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[hal,wpilib] Fix TimedRobot notifier race (#8445)

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It was possible for the alarm to fire between the set alarm and ack,
resulting in a hang on next wait. It's not possible to ack before set
alarm due to a race in sim step timing, so the fix is to provide an
atomic ack and set alarm; the easiest way to implement this in the API
was to change ack to optionally also set the alarm again.
This commit is contained in:
Peter Johnson
2025-12-04 09:59:59 -07:00
committed by GitHub
parent d1b1703c86
commit 934f8d9c15
12 changed files with 147 additions and 78 deletions
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12
wpilibc/src/main/native/cpp/framework/TimedRobot.cpp
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@@ -35,16 +35,14 @@ void TimedRobot::StartCompetition() {
auto callback = m_callbacks.pop();
int32_t status = 0;
HAL_SetNotifierAlarm(m_notifier, callback.expirationTime.count(), 0, true,
&status);
WPILIB_CheckErrorStatus(status, "UpdateNotifierAlarm");
// Acknowledge previous alarm after setting the next one to avoid a race
// against getting the next notifier timeout in HALSIM StepTiming.
if (first) {
first = false;
HAL_SetNotifierAlarm(m_notifier, callback.expirationTime.count(), 0, true,
&status);
WPILIB_CheckErrorStatus(status, "SetNotifierAlarm");
} else {
HAL_AcknowledgeNotifierAlarm(m_notifier, &status);
HAL_AcknowledgeNotifierAlarm(
m_notifier, true, callback.expirationTime.count(), 0, true, &status);
WPILIB_CheckErrorStatus(status, "AcknowledgeNotifierAlarm");
}