[hal] Revamp notifiers (#8424)

This changes the HAL notifier interface to:
- Use wpiutil signal objects. This means waiting is done through the
`WPI_WaitObject` API instead of a dedicated function and allows for
higher level code to simultaneously wait on notifiers and other events.
- Interval timers are supported at the HAL layer
- Handlers are now required to acknowledge notifications. This is
invisible to users unless they're directly using the HAL API.
- For interval timers, an overrun count is maintained to detect if the
handler didn't acknowledge

The underlying implementation still uses condition variables for the
actual waiting. In basic testing using this approach seemed to be lower
jitter than timerfd.

Currently, the simulation and systemcore implementations are nearly
identical except for a few additional sim hook bits. This could be
refactored, but keeping them separate may make sense to keep the
systemcore implementation easy to read and reason about, or if we ever
choose to use a different underlying timer implementation on systemcore.

The simulation side API is unchanged in form but does change in
function--waiting for notifiers now only waits for currently running (or
newly signaled) notifiers to acknowledge. To avoid a race condition in
sim stepTiming, users of the low level API must make any alarm updates
(especially for one-shot alarms) prior to acknowledging the previous
alarm.

The only current use of the interval timer feature is the `Notifier`
class. The `TimedRobot` implementation still uses a single notifier and
its own interval timing logic to ensure consistent callback order. Using
separate notifiers for each user-level interval would substantially
increase complexity. `Watchdog` also doesn't use the interval timer, as
it's looking for an amount of time since the last `set` call rather than
a recurring interval time.

To reduce flicker, the sim GUI uses a fade out when a timeout goes from
set to unset.

This fixes tsan for wpilib and commands, and also fixes some spurious
test failures.

wpilibj/src/main/java/org/wpilib/system/Notifier.java

@@ -13,6 +13,7 @@ import org.wpilib.driverstation.DriverStation;
 import org.wpilib.hardware.hal.NotifierJNI;
 import org.wpilib.units.measure.Frequency;
 import org.wpilib.units.measure.Time;
+import org.wpilib.util.WPIUtilJNI;
 
 /**
  * Notifiers run a user-provided callback function on a separate thread.
@@ -33,24 +34,13 @@ public class Notifier implements AutoCloseable {
   // The user-provided callback.
   private Runnable m_callback;
 
-  // The time, in seconds, at which the callback should be called. Has the same
-  // zero as RobotController.getFPGATime().
-  private double m_expirationTime;
-
-  // If periodic, stores the callback period in seconds; if single, stores the time until
-  // the callback call in seconds.
-  private double m_period;
-
-  // True if the callback is periodic
-  private boolean m_periodic;
-
   @Override
   public void close() {
     int handle = m_notifier.getAndSet(0);
     if (handle == 0) {
       return;
     }
-    NotifierJNI.stopNotifier(handle);
+    NotifierJNI.destroyNotifier(handle);
     // Join the thread to ensure the callback has exited.
     if (m_thread.isAlive()) {
       try {
@@ -60,28 +50,9 @@ public class Notifier implements AutoCloseable {
         Thread.currentThread().interrupt();
       }
     }
-    NotifierJNI.cleanNotifier(handle);
     m_thread = null;
   }
 
-  /**
-   * Update the alarm hardware to reflect the next alarm.
-   *
-   * @param triggerTimeMicroS the time in microseconds at which the next alarm will be triggered
-   */
-  private void updateAlarm(long triggerTimeMicroS) {
-    int notifier = m_notifier.get();
-    if (notifier == 0) {
-      return;
-    }
-    NotifierJNI.updateNotifierAlarm(notifier, triggerTimeMicroS);
-  }
-
-  /** Update the alarm hardware to reflect the next alarm. */
-  private void updateAlarm() {
-    updateAlarm((long) (m_expirationTime * 1e6));
-  }
-
   /**
    * Create a Notifier with the given callback.
    *
@@ -93,7 +64,7 @@ public class Notifier implements AutoCloseable {
     requireNonNullParam(callback, "callback", "Notifier");
 
     m_callback = callback;
-    m_notifier.set(NotifierJNI.initializeNotifier());
+    m_notifier.set(NotifierJNI.createNotifier());
 
     m_thread =
         new Thread(
@@ -103,8 +74,10 @@ public class Notifier implements AutoCloseable {
                 if (notifier == 0) {
                   break;
                 }
-                long curTime = NotifierJNI.waitForNotifierAlarm(notifier);
-                if (curTime == 0) {
+                try {
+                  WPIUtilJNI.waitForObject(notifier);
+                } catch (InterruptedException ex) {
+                  Thread.currentThread().interrupt();
                   break;
                 }
 
@@ -112,13 +85,6 @@ public class Notifier implements AutoCloseable {
                 m_processLock.lock();
                 try {
                   threadHandler = m_callback;
-                  if (m_periodic) {
-                    m_expirationTime += m_period;
-                    updateAlarm();
-                  } else {
-                    // Need to update the alarm to cause it to wait again
-                    updateAlarm(-1);
-                  }
                 } finally {
                   m_processLock.unlock();
                 }
@@ -127,6 +93,9 @@ public class Notifier implements AutoCloseable {
                 if (threadHandler != null) {
                   threadHandler.run();
                 }
+
+                // Acknowledge the alarm
+                NotifierJNI.acknowledgeNotifierAlarm(notifier);
               }
             });
     m_thread.setName("Notifier");
@@ -179,15 +148,7 @@ public class Notifier implements AutoCloseable {
    * @param delay Time in seconds to wait before the callback is called.
    */
   public void startSingle(double delay) {
-    m_processLock.lock();
-    try {
-      m_periodic = false;
-      m_period = delay;
-      m_expirationTime = RobotController.getFPGATime() * 1e-6 + delay;
-      updateAlarm();
-    } finally {
-      m_processLock.unlock();
-    }
+    NotifierJNI.setNotifierAlarm(m_notifier.get(), (long) (delay * 1e6), 0, false);
   }
 
   /**
@@ -209,15 +170,8 @@ public class Notifier implements AutoCloseable {
    *     call to this method.
    */
   public void startPeriodic(double period) {
-    m_processLock.lock();
-    try {
-      m_periodic = true;
-      m_period = period;
-      m_expirationTime = RobotController.getFPGATime() * 1e-6 + period;
-      updateAlarm();
-    } finally {
-      m_processLock.unlock();
-    }
+    long periodMicroS = (long) (period * 1e6);
+    NotifierJNI.setNotifierAlarm(m_notifier.get(), periodMicroS, periodMicroS, false);
   }
 
   /**
@@ -256,13 +210,7 @@ public class Notifier implements AutoCloseable {
    * complete.
    */
   public void stop() {
-    m_processLock.lock();
-    try {
-      m_periodic = false;
-      NotifierJNI.cancelNotifierAlarm(m_notifier.get());
-    } finally {
-      m_processLock.unlock();
-    }
+    NotifierJNI.cancelNotifierAlarm(m_notifier.get());
   }
 
   /**