diff options
| -rw-r--r-- | library/std/src/os/xous/services/ticktimer.rs | 4 | ||||
| -rw-r--r-- | library/std/src/sys/xous/locks/condvar.rs | 111 | ||||
| -rw-r--r-- | library/std/src/sys/xous/locks/mod.rs | 7 | ||||
| -rw-r--r-- | library/std/src/sys/xous/locks/mutex.rs | 116 | ||||
| -rw-r--r-- | library/std/src/sys/xous/locks/rwlock.rs | 72 | ||||
| -rw-r--r-- | library/std/src/sys/xous/mod.rs | 1 |
6 files changed, 310 insertions, 1 deletions
diff --git a/library/std/src/os/xous/services/ticktimer.rs b/library/std/src/os/xous/services/ticktimer.rs index 447f8f9304a..7759303fdbe 100644 --- a/library/std/src/os/xous/services/ticktimer.rs +++ b/library/std/src/os/xous/services/ticktimer.rs @@ -8,6 +8,8 @@ pub(crate) enum TicktimerScalar { UnlockMutex(usize /* cookie */), WaitForCondition(usize /* cookie */, usize /* timeout (ms) */), NotifyCondition(usize /* cookie */, usize /* count */), + FreeMutex(usize /* cookie */), + FreeCondition(usize /* cookie */), } impl Into<[usize; 5]> for TicktimerScalar { @@ -19,6 +21,8 @@ impl Into<[usize; 5]> for TicktimerScalar { TicktimerScalar::UnlockMutex(cookie) => [7, cookie, 0, 0, 0], TicktimerScalar::WaitForCondition(cookie, timeout_ms) => [8, cookie, timeout_ms, 0, 0], TicktimerScalar::NotifyCondition(cookie, count) => [9, cookie, count, 0, 0], + TicktimerScalar::FreeMutex(cookie) => [10, cookie, 0, 0, 0], + TicktimerScalar::FreeCondition(cookie) => [11, cookie, 0, 0, 0], } } } diff --git a/library/std/src/sys/xous/locks/condvar.rs b/library/std/src/sys/xous/locks/condvar.rs new file mode 100644 index 00000000000..1bb38dfa341 --- /dev/null +++ b/library/std/src/sys/xous/locks/condvar.rs @@ -0,0 +1,111 @@ +use super::mutex::Mutex; +use crate::os::xous::ffi::{blocking_scalar, scalar}; +use crate::os::xous::services::ticktimer_server; +use crate::sync::Mutex as StdMutex; +use crate::time::Duration; + +// The implementation is inspired by Andrew D. Birrell's paper +// "Implementing Condition Variables with Semaphores" + +pub struct Condvar { + counter: StdMutex<usize>, +} + +unsafe impl Send for Condvar {} +unsafe impl Sync for Condvar {} + +impl Condvar { + #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] + pub const fn new() -> Condvar { + Condvar { counter: StdMutex::new(0) } + } + + pub fn notify_one(&self) { + let mut counter = self.counter.lock().unwrap(); + if *counter <= 0 { + return; + } else { + *counter -= 1; + } + let result = blocking_scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::NotifyCondition(self.index(), 1).into(), + ); + drop(counter); + result.expect("failure to send NotifyCondition command"); + } + + pub fn notify_all(&self) { + let mut counter = self.counter.lock().unwrap(); + if *counter <= 0 { + return; + } + let result = blocking_scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::NotifyCondition(self.index(), *counter) + .into(), + ); + *counter = 0; + drop(counter); + + result.expect("failure to send NotifyCondition command"); + } + + fn index(&self) -> usize { + self as *const Condvar as usize + } + + pub unsafe fn wait(&self, mutex: &Mutex) { + let mut counter = self.counter.lock().unwrap(); + *counter += 1; + unsafe { mutex.unlock() }; + drop(counter); + + let result = blocking_scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::WaitForCondition(self.index(), 0).into(), + ); + unsafe { mutex.lock() }; + + result.expect("Ticktimer: failure to send WaitForCondition command"); + } + + pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool { + let mut counter = self.counter.lock().unwrap(); + *counter += 1; + unsafe { mutex.unlock() }; + drop(counter); + + let mut millis = dur.as_millis() as usize; + if millis == 0 { + millis = 1; + } + + let result = blocking_scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::WaitForCondition(self.index(), millis) + .into(), + ); + unsafe { mutex.lock() }; + + let result = result.expect("Ticktimer: failure to send WaitForCondition command")[0] == 0; + + // If we awoke due to a timeout, decrement the wake count, as that would not have + // been done in the `notify()` call. + if !result { + *self.counter.lock().unwrap() -= 1; + } + result + } +} + +impl Drop for Condvar { + fn drop(&mut self) { + scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::FreeCondition(self.index()).into(), + ) + .ok(); + } +} diff --git a/library/std/src/sys/xous/locks/mod.rs b/library/std/src/sys/xous/locks/mod.rs new file mode 100644 index 00000000000..f3c5c5d9fb0 --- /dev/null +++ b/library/std/src/sys/xous/locks/mod.rs @@ -0,0 +1,7 @@ +mod condvar; +mod mutex; +mod rwlock; + +pub use condvar::*; +pub use mutex::*; +pub use rwlock::*; diff --git a/library/std/src/sys/xous/locks/mutex.rs b/library/std/src/sys/xous/locks/mutex.rs new file mode 100644 index 00000000000..ea51776d54e --- /dev/null +++ b/library/std/src/sys/xous/locks/mutex.rs @@ -0,0 +1,116 @@ +use crate::os::xous::ffi::{blocking_scalar, do_yield, scalar}; +use crate::os::xous::services::ticktimer_server; +use crate::sync::atomic::{AtomicBool, AtomicUsize, Ordering::Relaxed, Ordering::SeqCst}; + +pub struct Mutex { + /// The "locked" value indicates how many threads are waiting on this + /// Mutex. Possible values are: + /// 0: The lock is unlocked + /// 1: The lock is locked and uncontended + /// >=2: The lock is locked and contended + /// + /// A lock is "contended" when there is more than one thread waiting + /// for a lock, or it is locked for long periods of time. Rather than + /// spinning, these locks send a Message to the ticktimer server + /// requesting that they be woken up when a lock is unlocked. + locked: AtomicUsize, + + /// Whether this Mutex ever was contended, and therefore made a trip + /// to the ticktimer server. If this was never set, then we were never + /// on the slow path and can skip deregistering the mutex. + contended: AtomicBool, +} + +impl Mutex { + #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] + pub const fn new() -> Mutex { + Mutex { locked: AtomicUsize::new(0), contended: AtomicBool::new(false) } + } + + fn index(&self) -> usize { + self as *const Mutex as usize + } + + #[inline] + pub unsafe fn lock(&self) { + // Try multiple times to acquire the lock without resorting to the ticktimer + // server. For locks that are held for a short amount of time, this will + // result in the ticktimer server never getting invoked. The `locked` value + // will be either 0 or 1. + for _attempts in 0..3 { + if unsafe { self.try_lock() } { + return; + } + do_yield(); + } + + // Try one more time to lock. If the lock is released between the previous code and + // here, then the inner `locked` value will be 1 at the end of this. If it was not + // locked, then the value will be more than 1, for example if there are multiple other + // threads waiting on this lock. + if unsafe { self.try_lock_or_poison() } { + return; + } + + // When this mutex is dropped, we will need to deregister it with the server. + self.contended.store(true, Relaxed); + + // The lock is now "contended". When the lock is released, a Message will get sent to the + // ticktimer server to wake it up. Note that this may already have happened, so the actual + // value of `lock` may be anything (0, 1, 2, ...). + blocking_scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::LockMutex(self.index()).into(), + ) + .expect("failure to send LockMutex command"); + } + + #[inline] + pub unsafe fn unlock(&self) { + let prev = self.locked.fetch_sub(1, SeqCst); + + // If the previous value was 1, then this was a "fast path" unlock, so no + // need to involve the Ticktimer server + if prev == 1 { + return; + } + + // If it was 0, then something has gone seriously wrong and the counter + // has just wrapped around. + if prev == 0 { + panic!("mutex lock count underflowed"); + } + + // Unblock one thread that is waiting on this message. + scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::UnlockMutex(self.index()).into(), + ) + .expect("failure to send UnlockMutex command"); + } + + #[inline] + pub unsafe fn try_lock(&self) -> bool { + self.locked.compare_exchange(0, 1, SeqCst, SeqCst).is_ok() + } + + #[inline] + pub unsafe fn try_lock_or_poison(&self) -> bool { + self.locked.fetch_add(1, SeqCst) == 0 + } +} + +impl Drop for Mutex { + fn drop(&mut self) { + // If there was Mutex contention, then we involved the ticktimer. Free + // the resources associated with this Mutex as it is deallocated. + if self.contended.load(Relaxed) { + scalar( + ticktimer_server(), + crate::os::xous::services::TicktimerScalar::FreeMutex(self.index()).into(), + ) + .ok(); + } + } +} diff --git a/library/std/src/sys/xous/locks/rwlock.rs b/library/std/src/sys/xous/locks/rwlock.rs new file mode 100644 index 00000000000..618da758adf --- /dev/null +++ b/library/std/src/sys/xous/locks/rwlock.rs @@ -0,0 +1,72 @@ +use crate::os::xous::ffi::do_yield; +use crate::sync::atomic::{AtomicIsize, Ordering::SeqCst}; + +pub struct RwLock { + /// The "mode" value indicates how many threads are waiting on this + /// Mutex. Possible values are: + /// -1: The lock is locked for writing + /// 0: The lock is unlocked + /// >=1: The lock is locked for reading + /// + /// This currently spins waiting for the lock to be freed. An + /// optimization would be to involve the ticktimer server to + /// coordinate unlocks. + mode: AtomicIsize, +} + +unsafe impl Send for RwLock {} +unsafe impl Sync for RwLock {} + +impl RwLock { + #[inline] + #[rustc_const_stable(feature = "const_locks", since = "1.63.0")] + pub const fn new() -> RwLock { + RwLock { mode: AtomicIsize::new(0) } + } + + #[inline] + pub unsafe fn read(&self) { + while !unsafe { self.try_read() } { + do_yield(); + } + } + + #[inline] + pub unsafe fn try_read(&self) -> bool { + // Non-atomically determine the current value. + let current = self.mode.load(SeqCst); + + // If it's currently locked for writing, then we cannot read. + if current < 0 { + return false; + } + + // Attempt to lock. If the `current` value has changed, then this + // operation will fail and we will not obtain the lock even if we + // could potentially keep it. + let new = current + 1; + self.mode.compare_exchange(current, new, SeqCst, SeqCst).is_ok() + } + + #[inline] + pub unsafe fn write(&self) { + while !unsafe { self.try_write() } { + do_yield(); + } + } + + #[inline] + pub unsafe fn try_write(&self) -> bool { + self.mode.compare_exchange(0, -1, SeqCst, SeqCst).is_ok() + } + + #[inline] + pub unsafe fn read_unlock(&self) { + self.mode.fetch_sub(1, SeqCst); + } + + #[inline] + pub unsafe fn write_unlock(&self) { + assert_eq!(self.mode.compare_exchange(-1, 0, SeqCst, SeqCst), Ok(-1)); + } +} diff --git a/library/std/src/sys/xous/mod.rs b/library/std/src/sys/xous/mod.rs index 79d9c00f64a..6d5c218d195 100644 --- a/library/std/src/sys/xous/mod.rs +++ b/library/std/src/sys/xous/mod.rs @@ -11,7 +11,6 @@ pub mod env; pub mod fs; #[path = "../unsupported/io.rs"] pub mod io; -#[path = "../unsupported/locks/mod.rs"] pub mod locks; #[path = "../unsupported/net.rs"] pub mod net; |