Remove uses of unstable feature(cfg_target_has_atomic) #698
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I appreciate the work, I recently encountered this issue. |
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| # There is no `"max-atomic-width" == 16` or `"max-atomic-width" == 8` targets. |
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Both "avr-unknown-gnu-atmega328" and "msp430-none-elf", which are "target-pointer-width" == "16", do not support atomic:
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Detect platforms that do not support AtomicU64 by using the same way. AFAIK, this is more robust than the current way that uses autocfg. See also rust-lang/futures-rs#2294.
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707: Prepare for the next release r=taiki-e a=taiki-e - crossbeam-epoch 0.9.4 -> 0.9.5 - Fix UB in `Pointable` impl of `[MaybeUninit<T>]` (#694) - Support targets that do not have atomic CAS on stable Rust (#698) - Fix breakage with nightly feature due to rust-lang/rust#84510 (#692) - crossbeam-queue 0.3.1 -> 0.3.2 - Support targets that do not have atomic CAS on stable Rust (#698) - crossbeam-utils 0.8.4 -> 0.8.5 - Add `AtomicCell::fetch_update` (#704) - Support targets that do not have atomic CAS on stable Rust (#698) - crossbeam 0.8.0 -> 0.8.1 - Support targets that do not have atomic CAS on stable Rust (#698) Closes #702 Co-authored-by: Taiki Endo <te316e89@gmail.com>
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Some no-std targets (e.g., ARMv6-M) do not support atomic CAS operations and cannot use Arc, etc.
Currently, we are using an unstable feature to detect them, but it has caused breakage in the past (#435).
Also, users of stable Rust are not able to compile crossbeam on those targets.
Instead of depending on unstable features of the compiler, this patch detects those targets using the TARGET environment variables provided by cargo for the build script, and a list of targets that do not support atomic CAS operations.
This way is the same as the way we recently adopted in futures and valuable, and was originally inspired by the way heapless and defmt do, but this doesn't maintain the target list manually. (It's not really fully automated, but it's very easy to update.)
Also, this completely removes the dependency on unstable features from crates other than crossbeam-epoch.
refs: rust-lang/rust#51953, rust-lang/futures-rs#2400, tokio-rs/valuable#12