} will be enough !

[gnzlbg]

Good find! Glad it works now!