Doesn't compile on thumbv6m-none-eabi

[chxry]

Building latest git version and v1.19.0 fails on thumbv6m-none-eabi with features=["no_std"].
All the errors are from spin using AtomicUsize operations.

error[E0599]: no method named `fetch_add` found for struct `AtomicUsize` in the current scope
   --> /home/chxry/.cargo/registry/src/index.crates.io-6f17d22bba15001f/spin-0.7.1/src/rw_lock.rs:197:31
    |
197 |         let value = self.lock.fetch_add(READER, Ordering::Acquire);
    |                               ^^^^^^^^^ method not found in `AtomicUsize

[schungx]

Maybe spin locking is not supported for that CPU...

If it isn't supported you may have to clone the repo for the time being and remove the use of the once_cell crate....

EDIT: I find that spin is pulled in by no-std-compat. You can simply disable the spin feature of that crate and see what compiler errors you get -- mostly with trying to set a seed for hashing.

[schungx]

A bit searching reveals that this problem is quite common on the v6m...

ARM targets with thumbv6m only provide load and store operations, and do not support Compare and Swap (CAS) operations, such as swap , fetch_add , etc.

tokio-rs/bytes#461
https://users.rust-lang.org/t/issue-with-atomicbool-when-trying-to-build-project-for-v6m/59729
fereidani/rclite#7

[schungx]

Wonder if you have any success?

[chxry]

For me doing this worked, however I haven't tested how this affects other systems.

[schungx]

This looks interesting. I was not aware of the compat_sync feature. Can you make a PR?

[chxry]

Fixed by #919