Sample
once_cell 1.21.4: Decide what still needs once_cell now that std has OnceLock, LazyLock, cell::OnceCell and cell::LazyCell, by measuring which once_cell APIs have a stable std equivalent on this rustc and which are still gated
Verified sample for cargo once_cell 1.21.4: Decide what still needs once_cell now that std has OnceLock, LazyLock, cell::OnceCell and cell::LazyCell, by…
sha256:36b55cf55782c3258dcb2509e721eb8edf4affdd15e52754fe01d12bb5fa27c9
This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured.
How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people.
MIT-0
Execution evidence
The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.
- Evidence basis
- Signed contract pass
- Verification receipts
- 2
- Signing keys that built it
- 2
Declared environment
rust 1 linux x64 rust 1 rust cargo
Verification-run environments
| Environment | Contract | Stages | Run |
|---|---|---|---|
| rust 1 · linux alpine/x64 · docker ed25519:a2ec939a4c60e243 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · cargo@1 |
2026-08-14 |
| rust 1 · linux alpine/x64 · docker ed25519:d91480838ac982c9 | PASS | compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS CONTAINER_RUN · cargo@1 |
2026-08-18 |
Case
MIGRATION- Goal
- Decide what still needs once_cell now that std has OnceLock, LazyLock, cell::OnceCell and cell::LazyCell, by measuring which once_cell APIs have a stable std equivalent on this rustc and which are still gated
- Packages
- Symbols
-
- std::sync::OnceLock
- OnceLock::set
- OnceLock::get_or_init
- OnceLock::take
- std::sync::LazyLock
- LazyLock::force
- LazyLock::force_mut
- std::cell::OnceCell
- std::cell::LazyCell
- once_cell::sync::OnceCell
- once_cell::sync::OnceCell::get_or_try_init
- once_cell::sync::Lazy
- once_cell::unsync::OnceCell
- Environment
- rust 1
- Created
- 2026-08-14T13:27:13Z
Contract
- assert a second OnceLock::set neither panics nor overwrites, and hands the rejected value straight back inside Err while the first value stays put
- assert get_or_init on an already filled cell never calls its closure, and that take() needs &mut so a shared cell stays write-once
- assert once_cell::sync::OnceCell::set has the identical hands-it-back contract
- assert get_or_init runs its closure exactly once when 16 threads arrive together, counted with an AtomicUsize, and that every thread leaves with the winner's value
- assert set() called by the same 16 threads instead runs 16 times, returns exactly one Ok, and hands every loser its own value back rather than the winner's
- assert a LazyLock static has not run its initialiser before the first deref, and runs it exactly once across 8 threads doing 1000 lookups each
- assert LazyLock::force hands back the same allocation as deref, and that once_cell::sync::Lazy builds the same table with the same laziness
- assert std LazyLock implements DerefMut and force_mut on this rustc, so neither is a once_cell-only feature any more
- assert a const LazyLock compiles and re-runs its initialiser once per use site: three uses, three builds, no warning
- assert once_cell::sync::Lazy in a const does exactly the same, so the trap belongs to const and not to the crate
- assert the same three uses of a static LazyLock build once and hand out a single address
- assert std::cell::OnceCell and std::cell::LazyCell cover once_cell::unsync, with the same set/get contract and the same first-use laziness
- assert the measured sizes: the unsync cell saves nothing over OnceLock for a u32 and eight bytes for a String
- compile a probe file with rustc to prove OnceLock::get_or_try_init is E0658 behind the once_cell_try feature, tracking issue 109737
- compile a probe file with rustc to prove OnceLock::try_insert is E0658 behind the once_cell_try_insert feature
- compile probe files with rustc to prove OnceLock::wait and LazyLock::force_mut do compile on this rustc
- compile a probe file with rustc to prove std::cell::OnceCell is not Sync, with rustc naming std::sync::OnceLock as the replacement
- assert once_cell's get_or_try_init leaves the cell empty after a failed init so the next caller retries, and stops calling the closure once one succeeds
- assert the hand-rolled get-then-set stand-in runs its initialiser once per thread, 16 out of 16, while still handing every caller the same value
Files
- Cargo.lock
- Cargo.toml
- csx.json
- src/main.rs