1 // Copyright 2020 The Pigweed Authors
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License"); you may not
4 // use this file except in compliance with the License. You may obtain a copy of
5 // the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
11 // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
12 // License for the specific language governing permissions and limitations under
13 // the License.
14
15 #include "pw_sync/timed_mutex.h"
16
17 #include <algorithm>
18
19 #include "FreeRTOS.h"
20 #include "pw_assert/check.h"
21 #include "pw_chrono/system_clock.h"
22 #include "pw_chrono_freertos/system_clock_constants.h"
23 #include "pw_interrupt/context.h"
24 #include "semphr.h"
25
26 using pw::chrono::SystemClock;
27
28 namespace pw::sync {
29
try_lock_for(SystemClock::duration timeout)30 bool TimedMutex::try_lock_for(SystemClock::duration timeout) {
31 // Enforce the pw::sync::TimedMutex IRQ contract.
32 PW_DCHECK(!interrupt::InInterruptContext());
33
34 // Use non-blocking try_acquire for negative and zero length durations.
35 if (timeout <= SystemClock::duration::zero()) {
36 return try_lock();
37 }
38
39 // In case the timeout is too long for us to express through the native
40 // FreeRTOS API, we repeatedly wait with shorter durations. Note that on a
41 // tick based kernel we cannot tell how far along we are on the current tick,
42 // ergo we add one whole tick to the final duration. However, this also means
43 // that the loop must ensure that timeout + 1 is less than the max timeout.
44 constexpr SystemClock::duration kMaxTimeoutMinusOne =
45 pw::chrono::freertos::kMaxTimeout - SystemClock::duration(1);
46 while (timeout > kMaxTimeoutMinusOne) {
47 if (xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_handle()),
48 static_cast<TickType_t>(kMaxTimeoutMinusOne.count())) ==
49 pdTRUE) {
50 return true;
51 }
52 timeout -= kMaxTimeoutMinusOne;
53 }
54 // On a tick based kernel we cannot tell how far along we are on the current
55 // tick, ergo we add one whole tick to the final duration.
56 return xSemaphoreTake(reinterpret_cast<SemaphoreHandle_t>(&native_handle()),
57 static_cast<TickType_t>(timeout.count() + 1)) == pdTRUE;
58 }
59
60 } // namespace pw::sync
61