From 3c29d865756fc290e412f7a74cda365d575f1a12 Mon Sep 17 00:00:00 2001
From: Sebastian Brockmeyer <937096+sebrockm@users.noreply.github.com>
Date: Sun, 15 Oct 2023 00:21:12 +0200
Subject: [PATCH] Push finished LBs back for reevaluation

---
 tsplp/src/BranchAndCutQueue.cpp | 34 +++++++++++++++++++++++++++++----
 tsplp/src/BranchAndCutQueue.hpp |  2 ++
 tsplp/src/MtspModel.cpp         | 19 +++++++++++++++---
 3 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/tsplp/src/BranchAndCutQueue.cpp b/tsplp/src/BranchAndCutQueue.cpp
index e08cd1d..6115e9f 100644
--- a/tsplp/src/BranchAndCutQueue.cpp
+++ b/tsplp/src/BranchAndCutQueue.cpp
@@ -66,6 +66,29 @@ void tsplp::BranchAndCutQueue::UpdateCurrentLowerBound(size_t threadId, double c
     m_workedOnLowerBounds.at(threadId) = currentLowerBound;
 }
 
+void tsplp::BranchAndCutQueue::PushResult(double lowerBound)
+{
+    bool needsNotify = false;
+
+    {
+        std::unique_lock lock { m_mutex };
+
+        if (m_isCleared)
+            return;
+
+        if (lowerBound < CalculateLowerBound())
+            throw std::logic_error("cannot push smaller lower bound");
+
+        needsNotify = m_heap.empty() && m_workedOnCount > 0;
+
+        m_heap.push_back({ lowerBound, {}, {}, true });
+        std::push_heap(begin(m_heap), end(m_heap), m_comparer);
+    }
+
+    if (needsNotify)
+        m_cv.notify_one();
+}
+
 void tsplp::BranchAndCutQueue::Push(
     double lowerBound, std::vector<Variable> fixedVariables0, std::vector<Variable> fixedVariables1)
 {
@@ -82,7 +105,8 @@ void tsplp::BranchAndCutQueue::Push(
 
         needsNotify = m_heap.empty() && m_workedOnCount > 0;
 
-        m_heap.push_back({ lowerBound, std::move(fixedVariables0), std::move(fixedVariables1) });
+        m_heap.push_back(
+            { lowerBound, std::move(fixedVariables0), std::move(fixedVariables1), false });
         std::push_heap(begin(m_heap), end(m_heap), m_comparer);
     }
 
@@ -116,11 +140,12 @@ void tsplp::BranchAndCutQueue::PushBranch(
         copyFixedVariables0.insert(
             copyFixedVariables0.end(), recursivelyFixed0.begin(), recursivelyFixed0.end());
 
-        m_heap.push_back({ lowerBound, std::move(fixedVariables0), std::move(fixedVariables1) });
+        m_heap.push_back(
+            { lowerBound, std::move(fixedVariables0), std::move(fixedVariables1), false });
         std::push_heap(begin(m_heap), end(m_heap), m_comparer);
 
         m_heap.push_back(
-            { lowerBound, std::move(copyFixedVariables0), std::move(copyFixedVariables1) });
+            { lowerBound, std::move(copyFixedVariables0), std::move(copyFixedVariables1), false });
         std::push_heap(begin(m_heap), end(m_heap), m_comparer);
     }
 
@@ -173,7 +198,7 @@ void tsplp::BranchAndCutQueue::Print() const
     std::unique_lock lock { m_mutex };
 
     std::cout << "BranchAndCutQueue:\nHeap:";
-    for (const auto& [lb, v0, v1] : m_heap)
+    for (const auto& [lb, v0, v1, r] : m_heap)
     {
         std::cout << "LB:" << lb << ", v0:";
         for (const auto& v : v0)
@@ -181,6 +206,7 @@ void tsplp::BranchAndCutQueue::Print() const
         std::cout << " v1:";
         for (const auto& v : v1)
             std::cout << v.GetId() << ",";
+        std::cout << " is result: " << r;
         std::cout << std::endl;
     }
 
diff --git a/tsplp/src/BranchAndCutQueue.hpp b/tsplp/src/BranchAndCutQueue.hpp
index b54abd0..60af5b0 100644
--- a/tsplp/src/BranchAndCutQueue.hpp
+++ b/tsplp/src/BranchAndCutQueue.hpp
@@ -18,6 +18,7 @@ struct SData
     double LowerBound = -std::numeric_limits<double>::max();
     std::vector<Variable> FixedVariables0 {};
     std::vector<Variable> FixedVariables1 {};
+    bool IsResult = false;
     bool operator>(SData const& sd) const { return LowerBound > sd.LowerBound; }
 };
 
@@ -67,6 +68,7 @@ class BranchAndCutQueue
 
     void ClearAll();
     void UpdateCurrentLowerBound(size_t threadId, double currentLowerBound);
+    void PushResult(double lowerBound);
     void Push(
         double lowerBound, std::vector<Variable> fixedVariables0,
         std::vector<Variable> fixedVariables1);
diff --git a/tsplp/src/MtspModel.cpp b/tsplp/src/MtspModel.cpp
index 9731639..68f075c 100644
--- a/tsplp/src/MtspModel.cpp
+++ b/tsplp/src/MtspModel.cpp
@@ -352,6 +352,20 @@ void tsplp::MtspModel::BranchAndCutSolve(
 
             auto& [sdata, nodeDoneNotifier] = *top;
 
+            if (sdata.IsResult)
+            {
+                const auto globalLowerBound
+                    = m_bestResult.UpdateLowerBound(queue.GetLowerBound()).Lower;
+                if (sdata.LowerBound > globalLowerBound)
+                {
+                    // As this was just popped but is not the global LB, this means other threads
+                    // are currently working on smaller LBs. Push it back to be reevaluated later.
+                    queue.PushResult(sdata.LowerBound);
+                }
+
+                continue;
+            }
+
             fixedVariables0 = std::move(sdata.FixedVariables0);
             fixedVariables1 = std::move(sdata.FixedVariables1);
 
@@ -414,6 +428,7 @@ void tsplp::MtspModel::BranchAndCutSolve(
                           << ": currentLowerBound=" << currentLowerBound
                           << " >= currentUpperBound=" << currentUpperBound << " skipping"
                           << std::endl;
+                queue.PushResult(currentLowerBound);
                 continue;
             }
 
@@ -492,14 +507,12 @@ void tsplp::MtspModel::BranchAndCutSolve(
                         currentLowerBound, CreatePathsFromVariables(model));
                 }
 
-                // make sure the this lower bound is set if it is the global one
-                m_bestResult.UpdateLowerBound(queue.GetLowerBound());
-
                 {
                     std::unique_lock lock { print_mutex };
                     std::cout << m_name << ", thread " << threadId
                               << ": non-fractional solution found: " << currentLowerBound
                               << std::endl;
+                    queue.PushResult(currentLowerBound);
                     continue;
                 }
             }