pw_sync: Adds semaphores & mutexes
Adds the BinarySemaphore, CountingSemaphore, and Mutex to the
pw_sync module along with an STL backend for each.
Change-Id: I54a3a64e702202a319ed2c9068bf37412d3fd240
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/24241
Reviewed-by: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Ewout van Bekkum <ewout@google.com>
diff --git a/pw_sync_stl/counting_semaphore.cc b/pw_sync_stl/counting_semaphore.cc
new file mode 100644
index 0000000..781aa77
--- /dev/null
+++ b/pw_sync_stl/counting_semaphore.cc
@@ -0,0 +1,59 @@
+// Copyright 2020 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/counting_semaphore.h"
+
+#include "pw_assert/assert.h"
+
+using pw::chrono::SystemClock;
+
+namespace pw::sync {
+
+void CountingSemaphore::release(ptrdiff_t update) {
+ PW_DCHECK_UINT_GE(update, 0);
+ {
+ std::lock_guard lock(native_type_.mutex);
+ PW_DCHECK_UINT_LE(update, CountingSemaphore::max() - native_type_.count);
+ native_type_.count += update;
+ native_type_.condition.notify_one();
+ }
+}
+
+void CountingSemaphore::acquire() {
+ std::unique_lock lock(native_type_.mutex);
+ native_type_.condition.wait(lock, [&] { return native_type_.count != 0; });
+ --native_type_.count;
+}
+
+bool CountingSemaphore::try_acquire() {
+ std::lock_guard lock(native_type_.mutex);
+ if (native_type_.count != 0) {
+ --native_type_.count;
+ return true;
+ }
+ return false;
+}
+
+bool CountingSemaphore::try_acquire_until(
+ SystemClock::time_point until_at_least) {
+ std::unique_lock lock(native_type_.mutex);
+ if (native_type_.condition.wait_until(
+ lock, until_at_least, [&] { return native_type_.count != 0; })) {
+ --native_type_.count;
+ return true;
+ }
+ return false;
+}
+
+} // namespace pw::sync