1 files changed, 56 insertions, 0 deletions
diff --git a/pw_sync_embos/timed_mutex.cc b/pw_sync_embos/timed_mutex.cc
new file mode 100644
index 000000000..c08bef473
--- /dev/null
+++ b/pw_sync_embos/timed_mutex.cc
@@ -0,0 +1,56 @@
+// 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_mutex.h"
+
+#include <algorithm>
+
+#include "RTOS.h"
+#include "pw_assert/assert.h"
+#include "pw_chrono/system_clock.h"
+#include "pw_chrono_embos/system_clock_constants.h"
+#include "pw_interrupt/context.h"
+
+using pw::chrono::SystemClock;
+
+namespace pw::sync {
+
+bool TimedMutex::try_lock_for(SystemClock::duration for_at_least) {
+  PW_DCHECK(!interrupt::InInterruptContext());
+
+  // Use non-blocking try_lock for negative and zero length durations.
+  if (for_at_least <= SystemClock::duration::zero()) {
+    return try_lock();
+  }
+
+  // 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.
+  constexpr SystemClock::duration kMaxTimeoutMinusOne =
+      pw::chrono::embos::kMaxTimeout - SystemClock::duration(1);
+  while (for_at_least > kMaxTimeoutMinusOne) {
+    const int lock_count = OS_UseTimed(
+        &native_handle(), static_cast<OS_TIME>(kMaxTimeoutMinusOne.count()));
+    if (lock_count != 0) {
+      PW_CHECK_UINT_EQ(1, lock_count, "Recursive locking is not permitted");
+      return true;
+    }
+    for_at_least -= kMaxTimeoutMinusOne;
+  }
+  const int lock_count = OS_UseTimed(
+      &native_handle(), static_cast<OS_TIME>(for_at_least.count() + 1));
+  PW_CHECK_UINT_LE(1, lock_count, "Recursive locking is not permitted");
+  return lock_count == 1;
+}
+
+}  // namespace pw::sync