Broken configuration of atomics with tokio/bytes

[jklmnn]

I'm currently using this crate on an rp2040 and noticed that with the latest master release here I get the following errors:

error[E0599]: no method named `fetch_add` found for reference `&AtomicUsize` in the current scope
    --> /.../.cargo/registry/src/index.crates.io-6f17d22bba15001f/bytes-1.9.0/src/bytes.rs:1131:27
     |
1131 |     let old_cnt = ref_cnt.fetch_add(1, Ordering::Relaxed);
     |                           ^^^^^^^^^ method not found in `&AtomicUsize`

I'm using tokio-rs/bytes@16fd473 (see tokio-rs/bytes#467) and it works fine with mqttrs 0.4.1. It breaks with master and the problematic change seems to be 9f70f89 by @mchodzikiewicz. I see that there is 6e06377 but it doesn't seem to address the problem fully. Unfortunately I don't understand enough of the inner workings of Cargo to provide a fix.

My Cargo.toml is

[dependencies]
cortex-m-rt = "0.7.5"
defmt = "0.3.10"
defmt-rtt = "0.4.1"
embassy-time = "0.4.0"
static_cell = "2.1.0"
no-std-net = "0.6.0"

[dependencies.bytes]
#version = "1.9"
git = "https://github.com/tokio-rs/bytes.git"
rev = "16fd473d5c6ca20787e157ec19afc469438fc66b"
default-features = false
features = ["extra-platforms"]

[dependencies.cyw43]
version = "0.3.0"
features = ["defmt", "firmware-logs"]

[dependencies.cyw43-pio]
version = "0.3.0"
features = ["defmt"]

[dependencies.embassy-executor]
version = "0.7.0"
features = ["arch-cortex-m", "executor-thread", "defmt", "task-arena-size-16384"]

[dependencies.embassy-net]
version = "0.6.0"
features = ["defmt", "tcp", "udp", "raw", "dhcpv4", "medium-ethernet", "dns", "proto-ipv4", "proto-ipv6", "multicast"]

[dependencies.embassy-rp]
version = "0.3.0"
features = ["defmt", "unstable-pac", "time-driver", "critical-section-impl", "rp2040"]

[dependencies.mqttrs]
#version = "0.4"
git = "https://github.com/00imvj00/mqttrs.git"
rev = "6296bab1673b9d7d316165d46e2836d03a6e5965"
default-features = false

[dependencies.panic-probe]
version = "0.3.2"
features = ["print-defmt"]

[dependencies.portable-atomic]
version = "1.10"
default-features = false
features = ["critical-section"]

[dependencies.rp2040-hal]
version = "0.11"
features = ["critical-section-impl"]

[00imvj00]

@mchodzikiewicz, please check this out and see if we can resolve it. I would appreciate the help.

[mchodzikiewicz]

I can reproduce it in my project for esp32c3 (that also doesn't have hardware atomics) - I'll dig into it later today

[mchodzikiewicz]

@jklmnn there was bytes release yesterday including commit you use, I have a slight suspicion that it was an odd version mismatch (cargo gets a bit weird with semver when you source a git commit instead of released crate), can you try to use published version of bytes 1.10.0?

It resolved my reproducer but I am not sure if it is universal

[mchodzikiewicz]

Also, do you have a specific reason to use bytes over heapless?

That's not a solution for this specific issue but rather a hint I want to say out loud. I find avoiding usage of alloc more robust on small targets

[jklmnn]

@mchodzikiewicz The atomic error is gone with bytes 1.10 however now I get

error: no global memory allocator found but one is required; link to std or add `#[global_allocator]` to a static item that implements the GlobalAlloc trait

This problem starts to appear with 9f70f89. The commits before it work just fine. If I remove the explicit dependency to bytes I get the original error again. It's still pulling bytes.

Also, do you have a specific reason to use bytes over heapless?

Mostly because the README said so. But it doesn't seem to make a difference if I remove bytes from my dependencies, it's still pulling it, just without the correct features.

[jklmnn]

The problem seems to be that 9f70f89#diff-2e9d962a08321605940b5a657135052fbcef87b5e360662bb527c96d9a615542L25 makes bytes non-optional. If I change it to

diff --git a/Cargo.toml b/Cargo.toml
index 0638cf0..13e9cd7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -23,7 +23,7 @@ std = ["bytes/std", "serde/std"]
 defmt = ["dep:defmt", "heapless/defmt-03"]
 
 [dependencies]
-bytes = { version = "1.0", default-features = false}
+bytes = { version = "1.0", default-features = false, optional = true}
 serde = { version = "1.0", features = ["derive"], optional = true }
 heapless = { version = "0.8" }
 defmt = { version = "0.3.10", optional = true }

It builds and runs just fine with the latest commit.

Tbh I'm not sure why you changed it to be non-optional, so I can't say whether this breaks something else.

[mchodzikiewicz]

Yup, that's it - it's a rebase artifact I didn't catch, sorry, issue a PR that brings back bytes being optional or I'll do it later today

[jklmnn]

I opened #52.