From e526e48df837d282f4a59554750769b21bbc2104 Mon Sep 17 00:00:00 2001
From: Lunkhound <lunkhound@gmail.com>
Date: Tue, 13 Mar 2018 04:19:02 -0700
Subject: [PATCH] parallel solver: slightly overallocate to reduce how often
 allocation is needed

---
 .../ConstraintSolver/btBatchedConstraints.cpp |  6 ++++++
 .../btSequentialImpulseConstraintSolverMt.cpp | 20 +++++++++++++++----
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/BulletDynamics/ConstraintSolver/btBatchedConstraints.cpp b/src/BulletDynamics/ConstraintSolver/btBatchedConstraints.cpp
index 310601659..84a00dc63 100644
--- a/src/BulletDynamics/ConstraintSolver/btBatchedConstraints.cpp
+++ b/src/BulletDynamics/ConstraintSolver/btBatchedConstraints.cpp
@@ -892,6 +892,12 @@ static void setupSpatialGridBatchesMt(
         memHelper.addChunk( (void**) &constraintBatchIds, sizeof( int ) * numConstraints );
         memHelper.addChunk( (void**) &constraintRowBatchIds, sizeof( int ) * numConstraintRows );
         size_t scratchSize = memHelper.getSizeToAllocate();
+        // if we need to reallocate
+        if (scratchMemory->capacity() < scratchSize)
+        {
+            // allocate 6.25% extra to avoid repeated reallocs
+            scratchMemory->reserve( scratchSize + scratchSize/16 );
+        }
         scratchMemory->resizeNoInitialize( scratchSize );
         char* memPtr = &scratchMemory->at(0);
         memHelper.setChunkPointers( memPtr );
diff --git a/src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolverMt.cpp b/src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolverMt.cpp
index b9ad17a03..4ccf7b247 100644
--- a/src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolverMt.cpp
+++ b/src/BulletDynamics/ConstraintSolver/btSequentialImpulseConstraintSolverMt.cpp
@@ -568,10 +568,22 @@ void btSequentialImpulseConstraintSolverMt::allocAllContactConstraints(btPersist
                 }
             }
         }
-        m_tmpSolverContactConstraintPool.resizeNoInitialize(numContacts);
-        m_rollingFrictionIndexTable.resizeNoInitialize(numContacts);
-        m_tmpSolverContactFrictionConstraintPool.resizeNoInitialize(numContacts*m_numFrictionDirections);
-        m_tmpSolverContactRollingFrictionConstraintPool.resizeNoInitialize(numRollingFrictionConstraints);
+        {
+            BT_PROFILE( "allocPools" );
+            if ( m_tmpSolverContactConstraintPool.capacity() < numContacts )
+            {
+                // if we need to reallocate, reserve some extra so we don't have to reallocate again next frame
+                int extraReserve = numContacts / 16;
+                m_tmpSolverContactConstraintPool.reserve( numContacts + extraReserve );
+                m_rollingFrictionIndexTable.reserve( numContacts + extraReserve );
+                m_tmpSolverContactFrictionConstraintPool.reserve( ( numContacts + extraReserve )*m_numFrictionDirections );
+                m_tmpSolverContactRollingFrictionConstraintPool.reserve( numRollingFrictionConstraints + extraReserve );
+            }
+            m_tmpSolverContactConstraintPool.resizeNoInitialize( numContacts );
+            m_rollingFrictionIndexTable.resizeNoInitialize( numContacts );
+            m_tmpSolverContactFrictionConstraintPool.resizeNoInitialize( numContacts*m_numFrictionDirections );
+            m_tmpSolverContactRollingFrictionConstraintPool.resizeNoInitialize( numRollingFrictionConstraints );
+        }
     }
     {
         AllocContactConstraintsLoop loop(this, &cachedInfoArray[0]);