[hal] Add function for changing HAL Notifier thread priority (#3218)

hal/src/main/java/edu/wpi/first/hal/NotifierJNI.java

@@ -14,6 +14,9 @@ public class NotifierJNI extends JNIWrapper {
   /** Initializes the notifier. */
   public static native int initializeNotifier();
 
+  /** Sets the HAL notifier thread priority. */
+  public static native boolean setHALThreadPriority(boolean realTime, int priority);
+
   /** Sets the name of the notifier. */
   public static native void setNotifierName(int notifierHandle, String name);
 

hal/src/main/native/athena/Notifier.cpp

@@ -17,6 +17,7 @@
 #include "hal/ChipObject.h"
 #include "hal/Errors.h"
 #include "hal/HAL.h"
+#include "hal/Threads.h"
 #include "hal/handles/UnlimitedHandleResource.h"
 
 using namespace hal;
@@ -156,6 +157,12 @@ HAL_NotifierHandle HAL_InitializeNotifier(int32_t* status) {
   return handle;
 }
 
+HAL_Bool HAL_SetNotifierThreadPriority(HAL_Bool realTime, int32_t priority,
+                                       int32_t* status) {
+  auto native = notifierThread.native_handle();
+  return HAL_SetThreadPriority(&native, realTime, priority, status);
+}
+
 void HAL_SetNotifierName(HAL_NotifierHandle notifierHandle, const char* name,
                          int32_t* status) {}
 

hal/src/main/native/cpp/jni/NotifierJNI.cpp

@@ -36,6 +36,19 @@ Java_edu_wpi_first_hal_NotifierJNI_initializeNotifier
   return (jint)notifierHandle;
 }
 
+/*
+ * Class:     edu_wpi_first_hal_NotifierJNI
+ * Method:    setHALThreadPriority
+ * Signature: (ZI)Z
+ */
+JNIEXPORT jboolean JNICALL
+Java_edu_wpi_first_hal_NotifierJNI_setHALThreadPriority
+  (JNIEnv* env, jclass, jboolean realTime, jint priority)
+{
+  int32_t status = 0;
+  return HAL_SetNotifierThreadPriority(realTime, priority, &status);
+}
+
 /*
  * Class:     edu_wpi_first_hal_NotifierJNI
  * Method:    setNotifierName

hal/src/main/native/include/hal/Notifier.h

@@ -30,6 +30,25 @@ extern "C" {
  */
 HAL_NotifierHandle HAL_InitializeNotifier(int32_t* status);
 
+/**
+ * Sets the HAL notifier thread priority.
+ *
+ * The HAL notifier thread is responsible for managing the FPGA's notifier
+ * interrupt and waking up user's Notifiers when it's their time to run.
+ * Giving the HAL notifier thread real-time priority helps ensure the user's
+ * real-time Notifiers, if any, are notified to run in a timely manner.
+ *
+ * @param realTime Set to true to set a real-time priority, false for standard
+ *                 priority.
+ * @param priority Priority to set the thread to. For real-time, this is 1-99
+ *                 with 99 being highest. For non-real-time, this is forced to
+ *                 0. See "man 7 sched" for more details.
+ * @param status   Error status variable. 0 on success.
+ * @return         True on success.
+ */
+HAL_Bool HAL_SetNotifierThreadPriority(HAL_Bool realTime, int32_t priority,
+                                       int32_t* status);
+
 /**
  * Sets the name of a notifier.
  *

hal/src/main/native/sim/Notifier.cpp

@@ -174,6 +174,11 @@ HAL_NotifierHandle HAL_InitializeNotifier(int32_t* status) {
   return handle;
 }
 
+HAL_Bool HAL_SetNotifierThreadPriority(HAL_Bool realTime, int32_t priority,
+                                       int32_t* status) {
+  return true;
+}
+
 void HAL_SetNotifierName(HAL_NotifierHandle notifierHandle, const char* name,
                          int32_t* status) {
   auto notifier = notifierHandles->Get(notifierHandle);

wpilibc/src/main/native/cpp/Notifier.cpp

@@ -200,3 +200,8 @@ void Notifier::UpdateAlarm(uint64_t triggerTime) {
 void Notifier::UpdateAlarm() {
   UpdateAlarm(static_cast<uint64_t>(m_expirationTime * 1e6));
 }
+
+bool Notifier::SetHALThreadPriority(bool realTime, int32_t priority) {
+  int32_t status = 0;
+  return HAL_SetNotifierThreadPriority(realTime, priority, &status);
+}

wpilibc/src/main/native/include/frc/Notifier.h

@@ -143,6 +143,23 @@ class Notifier : public ErrorBase {
    */
   void Stop();
 
+  /**
+   * Sets the HAL notifier thread priority.
+   *
+   * The HAL notifier thread is responsible for managing the FPGA's notifier
+   * interrupt and waking up user's Notifiers when it's their time to run.
+   * Giving the HAL notifier thread real-time priority helps ensure the user's
+   * real-time Notifiers, if any, are notified to run in a timely manner.
+   *
+   * @param realTime Set to true to set a real-time priority, false for standard
+   *                 priority.
+   * @param priority Priority to set the thread to. For real-time, this is 1-99
+   *                 with 99 being highest. For non-real-time, this is forced to
+   *                 0. See "man 7 sched" for more details.
+   * @return         True on success.
+   */
+  static bool SetHALThreadPriority(bool realTime, int32_t priority);
+
  private:
   /**
    * Update the HAL alarm time.

wpilibj/src/main/java/edu/wpi/first/wpilibj/Notifier.java

@@ -213,4 +213,21 @@ public class Notifier implements AutoCloseable {
       m_processLock.unlock();
     }
   }
+
+  /**
+   * Sets the HAL notifier thread priority.
+   *
+   * <p>The HAL notifier thread is responsible for managing the FPGA's notifier interrupt and waking
+   * up user's Notifiers when it's their time to run. Giving the HAL notifier thread real-time
+   * priority helps ensure the user's real-time Notifiers, if any, are notified to run in a timely
+   * manner.
+   *
+   * @param realTime Set to true to set a real-time priority, false for standard priority.
+   * @param priority Priority to set the thread to. For real-time, this is 1-99 with 99 being
+   *     highest. For non-real-time, this is forced to 0. See "man 7 sched" for more details.
+   * @return True on success.
+   */
+  public static boolean setHALThreadPriority(boolean realTime, int priority) {
+    return NotifierJNI.setHALThreadPriority(realTime, priority);
+  }
 }