realtime_box.hpp

// Copyright (c) 2009, Willow Garage, Inc.
// Copyright (c) 2024, Lennart Nachtigall
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//    * Redistributions of source code must retain the above copyright
//      notice, this list of conditions and the following disclaimer.
//
//    * Redistributions in binary form must reproduce the above copyright
//      notice, this list of conditions and the following disclaimer in the
//      documentation and/or other materials provided with the distribution.
//
//    * Neither the name of the Willow Garage, Inc. nor the names of its
//      contributors may be used to endorse or promote products derived from
//      this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
 
// Author: Stuart Glaser
// Author: Lennart Nachtigall
 
#ifndef REALTIME_TOOLS__REALTIME_BOX_HPP_
#define REALTIME_TOOLS__REALTIME_BOX_HPP_
 
#include <functional>
#include <initializer_list>
#include <mutex>
#include <optional>
#include <utility>
 
#include <rcpputils/pointer_traits.hpp>
 
namespace realtime_tools
{
 
template <typename T>
constexpr auto is_ptr_or_smart_ptr = rcpputils::is_pointer<T>::value;
 
template <class T, typename mutex_type = std::mutex>
class RealtimeBoxBase
{
  static_assert(std::is_copy_constructible_v<T>, "Passed type must be copy constructible");
 
public:
  using mutex_t = mutex_type;
  using type = T;
  // Provide various constructors
  constexpr explicit RealtimeBoxBase(const T & init = T{}) : value_(init) {}
  constexpr explicit RealtimeBoxBase(const T && init) : value_(std::move(init)) {}
 
  // Copy constructor
  constexpr RealtimeBoxBase(const RealtimeBoxBase & o)
  {
    // Lock the other box mutex
    std::unique_lock<mutex_t> lock(o.lock_);
    // We do not need to lock our own mutex because we are currently in the process of being created
    value_ = o.value_;
  }
 
  // Copy assignment constructor
  constexpr RealtimeBoxBase & operator=(const RealtimeBoxBase & o)
  {
    // Check for self assignment (and a potential deadlock)
    if (&o != this) {
      // Lock the other box mutex
      std::unique_lock<mutex_t> lock_other(o.lock_);
      std::unique_lock<mutex_t> lock_self(lock_);
 
      value_ = o.value_;
    }
    return *this;
  }
 
  constexpr RealtimeBoxBase(RealtimeBoxBase && o)
  {
    // Lock the other box mutex
    std::unique_lock<mutex_t> lock(o.lock_);
    // We do not need to lock our own mutex because we are currently in the process of being created
    value_ = std::move(o.value_);
  }
 
  // Only enabled for types that can be constructed from an initializer list
  template <typename U = T>
  constexpr RealtimeBoxBase(
    const std::initializer_list<U> & init,
    std::enable_if_t<std::is_constructible_v<U, std::initializer_list<U>>>)
  : value_(init)
  {
  }
 
  constexpr RealtimeBoxBase & operator=(RealtimeBoxBase && o)
  {
    // Check for self assignment (and a potential deadlock)
    if (&o != this) {
      // Lock the other box mutex
      std::unique_lock<mutex_t> lock_other(o.lock_);
      std::unique_lock<mutex_t> lock_self(lock_);
 
      value_ = std::move(o.value_);
    }
    return *this;
  }
 
  template <typename U = T>
  typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, bool> try_set(const T & value)
  {
    std::unique_lock<mutex_t> guard(lock_, std::defer_lock);
    if (!guard.try_lock()) {
      return false;
    }
    value_ = value;
    return true;
  }
 
  bool try_set(const std::function<void(T &)> & func)
  {
    std::unique_lock<mutex_t> guard(lock_, std::defer_lock);
    if (!guard.try_lock()) {
      return false;
    }
 
    func(value_);
    return true;
  }
 
  template <typename U = T>
  [[nodiscard]] typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, std::optional<U>> try_get() const
  {
    std::unique_lock<mutex_t> guard(lock_, std::defer_lock);
    if (!guard.try_lock()) {
      return std::nullopt;
    }
    return value_;
  }
 
  bool try_get(const std::function<void(const T &)> & func)
  {
    std::unique_lock<mutex_t> guard(lock_, std::defer_lock);
    if (!guard.try_lock()) {
      return false;
    }
 
    func(value_);
    return true;
  }
 
  template <typename U = T>
  typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, void> set(const T & value)
  {
    std::lock_guard<mutex_t> guard(lock_);
    // cppcheck-suppress missingReturn
    value_ = value;
  }
 
  void set(const std::function<void(T &)> & func)
  {
    std::lock_guard<mutex_t> guard(lock_);
    if (!func) {
      if constexpr (is_ptr_or_smart_ptr<T>) {
        value_ = nullptr;
        return;
      }
    }
    func(value_);
  }
 
  template <typename U = T>
  [[nodiscard]] typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, U> get() const
  {
    std::lock_guard<mutex_t> guard(lock_);
    return value_;
  }
 
  template <typename U = T>
  typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, void> get(T & in) const
  {
    std::lock_guard<mutex_t> guard(lock_);
    // cppcheck-suppress missingReturn
    in = value_;
  }
 
  void get(const std::function<void(const T &)> & func)
  {
    std::lock_guard<mutex_t> guard(lock_);
    func(value_);
  }
 
  template <typename U = T>
  typename std::enable_if_t<!is_ptr_or_smart_ptr<U>, void> operator=(const T & value)
  {
    set(value);
  }
 
  template <typename U = T, typename = typename std::enable_if_t<!is_ptr_or_smart_ptr<U>>>
  [[nodiscard]] operator T() const
  {
    // Only makes sense with the getNonRT method otherwise we would return an std::optional
    return get();
  }
 
  template <typename U = T, typename = typename std::enable_if_t<!is_ptr_or_smart_ptr<U>>>
  [[nodiscard]] operator std::optional<T>() const
  {
    return try_get();
  }
 
  // In case one wants to actually use a pointer
  // in this implementation we allow accessing the lock directly.
  // Note: Be careful with lock.unlock().
  // It may only be called from the thread that locked the mutex!
  [[nodiscard]] const mutex_t & get_mutex() const { return lock_; }
  [[nodiscard]] mutex_t & get_mutex() { return lock_; }
 
private:
  T value_;
 
  // Protects access to the thing in the box.  This mutex is
  // guaranteed to be locked for no longer than the duration of the
  // copy, so as long as the copy is realtime safe and the OS has
  // priority inheritance for mutexes, this lock can be safely locked
  // from within realtime.
  mutable mutex_t lock_;
};
 
// Introduce some easier to use names
 
// Provide specialisations for different mutex types
template <typename T>
using RealtimeBoxStandard = RealtimeBoxBase<T, std::mutex>;
 
template <typename T>
using RealtimeBoxRecursive = RealtimeBoxBase<T, std::recursive_mutex>;
 
// This is the specialisation we recommend to use in the end
template <typename T>
using RealtimeBox = RealtimeBoxStandard<T>;
 
}  // namespace realtime_tools
 
#endif  // REALTIME_TOOLS__REALTIME_BOX_HPP_