From a0f1b0ee01d461607660d2d56b5b1bdc57e0d3fb Mon Sep 17 00:00:00 2001
From: Dario Nieuwenhuis <dirbaio@dirbaio.net>
Date: Fri, 29 Jul 2022 21:58:35 +0200
Subject: Split embassy crate into embassy-executor, embassy-util.

---
 embassy-executor/src/time/driver_std.rs | 208 ++++++++++++++++++++++++++++++++
 1 file changed, 208 insertions(+)
 create mode 100644 embassy-executor/src/time/driver_std.rs

(limited to 'embassy-executor/src/time/driver_std.rs')

diff --git a/embassy-executor/src/time/driver_std.rs b/embassy-executor/src/time/driver_std.rs
new file mode 100644
index 000000000..cb66f7c19
--- /dev/null
+++ b/embassy-executor/src/time/driver_std.rs
@@ -0,0 +1,208 @@
+use std::cell::UnsafeCell;
+use std::mem::MaybeUninit;
+use std::sync::{Condvar, Mutex, Once};
+use std::time::{Duration as StdDuration, Instant as StdInstant};
+use std::{mem, ptr, thread};
+
+use atomic_polyfill::{AtomicU8, Ordering};
+
+use crate::time::driver::{AlarmHandle, Driver};
+
+const ALARM_COUNT: usize = 4;
+
+struct AlarmState {
+    timestamp: u64,
+
+    // This is really a Option<(fn(*mut ()), *mut ())>
+    // but fn pointers aren't allowed in const yet
+    callback: *const (),
+    ctx: *mut (),
+}
+
+unsafe impl Send for AlarmState {}
+
+impl AlarmState {
+    const fn new() -> Self {
+        Self {
+            timestamp: u64::MAX,
+            callback: ptr::null(),
+            ctx: ptr::null_mut(),
+        }
+    }
+}
+
+struct TimeDriver {
+    alarm_count: AtomicU8,
+
+    once: Once,
+    alarms: UninitCell<Mutex<[AlarmState; ALARM_COUNT]>>,
+    zero_instant: UninitCell<StdInstant>,
+    signaler: UninitCell<Signaler>,
+}
+
+const ALARM_NEW: AlarmState = AlarmState::new();
+crate::time_driver_impl!(static DRIVER: TimeDriver = TimeDriver {
+    alarm_count: AtomicU8::new(0),
+
+    once: Once::new(),
+    alarms: UninitCell::uninit(),
+    zero_instant: UninitCell::uninit(),
+    signaler: UninitCell::uninit(),
+});
+
+impl TimeDriver {
+    fn init(&self) {
+        self.once.call_once(|| unsafe {
+            self.alarms.write(Mutex::new([ALARM_NEW; ALARM_COUNT]));
+            self.zero_instant.write(StdInstant::now());
+            self.signaler.write(Signaler::new());
+
+            thread::spawn(Self::alarm_thread);
+        });
+    }
+
+    fn alarm_thread() {
+        let zero = unsafe { DRIVER.zero_instant.read() };
+        loop {
+            let now = DRIVER.now();
+
+            let mut next_alarm = u64::MAX;
+            {
+                let alarms = &mut *unsafe { DRIVER.alarms.as_ref() }.lock().unwrap();
+                for alarm in alarms {
+                    if alarm.timestamp <= now {
+                        alarm.timestamp = u64::MAX;
+
+                        // Call after clearing alarm, so the callback can set another alarm.
+
+                        // safety:
+                        // - we can ignore the possiblity of `f` being unset (null) because of the safety contract of `allocate_alarm`.
+                        // - other than that we only store valid function pointers into alarm.callback
+                        let f: fn(*mut ()) = unsafe { mem::transmute(alarm.callback) };
+                        f(alarm.ctx);
+                    } else {
+                        next_alarm = next_alarm.min(alarm.timestamp);
+                    }
+                }
+            }
+
+            // Ensure we don't overflow
+            let until = zero
+                .checked_add(StdDuration::from_micros(next_alarm))
+                .unwrap_or_else(|| StdInstant::now() + StdDuration::from_secs(1));
+
+            unsafe { DRIVER.signaler.as_ref() }.wait_until(until);
+        }
+    }
+}
+
+impl Driver for TimeDriver {
+    fn now(&self) -> u64 {
+        self.init();
+
+        let zero = unsafe { self.zero_instant.read() };
+        StdInstant::now().duration_since(zero).as_micros() as u64
+    }
+
+    unsafe fn allocate_alarm(&self) -> Option<AlarmHandle> {
+        let id = self.alarm_count.fetch_update(Ordering::AcqRel, Ordering::Acquire, |x| {
+            if x < ALARM_COUNT as u8 {
+                Some(x + 1)
+            } else {
+                None
+            }
+        });
+
+        match id {
+            Ok(id) => Some(AlarmHandle::new(id)),
+            Err(_) => None,
+        }
+    }
+
+    fn set_alarm_callback(&self, alarm: AlarmHandle, callback: fn(*mut ()), ctx: *mut ()) {
+        self.init();
+        let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
+        let alarm = &mut alarms[alarm.id() as usize];
+        alarm.callback = callback as *const ();
+        alarm.ctx = ctx;
+    }
+
+    fn set_alarm(&self, alarm: AlarmHandle, timestamp: u64) {
+        self.init();
+        let mut alarms = unsafe { self.alarms.as_ref() }.lock().unwrap();
+        let alarm = &mut alarms[alarm.id() as usize];
+        alarm.timestamp = timestamp;
+        unsafe { self.signaler.as_ref() }.signal();
+    }
+}
+
+struct Signaler {
+    mutex: Mutex<bool>,
+    condvar: Condvar,
+}
+
+impl Signaler {
+    fn new() -> Self {
+        Self {
+            mutex: Mutex::new(false),
+            condvar: Condvar::new(),
+        }
+    }
+
+    fn wait_until(&self, until: StdInstant) {
+        let mut signaled = self.mutex.lock().unwrap();
+        while !*signaled {
+            let now = StdInstant::now();
+
+            if now >= until {
+                break;
+            }
+
+            let dur = until - now;
+            let (signaled2, timeout) = self.condvar.wait_timeout(signaled, dur).unwrap();
+            signaled = signaled2;
+            if timeout.timed_out() {
+                break;
+            }
+        }
+        *signaled = false;
+    }
+
+    fn signal(&self) {
+        let mut signaled = self.mutex.lock().unwrap();
+        *signaled = true;
+        self.condvar.notify_one();
+    }
+}
+
+pub(crate) struct UninitCell<T>(MaybeUninit<UnsafeCell<T>>);
+unsafe impl<T> Send for UninitCell<T> {}
+unsafe impl<T> Sync for UninitCell<T> {}
+
+impl<T> UninitCell<T> {
+    pub const fn uninit() -> Self {
+        Self(MaybeUninit::uninit())
+    }
+
+    pub unsafe fn as_ptr(&self) -> *const T {
+        (*self.0.as_ptr()).get()
+    }
+
+    pub unsafe fn as_mut_ptr(&self) -> *mut T {
+        (*self.0.as_ptr()).get()
+    }
+
+    pub unsafe fn as_ref(&self) -> &T {
+        &*self.as_ptr()
+    }
+
+    pub unsafe fn write(&self, val: T) {
+        ptr::write(self.as_mut_ptr(), val)
+    }
+}
+
+impl<T: Copy> UninitCell<T> {
+    pub unsafe fn read(&self) -> T {
+        ptr::read(self.as_mut_ptr())
+    }
+}
-- 
cgit