[hal,sim] Add notifier generation counter to WaitForProgramStart (#8947)

This fixes simulation WaitForProgramStart(true) potentially advancing
due to a stale or pre-start notifier created before SetProgramStarted()
was called.

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

@@ -21,6 +21,7 @@ static std::atomic<int64_t> programState{0};
 static std::atomic<uint64_t> programStartTime{0};
 static std::atomic<uint64_t> programPauseTime{0};
 static std::atomic<uint64_t> programStepTime{0};
+static std::atomic<uint64_t> programStartNotifierAlarmCount{0};
 
 namespace wpi::hal::init {
 void InitializeMockHooks() {
@@ -67,6 +68,7 @@ uint64_t GetMonotonicTime() {
 }
 
 void SetProgramStarted(bool started) {
+  programStartNotifierAlarmCount = GetNotifierAlarmSetCount();
   programStarted = started;
 }
 bool GetProgramStarted() {
@@ -88,9 +90,11 @@ void HALSIM_WaitForProgramStart(HAL_Bool waitForFirstNotifier) {
   }
 
   // Frameworks observe program start before arming their first notifier alarm.
-  // Wait for that alarm so a following StepTiming() can see and service it.
+  // Wait for an alarm armed after that program-start edge so a stale notifier
+  // cannot satisfy this check.
   while (waitForFirstNotifier &&
-         HALSIM_GetNextNotifierTimeout() == UINT64_MAX) {
+         (GetNotifierAlarmSetCount() == programStartNotifierAlarmCount ||
+          HALSIM_GetNextNotifierTimeout() == UINT64_MAX)) {
     count++;
     if (count % 10 == 0) {
       wpi::util::print("Waiting for first notifier alarm: {}\n", count);

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

@@ -74,6 +74,7 @@ class NotifierInstance {
 };
 
 static NotifierInstance* notifierInstance;
+static std::atomic<uint64_t> notifierAlarmSetCount{0};
 
 namespace wpi::hal::init {
 void InitializeNotifier() {
@@ -209,6 +210,10 @@ void wpi::hal::WakeupWaitNotifiers() {
   DoWaitNotifiers(thr, signaled);
 }
 
+uint64_t wpi::hal::GetNotifierAlarmSetCount() {
+  return notifierAlarmSetCount;
+}
+
 extern "C" {
 
 HAL_NotifierHandle HAL_CreateNotifier(int32_t* status) {
@@ -268,6 +273,7 @@ void HAL_SetNotifierAlarm(HAL_NotifierHandle notifierHandle, uint64_t alarmTime,
   notifier->intervalTime = intervalTime;
   notifier->overrunCount = 0;
   thr->m_alarmQueue.push({notifierHandle, notifier});
+  ++notifierAlarmSetCount;
 
   // wake up notifier thread if needed
   if (alarmTime < prevWakeup) {

hal/src/main/native/sim/NotifierInternal.hpp

@@ -4,10 +4,13 @@
 
 #pragma once
 
+#include <stdint.h>
+
 namespace wpi::hal {
 void PauseNotifiers();
 void ResumeNotifiers();
 void WakeupNotifiers();
 void WaitNotifiers();
 void WakeupWaitNotifiers();
+uint64_t GetNotifierAlarmSetCount();
 }  // namespace wpi::hal