pw_rpc: Adjust alarm_timer_test

Tweaks AlarmTimerTest.Restart to be more robust and less prone to flake.

Bug: b/317990451
Change-Id: I8bd95106994c4ab217fd92d6afe74b1c380dfe81
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/186274
Commit-Queue: Auto-Submit <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Pigweed-Auto-Submit: Armando Montanez <[email protected]>
Reviewed-by: Erik Gilling <[email protected]>

pw_rpc/fuzz/alarm_timer_test.cc

@@ -32,14 +32,45 @@ TEST(AlarmTimerTest, Start) {
 }
 
 TEST(AlarmTimerTest, Restart) {
-  sync::BinarySemaphore sem;
-  AlarmTimer timer([&sem](chrono::SystemClock::time_point) { sem.release(); });
-  timer.Start(50ms);
-  for (size_t i = 0; i < 10; ++i) {
+  sync::BinarySemaphore final_sem;
+  sync::BinarySemaphore kick_sem;
+  constexpr auto kTimerDuration = 200ms;
+  constexpr auto kTimerKickDuration = 10ms;
+  constexpr size_t kNumRestarts = 10;
+  static_assert(kTimerKickDuration < kTimerDuration);
+
+  AlarmTimer timer(
+      [&final_sem](chrono::SystemClock::time_point) { final_sem.release(); });
+  AlarmTimer timer_kicker(
+      [&kick_sem](chrono::SystemClock::time_point) { kick_sem.release(); });
+
+  timer.Start(chrono::SystemClock::for_at_least(kTimerDuration));
+
+  bool acquired = false;
+  const auto start = chrono::SystemClock::now();
+  for (size_t i = 0; i < kNumRestarts; ++i) {
+    // Be overly aggressive with restarting the timer, the point is to ensure
+    // that it doesn't time out when restareted. Since this tests timings, it
+    // inherrently is very prone to flake in some environments (e.g. heavy load
+    // on a Windows machine).
     timer.Restart();
-    EXPECT_FALSE(sem.try_acquire_for(chrono::SystemClock::for_at_least(10us)));
+    timer_kicker.Start(chrono::SystemClock::for_at_least(kTimerKickDuration));
+    timer.Restart();
+    kick_sem.acquire();
+    timer.Restart();
+
+    acquired = final_sem.try_acquire();
+    EXPECT_FALSE(acquired);
+    if (acquired) {
+      break;
+    }
   }
-  sem.acquire();
+
+  if (!acquired) {
+    final_sem.acquire();
+  }
+  auto end = chrono::SystemClock::now();
+  EXPECT_GT(end - start, kTimerKickDuration * kNumRestarts + kTimerDuration);
 }
 
 TEST(AlarmTimerTest, Cancel) {