From cdb6502632e2c667e3ce29078dae3f714dd8ab3c Mon Sep 17 00:00:00 2001
From: Christopher Serr <christopher.serr@gmail.com>
Date: Mon, 4 Nov 2024 12:27:35 +0100
Subject: [PATCH] Use `CLOCK_BOOTTIME` on Fuchsia (#848)

Fuchsia added kernel support for a monotonic clock that keeps running
while the system is suspended. They technically have not yet exposed it
through their libc, but one maintainer said that they will do so soon.
---
 Cargo.toml                 |  4 ++--
 src/platform/normal/mod.rs | 27 ++++++++++++---------------
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 9d36b71e..d9a07b2e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -84,7 +84,7 @@ tiny-skia = { version = "0.11.1", default-features = false, features = [
 tiny-skia-path = { version = "0.11.1", default-features = false, optional = true }
 
 # SVG Rendering
-foldhash = { version = "0.1.3", optional = true }
+foldhash = { version = "0.1.3", default-features = false, optional = true }
 
 # Networking
 splits-io-api = { version = "0.4.0", optional = true }
@@ -117,7 +117,7 @@ windows-sys = { version = "0.59.0", features = [
     "Win32_Graphics_Gdi",
 ], optional = true }
 
-[target.'cfg(any(target_os = "linux", target_os = "l4re", target_os = "android", target_os = "macos", target_os = "ios"))'.dependencies]
+[target.'cfg(any(target_os = "linux", target_os = "l4re", target_os = "android", target_os = "fuchsia", target_os = "macos", target_os = "ios"))'.dependencies]
 # We need libc for our own implementation of Instant
 libc = { version = "0.2.101", optional = true }
 
diff --git a/src/platform/normal/mod.rs b/src/platform/normal/mod.rs
index fe6f2f48..13b2b265 100644
--- a/src/platform/normal/mod.rs
+++ b/src/platform/normal/mod.rs
@@ -19,8 +19,8 @@ cfg_if::cfg_if! {
     // correctly implemented in Linux and due to backwards compatibility
     // concerns they were never able to fix it properly. Thus `CLOCK_MONOTONIC`
     // means uptime on Linux whereas on other Unixes it means real time (the BSD
-    // family). So the solution is to use this on all operating systems that are
-    // based on the Linux kernel.
+    // family). As a solution the Linux kernel provides `CLOCK_BOOTTIME` to
+    // measure the real time.
     //
     // # macOS and iOS
     //
@@ -36,26 +36,19 @@ cfg_if::cfg_if! {
     //
     // # Fuchsia
     //
-    // Fuchsia is based on the new Zircon kernel. It has two functions for
-    // querying the time:
+    // Fuchsia is based on the new Zircon kernel. It has `zx_clock_get_boot` to
+    // query the real time  and `zx_clock_get_monotonic` to query the uptime.
     //
-    // zx_clock_get:
-    // https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_get
-    // zx_clock_get_monotonic:
-    // https://fuchsia.dev/fuchsia-src/reference/syscalls/clock_get_monotonic
+    // https://fuchsia.dev/reference/syscalls/clock_get_boot
     //
-    // `zx_clock_get_monotonic` specifically calls out that it `does not adjust
-    // during sleep` which seems to mean that it doesn't count the time the OS
-    // is suspended. This is further evidenced by their libc implementation not
-    // treating `CLOCK_BOOTTIME` differently and a bug ticket being linked
-    // there:
-    // https://cs.opensource.google/fuchsia/fuchsia/+/main:zircon/third_party/ulib/musl/src/time/clock_gettime.c;l=40;drc=35e7a15cb21e16f0705560e5812b7a045d42c8a5
+    // They are supposed to be available through `CLOCK_BOOTTIME` and
+    // `CLOCK_MONOTONIC` respectively, just like on Linux.
     //
     // # WASI
     //
     // https://github.com/WebAssembly/WASI/blob/5ab83a68d4eb4f218a898ed03b963b7393caaedc/phases/snapshot/docs.md#variant-cases
     //
-    // WASI seems to underspecify its `monotonic` a bit, but says that it `is
+    // WASI seems to under specify its `monotonic` a bit, but says that it `is
     // defined as a clock measuring real time`, making it sound like a compliant
     // implementation should measure the time the OS is suspended as well.
     //
@@ -98,10 +91,14 @@ cfg_if::cfg_if! {
     // the Linux kernel and instead has its own implementation in JavaScript
     // where it actually errors out on `CLOCK_BOOTTIME`:
     // https://github.com/emscripten-core/emscripten/blob/9bdb310b89472a0f4d64f36e4a79273d8dc7fa98/system/lib/libc/emscripten_time.c#L50-L57
+    //
+    // And we add Fuchsia to this list as it's based on the Zircon kernel which
+    // uses `CLOCK_BOOTTIME` in the same way as Linux.
     if #[cfg(any(
         target_os = "linux",
         target_os = "l4re",
         target_os = "android",
+        target_os = "fuchsia",
     ))] {
         use core::{mem::MaybeUninit, ops::Sub};