Compilation errors due to missing atomics even though atomic feature is not enabled

[arctic-alpaca]

Hi,
I'm trying to use bitvec with aya which uses bpf-linker to create BPF programs. Atomics are not available for the BPF targets.

As per readme, bitvec = {version = "1.0.1", default-features = false} should disable the use of atomics in bitvec but I still get compilation errors:

error[E0432]: unresolved imports `core::sync::atomic::AtomicBool`, `core::sync::atomic::AtomicI8`, `core::sync::atomic::AtomicU8`
  --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/lib.rs:44:34
   |
44 |         use core::sync::atomic::{AtomicBool, AtomicI8, AtomicU8};
   |                                  ^^^^^^^^^^  ^^^^^^^^  ^^^^^^^^ no `AtomicU8` in `sync::atomic`
   |                                  |           |
   |                                  |           no `AtomicI8` in `sync::atomic`
   |                                  no `AtomicBool` in `sync::atomic`
   |
help: a similar name exists in the module
   |
44 |         use core::sync::atomic::{AtomicBool, AtomicI64, AtomicU8};
   |                                              ~~~~~~~~~
help: a similar name exists in the module
   |
44 |         use core::sync::atomic::{AtomicBool, AtomicI8, AtomicU64};
   |                                                        ~~~~~~~~~

error[E0432]: unresolved imports `core::sync::atomic::AtomicI16`, `core::sync::atomic::AtomicU16`
  --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/lib.rs:47:34
   |
47 |         use core::sync::atomic::{AtomicI16, AtomicU16};
   |                                  ^^^^^^^^^  ^^^^^^^^^ no `AtomicU16` in `sync::atomic`
   |                                  |
   |                                  no `AtomicI16` in `sync::atomic`
   |
help: a similar name exists in the module
   |
47 |         use core::sync::atomic::{AtomicI64, AtomicU16};
   |                                  ~~~~~~~~~
help: a similar name exists in the module
   |
47 |         use core::sync::atomic::{AtomicI16, AtomicU64};
   |                                             ~~~~~~~~~

error[E0432]: unresolved imports `core::sync::atomic::AtomicI32`, `core::sync::atomic::AtomicU32`
  --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/lib.rs:50:34
   |
50 |         use core::sync::atomic::{AtomicI32, AtomicU32};
   |                                  ^^^^^^^^^  ^^^^^^^^^ no `AtomicU32` in `sync::atomic`
   |                                  |
   |                                  no `AtomicI32` in `sync::atomic`
   |
help: a similar name exists in the module
   |
50 |         use core::sync::atomic::{AtomicI64, AtomicU32};
   |                                  ~~~~~~~~~
help: a similar name exists in the module
   |
50 |         use core::sync::atomic::{AtomicI32, AtomicU64};
   |                                             ~~~~~~~~~

error[E0412]: cannot find type `AtomicBool` in module `core::sync::atomic`
  --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:10:43
   |
10 |     if atomic(bool) { core::sync::atomic::AtomicBool }
   |                                           ^^^^^^^^^^ not found in `core::sync::atomic`

error[E0412]: cannot find type `AtomicI8` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:16:40
     |
16   |       if atomic(8) { core::sync::atomic::AtomicI8 }
     |                                          ^^^^^^^^ help: a struct with a similar name exists: `AtomicI64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2858:1
     |
2858 | / atomic_int! {
2859 | |     cfg(target_has_atomic = "64"),
2860 | |     cfg(target_has_atomic_equal_alignment = "64"),
2861 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2875 | |     i64 AtomicI64 ATOMIC_I64_INIT
2876 | | }
     | |_- similarly named struct `AtomicI64` defined here

error[E0412]: cannot find type `AtomicU8` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:22:40
     |
22   |       if atomic(8) { core::sync::atomic::AtomicU8 }
     |                                          ^^^^^^^^ help: a struct with a similar name exists: `AtomicU64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2878:1
     |
2878 | / atomic_int! {
2879 | |     cfg(target_has_atomic = "64"),
2880 | |     cfg(target_has_atomic_equal_alignment = "64"),
2881 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2895 | |     u64 AtomicU64 ATOMIC_U64_INIT
2896 | | }
     | |_- similarly named struct `AtomicU64` defined here

error[E0412]: cannot find type `AtomicI16` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:28:41
     |
28   |       if atomic(16) { core::sync::atomic::AtomicI16 }
     |                                           ^^^^^^^^^ help: a struct with a similar name exists: `AtomicI64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2858:1
     |
2858 | / atomic_int! {
2859 | |     cfg(target_has_atomic = "64"),
2860 | |     cfg(target_has_atomic_equal_alignment = "64"),
2861 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2875 | |     i64 AtomicI64 ATOMIC_I64_INIT
2876 | | }
     | |_- similarly named struct `AtomicI64` defined here

error[E0412]: cannot find type `AtomicU16` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:34:41
     |
34   |       if atomic(16) { core::sync::atomic::AtomicU16 }
     |                                           ^^^^^^^^^ help: a struct with a similar name exists: `AtomicU64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2878:1
     |
2878 | / atomic_int! {
2879 | |     cfg(target_has_atomic = "64"),
2880 | |     cfg(target_has_atomic_equal_alignment = "64"),
2881 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2895 | |     u64 AtomicU64 ATOMIC_U64_INIT
2896 | | }
     | |_- similarly named struct `AtomicU64` defined here

error[E0412]: cannot find type `AtomicI32` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:40:41
     |
40   |       if atomic(32) { core::sync::atomic::AtomicI32 }
     |                                           ^^^^^^^^^ help: a struct with a similar name exists: `AtomicI64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2858:1
     |
2858 | / atomic_int! {
2859 | |     cfg(target_has_atomic = "64"),
2860 | |     cfg(target_has_atomic_equal_alignment = "64"),
2861 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2875 | |     i64 AtomicI64 ATOMIC_I64_INIT
2876 | | }
     | |_- similarly named struct `AtomicI64` defined here

error[E0412]: cannot find type `AtomicU32` in module `core::sync::atomic`
    --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-0.7.0/src/types.rs:46:41
     |
46   |       if atomic(32) { core::sync::atomic::AtomicU32 }
     |                                           ^^^^^^^^^ help: a struct with a similar name exists: `AtomicU64`
     |
    ::: /home/arctic-alpaca/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/sync/atomic.rs:2878:1
     |
2878 | / atomic_int! {
2879 | |     cfg(target_has_atomic = "64"),
2880 | |     cfg(target_has_atomic_equal_alignment = "64"),
2881 | |     stable(feature = "integer_atomics_stable", since = "1.34.0"),
...    |
2895 | |     u64 AtomicU64 ATOMIC_U64_INIT
2896 | | }
     | |_- similarly named struct `AtomicU64` defined here

This looks like it is similar to the issue raised in the radium repo ferrilab/ferrilab#1.

[arctic-alpaca]

As suggested in ferrilab/ferrilab#1, I tried to (naively) update bitvec to radium 1.0.0 here: https://github.com/arctic-alpaca/bitvec
The bitvec tests seem to pass as before the update but when using the updated version in my project, I encountered this error from radium:

error[E0277]: `*mut T` cannot be sent between threads safely
   --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-1.0.0/src/types.rs:201:19
    |
201 |               type Nucleus = $radium$(<$t>)?;
    |                              ^^^^^^^^^^^^^ `*mut T` cannot be sent between threads safely
...
223 | / alias! {
224 | |     "8" => {
225 | |         bool => RadiumBool => AtomicBool;
226 | |         i8 => RadiumI8 => AtomicI8;
...   |
249 | |     }
250 | | }
    | |_- in this macro invocation
    |
    = help: the trait `Send` is not implemented for `*mut T`
    = help: the trait `Send` is implemented for `&T`
    = note: required for `Cell<*mut T>` to implement `Send`
note: required by a bound in `marker::Nuclear::Nucleus`
   --> /home/arctic-alpaca/.cargo/registry/src/github.51.al-1ecc6299db9ec823/radium-1.0.0/src/marker.rs:45:38
    |
45  |     type Nucleus: Radium<Item = Self> + Send;
    |                                         ^^^^ required by this bound in `Nuclear::Nucleus`
    = note: this error originates in the macro `alias` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.

After removing the Send bound (https://github.com/arctic-alpaca/ferrilab), I was able to use bitvec in my project. I do not know what the implication/effect of removing the Send bound is or if my simple update of bitvec has any side effects. If desired, I'd be happy to create a PR.

EDIT: After realizing you are migrating to a monorepo, I pushed the bitvec changes to the monorepo fork: https://github.com/arctic-alpaca/ferrilab

[myrrlyn]

Hi! I apologize for the long delay; I have had a very stressful winter and have not had the time or energy to check this repository in a timely manner. I'm trying to catch up now.

Thank you for your time investigating this, and for duplicating effort in the monorepo. radium is a really annoying project to manage. Being able to punt to the compiler as of Rust 1.60 is a huge relief, and I have already migrated to radium 1 in my working copy.

I suspect that the reason for your initial error is just that radium 0 requires that we manually process target definitions taken from the compiler, and I don't think we collected BPF targets last time we did that.

I am pretty sure I can migrate to radium 1 without a major-version bump, so I intend to do so in bitvec 1.1.

---

If you require a Send bound, then Nucleus is failing as expected when your final target doesn't have the requisite atomic. It silently falls back to Cell, which isn't threadsafe. You'd have to either #[cfg]-guard your type on the presence of the needed atomic, or do exactly what you did: remove the bound here, and then encounter compiler errors when you attempt to do multithreading on a target without proper atomics.

The advantage is that now your errors occur at the use site, not at the declaration site: thread::spawn will fail, instead of your typedecl.

I think the fact that Cell<*mut T> isn't Send is an irritating discrepancy: AtomicPtr is Send, and Cells are Send when their interior is. The reason that Cell<*mut T> isn't Send is that the pointer might become invalid to dereference if a foreign thread has a time delay between receipt and use. This, however, is equally true of the pointer value stored inside an AtomicPtr!

Unfortunately, I'm pretty sure impl<T> Send for Cell<*mut T> collides with impl<T: Send> Send for Cell<T> (pointers aren't fundamental types like references are), and removing the Send impl on atomic pointers is a breaking change, so we're just left with it.

I hope this helps!

[ProfFan]

Hello @myrrlyn thanks for the amazing library. However, I think this issue has not been solved, the main branch still refers to radium v0.7.