63 lines
2.3 KiB
C++
63 lines
2.3 KiB
C++
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// Copyright 2021 The Pigweed Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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#include "pw_sync/timed_mutex.h"
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#include <algorithm>
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#include "RTOS.h"
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#include "pw_assert/check.h"
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#include "pw_chrono/system_clock.h"
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#include "pw_chrono_embos/system_clock_constants.h"
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#include "pw_interrupt/context.h"
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using pw::chrono::SystemClock;
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namespace pw::sync {
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bool TimedMutex::try_lock_for(SystemClock::duration timeout) {
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// Enforce the pw::sync::TimedMutex IRQ contract.
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PW_DCHECK(!interrupt::InInterruptContext());
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// Use non-blocking try_lock for negative and zero length durations.
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if (timeout <= SystemClock::duration::zero()) {
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return try_lock();
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}
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// In case the timeout is too long for us to express through the native
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// embOS API, we repeatedly wait with shorter durations. Note that on a tick
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// based kernel we cannot tell how far along we are on the current tick, ergo
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// we add one whole tick to the final duration. However, this also means that
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// the loop must ensure that timeout + 1 is less than the max timeout.
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constexpr SystemClock::duration kMaxTimeoutMinusOne =
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pw::chrono::embos::kMaxTimeout - SystemClock::duration(1);
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while (timeout > kMaxTimeoutMinusOne) {
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const int lock_count = OS_UseTimed(
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&native_handle(), static_cast<OS_TIME>(kMaxTimeoutMinusOne.count()));
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if (lock_count != 0) {
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PW_DCHECK_UINT_EQ(1, lock_count, "Recursive locking is not permitted");
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return true;
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}
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timeout -= kMaxTimeoutMinusOne;
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}
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// On a tick based kernel we cannot tell how far along we are on the current
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// tick, ergo we add one whole tick to the final duration.
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const int lock_count =
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OS_UseTimed(&native_handle(), static_cast<OS_TIME>(timeout.count() + 1));
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PW_DCHECK_UINT_LE(1, lock_count, "Recursive locking is not permitted");
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return lock_count == 1;
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}
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} // namespace pw::sync
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