Feature/available capacity of ipm

rclcpp/include/rclcpp/experimental/buffers/buffer_implementation_base.hpp

@@ -33,6 +33,7 @@ class BufferImplementationBase
 
   virtual void clear() = 0;
   virtual bool has_data() const = 0;
+  virtual size_t available_capacity() const = 0;
 };
 
 }  // namespace buffers

rclcpp/include/rclcpp/experimental/buffers/intra_process_buffer.hpp

@@ -44,6 +44,7 @@ class IntraProcessBufferBase
 
   virtual bool has_data() const = 0;
   virtual bool use_take_shared_method() const = 0;
+  virtual size_t available_capacity() const = 0;
 };
 
 template<
@@ -143,6 +144,11 @@ class TypedIntraProcessBuffer : public IntraProcessBuffer<MessageT, Alloc, Messa
     return std::is_same<BufferT, MessageSharedPtr>::value;
   }
 
+  size_t available_capacity() const override
+  {
+    return buffer_->available_capacity();
+  }
+
 private:
   std::unique_ptr<BufferImplementationBase<BufferT>> buffer_;
 

rclcpp/include/rclcpp/experimental/buffers/ring_buffer_implementation.hpp

@@ -148,6 +148,18 @@ class RingBufferImplementation : public BufferImplementationBase<BufferT>
     return is_full_();
   }
 
+  /// Get the remaining capacity to store messages
+  /**
+   * This member function is thread-safe.
+   *
+   * \return the number of free capacity for new messages
+   */
+  size_t available_capacity() const
+  {
+    std::lock_guard<std::mutex> lock(mutex_);
+    return available_capacity_();
+  }
+
   void clear()
   {
     TRACEPOINT(rclcpp_ring_buffer_clear, static_cast<const void *>(this));
@@ -189,6 +201,17 @@ class RingBufferImplementation : public BufferImplementationBase<BufferT>
     return size_ == capacity_;
   }
 
+  /// Get the remaining capacity to store messages
+  /**
+   * This member function is not thread-safe.
+   *
+   * \return the number of free capacity for new messages
+   */
+  inline size_t available_capacity_() const
+  {
+    return capacity_ - size_;
+  }
+
   size_t capacity_;
 
   std::vector<BufferT> ring_buffer_;

rclcpp/include/rclcpp/experimental/intra_process_manager.hpp

@@ -306,6 +306,11 @@ class IntraProcessManager
   rclcpp::experimental::SubscriptionIntraProcessBase::SharedPtr
   get_subscription_intra_process(uint64_t intra_process_subscription_id);
 
+  /// Return the lowest available capacity for all subscription buffers for a publisher id.
+  RCLCPP_PUBLIC
+  size_t
+  lowest_available_capacity(const uint64_t intra_process_publisher_id) const;
+
 private:
   struct SplittedSubscriptions
   {

rclcpp/include/rclcpp/experimental/subscription_intra_process_base.hpp

@@ -62,6 +62,11 @@ class SubscriptionIntraProcessBase : public rclcpp::Waitable
   void
   add_to_wait_set(rcl_wait_set_t * wait_set) override;
 
+  RCLCPP_PUBLIC
+  virtual
+  size_t
+  available_capacity() const = 0;
+
   bool
   is_ready(rcl_wait_set_t * wait_set) override = 0;
 

rclcpp/include/rclcpp/experimental/subscription_intra_process_buffer.hpp

@@ -169,6 +169,11 @@ class SubscriptionIntraProcessBuffer : public SubscriptionROSMsgIntraProcessBuff
     return buffer_->use_take_shared_method();
   }
 
+  size_t available_capacity() const override
+  {
+    return buffer_->available_capacity();
+  }
+
 protected:
   void
   trigger_guard_condition() override

rclcpp/include/rclcpp/publisher_base.hpp

@@ -215,6 +215,17 @@ class PublisherBase : public std::enable_shared_from_this<PublisherBase>
   std::vector<rclcpp::NetworkFlowEndpoint>
   get_network_flow_endpoints() const;
 
+  /// Return the lowest available capacity for all subscription buffers.
+  /**
+   * For intraprocess communication return the lowest buffer capacity for all subscriptions.
+   * If intraprocess is disabled or no intraprocess subscriptions present, return maximum of size_t.
+   * On failure return 0.
+   * \return lowest buffer capacity for all subscriptions
+   */
+  RCLCPP_PUBLIC
+  size_t
+  lowest_available_ipm_capacity() const;
+
   /// Wait until all published messages are acknowledged or until the specified timeout elapses.
   /**
    * This method waits until all published messages are acknowledged by all matching

rclcpp/src/rclcpp/intra_process_manager.cpp

@@ -225,5 +225,52 @@ IntraProcessManager::can_communicate(
   return true;
 }
 
+size_t
+IntraProcessManager::lowest_available_capacity(const uint64_t intra_process_publisher_id) const
+{
+  size_t capacity = std::numeric_limits<size_t>::max();
+
+  auto publisher_it = pub_to_subs_.find(intra_process_publisher_id);
+  if (publisher_it == pub_to_subs_.end()) {
+    // Publisher is either invalid or no longer exists.
+    RCLCPP_WARN(
+      rclcpp::get_logger("rclcpp"),
+      "Calling lowest_available_capacity for invalid or no longer existing publisher id");
+    return 0u;
+  }
+
+  if (publisher_it->second.take_shared_subscriptions.empty() &&
+    publisher_it->second.take_ownership_subscriptions.empty())
+  {
+    // no subscriptions available
+    return 0u;
+  }
+
+  auto available_capacity = [this, &capacity](const uint64_t intra_process_subscription_id)
+    {
+      auto subscription_it = subscriptions_.find(intra_process_subscription_id);
+      if (subscription_it != subscriptions_.end()) {
+        auto subscription = subscription_it->second.lock();
+        if (subscription) {
+          capacity = std::min(capacity, subscription->available_capacity());
+        }
+      } else {
+        // Subscription is either invalid or no longer exists.
+        RCLCPP_WARN(
+          rclcpp::get_logger("rclcpp"),
+          "Calling available_capacity for invalid or no longer existing subscription id");
+      }
+    };
+
+  for (const auto sub_id : publisher_it->second.take_shared_subscriptions) {
+    available_capacity(sub_id);
+  }
+
+  for (const auto sub_id : publisher_it->second.take_ownership_subscriptions) {
+    available_capacity(sub_id);
+  }
+
+  return capacity;
+}
 }  // namespace experimental
 }  // namespace rclcpp

rclcpp/src/rclcpp/publisher_base.cpp

@@ -384,3 +384,22 @@ std::vector<rclcpp::NetworkFlowEndpoint> PublisherBase::get_network_flow_endpoin
 
   return network_flow_endpoint_vector;
 }
+
+size_t PublisherBase::lowest_available_ipm_capacity() const
+{
+  if (!intra_process_is_enabled_) {
+    return 0u;
+  }
+
+  auto ipm = weak_ipm_.lock();
+
+  if (!ipm) {
+    // TODO(ivanpauno): should this raise an error?
+    RCLCPP_WARN(
+      rclcpp::get_logger("rclcpp"),
+      "Intra process manager died for a publisher.");
+    return 0u;
+  }
+
+  return ipm->lowest_available_capacity(intra_process_publisher_id_);
+}

rclcpp/test/rclcpp/test_intra_process_buffer.cpp

@@ -238,3 +238,75 @@ TEST(TestIntraProcessBuffer, unique_buffer_consume) {
   EXPECT_EQ(original_value, *popped_unique_msg);
   EXPECT_EQ(original_message_pointer, popped_message_pointer);
 }
+
+/*
+  Check the available buffer capacity while storing and consuming data from an intra-process
+  buffer.
+  The initial available buffer capacity should equal the buffer size.
+  Inserting a message should decrease the available buffer capacity by 1.
+  Consuming a message should increase the available buffer capacity by 1.
+ */
+TEST(TestIntraProcessBuffer, available_capacity) {
+  using MessageT = char;
+  using Alloc = std::allocator<void>;
+  using Deleter = std::default_delete<MessageT>;
+  using SharedMessageT = std::shared_ptr<const MessageT>;
+  using UniqueMessageT = std::unique_ptr<MessageT, Deleter>;
+  using UniqueIntraProcessBufferT = rclcpp::experimental::buffers::TypedIntraProcessBuffer<
+    MessageT, Alloc, Deleter, UniqueMessageT>;
+
+  constexpr auto history_depth = 5u;
+
+  auto buffer_impl =
+    std::make_unique<rclcpp::experimental::buffers::RingBufferImplementation<UniqueMessageT>>(
+    history_depth);
+
+  UniqueIntraProcessBufferT intra_process_buffer(std::move(buffer_impl));
+
+  EXPECT_EQ(history_depth, intra_process_buffer.available_capacity());
+
+  auto original_unique_msg = std::make_unique<char>('a');
+  auto original_message_pointer = reinterpret_cast<std::uintptr_t>(original_unique_msg.get());
+  auto original_value = *original_unique_msg;
+
+  intra_process_buffer.add_unique(std::move(original_unique_msg));
+
+  EXPECT_EQ(history_depth - 1u, intra_process_buffer.available_capacity());
+
+  SharedMessageT popped_shared_msg;
+  popped_shared_msg = intra_process_buffer.consume_shared();
+  auto popped_message_pointer = reinterpret_cast<std::uintptr_t>(popped_shared_msg.get());
+
+  EXPECT_EQ(history_depth, intra_process_buffer.available_capacity());
+  EXPECT_EQ(original_value, *popped_shared_msg);
+  EXPECT_EQ(original_message_pointer, popped_message_pointer);
+
+  original_unique_msg = std::make_unique<char>('b');
+  original_message_pointer = reinterpret_cast<std::uintptr_t>(original_unique_msg.get());
+  original_value = *original_unique_msg;
+
+  intra_process_buffer.add_unique(std::move(original_unique_msg));
+
+  auto second_unique_msg = std::make_unique<char>('c');
+  auto second_message_pointer = reinterpret_cast<std::uintptr_t>(second_unique_msg.get());
+  auto second_value = *second_unique_msg;
+
+  intra_process_buffer.add_unique(std::move(second_unique_msg));
+
+  EXPECT_EQ(history_depth - 2u, intra_process_buffer.available_capacity());
+
+  UniqueMessageT popped_unique_msg;
+  popped_unique_msg = intra_process_buffer.consume_unique();
+  popped_message_pointer = reinterpret_cast<std::uintptr_t>(popped_unique_msg.get());
+
+  EXPECT_EQ(history_depth - 1u, intra_process_buffer.available_capacity());
+  EXPECT_EQ(original_value, *popped_unique_msg);
+  EXPECT_EQ(original_message_pointer, popped_message_pointer);
+
+  popped_unique_msg = intra_process_buffer.consume_unique();
+  popped_message_pointer = reinterpret_cast<std::uintptr_t>(popped_unique_msg.get());
+
+  EXPECT_EQ(history_depth, intra_process_buffer.available_capacity());
+  EXPECT_EQ(second_value, *popped_unique_msg);
+  EXPECT_EQ(second_message_pointer, popped_message_pointer);
+}