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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 "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_for(SystemClock::duration timeout) {
// 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);
taskENTER_CRITICAL();
{
const bool notified = native_handle().notified;
// Don't block for negative or zero length durations.
if (notified || (timeout <= SystemClock::duration::zero())) {
native_handle().notified = false;
taskEXIT_CRITICAL();
return notified;
}
// Not notified yet, set the task handle for a one-time notification.
native_handle().blocked_thread = xTaskGetCurrentTaskHandle();
}
taskEXIT_CRITICAL();
const bool notified = [&]() {
// In case the timeout is too long for us to express through the native
// FreeRTOS API, we repeatedly wait with shorter durations. Note that on a
// tick based kernel we cannot tell how far along we are on the current
// tick, ergo we add one whole tick to the final duration. However, this
// also means that the loop must ensure that timeout + 1 is less than the
// max timeout.
constexpr SystemClock::duration kMaxTimeoutMinusOne =
pw::chrono::freertos::kMaxTimeout - SystemClock::duration(1);
// In case the timeout is too long for us to express through the native
// FreeRTOS API, we repeatedly wait with shorter durations.
while (timeout > kMaxTimeoutMinusOne) {
if (WaitForNotification(
static_cast<TickType_t>(kMaxTimeoutMinusOne.count())) == pdTRUE) {
return true;
}
timeout -= kMaxTimeoutMinusOne;
}
// On a tick based kernel we cannot tell how far along we are on the current
// tick, ergo we add one whole tick to the final duration.
return WaitForNotification(static_cast<TickType_t>(timeout.count() + 1)) ==
pdTRUE;
}();
taskENTER_CRITICAL();
if (notified) {
// Note that this may hide another notification, however this is considered
// a form of notification saturation just like as if this happened before
// acquire() was invoked.
native_handle().notified = false;
// The task handle and notification state were cleared by the notifier.
} else {
// Note that we do NOT want to clear the notified value so the next call
// can detect the notification which came after we timed out but before this
// critical section.
//
// However, we do need to clear the task handle if we weren't notified and
// the notification state in case we were notified to ensure we can block
// in the future.
native_handle().blocked_thread = nullptr;
#ifdef configTASK_NOTIFICATION_ARRAY_ENTRIES
xTaskNotifyStateClearIndexed(
nullptr, pw::sync::freertos::config::kThreadNotificationIndex);
#else // !configTASK_NOTIFICATION_ARRAY_ENTRIES
xTaskNotifyStateClear(nullptr);
#endif // configTASK_NOTIFICATION_ARRAY_ENTRIES
}
taskEXIT_CRITICAL();
return notified;
}
} // namespace pw::sync
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