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// Copyright 2021 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
#include "pw_sync/timed_thread_notification.h"
#include <algorithm>
#include <optional>
#include "FreeRTOS.h"
#include "pw_assert/check.h"
#include "pw_chrono/system_clock.h"
#include "pw_chrono_freertos/system_clock_constants.h"
#include "pw_interrupt/context.h"
#include "pw_sync_freertos/config.h"
#include "task.h"
using pw::chrono::SystemClock;
namespace pw::sync {
namespace {
BaseType_t WaitForNotification(TickType_t xTicksToWait) {
#ifdef configTASK_NOTIFICATION_ARRAY_ENTRIES
return xTaskNotifyWaitIndexed(
pw::sync::freertos::config::kThreadNotificationIndex,
0, // Clear no bits on entry.
0, // Clear no bits on exit.
nullptr, // Don't care about the notification value.
xTicksToWait);
#else // !configTASK_NOTIFICATION_ARRAY_ENTRIES
return xTaskNotifyWait(0, // Clear no bits on entry.
0, // Clear no bits on exit.
nullptr, // Don't care about the notification value.
xTicksToWait);
#endif // configTASK_NOTIFICATION_ARRAY_ENTRIES
}
} // namespace
bool TimedThreadNotification::try_acquire_until(
const SystemClock::time_point deadline) {
// Enforce the pw::sync::TImedThreadNotification IRQ contract.
PW_DCHECK(!interrupt::InInterruptContext());
// Enforce that only a single thread can block at a time.
PW_DCHECK(native_handle().blocked_thread == nullptr);
// Ensure that no one forgot to clean up nor corrupted the task notification
// state in the TCB.
PW_DCHECK(xTaskNotifyStateClear(nullptr) == pdFALSE);
{
std::lock_guard lock(native_handle().shared_spin_lock);
const bool notified = native_handle().notified;
// Don't block if we've already reached the specified deadline time.
if (notified || (SystemClock::now() >= deadline)) {
native_handle().notified = false;
return notified;
}
// Not notified yet, set the task handle for a one-time notification.
native_handle().blocked_thread = xTaskGetCurrentTaskHandle();
}
// xTaskNotifyWait may spuriously return pdFALSE due to vTaskSuspend &
// vTaskResume. Ergo, loop until we have been notified or the specified
// deadline time has been reached (whichever comes first).
for (SystemClock::time_point now = SystemClock::now(); now < deadline;
now = SystemClock::now()) {
// Note that this must be greater than zero, due to the condition above.
const SystemClock::duration timeout =
std::min(deadline - now, pw::chrono::freertos::kMaxTimeout);
if (WaitForNotification(static_cast<TickType_t>(timeout.count())) ==
pdTRUE) {
break; // We were notified!
}
}
std::lock_guard lock(native_handle().shared_spin_lock);
// We need to clear the thread notification state in case we were
// notified after timing out but before entering this critical section.
#ifdef configTASK_NOTIFICATION_ARRAY_ENTRIES
xTaskNotifyStateClearIndexed(
nullptr, pw::sync::freertos::config::kThreadNotificationIndex);
#else // !configTASK_NOTIFICATION_ARRAY_ENTRIES
xTaskNotifyStateClear(nullptr);
#endif // configTASK_NOTIFICATION_ARRAY_ENTRIES
// Instead of determining whether we were notified above while blocking in
// the loop above, we instead read it in this subsequent critical section in
// order to also include notifications which arrived after we timed out but
// before we entered this critical section.
const bool notified = native_handle().notified;
native_handle().notified = false;
native_handle().blocked_thread = nullptr;
return notified;
}
} // namespace pw::sync
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