1 files changed, 90 insertions, 0 deletions
diff --git a/library/std/src/sys/hermit/condvar.rs b/library/std/src/sys/hermit/condvar.rs
new file mode 100644
index 000000000..22059ca0d
--- /dev/null
+++ b/library/std/src/sys/hermit/condvar.rs
@@ -0,0 +1,90 @@
+use crate::ffi::c_void;
+use crate::ptr;
+use crate::sync::atomic::{AtomicUsize, Ordering::SeqCst};
+use crate::sys::hermit::abi;
+use crate::sys::locks::Mutex;
+use crate::sys_common::lazy_box::{LazyBox, LazyInit};
+use crate::time::Duration;
+
+// The implementation is inspired by Andrew D. Birrell's paper
+// "Implementing Condition Variables with Semaphores"
+
+pub struct Condvar {
+    counter: AtomicUsize,
+    sem1: *const c_void,
+    sem2: *const c_void,
+}
+
+pub(crate) type MovableCondvar = LazyBox<Condvar>;
+
+impl LazyInit for Condvar {
+    fn init() -> Box<Self> {
+        Box::new(Self::new())
+    }
+}
+
+unsafe impl Send for Condvar {}
+unsafe impl Sync for Condvar {}
+
+impl Condvar {
+    pub fn new() -> Self {
+        let mut condvar =
+            Self { counter: AtomicUsize::new(0), sem1: ptr::null(), sem2: ptr::null() };
+        unsafe {
+            let _ = abi::sem_init(&mut condvar.sem1, 0);
+            let _ = abi::sem_init(&mut condvar.sem2, 0);
+        }
+        condvar
+    }
+
+    pub unsafe fn notify_one(&self) {
+        if self.counter.load(SeqCst) > 0 {
+            self.counter.fetch_sub(1, SeqCst);
+            abi::sem_post(self.sem1);
+            abi::sem_timedwait(self.sem2, 0);
+        }
+    }
+
+    pub unsafe fn notify_all(&self) {
+        let counter = self.counter.swap(0, SeqCst);
+        for _ in 0..counter {
+            abi::sem_post(self.sem1);
+        }
+        for _ in 0..counter {
+            abi::sem_timedwait(self.sem2, 0);
+        }
+    }
+
+    pub unsafe fn wait(&self, mutex: &Mutex) {
+        self.counter.fetch_add(1, SeqCst);
+        mutex.unlock();
+        abi::sem_timedwait(self.sem1, 0);
+        abi::sem_post(self.sem2);
+        mutex.lock();
+    }
+
+    pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
+        self.counter.fetch_add(1, SeqCst);
+        mutex.unlock();
+        let millis = dur.as_millis().min(u32::MAX as u128) as u32;
+
+        let res = if millis > 0 {
+            abi::sem_timedwait(self.sem1, millis)
+        } else {
+            abi::sem_trywait(self.sem1)
+        };
+
+        abi::sem_post(self.sem2);
+        mutex.lock();
+        res == 0
+    }
+}
+
+impl Drop for Condvar {
+    fn drop(&mut self) {
+        unsafe {
+            let _ = abi::sem_destroy(self.sem1);
+            let _ = abi::sem_destroy(self.sem2);
+        }
+    }
+}