Support Linux on MIPS and ARMv5TE

[tatsuya6502]

This pull request is for supporting Linux on 32-bit MIPS and ARMv5TE. These platforms does not provide std::sync::atomic::AtomicU64 so currently both Moka and quanta will not compile.

After merging this PR, Moka will compile on 32-bit MIPS. For ARMv5TE, you need to add default-features = false to "moka" dependency in Cargo.toml and then Moka will compile.

After this PR is merged, you can resolve the errors by disabling the default features by adding default-features = false to the dependency declaration in Cargo.toml. This will remove quanta from the dependencies and enable a fall-back implementation in Moka.

Changes

• Add a cargo feature quanta atomic64 and make it a default feature.
• Add a module common::time and conditionally choose the source file from "time_quanta.rs" or "time_compat.rs".
  • time_quanta.rs file has type aliases to quanta::{Instant, Clock, Mock}. It also has AtomicInstant holding an AtomicU64.
  • time_compat.rs file has Instant based on std::time::Instant and quanta-like Clock and Mock. It also has AtomicInstant holding a RwLock<Option<Instant>>.
• Update Cache, etc. modules to use common::time instead of quanta.
• Add a step to GitHub Actions to test future feature without quanta/AtomicU64.

---

Fixes #38.

[messense]

Note that I've also opened metrics-rs/quanta#55 to fix quanta on these platforms, so maybe after that lands moka can still use quanta but not AtomicU64. In this case I think the feature name should not be quanta.

[tatsuya6502]

Thanks. Good point.

Hmm. I am having hard time to come up with a good short name for the feature. Moka uses AtomicU64 as a lightweight atomic type for timestamps. It is for space efficiency and also high performance.

So... perhaps, atomic-time, ... or just atomic-u64/atomic64?

I think atomic64 might be OK. It may be too straightforward, but works. It will be easy to understand that you need to disable atomic64 feature if platform does not support 64-bit atomic types.

[messense]

Thank you.

[messense]

I've just tested this on a mipsel router, it compiles and runs, but hits seanmonstar/num_cpus#69 , I think this line should be changed to use 1 if num_cpus::get() returns 0

moka/src/common/thread_pool.rs

Line 56 in 988816a

let num_threads = num_cpus::get();

See also rust-lang/futures-rs#1835

[tatsuya6502]

Thanks for testing on the real hardware. I did not realize it could return 0. Changed to use 1 when it returns 0.

[tatsuya6502]

Verified the followings:

1. Ran cargo build for the following targets using Docker images messense/rust-musl-cross and verified they succeeded:
   • armv5te-unknown-linux-musleabi
   • mips-unknown-linux-musl
   • mipsel-unknown-linux-musl
   • commit: d91c5ce
2. Ran regular prerelease load tests using mokabench on x86_64-unknown-linux-gnu. Verified that the test runs with and without the default features found no new issue.
   • commit: 4407e87
   • NOTE: This known issue is still occurring: Segmentation faults in moka-cht under heavy workloads on a many-core machine #34

Test 1

% git remote -v
origin	git@github.com:moka-rs/moka.git (fetch)
origin	git@github.com:moka-rs/moka.git (push)

$ git log -1
commit d91c5ce4bbd6d403e1fe37fa9ed1831225b18434 (HEAD -> mips-armv5, origin/mips-armv5)
Author: Tatsuya Kawano
Date:   Fri Sep 10 20:19:23 2021 +0800

    Bump the version to v0.5.3


$ sudo rm -rf release

$ docker run -it --rm -v $(pwd):/home/rust/src \
  --mount source=cargo-registry,target=/root/.cargo/registry \
  messense/rust-musl-cross:armv5te-musleabi \
  cargo build --no-default-features --features future --target armv5te-unknown-linux-musleabi
   ...
   Compiling moka v0.5.3 (/home/rust/src)
   ...
    Finished dev [unoptimized + debuginfo] target(s) in 32.67s

$ echo $?
0

$ docker run -it --rm -v $(pwd):/home/rust/src \
  --mount source=cargo-registry,target=/root/.cargo/registry \
  messense/rust-musl-cross:mips-musl \
  sh -c "RUSTFLAGS='-C target-feature=+crt-static -C link-arg=-s' \
    cargo build --no-default-features --features future --target mips-unknown-linux-musl"
   ...
   Compiling moka v0.5.3 (/home/rust/src)
   ...
    Finished dev [unoptimized + debuginfo] target(s) in 8.96s
$ echo $?
0

$ docker run -it --rm -v $(pwd):/home/rust/src \
  --mount source=cargo-registry,target=/root/.cargo/registry \
  messense/rust-musl-cross:mipsel-musl \
  sh -c "RUSTFLAGS='-C target-feature=+crt-static -C link-arg=-s' \
    cargo build --no-default-features --features future --target mipsel-unknown-linux-musl"
   ...
   Compiling moka v0.5.3 (/home/rust/src)
   ...
    Finished dev [unoptimized + debuginfo] target(s) in 8.82s
$ echo $?
0

[messense]

Test again on mipsel router and I'm happy to report that it works™.

[tatsuya6502]

Thank you for testing. I am merging this and will publish v0.5.3 to crate.io soon.