82 lines
2.6 KiB
Markdown
82 lines
2.6 KiB
Markdown
# Platform Abstraction Layer — Development History
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> Stage 1 of the in-browser swactor runtime. Makes core swactor compile for
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> `wasm32-unknown-unknown` without behavioral changes on native targets.
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---
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## Changes
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### 1. `web-time` dependency + `wasm` feature flag
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**File**: `Cargo.toml`
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Added `web-time` as an optional dependency and a `wasm` feature that bundles
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`no_random` + `web-time`:
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```toml
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wasm = ["no_random", "dep:web-time"]
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web-time = { version = "0.2", optional = true }
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```
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`web-time` is a drop-in replacement for `std::time::Instant`:
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- Native: re-exports `std::time::Instant` (zero-cost)
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- wasm32: uses `performance.now()` via `js-sys`
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### 2. Platform-aware `Instant` re-export
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**File**: `src/lib.rs`
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```rust
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#[cfg(feature = "wasm")]
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pub(crate) use web_time::Instant;
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#[cfg(not(feature = "wasm"))]
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pub(crate) use std::time::Instant;
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```
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All modules (`runtime.rs`, `worker.rs`) now use `crate::Instant` instead of
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`std::time::Instant`. Single point of truth — no cfg noise in consumer code.
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### 3. cfg-gated `Runtime::run()` and `RuntimeHandle`
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**File**: `src/runtime.rs`
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`Runtime::run()` calls `std::thread::spawn()` which is not available on wasm32.
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Both `run()` and `RuntimeHandle` (which holds `JoinHandle<()>`) are gated:
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```rust
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#[cfg(not(target_arch = "wasm32"))]
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pub fn run(self) -> Result<RuntimeHandle, Error> { ... }
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```
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On wasm32, the browser crate will provide its own `run()` via Web Workers.
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`tick()` remains available on all platforms for single-threaded driving.
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### 4. Updated `crates/wasm/` to use `wasm` feature
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**File**: `crates/wasm/Cargo.toml`
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Changed from `features = ["no_random"]` to `features = ["wasm"]` to pick up
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the `web-time` Instant on wasm32.
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## What Did NOT Need Abstraction
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Key discovery: on wasm32 with the `+atomics` target feature, most of
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`std::sync` and `std::thread` works:
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- `OnceLock<Thread>` — compiles and works (futex-based)
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- `Thread::unpark()` — works (futex → `memory.atomic.notify`)
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- `thread::park_timeout()` — works (futex → `memory.atomic.wait32`)
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- `thread::yield_now()` — works (no-op on wasm)
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- `Mutex`, `RwLock` — work (futex-based)
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- `crossbeam-queue` — works (uses `core::sync::atomic`)
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- `AtomicBool/Usize/U64` — work (wasm atomic instructions)
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Only `std::thread::spawn()` and `JoinHandle` are not functional on wasm32.
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## Verification
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- `cargo test` — all native tests pass (no regressions)
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- `cargo test --features wasm` — all native tests pass with wasm feature
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- `cargo build --target wasm32-unknown-unknown --features wasm --no-default-features` — compiles
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- `cargo build --target wasm32-unknown-unknown -p wasm` — existing PoC crate compiles
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