Bugfix: wait for the reactor to confirm the modification

Author: ivmarkov

src/reactor.rs

@@ -4,6 +4,7 @@ use core::task::Waker;
 
 use std::io::{self, ErrorKind};
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
+use std::sync::MutexGuard;
 
 use enumset::{EnumSet, EnumSetType};
 
@@ -82,13 +83,15 @@ struct Registration {
 struct Registrations<const N: usize> {
     vec: heapless::Vec<Registration, N>,
     event_fd: Option<OwnedFd>,
+    waiting: usize,
 }
 
 impl<const N: usize> Registrations<N> {
     const fn new() -> Self {
         Self {
             vec: heapless::Vec::new(),
             event_fd: None,
+            waiting: 0,
         }
     }
 
@@ -129,8 +132,6 @@ impl<const N: usize> Registrations<N> {
 
         self.vec.swap_remove(index);
 
-        self.notify()?;
-
         Ok(())
     }
 
@@ -147,8 +148,6 @@ impl<const N: usize> Registrations<N> {
             }
         }
 
-        self.notify()?;
-
         Ok(())
     }
 
@@ -312,13 +311,15 @@ impl<const N: usize> Registrations<N> {
 
 pub struct Reactor<const N: usize> {
     registrations: std::sync::Mutex<Registrations<N>>,
+    condvar: std::sync::Condvar,
     started: AtomicBool,
 }
 
 impl<const N: usize> Reactor<N> {
     const fn new() -> Self {
         Self {
             registrations: std::sync::Mutex::new(Registrations::new()),
+            condvar: std::sync::Condvar::new(),
             started: AtomicBool::new(false),
         }
     }
@@ -340,23 +341,23 @@ impl<const N: usize> Reactor<N> {
     }
 
     pub(crate) fn register(&self, fd: RawFd) -> io::Result<()> {
-        self.lock(|regs| regs.register(fd))
+        self.lock_modify(|regs| regs.register(fd))
     }
 
     pub(crate) fn deregister(&self, fd: RawFd) -> io::Result<()> {
-        self.lock(|regs| regs.deregister(fd))
+        self.lock_modify(|regs| regs.deregister(fd))
     }
 
     // pub(crate) fn set(&self, fd: RawFd, event: Event, waker: &Waker) -> io::Result<()> {
     //     self.lock(|regs| regs.set(fd, event, waker))
     // }
 
     pub(crate) fn fetch(&self, fd: RawFd, event: Event) -> io::Result<bool> {
-        self.lock(|regs| regs.fetch(fd, event))
+        self.lock_modify(|regs| regs.fetch(fd, event))
     }
 
     pub(crate) fn fetch_or_set(&self, fd: RawFd, event: Event, waker: &Waker) -> io::Result<bool> {
-        self.lock(|regs| {
+        self.lock_modify(|regs| {
             if regs.fetch(fd, event)? {
                 Ok(true)
             } else {
@@ -368,58 +369,100 @@ impl<const N: usize> Reactor<N> {
     }
 
     fn run(&self) -> io::Result<()> {
-        if !self.lock(Registrations::create_notification)? {
+        if !self.lock(|mut guard| guard.create_notification())? {
             Err(ErrorKind::AlreadyExists)?;
         }
 
         debug!("Running");
 
+        let mut fds = Fds::new();
+        let mut update = false;
+
         let result = loop {
-            let result = self.wait();
+            let max = self.lock_apply(|inner| {
+                if !update {
+                    update = true;
+                } else {
+                    inner.update_events(&fds)?;
+                }
+
+                inner.set_fds(&mut fds)
+            });
+
+            let result = match max {
+                Err(err) => Err(err),
+                Ok(None) => unreachable!("EventFD is not there?"),
+                Ok(Some(max)) => {
+                    debug!("Start select");
+
+                    let result = syscall_los!(unsafe {
+                        sys::select(
+                            max + 1,
+                            fds.read.assume_init_mut(),
+                            fds.write.assume_init_mut(),
+                            fds.except.assume_init_mut(),
+                            core::ptr::null_mut(),
+                        )
+                    });
+
+                    debug!("End select");
+
+                    result.map(|_| ())
+                }
+            };
 
             if result.is_err() {
                 break result;
             }
         };
 
-        if !self.lock(Registrations::destroy_notification)? {
+        if !self.lock(|mut guard| guard.destroy_notification())? {
             Err(ErrorKind::NotFound)?;
         }
 
         result
     }
 
-    fn wait(&self) -> io::Result<()> {
-        let mut fds = Fds::new();
-
-        if let Some(max) = self.lock(|inner| inner.set_fds(&mut fds))? {
-            debug!("Start select");
+    fn lock_modify<F, R>(&self, f: F) -> io::Result<R>
+    where
+        F: FnOnce(&mut Registrations<N>) -> io::Result<R>,
+    {
+        self.lock(|mut guard| {
+            guard.waiting += 1;
 
-            syscall_los!(unsafe {
-                sys::select(
-                    max + 1,
-                    fds.read.assume_init_mut(),
-                    fds.write.assume_init_mut(),
-                    fds.except.assume_init_mut(),
-                    core::ptr::null_mut(),
-                )
-            })?;
+            let result = f(&mut guard);
 
-            debug!("End select");
+            guard.notify()?;
 
-            self.lock(|inner| inner.update_events(&fds))?;
-        }
+            let _guard = self
+                .condvar
+                .wait_while(guard, |registrations| registrations.waiting > 0)
+                .unwrap();
 
-        Ok(())
+            result
+        })
     }
 
-    fn lock<F, R>(&self, f: F) -> io::Result<R>
+    fn lock_apply<F, R>(&self, f: F) -> io::Result<R>
     where
         F: FnOnce(&mut Registrations<N>) -> io::Result<R>,
     {
-        let mut inner = self.registrations.lock().unwrap();
+        self.lock(|mut guard| {
+            let result = f(&mut guard);
+
+            guard.waiting = 0;
 
-        f(&mut inner)
+            self.condvar.notify_all();
+
+            result
+        })
+    }
+
+    fn lock<F, R>(&self, f: F) -> io::Result<R>
+    where
+        F: FnOnce(MutexGuard<Registrations<N>>) -> io::Result<R>,
+    {
+        f(self.registrations.lock().unwrap())
     }
 }