Lots of comments

rclcpp/include/rclcpp/executor.hpp

@@ -136,10 +136,11 @@ public:
     }
   }
 
-  /// Add a node to executor, complete the next available unit of work, and remove the node.
+  /// Add a node to executor, execute the next available unit of work, and remove the node.
   /* \param[in] node Shared pointer to the node to add.
    * \param[in] timeout How long to wait for work to become available. Negative values cause
-   * spin_node_once to block indefinitely 
+   * spin_node_once to block indefinitely (the default behavior). A timeout of 0 causes this
+   * function to be non-blocking.
    */
   template<typename T = std::milli>
   void spin_node_once(rclcpp::node::Node::SharedPtr & node,
@@ -154,7 +155,9 @@ public:
     this->remove_node(node, false);
   }
 
-// TODO
+  /// Add a node, complete all immediately available work, and remove the node.
+  /* \param[in] node Shared pointer to the node to add.
+   */
   void spin_node_some(rclcpp::node::Node::SharedPtr & node)
   {
     this->add_node(node, false);
@@ -162,7 +165,12 @@ public:
     this->remove_node(node, false);
   }
 
-// TODO
+  /// Complete all available queued work without blocking.
+  /* This function can be overridden. The default implementation is suitable for a
+   * single-threaded model of execution.
+   * Adding subscriptions, timers, services, etc. with blocking callbacks will cause this function
+   * to block (which may have unintended consequences).
+   */
   virtual void spin_some()
   {
     while (AnyExecutable::SharedPtr any_exec =
@@ -172,8 +180,11 @@ public:
     }
   }
 
-// TODO
+  /// Support dynamic switching of the memory strategy.
-  // Support dynamic switching of memory strategy
+  /* Switching the memory strategy while the executor is spinning in another threading could have
+   * unintended consequences.
+   * \param[in] memory_strategy Shared pointer to the memory strategy to set.
+   */
   void
   set_memory_strategy(memory_strategy::MemoryStrategy::SharedPtr memory_strategy)
   {
@@ -184,8 +195,10 @@ public:
   }
 
 protected:
+  /// Find the next available executable and do the work associated with it.
+  // \param[in] any_exec Union structure that can hold any executable type (timer, subscription,
+  // service, client).
   void
-// TODO
   execute_any_executable(AnyExecutable::SharedPtr & any_exec)
   {
     if (!any_exec) {
@@ -938,8 +951,10 @@ protected:
     return any_exec;
   }
 
+  /// Guard condition for signaling the rmw layer to wake up for special events.
   rmw_guard_condition_t * interrupt_guard_condition_;
 
+  /// The memory strategy: an interface for handling user-defined memory allocation strategies.
   memory_strategy::MemoryStrategy::SharedPtr memory_strategy_;
 
 private:

rclcpp/include/rclcpp/executors/single_threaded_executor.hpp

@@ -36,18 +36,24 @@ namespace executors
 namespace single_threaded_executor
 {
 
-// TODO
+/// Single-threaded executor implementation
+// This is the default executor created by rclcpp::spin.
 class SingleThreadedExecutor : public executor::Executor
 {
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(SingleThreadedExecutor);
 
+  /// Default constructor. See the default constructor for Executor.
   SingleThreadedExecutor(memory_strategy::MemoryStrategy::SharedPtr ms =
     memory_strategy::create_default_strategy())
   : executor::Executor(ms) {}
 
+  /// Default destrcutor.
   virtual ~SingleThreadedExecutor() {}
 
+  /// Single-threaded implementation of spin.
+  // This function will block until work comes in, execute it, and keep blocking.
+  // It will only be interrupt by a CTRL-C (managed by the global signal handler).
   void spin()
   {
     while (rclcpp::utilities::ok()) {

rclcpp/include/rclcpp/memory_strategy.hpp

@@ -30,7 +30,11 @@ class Executor;
 namespace memory_strategy
 {
 
-// TODO
+/// Delegate for handling memory allocations while the Executor is executing.
+/* By default, the memory strategy dynamically allocates memory for structures that come in from
+ * the rmw implementation after the executor waits for work, based on the number of entities that
+ * come through.
+ */
 class MemoryStrategy
 {
 
@@ -38,23 +42,41 @@ class MemoryStrategy
 
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(MemoryStrategy);
+
+  /// Borrow memory for storing data for subscriptions, services, clients, or guard conditions.
+  /* The default implementation ignores the handle type and dynamically allocates the memory.
+   * \param[in] The type of entity that this function is requesting for.
+   * \param[in] The number of handles to borrow.
+   * \return Pointer to the allocated handles.
+   */
   virtual void ** borrow_handles(HandleType type, size_t number_of_handles)
   {
     (void)type;
     return static_cast<void **>(alloc(sizeof(void *) * number_of_handles));
   }
 
+  /// Return the memory borrowed in borrow_handles.
+  /* return_handles should always mirror the way memory was borrowed in borrow_handles.
+   * \param[in] The type of entity that this function is returning.
+   * \param[in] Pointer to the handles returned.
+   */
   virtual void return_handles(HandleType type, void ** handles)
   {
     (void)type;
     this->free(handles);
   }
 
+  /// Provide a newly initialized AnyExecutable object.
+  // \return Shared pointer to the fresh executable.
   virtual executor::AnyExecutable::SharedPtr instantiate_next_executable()
   {
     return std::make_shared<executor::AnyExecutable>();
   }
 
+  /// Implementation of a general-purpose allocation function.
+  /* \param[in] size Number of bytes to allocate.
+   * \return Pointer to the allocated chunk of memory.
+   */
   virtual void * alloc(size_t size)
   {
     if (size == 0) {
@@ -63,6 +85,9 @@ public:
     return std::malloc(size);
   }
 
+  /// Implementation of a general-purpose free.
+  /* \param[in] Pointer to deallocate.
+   */
   virtual void free(void * ptr)
   {
     return std::free(ptr);

rclcpp/include/rclcpp/message_memory_strategy.hpp

@@ -24,7 +24,8 @@ namespace rclcpp
 namespace message_memory_strategy
 {
 
-// TODO
+/// Default allocation strategy for messages received by subscriptions.
+// A message memory strategy must be templated on the type of the subscription it belongs to.
 template<typename MessageT>
 class MessageMemoryStrategy
 {
@@ -32,16 +33,21 @@ class MessageMemoryStrategy
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(MessageMemoryStrategy);
 
+  /// Default factory method
   static SharedPtr create_default()
   {
     return SharedPtr(new MessageMemoryStrategy<MessageT>);
   }
 
+  /// By default, dynamically allocate a new message.
+  // \return Shared pointer to the new message.
   virtual std::shared_ptr<MessageT> borrow_message()
   {
     return std::shared_ptr<MessageT>(new MessageT);
   }
 
+  /// Release ownership of the message, which will deallocate it if it has no more owners.
+  // \param[in] Shared pointer to the message we are returning.
   virtual void return_message(std::shared_ptr<MessageT> & msg)
   {
     msg.reset();

rclcpp/include/rclcpp/node.hpp

@@ -92,11 +92,7 @@ struct function_traits<ReturnTypeT (ClassT::*)(Args ...) const>
   : public function_traits<ReturnTypeT(ClassT &, Args ...)>
 {};
 
-/* ROS Node Interface.
+/// Node is the single point of entry for creating publishers and subscribers.
- *
- * This is the single point of entry for creating publishers and subscribers.
- */
-// TODO
 class Node
 {
   friend class rclcpp::executor::Executor;
@@ -104,30 +100,51 @@ class Node
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(Node);
 
-// TODO: ALL public functions
+  /// Create a new node with the specified name.
-  /* Create a node based on the node name. */
+  /* \param[in] node_name Name of the node.
+   * \param[in] use_intra_process_comms True to use the optimized intra-process communication
+   * pipeline to pass messages between nodes in the same process using shared memory.
+   */
   Node(const std::string & node_name, bool use_intra_process_comms = false);
-  /* Create a node based on the node name and a rclcpp::context::Context. */
+
+  /// Create a node based on the node name and a rclcpp::context::Context.
+  /* \param[in] node_name Name of the node.
+   * \param[in] context The context for the node (usually represents the state of a process).
+   * \param[in] use_intra_process_comms True to use the optimized intra-process communication
+   * pipeline to pass messages between nodes in the same process using shared memory.
+   */
   Node(
     const std::string & node_name, rclcpp::context::Context::SharedPtr context,
     bool use_intra_process_comms = false);
 
-  /* Get the name of the node. */
+  /// Get the name of the node.
+  // \return The name of the node.
   const std::string &
   get_name() const {return name_; }
 
-  /* Create and return a callback group. */
+  /// Create and return a callback group.
   rclcpp::callback_group::CallbackGroup::SharedPtr
   create_callback_group(rclcpp::callback_group::CallbackGroupType group_type);
 
-  /* Create and return a Publisher. */
+  /// Create and return a Publisher.
+  /* \param[in] topic_name The topic for this publisher to publish on.
+   * \param[in] qos_profile The quality of service profile to pass on to the rmw implementation.
+   * \return Shared pointer to the created publisher.
+   */
   template<typename MessageT>
   rclcpp::publisher::Publisher::SharedPtr
   create_publisher(
     const std::string & topic_name, const rmw_qos_profile_t & qos_profile);
 
-  /* Create and return a Subscription. */
+  /// Create and return a Subscription.
-
+  /* \param[in] topic_name The topic to subscribe on.
+   * \param[in] qos_profile The quality of service profile to pass on to the rmw implementation.
+   * \param[in] callback The user-defined callback function.
+   * \param[in] group The callback group for this subscription. NULL for no callback group.
+   * \param[in] ignore_local_publications True to ignore local publications.
+   * \param[in] msg_mem_strat The message memory strategy to use for allocating messages.
+   * \return Shared pointer to the created subscription.
+   */
   /* TODO(jacquelinekay):
      Windows build breaks when static member function passed as default
      argument to msg_mem_strat, nullptr is a workaround.
@@ -143,13 +160,22 @@ public:
     typename rclcpp::message_memory_strategy::MessageMemoryStrategy<MessageT>::SharedPtr
     msg_mem_strat = nullptr);
 
-  /* Create a timer. */
+  /// Create a timer.
+  /* \param[in] period Time interval between triggers of the callback.
+   * \param[in] callback User-defined callback function.
+   * \param[in] group Callback group to execute this timer's callback in.
+   */
   rclcpp::timer::WallTimer::SharedPtr
   create_wall_timer(
     std::chrono::nanoseconds period,
     rclcpp::timer::CallbackType callback,
     rclcpp::callback_group::CallbackGroup::SharedPtr group = nullptr);
 
+  /// Create a timer with a sub-nanosecond precision update period.
+  /* \param[in] period Time interval between triggers of the callback.
+   * \param[in] callback User-defined callback function.
+   * \param[in] group Callback group to execute this timer's callback in.
+   */
   rclcpp::timer::WallTimer::SharedPtr
   create_wall_timer(
     std::chrono::duration<long double, std::nano> period,

rclcpp/include/rclcpp/publisher.hpp

@@ -39,15 +39,22 @@ class Node;
 namespace publisher
 {
 
-// TODO
+/// A publisher publishes messages of any type to a topic.
 class Publisher
 {
   friend rclcpp::node::Node;
 
-// TODO
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(Publisher);
 
+  /// Default constructor.
+  /* Typically, a publisher is not created through this method, but instead is created through a
+   * call to `Node::create_publisher`.
+   * \param[in] node_handle The corresponding rmw representation of the owner node.
+   * \param[in] publisher_handle The rmw publisher handle corresponding to this publisher.
+   * \param[in] topic The topic that this publisher publishes on.
+   * \param[in] queue_size The maximum number of unpublished messages to queue.
+   */
   Publisher(
     std::shared_ptr<rmw_node_t> node_handle,
     rmw_publisher_t * publisher_handle,
@@ -67,6 +74,7 @@ public:
     }
   }
 
+  /// Default destructor.
   virtual ~Publisher()
   {
     if (intra_process_publisher_handle_) {
@@ -87,6 +95,10 @@ public:
     }
   }
 
+  /// Send a message to the topic for this publisher.
+  /* This function is templated on the input message type, MessageT.
+   * \param[in] msg A shared pointer to the message to send.
+   */
   template<typename MessageT>
   void
   publish(std::shared_ptr<MessageT> & msg)
@@ -114,36 +126,54 @@ public:
     }
   }
 
+  /// Get the topic that this publisher publishes on.
+  // \return The topic name.
   const std::string &
   get_topic_name() const
   {
     return topic_;
   }
 
+  /// Get the queue size for this publisher.
+  // \return The queue size.
   size_t
   get_queue_size() const
   {
     return queue_size_;
   }
 
+  /// Get the global identifier for this publisher (used in rmw and by DDS).
+  // \return The gid.
   const rmw_gid_t &
   get_gid() const
   {
     return rmw_gid_;
   }
 
+  /// Get the global identifier for this publisher used by intra-process communication.
+  // \return The intra-process gid.
   const rmw_gid_t &
   get_intra_process_gid() const
   {
     return intra_process_rmw_gid_;
   }
 
+  /// Compare this publisher to a gid.
+  /* Note that this function calls the next function.
+   * \param[in] gid Reference to a gid.
+   * \return True if the publisher's gid matches the input.
+   */
   bool
   operator==(const rmw_gid_t & gid) const
   {
     return *this == &gid;
   }
 
+  /// Compare this publisher to a pointer gid.
+  /* A wrapper for comparing this publisher's gid to the input using rmw_compare_gids_equal.
+   * \param[in] gid A pointer to a gid.
+   * \return True if this publisher's gid matches the input.
+   */
   bool
   operator==(const rmw_gid_t * gid) const
   {

rclcpp/include/rclcpp/rclcpp.hpp

@@ -51,6 +51,8 @@ operator"" _ns(long double ns)
     std::chrono::duration<long double, std::nano>(ns));
 }
 
+// Namespace escalations.
+// For example, this next line escalates type "rclcpp:node::Node" to "rclcpp::Node"
 using rclcpp::node::Node;
 using rclcpp::publisher::Publisher;
 using rclcpp::subscription::SubscriptionBase;
@@ -66,12 +68,16 @@ using rclcpp::utilities::shutdown;
 using rclcpp::utilities::init;
 using rclcpp::utilities::sleep_for;
 
+/// Create a default single-threaded executor and execute any immediately available work.
+// \param[in] node_ptr Shared pointer to the node to spin.
 void spin_some(Node::SharedPtr & node_ptr)
 {
   rclcpp::executors::SingleThreadedExecutor executor;
   executor.spin_node_some(node_ptr);
 }
 
+/// Create a default single-threaded executor and spin the specified node.
+// \param[in] node_ptr Shared pointer to the node to spin.
 void spin(Node::SharedPtr & node_ptr)
 {
   rclcpp::executors::SingleThreadedExecutor executor;

rclcpp/include/rclcpp/strategies/message_pool_memory_strategy.hpp

@@ -25,7 +25,12 @@ namespace strategies
 namespace message_pool_memory_strategy
 {
 
-// TODO
+/// Completely static memory allocation strategy for messages.
+/* Templated on the type of message pooled by this class and the size of the message pool.
+ * Templating allows the program to determine the memory required for this object at compile time.
+ * The size of the message pool should be at least the largest number of concurrent accesses to
+ * the subscription (usually the number of threads).
+ */
 template<typename MessageT, size_t Size,
 typename std::enable_if<rosidl_generator_traits::has_fixed_size<MessageT>::value>::type * =
 nullptr>
@@ -34,6 +39,8 @@ class MessagePoolMemoryStrategy
 {
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(MessagePoolMemoryStrategy);
+
+  /// Default constructor
   MessagePoolMemoryStrategy()
   : next_array_index_(0)
   {
@@ -43,6 +50,11 @@ public:
     }
   }
 
+  /// Borrow a message from the message pool.
+  /* Manage the message pool ring buffer.
+   * Throw an exception if the next message was not available.
+   * \return Shared pointer to the borrowed message.
+   */
   std::shared_ptr<MessageT> borrow_message()
   {
     size_t current_index = next_array_index_;
@@ -57,6 +69,10 @@ public:
     return pool_[current_index].msg_ptr_;
   }
 
+  /// Return a message to the message pool.
+  /* Manage metadata in the message pool ring buffer to release the message.
+   * \param[in] msg Shared pointer to the message to return.
+   */
   void return_message(std::shared_ptr<MessageT> & msg)
   {
     for (size_t i = 0; i < Size; ++i) {

rclcpp/include/rclcpp/strategies/static_memory_strategy.hpp

@@ -27,7 +27,8 @@ namespace memory_strategies
 
 namespace static_memory_strategy
 {
-// TODO
+
+/// Representation of the upper bounds on the memory pools managed by StaticMemoryStrategy.
 struct ObjectPoolBounds
 {
 public:
@@ -38,41 +39,68 @@ public:
   size_t max_guard_conditions;
   size_t pool_size;
 
+  /// Default constructor attempts to set reasonable default limits on the fields.
   ObjectPoolBounds()
   : max_subscriptions(10), max_services(10), max_clients(10),
     max_executables(1), max_guard_conditions(2), pool_size(1024)
   {}
 
+  // Setters implement named parameter idiom/method chaining
+
+  /// Set the maximum number of subscriptions.
+  /* \param[in] subscriptions Maximum number of subscriptions.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_max_subscriptions(size_t subscriptions)
   {
     max_subscriptions = subscriptions;
     return *this;
   }
 
+  /// Set the maximum number of services.
+  /* \param[in] services Maximum number of services.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_max_services(size_t services)
   {
     max_services = services;
     return *this;
   }
 
+  /// Set the maximum number of clients.
+  /* \param[in] clients Maximum number of clients.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_max_clients(size_t clients)
   {
     max_clients = clients;
     return *this;
   }
 
+  /// Set the maximum number of guard conditions.
+  /* \param[in] guard conditions Maximum number of guard conditions.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_max_guard_conditions(size_t guard_conditions)
   {
     max_guard_conditions = guard_conditions;
     return *this;
   }
 
+  /// Set the maximum number of executables.
+  /* \param[in] executables Maximum number of executables.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_max_executables(size_t executables)
   {
     max_executables = executables;
     return *this;
   }
 
+  /// Set the maximum memory pool size.
+  /* \param[in] executables Maximum memory pool size.
+   * \return Reference to this object, for method chaining.
+   */
   ObjectPoolBounds & set_memory_pool_size(size_t pool)
   {
     pool_size = pool;
@@ -81,10 +109,19 @@ public:
 };
 
 
-// TODO
+/// Static memory allocation alternative to the default memory strategy.
+/* The name is a bit of a misnomer. The memory managed by this class is actually allocated
+ * dynamically in the constructor, but no subsequent accesses to the class (besides the destructor)
+ * allocate or free memory.
+ * StaticMemoryStrategy puts a hard limit on the number of subscriptions, etc. that can be executed
+ * in one iteration of `Executor::spin`. Thus it allows for memory allocation optimization for
+ * situations where a limit on the number of such entities is known.
+ */
 class StaticMemoryStrategy : public memory_strategy::MemoryStrategy
 {
 public:
+  /// Default constructor.
+  // \param[in] bounds Representation of the limits on memory managed by this class.
   StaticMemoryStrategy(ObjectPoolBounds bounds = ObjectPoolBounds())
   : bounds_(bounds), memory_pool_(nullptr), subscription_pool_(nullptr),
     service_pool_(nullptr), guard_condition_pool_(nullptr), executable_pool_(nullptr)
@@ -132,6 +169,7 @@ public:
     }
   }
 
+  /// Default destructor. Free all allocated memory.
   ~StaticMemoryStrategy()
   {
     if (bounds_.pool_size) {
@@ -151,6 +189,11 @@ public:
     }
   }
 
+  /// Borrow handles by returning a pointer to the preallocated object pool for the specified type.
+  /* \param[in] The type of entity that this function is requesting for.
+   * \param[in] The number of handles to borrow.
+   * \return Pointer to the allocated handles.
+   */
   void ** borrow_handles(HandleType type, size_t number_of_handles)
   {
     switch (type) {
@@ -184,6 +227,10 @@ public:
     throw std::runtime_error("Unrecognized enum, could not borrow handle memory.");
   }
 
+  /// Return the borrowed handles by clearing the object pool for the correspondign type.
+  /* \param[in] The type of entity that this function is returning.
+   * \param[in] Pointer to the handles returned.
+   */
   void return_handles(HandleType type, void ** handles)
   {
     (void)handles;
@@ -213,10 +260,12 @@ public:
     }
   }
 
+  /// Instantiate the next executable by borrowing space from the preallocated executables pool.
+  // \return Shared pointer to the executable.
   executor::AnyExecutable::SharedPtr instantiate_next_executable()
   {
     if (exec_seq_ >= bounds_.max_executables) {
-      // wrap around
+      // wrap around (ring buffer logic)
       exec_seq_ = 0;
     }
     size_t prev_exec_seq_ = exec_seq_;
@@ -226,6 +275,7 @@ public:
       throw std::runtime_error("Executable pool member was NULL");
     }
 
+    // Make sure to clear the executable fields.
     executable_pool_[prev_exec_seq_]->subscription.reset();
     executable_pool_[prev_exec_seq_]->timer.reset();
     executable_pool_[prev_exec_seq_]->service.reset();
@@ -236,6 +286,10 @@ public:
     return executable_pool_[prev_exec_seq_];
   }
 
+  /// General allocate: reserve space in the memory pool reserved by this function.
+  /* \param[in] size Number of bytes to allocate.
+   * \return Pointer to the allocated chunk of memory.
+   */
   void * alloc(size_t size)
   {
     // Extremely naive static allocation strategy
@@ -255,6 +309,9 @@ public:
     return memory_pool_[prev_pool_seq];
   }
 
+  /// Release the allocated memory in the memory pool.
+  /* \param[in] Pointer to deallocate.
+   */
   void free(void * ptr)
   {
     if (memory_map_.count(ptr) == 0) {

rclcpp/include/rclcpp/subscription.hpp

@@ -45,14 +45,20 @@ class Node;
 namespace subscription
 {
 
+/// Virtual base class for subscriptions. This pattern allows us to iterate over different template
+/// specializations of Subscription, among other things.
 class SubscriptionBase
 {
   friend class rclcpp::executor::Executor;
 
-// TODO
 public:
   RCLCPP_SMART_PTR_DEFINITIONS_NOT_COPYABLE(SubscriptionBase);
 
+  /// Default constructor.
+  /* \param[in] node_handle The rmw representation of the node that owns this subscription.
+   * \param[in] topic_name Name of the topic to subscribe to.
+   * \param[in] ignore_local_publications True to ignore local publications (unused).
+   */
   SubscriptionBase(
     std::shared_ptr<rmw_node_t> node_handle,
     rmw_subscription_t * subscription_handle,
@@ -68,6 +74,7 @@ public:
     (void)ignore_local_publications_;
   }
 
+  /// Default destructor.
   virtual ~SubscriptionBase()
   {
     if (subscription_handle_) {
@@ -89,14 +96,26 @@ public:
     }
   }
 
+  /// Get the topic that this subscription is subscribed on.
   const std::string & get_topic_name() const
   {
     return this->topic_name_;
   }
 
+  /// Borrow a new message.
+  // \return Shared pointer to the fresh message.
   virtual std::shared_ptr<void> create_message() = 0;
+
+  /// Check if we need to handle the message, and execute the callback if we do.
+  /* \param[in] message Shared pointer to the message to handle.
+   * \param[in] sender_id Global identifier of the entity that sent this message.
+   */
   virtual void handle_message(std::shared_ptr<void> & message, const rmw_gid_t * sender_id) = 0;
+
+  /// Return the message borrowed in create_message.
+  // \param[in] Shared pointer to the returned message.
   virtual void return_message(std::shared_ptr<void> & message) = 0;
+
   virtual void handle_intra_process_message(rcl_interfaces::msg::IntraProcessMessage & ipm) = 0;
 
 protected:
@@ -114,17 +133,25 @@ private:
 
 };
 
-// TODO
+/// Subscription implementation, templated on the type of message this subscription receives.
 template<typename MessageT>
 class Subscription : public SubscriptionBase
 {
   friend class rclcpp::node::Node;
 
-// TODO
 public:
   using CallbackType = std::function<void(const std::shared_ptr<MessageT> &)>;
   RCLCPP_SMART_PTR_DEFINITIONS(Subscription);
 
+  /// Default constructor.
+  /* The constructor for a subscription is almost never called directly. Instead, subscriptions
+   * should be instantiated through Node::create_subscription.
+   * \param[in] node_handle rmw representation of the node that owns this subscription.
+   * \param[in] topic_name Name of the topic to subscribe to.
+   * \param[in] ignore_local_publications True to ignore local publications (unused).
+   * \param[in] callback User-defined callback to call when a message is received.
+   * \param[in] memory_strategy The memory strategy to be used for managing message memory.
+   */
   Subscription(
     std::shared_ptr<rmw_node_t> node_handle,
     rmw_subscription_t * subscription_handle,
@@ -140,14 +167,21 @@ public:
     matches_any_intra_process_publishers_(nullptr)
   {}
 
+  /// Support dynamically setting the message memory strategy.
+  /* Behavior may be undefined if called while the subscription could be executing.
+   * \param[in] message_memory_strategy Shared pointer to the memory strategy to set.
+   */
   void set_message_memory_strategy(
     typename message_memory_strategy::MessageMemoryStrategy<MessageT>::SharedPtr message_memory_strategy)
   {
     message_memory_strategy_ = message_memory_strategy;
   }
-
   std::shared_ptr<void> create_message()
   {
+    /* The default message memory strategy provides a dynamically allocated message on each call to
+     * create_message, though alternative memory strategies that re-use a preallocated message may be
+     * used (see rclcpp/strategies/message_pool_memory_strategy.hpp).
+     */
     return message_memory_strategy_->borrow_message();
   }
 

rclcpp/include/rclcpp/timer.hpp

@@ -66,12 +66,20 @@ public:
     this->canceled_ = true;
   }
 
+  /// Check how long the timer has until its next scheduled callback.
+  // \return A std::chrono::duration representing the relative time until the next callback.
   virtual std::chrono::nanoseconds
   time_until_trigger() = 0;
 
+  /// Is the clock steady (i.e. is the time between ticks constant?)
+  // \return True if the clock used by this timer is steady.
   virtual bool is_steady() = 0;
 
-  // Interface for externally triggering the timer event
+  /// Check if the timer needs to trigger the callback.
+  /* This function expects its caller to immediately trigger the callback after this function,
+   * since it maintains the last time the callback was triggered.
+   * \return True if the timer needs to trigger.
+   */
   virtual bool check_and_trigger() = 0;
 
 protected:
@@ -82,7 +90,7 @@ protected:
 
 };
 
-// TODO
+/// Generic timer templated on the clock type. Periodically executes a user-specified callback.
 template<class Clock = std::chrono::high_resolution_clock>
 class GenericTimer : public TimerBase
 {
@@ -91,6 +99,10 @@ class GenericTimer : public TimerBase
 public:
   RCLCPP_SMART_PTR_DEFINITIONS(GenericTimer);
 
+  /// Default constructor.
+  /* \param[in] period The interval at which the timer fires.
+   * \param[in] callback User-specified callback function. 
+   */
   GenericTimer(std::chrono::nanoseconds period, CallbackType callback)
   : TimerBase(period, callback), loop_rate_(period)
   {
@@ -99,12 +111,13 @@ public:
     last_triggered_time_ = Clock::now() - period;
   }
 
+  /// Default destructor.
   virtual ~GenericTimer()
   {
+    // Stop the timer from running.
     cancel();
   }
 
-  // return: true to trigger callback on the next "execute_timer" call in executor
   bool
   check_and_trigger()
   {

rclcpp/include/rclcpp/utilities.hpp

@@ -38,10 +38,14 @@
 
 namespace
 {
+/// Represent the status of the global interrupt signal.
 volatile sig_atomic_t g_signal_status = 0;
+/// Guard condition for interrupting the rmw implementation when the global interrupt signal fired.
 rmw_guard_condition_t * g_sigint_guard_cond_handle = \
   rmw_create_guard_condition();
+/// Condition variable for timed sleep (see sleep_for).
 std::condition_variable g_interrupt_condition_variable;
+/// Mutex for protecting the global condition variable.
 std::mutex g_interrupt_mutex;
 
 #ifdef HAS_SIGACTION
@@ -50,6 +54,9 @@ struct sigaction old_action;
 void (* old_signal_handler)(int) = 0;
 #endif
 
+/// When the interrupt signal fires, the signal handler notifies the condition variable to wake up
+/// and triggers the interrupt guard condition, so that all global threads managed by rclcpp
+/// are interrupted.
 void
 #ifdef HAS_SIGACTION
 signal_handler(int signal_value, siginfo_t * siginfo, void * context)
@@ -98,7 +105,10 @@ RMW_THREAD_LOCAL size_t thread_id = 0;
 namespace utilities
 {
 
-// TODO
+/// Initialize communications via the rmw implementation and set up a global signal handler.
+/* \param[in] argc Number of arguments.
+ * \param[in] argv Argument vector. Will eventually be used for passing options to rclcpp.
+ */
 void
 init(int argc, char * argv[])
 {
@@ -139,14 +149,15 @@ init(int argc, char * argv[])
   }
 }
 
-// TODO
+/// Check rclcpp's status.
+// \return True if SIGINT hasn't fired yet, false otherwise.
 bool
 ok()
 {
   return ::g_signal_status == 0;
 }
 
-// TODO
+/// Notify the signal handler and rmw that rclcpp is shutting down.
 void
 shutdown()
 {
@@ -160,13 +171,17 @@ shutdown()
 }
 
 
+/// Get a handle to the rmw guard condition that manages the signal handler.
 rmw_guard_condition_t *
 get_global_sigint_guard_condition()
 {
   return ::g_sigint_guard_cond_handle;
 }
 
-// TODO
+/// Use the global condition variable to block for the specified amount of time.
+/* \param[in] nanoseconds A std::chrono::duration representing how long to sleep for.
+ * \return True if the condition variable did not timeout.
+ */
 bool
 sleep_for(const std::chrono::nanoseconds & nanoseconds)
 {