From 2f69f0e7f16e1ab1582fb427eaeb642a1958e69b Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jeremy@system76.com>
Date: Wed, 23 Dec 2020 12:18:17 -0700
Subject: [PATCH] Add simple semaphore implementation using futex
---
src/sync/mod.rs | 2 ++
src/sync/semaphore.rs | 46 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 48 insertions(+)
create mode 100644 src/sync/semaphore.rs
diff --git a/src/sync/mod.rs b/src/sync/mod.rs
index 758365c7..430abd5b 100644
--- a/src/sync/mod.rs
+++ b/src/sync/mod.rs
@@ -1,9 +1,11 @@
pub mod mutex;
pub mod once;
+pub mod semaphore;
pub use self::{
mutex::{Mutex, MutexGuard},
once::Once,
+ semaphore::Semaphore,
};
use crate::platform::{types::*, Pal, Sys};
diff --git a/src/sync/semaphore.rs b/src/sync/semaphore.rs
new file mode 100644
index 00000000..7734c58a
--- /dev/null
+++ b/src/sync/semaphore.rs
@@ -0,0 +1,46 @@
+// From https://www.remlab.net/op/futex-misc.shtml
+//TODO: improve implementation
+
+use crate::platform::{types::*, Pal, Sys};
+use super::AtomicLock;
+use core::sync::atomic::Ordering;
+
+pub struct Semaphore {
+ lock: AtomicLock,
+}
+
+impl Semaphore {
+ pub const fn new(value: c_int) -> Self {
+ Self {
+ lock: AtomicLock::new(value),
+ }
+ }
+
+ pub fn post(&self) {
+ self.lock.fetch_add(1, Ordering::Relaxed);
+ self.lock.notify_one();
+ }
+
+ pub fn wait(&self) {
+ let mut value = 1;
+
+ loop {
+ match self.lock.compare_exchange_weak(
+ value,
+ value - 1,
+ Ordering::Acquire,
+ Ordering::Relaxed
+ ) {
+ Ok(ok) => return,
+ Err(err) => {
+ value = err;
+ }
+ }
+
+ if value == 0 {
+ self.lock.wait_if(0);
+ value = 1;
+ }
+ }
+ }
+}
--
GitLab