From f64eef876ab1591ee057aaab138fd99b3c24b044 Mon Sep 17 00:00:00 2001
From: gaschler <gaschlera@gmail.com>
Date: Tue, 16 Jan 2018 16:21:22 +0100
Subject: [PATCH] Optional GetBlockingTrajectoryId (#820)

[RFC=0008](https://github.com/googlecartographer/rfcs/blob/master/text/0008-collator-interface.md)
---
 cartographer/sensor/collator.cc          | 4 ++--
 cartographer/sensor/collator.h           | 2 +-
 cartographer/sensor/collator_interface.h | 8 +++++---
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/cartographer/sensor/collator.cc b/cartographer/sensor/collator.cc
index 3b18e33..2fbcfb2 100644
--- a/cartographer/sensor/collator.cc
+++ b/cartographer/sensor/collator.cc
@@ -47,8 +47,8 @@ void Collator::AddSensorData(const int trajectory_id,
 
 void Collator::Flush() { queue_.Flush(); }
 
-int Collator::GetBlockingTrajectoryId() const {
-  return queue_.GetBlocker().trajectory_id;
+common::optional<int> Collator::GetBlockingTrajectoryId() const {
+  return common::optional<int>(queue_.GetBlocker().trajectory_id);
 }
 
 }  // namespace sensor
diff --git a/cartographer/sensor/collator.h b/cartographer/sensor/collator.h
index abf0e8c..c696613 100644
--- a/cartographer/sensor/collator.h
+++ b/cartographer/sensor/collator.h
@@ -47,7 +47,7 @@ class Collator : public CollatorInterface {
 
   void Flush() override;
 
-  int GetBlockingTrajectoryId() const override;
+  common::optional<int> GetBlockingTrajectoryId() const override;
 
  private:
   // Queue keys are a pair of trajectory ID and sensor identifier.
diff --git a/cartographer/sensor/collator_interface.h b/cartographer/sensor/collator_interface.h
index 2183a08..eb1d787 100644
--- a/cartographer/sensor/collator_interface.h
+++ b/cartographer/sensor/collator_interface.h
@@ -22,6 +22,7 @@
 #include <unordered_set>
 #include <vector>
 
+#include "cartographer/common/optional.h"
 #include "cartographer/sensor/data.h"
 
 namespace cartographer {
@@ -57,9 +58,10 @@ class CollatorInterface {
   virtual void Flush() = 0;
 
   // Must only be called if at least one unfinished trajectory exists. Returns
-  // the ID of the trajectory that needs more data before the Collator is
-  // unblocked.
-  virtual int GetBlockingTrajectoryId() const = 0;
+  // the ID of the trajectory that needs more data before CollatorInterface is
+  // unblocked. Returns 'nullopt' for implementations that do not wait for a
+  // particular trajectory.
+  virtual common::optional<int> GetBlockingTrajectoryId() const = 0;
 };
 
 }  // namespace sensor