From 05cb45ca14469f92f07c11f35a599ac6f87539fa Mon Sep 17 00:00:00 2001
From: Stephen Seo <seo.disparate@gmail.com>
Date: Tue, 3 Sep 2019 15:15:09 +0900
Subject: [PATCH] Prevent exceptions being thrown in TSQueue

TSQueue's top() and top_and_pop() now return std::optional<T> instead of
just T.
---
 cpp_impl/src/TSQueue.hpp          | 21 ++++++++++++++-------
 cpp_impl/src/UDPConnection.cpp    |  4 ++--
 cpp_impl/src/test/TestTSQueue.cpp |  2 +-
 3 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/cpp_impl/src/TSQueue.hpp b/cpp_impl/src/TSQueue.hpp
index 1985eee..81dadf5 100644
--- a/cpp_impl/src/TSQueue.hpp
+++ b/cpp_impl/src/TSQueue.hpp
@@ -6,6 +6,7 @@
 #include <cstdlib>
 #include <memory>
 #include <mutex>
+#include <optional>
 
 #include <RB/RingBuffer.hpp>
 
@@ -23,9 +24,9 @@ class TSQueue {
     TSQueue &operator=(TSQueue &&other);
 
     bool push(const T &data);
-    T top();
+    std::optional<T> top();
     bool pop();
-    T top_and_pop();
+    std::optional<T> top_and_pop();
     void clear();
     void changeCapacity(unsigned int newCapacity);
     unsigned int size();
@@ -81,9 +82,12 @@ bool TSQueue<T>::push(const T &data) {
 }
 
 template <typename T>
-T TSQueue<T>::top() {
+std::optional<T> TSQueue<T>::top() {
     std::lock_guard<std::mutex> lock(mutex);
-    T value = rb.top();
+    std::optional<T> value = std::nullopt;
+    if(!rb.empty()) {
+        value = rb.top();
+    }
     return value;
 }
 
@@ -98,10 +102,13 @@ bool TSQueue<T>::pop() {
 }
 
 template <typename T>
-T TSQueue<T>::top_and_pop() {
+std::optional<T> TSQueue<T>::top_and_pop() {
     std::lock_guard<std::mutex> lock(mutex);
-    T value = rb.top();
-    rb.pop();
+    std::optional<T> value = std::nullopt;
+    if(!rb.empty()) {
+        value = rb.top();
+        rb.pop();
+    }
     return value;
 }
 
diff --git a/cpp_impl/src/UDPConnection.cpp b/cpp_impl/src/UDPConnection.cpp
index 7292a02..4b924bd 100644
--- a/cpp_impl/src/UDPConnection.cpp
+++ b/cpp_impl/src/UDPConnection.cpp
@@ -496,11 +496,11 @@ void UDPC_update(UDPC_HContext ctx) {
             bool isResending = false;
             if(!iter->second.priorityPkts.empty()) {
                 // TODO verify getting struct copy is valid
-                pInfo = iter->second.priorityPkts.top();
+                pInfo = std::move(iter->second.priorityPkts.top().value());
                 iter->second.priorityPkts.pop();
                 isResending = true;
             } else {
-                pInfo = iter->second.sendPkts.top();
+                pInfo = std::move(iter->second.sendPkts.top().value());
                 iter->second.sendPkts.pop();
             }
             std::unique_ptr<char[]> buf = std::make_unique<char[]>(20 + pInfo.dataSize);
diff --git a/cpp_impl/src/test/TestTSQueue.cpp b/cpp_impl/src/test/TestTSQueue.cpp
index 58e2a7d..fc6dc20 100644
--- a/cpp_impl/src/test/TestTSQueue.cpp
+++ b/cpp_impl/src/test/TestTSQueue.cpp
@@ -133,7 +133,7 @@ TEST(TSQueue, Concurrent)
 
     int top;
     for(int i = 0; i < 4; ++i) {
-        top = q.top();
+        top = q.top().value();
         EXPECT_TRUE(q.pop());
         EXPECT_EQ(q.size(), 3 - i);
         printf("%d ", top);