Merge pull request #37 from andylokandy/fixxx3

feat: add std fallback

.github/workflows/ci.yml

@@ -15,6 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-latest, ubuntu-latest, windows-latest]
+        features: ["atomic", "atomic,fallback-coarse"]
         rust: [stable]
     env:
       RUST_BACKTRACE: 1
@@ -29,13 +30,13 @@ jobs:
     - name: Check format
       run: cargo fmt --all -- --check
     - name: Build
-      run: cargo build --workspace --all-targets --all-features
+      run: cargo build --workspace --all-targets --features ${{ matrix.features }}
     - name: Clippy
-      run: cargo clippy --workspace --all-targets --all-features -- -D warnings
+      run: cargo clippy --workspace --all-targets --features ${{ matrix.features }} -- -D warnings
     - name: Run tests
-      run: cargo test --workspace --all-targets --all-features -- --nocapture
+      run: cargo test --workspace --all-targets --features ${{ matrix.features }} -- --nocapture
     - name: Run benches
-      run: cargo bench --workspace --all-targets --all-features
+      run: cargo bench --workspace --all-targets --features ${{ matrix.features }}
 
   build-wasm:
     runs-on: ubuntu-latest

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "minstant"
-version = "0.1.6"
+version = "0.1.7"
 authors = ["The TiKV Authors"]
 edition = "2021"
 license = "MIT"
@@ -16,11 +16,12 @@ rustdoc-args = ["--cfg", "docsrs"]
 
 [dependencies]
 ctor = "0.1.20"
-coarsetime = "0.1"
+coarsetime = { version = "0.1", optional = true }
 web-time = "1.0"
 
 [features]
 atomic = []
+fallback-coarse = ["coarsetime"]
 
 [dev-dependencies]
 criterion = "0.3"

README.md

@@ -29,7 +29,14 @@ This library is used by a high performance tracing library [`minitrace-rust`](ht
 
 ## Platform Support
 
-Currently, only the Linux on `x86` or `x86_64` is backed by [TSC](https://en.wikipedia.org/wiki/Time_Stamp_Counter). On other platforms, `minstant` falls back to coarse time. If TSC is unstable, it will also fall back to coarse time.
+Currently, only the Linux on `x86` or `x86_64` is backed by [TSC](https://en.wikipedia.org/wiki/Time_Stamp_Counter). On other platforms, `minstant` falls back to `std::time`. If TSC is unstable, it will also fall back to `std::time`.
+
+If speed is privileged over accuracy when fallback occurs, you can use `fallback-corase` feature to use corase time:
+
+```toml
+[dependencies]
+minstant = { version = "0.1", features = ["fallback-coarse"] }
+```
 
 ## Benchmark
 

src/instant.rs

@@ -14,6 +14,9 @@ use web_time::{SystemTime, UNIX_EPOCH};
 pub struct Instant(u64);
 
 impl Instant {
+    /// A default `Instant` that can be seen as a fixed but random moment.
+    pub const ZERO: Instant = Instant(0);
+
     #[inline]
     /// Returns an instant corresponding to "now".
     ///

src/lib.rs

@@ -60,25 +60,34 @@ pub fn is_tsc_available() -> bool {
 
 #[inline]
 pub(crate) fn current_cycle() -> u64 {
-    let coarse_cycle = || {
-        let coarse = coarsetime::Instant::now_without_cache_update();
-        coarsetime::Duration::from_ticks(coarse.as_ticks()).as_nanos()
-    };
-
     #[cfg(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64")))]
     {
         if tsc_now::is_tsc_available() {
             tsc_now::current_cycle()
         } else {
-            coarse_cycle()
+            current_cycle_fallback()
         }
     }
     #[cfg(not(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64"))))]
     {
-        coarse_cycle()
+        current_cycle_fallback()
     }
 }
 
+#[cfg(not(feature = "fallback-coarse"))]
+pub(crate) fn current_cycle_fallback() -> u64 {
+    web_time::SystemTime::now()
+        .duration_since(web_time::UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0)
+}
+
+#[cfg(feature = "fallback-coarse")]
+pub(crate) fn current_cycle_fallback() -> u64 {
+    let coarse = coarsetime::Instant::now_without_cache_update();
+    coarsetime::Duration::from_ticks(coarse.as_ticks()).as_nanos()
+}
+
 #[inline]
 pub(crate) fn nanos_per_cycle() -> f64 {
     #[cfg(all(target_os = "linux", any(target_arch = "x86", target_arch = "x86_64")))]