checker.h

// Copyright 2025 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.
#pragma once
 
#include <atomic>
#include <optional>
 
#include "pw_sync/lock_annotations.h"
#include "pw_thread/config.h"
#include "pw_thread/thread.h"
 
namespace pw {
 
 
class PW_LOCKABLE("pw::ThreadChecker") ThreadChecker {
 public:
  explicit ThreadChecker(Thread::id id) : self_(id) {}
 
  // Implementation of the BaseLockable requirement
  void lock() PW_EXCLUSIVE_LOCK_FUNCTION() {
#if PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
    // Hitting this assert means that access to this checker from multiple
    // threads was detected.
    PW_ASSERT(pw::this_thread::get_id() == self_);
#endif  // PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
  }
  void unlock() PW_UNLOCK_FUNCTION() {}
 
 private:
  Thread::id self_;
};
 
class PW_LOCKABLE("pw::LazyInitThreadChecker") LazyInitThreadChecker {
 public:
  constexpr LazyInitThreadChecker()
#if PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
      : thread_id_()
#endif
  {
  }
 
  // Implementation of the BaseLockable requirement
  void lock() PW_EXCLUSIVE_LOCK_FUNCTION() {
#if PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
    Thread::id stored_id = thread_id_.load(std::memory_order_acquire);
    if (stored_id == Thread::id()) {
      // The checker has not been initialized yet. Attempt to claim it for the
      // current thread.
      const Thread::id current_id = pw::this_thread::get_id();
      // A default constructed id which is used as the expected value.
      Thread::id uninitialized_id;
      // Attempt to swap the uninitialized ID with the current thread's ID.
      // This is done with release semantics to ensure that all prior writes
      // on this thread are visible on other threads.
      if (thread_id_.compare_exchange_strong(
              uninitialized_id, current_id, std::memory_order_acq_rel)) {
        // This thread successfully claimed the checker.
        stored_id = current_id;
      } else {
        // Another thread claimed the checker. `uninitialized_id` is now updated
        // with the stored value.
        stored_id = uninitialized_id;
      }
    }
 
    // Hitting this assert means that access to this checker from multiple
    // threads was detected.
    PW_ASSERT(pw::this_thread::get_id() == stored_id);
#endif  // PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
  }
  void unlock() PW_UNLOCK_FUNCTION() {}
 
 private:
#if PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
  std::atomic<Thread::id> thread_id_;
#endif  // PW_THREAD_CHECKER_RUNTIME_ASSERT_ENABLED
};
 
}  // namespace pw