Merge branch 'sync_sync_with_async' into 'master'

Merge logic of sync and async physics simulation

See merge request OpenMW/openmw!1250

apps/openmw/mwphysics/mtphysics.cpp

@@ -22,31 +22,82 @@
 
 namespace
 {
-    /// @brief A scoped lock that is either shared or exclusive depending on configuration
+    /// @brief A scoped lock that is either exclusive or inexistent depending on configuration
+    template<class Mutex>
+    class MaybeExclusiveLock
+    {
+        public:
+            /// @param mutex a mutex
+            /// @param threadCount decide wether the excluse lock will be taken
+            MaybeExclusiveLock(Mutex& mutex, int threadCount) : mMutex(mutex), mThreadCount(threadCount)
+            {
+                assert(threadCount >= 0);
+                if (mThreadCount > 0)
+                    mMutex.lock();
+            }
+
+            ~MaybeExclusiveLock()
+            {
+                if (mThreadCount > 0)
+                    mMutex.unlock();
+            }
+
+        private:
+            Mutex& mMutex;
+            unsigned int mThreadCount;
+    };
+
+    /// @brief A scoped lock that is either shared or inexistent depending on configuration
     template<class Mutex>
     class MaybeSharedLock
     {
         public:
             /// @param mutex a shared mutex
-            /// @param canBeSharedLock decide wether the lock will be shared or exclusive
+            /// @param threadCount decide wether the shared lock will be taken
-            MaybeSharedLock(Mutex& mutex, bool canBeSharedLock) : mMutex(mutex), mCanBeSharedLock(canBeSharedLock)
+            MaybeSharedLock(Mutex& mutex, int threadCount) : mMutex(mutex), mThreadCount(threadCount)
             {
-                if (mCanBeSharedLock)
+                assert(threadCount >= 0);
+                if (mThreadCount > 0)
                     mMutex.lock_shared();
-                else
-                    mMutex.lock();
             }
 
             ~MaybeSharedLock()
             {
-                if (mCanBeSharedLock)
+                if (mThreadCount > 0)
                     mMutex.unlock_shared();
-                else
+            }
+
+        private:
+            Mutex& mMutex;
+            unsigned int mThreadCount;
+    };
+
+    /// @brief A scoped lock that is either shared, exclusive or inexistent depending on configuration
+    template<class Mutex>
+    class MaybeLock
+    {
+        public:
+            /// @param mutex a shared mutex
+            /// @param threadCount decide wether the lock will be shared, exclusive or inexistent
+            MaybeLock(Mutex& mutex, int threadCount) : mMutex(mutex), mThreadCount(threadCount)
+            {
+                assert(threadCount >= 0);
+                if (mThreadCount > 1)
+                    mMutex.lock_shared();
+                else if(mThreadCount == 1)
+                    mMutex.lock();
+            }
+
+            ~MaybeLock()
+            {
+                if (mThreadCount > 1)
+                    mMutex.unlock_shared();
+                else if(mThreadCount == 1)
                     mMutex.unlock();
             }
         private:
             Mutex& mMutex;
-            bool mCanBeSharedLock;
+            unsigned int mThreadCount;
     };
 
     bool isUnderWater(const MWPhysics::ActorFrameData& actorData)
@@ -54,29 +105,6 @@ namespace
         return actorData.mPosition.z() < actorData.mSwimLevel;
     }
 
-    void handleFall(MWPhysics::ActorFrameData& actorData, bool simulationPerformed)
-    {
-        const float heightDiff = actorData.mPosition.z() - actorData.mOldHeight;
-
-        const bool isStillOnGround = (simulationPerformed && actorData.mWasOnGround && actorData.mIsOnGround);
-
-        if (isStillOnGround || actorData.mFlying || isUnderWater(actorData) || actorData.mSlowFall < 1)
-            actorData.mNeedLand = true;
-        else if (heightDiff < 0)
-            actorData.mFallHeight += heightDiff;
-    }
-
-    void updateMechanics(MWPhysics::Actor& actor, MWPhysics::ActorFrameData& actorData)
-    {
-        auto ptr = actor.getPtr();
-
-        MWMechanics::CreatureStats& stats = ptr.getClass().getCreatureStats(ptr);
-        if (actorData.mNeedLand)
-            stats.land(ptr == MWMechanics::getPlayer() && (actorData.mFlying || isUnderWater(actorData)));
-        else if (actorData.mFallHeight < 0)
-            stats.addToFallHeight(-actorData.mFallHeight);
-    }
-
     osg::Vec3f interpolateMovements(MWPhysics::Actor& actor, MWPhysics::ActorFrameData& actorData, float timeAccum, float physicsDt)
     {
         const float interpolationFactor = std::clamp(timeAccum / physicsDt, 0.0f, 1.0f);
@@ -85,14 +113,14 @@ namespace
 
     namespace Config
     {
-        /// @return either the number of thread as configured by the user, or 1 if Bullet doesn't support multithreading
+        /// @return either the number of thread as configured by the user, or 1 if Bullet doesn't support multithreading and user requested more than 1 background threads
-        int computeNumThreads(bool& threadSafeBullet)
+        int computeNumThreads()
         {
             int wantedThread = Settings::Manager::getInt("async num threads", "Physics");
 
             auto broad = std::make_unique<btDbvtBroadphase>();
             auto maxSupportedThreads = broad->m_rayTestStacks.size();
-            threadSafeBullet = (maxSupportedThreads > 1);
+            auto threadSafeBullet = (maxSupportedThreads > 1);
             if (!threadSafeBullet && wantedThread > 1)
             {
                 Log(Debug::Warning) << "Bullet was not compiled with multithreading support, 1 async thread will be used";
@@ -111,6 +139,7 @@ namespace MWPhysics
           , mTimeAccum(0.f)
           , mCollisionWorld(collisionWorld)
           , mDebugDrawer(debugDrawer)
+          , mNumThreads(Config::computeNumThreads())
           , mNumJobs(0)
           , mRemainingSteps(0)
           , mLOSCacheExpiry(Settings::Manager::getInt("lineofsight keep inactive cache", "Physics"))
@@ -130,8 +159,6 @@ namespace MWPhysics
           , mTimeEnd(0)
           , mFrameStart(0)
     {
-        mNumThreads = Config::computeNumThreads(mThreadSafeBullet);
-
         if (mNumThreads >= 1)
         {
             for (int i = 0; i < mNumThreads; ++i)
@@ -151,11 +178,12 @@ namespace MWPhysics
 
     PhysicsTaskScheduler::~PhysicsTaskScheduler()
     {
-        std::unique_lock lock(mSimulationMutex);
+        {
+            MaybeExclusiveLock lock(mSimulationMutex, mNumThreads);
             mQuit = true;
             mNumJobs = 0;
             mRemainingSteps = 0;
-        lock.unlock();
+        }
         mHasJob.notify_all();
         for (auto& thread : mThreads)
             thread.join();
@@ -212,7 +240,7 @@ namespace MWPhysics
         // This function run in the main thread.
         // While the mSimulationMutex is held, background physics threads can't run.
 
-        std::unique_lock lock(mSimulationMutex);
+        MaybeExclusiveLock lock(mSimulationMutex, mNumThreads);
         assert(actors.size() == actorsData.size());
 
         double timeStart = mTimer->tick();
@@ -220,11 +248,8 @@ namespace MWPhysics
         // start by finishing previous background computation
         if (mNumThreads != 0)
         {
-            for (size_t i = 0; i < mActors.size(); ++i)
+            syncWithMainThread();
-            {
+
-                updateMechanics(*mActors[i], mActorsFrameData[i]);
-                updateActor(*mActors[i], mActorsFrameData[i], mAdvanceSimulation, mTimeAccum, mPhysicsDt);
-            }
             if(mAdvanceSimulation)
                 mAsyncBudget.update(mTimer->delta_s(mAsyncStartTime, mTimeEnd), mPrevStepCount, mBudgetCursor);
             updateStats(frameStart, frameNumber, stats);
@@ -258,14 +283,14 @@ namespace MWPhysics
 
         if (mNumThreads == 0)
         {
-            syncComputation();
+            doSimulation();
+            syncWithMainThread();
             if(mAdvanceSimulation)
                 mBudget.update(mTimer->delta_s(timeStart, mTimer->tick()), numSteps, mBudgetCursor);
             return;
         }
 
         mAsyncStartTime = mTimer->tick();
-        lock.unlock();
         mHasJob.notify_all();
         if (mAdvanceSimulation)
             mBudget.update(mTimer->delta_s(timeStart, mTimer->tick()), 1, mBudgetCursor);
@@ -273,7 +298,7 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::resetSimulation(const ActorMap& actors)
     {
-        std::unique_lock lock(mSimulationMutex);
+        MaybeExclusiveLock lock(mSimulationMutex, mNumThreads);
         mBudget.reset(mDefaultPhysicsDt);
         mAsyncBudget.reset(0.0f);
         mActors.clear();
@@ -287,25 +312,25 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::rayTest(const btVector3& rayFromWorld, const btVector3& rayToWorld, btCollisionWorld::RayResultCallback& resultCallback) const
     {
-        MaybeSharedLock lock(mCollisionWorldMutex, mThreadSafeBullet);
+        MaybeLock lock(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->rayTest(rayFromWorld, rayToWorld, resultCallback);
     }
 
     void PhysicsTaskScheduler::convexSweepTest(const btConvexShape* castShape, const btTransform& from, const btTransform& to, btCollisionWorld::ConvexResultCallback& resultCallback) const
     {
-        MaybeSharedLock lock(mCollisionWorldMutex, mThreadSafeBullet);
+        MaybeLock lock(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->convexSweepTest(castShape, from, to, resultCallback);
     }
 
     void PhysicsTaskScheduler::contactTest(btCollisionObject* colObj, btCollisionWorld::ContactResultCallback& resultCallback)
     {
-        std::shared_lock lock(mCollisionWorldMutex);
+        MaybeSharedLock lock(mCollisionWorldMutex, mNumThreads);
         ContactTestWrapper::contactTest(mCollisionWorld, colObj, resultCallback);
     }
 
     std::optional<btVector3> PhysicsTaskScheduler::getHitPoint(const btTransform& from, btCollisionObject* target)
     {
-        MaybeSharedLock lock(mCollisionWorldMutex, mThreadSafeBullet);
+        MaybeLock lock(mCollisionWorldMutex, mNumThreads);
         // target the collision object's world origin, this should be the center of the collision object
         btTransform rayTo;
         rayTo.setIdentity();
@@ -322,33 +347,33 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::aabbTest(const btVector3& aabbMin, const btVector3& aabbMax, btBroadphaseAabbCallback& callback)
     {
-        std::shared_lock lock(mCollisionWorldMutex);
+        MaybeSharedLock lock(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->getBroadphase()->aabbTest(aabbMin, aabbMax, callback);
     }
 
     void PhysicsTaskScheduler::getAabb(const btCollisionObject* obj, btVector3& min, btVector3& max)
     {
-        std::shared_lock lock(mCollisionWorldMutex);
+        MaybeSharedLock lock(mCollisionWorldMutex, mNumThreads);
         obj->getCollisionShape()->getAabb(obj->getWorldTransform(), min, max);
     }
 
     void PhysicsTaskScheduler::setCollisionFilterMask(btCollisionObject* collisionObject, int collisionFilterMask)
     {
-        std::unique_lock lock(mCollisionWorldMutex);
+        MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
         collisionObject->getBroadphaseHandle()->m_collisionFilterMask = collisionFilterMask;
     }
 
     void PhysicsTaskScheduler::addCollisionObject(btCollisionObject* collisionObject, int collisionFilterGroup, int collisionFilterMask)
     {
         mCollisionObjects.insert(collisionObject);
-        std::unique_lock lock(mCollisionWorldMutex);
+        MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->addCollisionObject(collisionObject, collisionFilterGroup, collisionFilterMask);
     }
 
     void PhysicsTaskScheduler::removeCollisionObject(btCollisionObject* collisionObject)
     {
         mCollisionObjects.erase(collisionObject);
-        std::unique_lock lock(mCollisionWorldMutex);
+        MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->removeCollisionObject(collisionObject);
     }
 
@@ -360,14 +385,14 @@ namespace MWPhysics
         }
         else
         {
-            std::unique_lock lock(mUpdateAabbMutex);
+            MaybeExclusiveLock lock(mUpdateAabbMutex, mNumThreads);
             mUpdateAabb.insert(std::move(ptr));
         }
     }
 
     bool PhysicsTaskScheduler::getLineOfSight(const std::shared_ptr<Actor>& actor1, const std::shared_ptr<Actor>& actor2)
     {
-        std::unique_lock lock(mLOSCacheMutex);
+        MaybeExclusiveLock lock(mLOSCacheMutex, mNumThreads);
 
         auto req = LOSRequest(actor1, actor2);
         auto result = std::find(mLOSCache.begin(), mLOSCache.end(), req);
@@ -383,7 +408,7 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::refreshLOSCache()
     {
-        std::shared_lock lock(mLOSCacheMutex);
+        MaybeSharedLock lock(mLOSCacheMutex, mNumThreads);
         int job = 0;
         int numLOS = mLOSCache.size();
         while ((job = mNextLOS.fetch_add(1, std::memory_order_relaxed)) < numLOS)
@@ -402,7 +427,7 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::updateAabbs()
     {
-        std::scoped_lock lock(mUpdateAabbMutex);
+        MaybeExclusiveLock lock(mUpdateAabbMutex, mNumThreads);
         std::for_each(mUpdateAabb.begin(), mUpdateAabb.end(),
             [this](const std::shared_ptr<PtrHolder>& ptr) { updatePtrAabb(ptr); });
         mUpdateAabb.clear();
@@ -410,7 +435,7 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::updatePtrAabb(const std::shared_ptr<PtrHolder>& ptr)
     {
-        std::scoped_lock lock(mCollisionWorldMutex);
+        MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
         if (const auto actor = std::dynamic_pointer_cast<Actor>(ptr))
         {
             actor->updateCollisionObjectPosition();
@@ -436,27 +461,7 @@ namespace MWPhysics
             if (!mNewFrame)
                 mHasJob.wait(lock, [&]() { return mQuit || mNewFrame; });
 
-            mPreStepBarrier->wait([this] { afterPreStep(); });
+            doSimulation();
-
-            int job = 0;
-            while (mRemainingSteps && (job = mNextJob.fetch_add(1, std::memory_order_relaxed)) < mNumJobs)
-            {
-                MaybeSharedLock lockColWorld(mCollisionWorldMutex, mThreadSafeBullet);
-                MovementSolver::move(mActorsFrameData[job], mPhysicsDt, mCollisionWorld, *mWorldFrameData);
-            }
-
-            mPostStepBarrier->wait([this] { afterPostStep(); });
-
-            if (!mRemainingSteps)
-            {
-                while ((job = mNextJob.fetch_add(1, std::memory_order_relaxed)) < mNumJobs)
-                {
-                    handleFall(mActorsFrameData[job], mAdvanceSimulation);
-                }
-
-                refreshLOSCache();
-                mPostSimBarrier->wait([this] { afterPostSim(); });
-            }
         }
     }
 
@@ -466,7 +471,7 @@ namespace MWPhysics
         {
             if (mActors[i]->setPosition(mActorsFrameData[i].mPosition))
             {
-                std::scoped_lock lock(mCollisionWorldMutex);
+                MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
                 mActorsFrameData[i].mPosition = mActors[i]->getPosition(); // account for potential position change made by script
                 mActors[i]->updateCollisionObjectPosition();
                 mCollisionWorld->updateSingleAabb(mActors[i]->getCollisionObject());
@@ -476,6 +481,17 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::updateActor(Actor& actor, ActorFrameData& actorData, bool simulationPerformed, float timeAccum, float dt) const
     {
+        auto ptr = actor.getPtr();
+
+        MWMechanics::CreatureStats& stats = ptr.getClass().getCreatureStats(ptr);
+        const float heightDiff = actorData.mPosition.z() - actorData.mOldHeight;
+        const bool isStillOnGround = (simulationPerformed && actorData.mWasOnGround && actorData.mIsOnGround);
+
+        if (isStillOnGround || actorData.mFlying || isUnderWater(actorData) || actorData.mSlowFall < 1)
+            stats.land(ptr == MWMechanics::getPlayer() && (actorData.mFlying || isUnderWater(actorData)));
+        else if (heightDiff < 0)
+            stats.addToFallHeight(-heightDiff);
+
         actor.setSimulationPosition(interpolateMovements(actor, actorData, timeAccum, dt));
         actor.setLastStuckPosition(actorData.mLastStuckPosition);
         actor.setStuckFrames(actorData.mStuckFrames);
@@ -504,32 +520,29 @@ namespace MWPhysics
         resultCallback.m_collisionFilterGroup = 0xFF;
         resultCallback.m_collisionFilterMask = CollisionType_World|CollisionType_HeightMap|CollisionType_Door;
 
-        MaybeSharedLock lockColWorld(mCollisionWorldMutex, mThreadSafeBullet);
+        MaybeLock lockColWorld(mCollisionWorldMutex, mNumThreads);
         mCollisionWorld->rayTest(pos1, pos2, resultCallback);
 
         return !resultCallback.hasHit();
     }
 
-    void PhysicsTaskScheduler::syncComputation()
+    void PhysicsTaskScheduler::doSimulation()
     {
-        while (mRemainingSteps--)
+        while (mRemainingSteps)
         {
-            for (auto& actorData : mActorsFrameData)
+            mPreStepBarrier->wait([this] { afterPreStep(); });
+            int job = 0;
+            while ((job = mNextJob.fetch_add(1, std::memory_order_relaxed)) < mNumJobs)
             {
-                MovementSolver::unstuck(actorData, mCollisionWorld);
+                MaybeLock lockColWorld(mCollisionWorldMutex, mNumThreads);
-                MovementSolver::move(actorData, mPhysicsDt, mCollisionWorld, *mWorldFrameData);
+                MovementSolver::move(mActorsFrameData[job], mPhysicsDt, mCollisionWorld, *mWorldFrameData);
             }
 
-            updateActorsPositions();
+            mPostStepBarrier->wait([this] { afterPostStep(); });
         }
 
-        for (size_t i = 0; i < mActors.size(); ++i)
-        {
-            handleFall(mActorsFrameData[i], mAdvanceSimulation);
-            updateMechanics(*mActors[i], mActorsFrameData[i]);
-            updateActor(*mActors[i], mActorsFrameData[i], mAdvanceSimulation, mTimeAccum, mPhysicsDt);
-        }
         refreshLOSCache();
+        mPostSimBarrier->wait([this] { afterPostSim(); });
     }
 
     void PhysicsTaskScheduler::updateStats(osg::Timer_t frameStart, unsigned int frameNumber, osg::Stats& stats)
@@ -549,7 +562,7 @@ namespace MWPhysics
 
     void PhysicsTaskScheduler::debugDraw()
     {
-        std::shared_lock lock(mCollisionWorldMutex);
+        MaybeSharedLock lock(mCollisionWorldMutex, mNumThreads);
         mDebugDrawer->step();
     }
 
@@ -575,7 +588,7 @@ namespace MWPhysics
             return;
         for (size_t i = 0; i < mActors.size(); ++i)
         {
-            std::unique_lock lock(mCollisionWorldMutex);
+            MaybeExclusiveLock lock(mCollisionWorldMutex, mNumThreads);
             MovementSolver::unstuck(mActorsFrameData[i], mCollisionWorld);
         }
     }
@@ -594,7 +607,7 @@ namespace MWPhysics
     {
         mNewFrame = false;
         {
-            std::unique_lock lock(mLOSCacheMutex);
+            MaybeExclusiveLock lock(mLOSCacheMutex, mNumThreads);
             mLOSCache.erase(
                     std::remove_if(mLOSCache.begin(), mLOSCache.end(),
                         [](const LOSRequest& req) { return req.mStale; }),
@@ -602,4 +615,10 @@ namespace MWPhysics
         }
         mTimeEnd = mTimer->tick();
     }
+
+    void PhysicsTaskScheduler::syncWithMainThread()
+    {
+        for (size_t i = 0; i < mActors.size(); ++i)
+            updateActor(*mActors[i], mActorsFrameData[i], mAdvanceSimulation, mTimeAccum, mPhysicsDt);
+    }
 }

apps/openmw/mwphysics/mtphysics.hpp

@@ -61,7 +61,7 @@ namespace MWPhysics
             void releaseSharedStates(); // destroy all objects whose destructor can't be safely called from ~PhysicsTaskScheduler()
 
         private:
-            void syncComputation();
+            void doSimulation();
             void worker();
             void updateActorsPositions();
             void updateActor(Actor& actor, ActorFrameData& actorData, bool simulationPerformed, float timeAccum, float dt) const;
@@ -74,6 +74,7 @@ namespace MWPhysics
             void afterPreStep();
             void afterPostStep();
             void afterPostSim();
+            void syncWithMainThread();
 
             std::unique_ptr<WorldFrameData> mWorldFrameData;
             std::vector<std::shared_ptr<Actor>> mActors;
@@ -98,7 +99,6 @@ namespace MWPhysics
             int mLOSCacheExpiry;
             bool mNewFrame;
             bool mAdvanceSimulation;
-            bool mThreadSafeBullet;
             bool mQuit;
             std::atomic<int> mNextJob;
             std::atomic<int> mNextLOS;

apps/openmw/mwphysics/physicssystem.cpp

@@ -978,14 +978,12 @@ namespace MWPhysics
         , mWaterlevel(waterlevel)
         , mHalfExtentsZ(actor.getHalfExtents().z())
         , mOldHeight(0)
-        , mFallHeight(0)
         , mStuckFrames(0)
         , mFlying(MWBase::Environment::get().getWorld()->isFlying(actor.getPtr()))
         , mWasOnGround(actor.getOnGround())
         , mIsAquatic(actor.getPtr().getClass().isPureWaterCreature(actor.getPtr()))
         , mWaterCollision(waterCollision)
         , mSkipCollisionDetection(actor.skipCollisions() || !actor.getCollisionMode())
-        , mNeedLand(false)
     {
     }
 

apps/openmw/mwphysics/physicssystem.hpp

@@ -97,14 +97,12 @@ namespace MWPhysics
         const float mWaterlevel;
         const float mHalfExtentsZ;
         float mOldHeight;
-        float mFallHeight;
         unsigned int mStuckFrames;
         const bool mFlying;
         const bool mWasOnGround;
         const bool mIsAquatic;
         const bool mWaterCollision;
         const bool mSkipCollisionDetection;
-        bool mNeedLand;
     };
 
     struct WorldFrameData

components/misc/barrier.hpp

@@ -1,6 +1,7 @@
 #ifndef OPENMW_BARRIER_H
 #define OPENMW_BARRIER_H
 
+#include <cassert>
 #include <condition_variable>
 #include <mutex>
 
@@ -12,7 +13,9 @@ namespace Misc
         public:
             /// @param count number of threads to wait on
             explicit Barrier(int count) : mThreadCount(count), mRendezvousCount(0), mGeneration(0)
-            {}
+            {
+                assert(count >= 0);
+            }
 
             /// @brief stop execution of threads until count distinct threads reach this point
             /// @param func callable to be executed once after all threads have met
@@ -22,8 +25,8 @@ namespace Misc
                 std::unique_lock lock(mMutex);
 
                 ++mRendezvousCount;
-                const int currentGeneration = mGeneration;
+                const unsigned int currentGeneration = mGeneration;
-                if (mRendezvousCount == mThreadCount)
+                if (mRendezvousCount == mThreadCount || mThreadCount == 0)
                 {
                     ++mGeneration;
                     mRendezvousCount = 0;
@@ -37,9 +40,9 @@ namespace Misc
             }
 
         private:
-            int mThreadCount;
+            unsigned int mThreadCount;
-            int mRendezvousCount;
+            unsigned int mRendezvousCount;
-            int mGeneration;
+            unsigned int mGeneration;
             mutable std::mutex mMutex;
             std::condition_variable mRendezvous;
     };