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Merge branch 'fix_physics_deadlock' into 'master'
Fix deadlock in physics system (#6414) Closes #6414 See merge request OpenMW/openmw!1440
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commit
9d7a53b701
@ -267,7 +267,7 @@ namespace MWPhysics
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, mNumJobs(0)
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, mRemainingSteps(0)
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, mLOSCacheExpiry(Settings::Manager::getInt("lineofsight keep inactive cache", "Physics"))
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, mNewFrame(false)
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, mFrameCounter(0)
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, mAdvanceSimulation(false)
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, mQuit(false)
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, mNextJob(0)
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@ -302,13 +302,14 @@ namespace MWPhysics
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PhysicsTaskScheduler::~PhysicsTaskScheduler()
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{
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waitForWorkers();
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{
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MaybeExclusiveLock lock(mSimulationMutex, mNumThreads);
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mQuit = true;
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mNumJobs = 0;
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mRemainingSteps = 0;
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mHasJob.notify_all();
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}
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mHasJob.notify_all();
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for (auto& thread : mThreads)
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thread.join();
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}
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@ -361,6 +362,8 @@ namespace MWPhysics
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void PhysicsTaskScheduler::applyQueuedMovements(float & timeAccum, std::vector<Simulation>&& simulations, osg::Timer_t frameStart, unsigned int frameNumber, osg::Stats& stats)
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{
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waitForWorkers();
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// This function run in the main thread.
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// While the mSimulationMutex is held, background physics threads can't run.
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@ -393,7 +396,7 @@ namespace MWPhysics
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mPhysicsDt = newDelta;
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mSimulations = std::move(simulations);
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mAdvanceSimulation = (mRemainingSteps != 0);
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mNewFrame = true;
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++mFrameCounter;
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mNumJobs = mSimulations.size();
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mNextLOS.store(0, std::memory_order_relaxed);
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mNextJob.store(0, std::memory_order_release);
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@ -421,6 +424,7 @@ namespace MWPhysics
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void PhysicsTaskScheduler::resetSimulation(const ActorMap& actors)
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{
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waitForWorkers();
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MaybeExclusiveLock lock(mSimulationMutex, mNumThreads);
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mBudget.reset(mDefaultPhysicsDt);
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mAsyncBudget.reset(0.0f);
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@ -577,11 +581,15 @@ namespace MWPhysics
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void PhysicsTaskScheduler::worker()
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{
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std::size_t lastFrame = 0;
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std::shared_lock lock(mSimulationMutex);
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while (!mQuit)
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{
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if (!mNewFrame)
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mHasJob.wait(lock, [&]() { return mQuit || mNewFrame; });
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if (lastFrame == mFrameCounter)
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{
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mHasJob.wait(lock, [&] { return mQuit || lastFrame != mFrameCounter; });
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lastFrame = mFrameCounter;
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}
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doSimulation();
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}
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@ -663,6 +671,7 @@ namespace MWPhysics
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void PhysicsTaskScheduler::releaseSharedStates()
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{
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waitForWorkers();
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std::scoped_lock lock(mSimulationMutex, mUpdateAabbMutex);
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mSimulations.clear();
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mUpdateAabb.clear();
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@ -693,7 +702,6 @@ namespace MWPhysics
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void PhysicsTaskScheduler::afterPostSim()
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{
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mNewFrame = false;
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{
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MaybeExclusiveLock lock(mLOSCacheMutex, mNumThreads);
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mLOSCache.erase(
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@ -702,6 +710,10 @@ namespace MWPhysics
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mLOSCache.end());
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}
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mTimeEnd = mTimer->tick();
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std::unique_lock lock(mWorkersDoneMutex);
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++mWorkersFrameCounter;
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mWorkersDone.notify_all();
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}
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void PhysicsTaskScheduler::syncWithMainThread()
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@ -710,4 +722,19 @@ namespace MWPhysics
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for (auto& sim : mSimulations)
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std::visit(vis, sim);
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}
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// Attempt to acquire unique lock on mSimulationMutex while not all worker
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// threads are holding shared lock but will have to may lead to a deadlock because
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// C++ standard does not guarantee priority for exclusive and shared locks
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// for std::shared_mutex. For example microsoft STL implementation points out
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// for the absence of such priority:
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// https://docs.microsoft.com/en-us/windows/win32/sync/slim-reader-writer--srw--locks
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void PhysicsTaskScheduler::waitForWorkers()
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{
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if (mNumThreads == 0)
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return;
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std::unique_lock lock(mWorkersDoneMutex);
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if (mFrameCounter != mWorkersFrameCounter)
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mWorkersDone.wait(lock);
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}
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}
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@ -74,6 +74,7 @@ namespace MWPhysics
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void afterPostStep();
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void afterPostSim();
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void syncWithMainThread();
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void waitForWorkers();
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std::unique_ptr<WorldFrameData> mWorldFrameData;
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std::vector<Simulation> mSimulations;
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@ -95,13 +96,17 @@ namespace MWPhysics
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int mNumJobs;
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int mRemainingSteps;
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int mLOSCacheExpiry;
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bool mNewFrame;
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std::size_t mFrameCounter;
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bool mAdvanceSimulation;
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bool mQuit;
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std::atomic<int> mNextJob;
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std::atomic<int> mNextLOS;
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std::vector<std::thread> mThreads;
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std::size_t mWorkersFrameCounter = 0;
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std::condition_variable mWorkersDone;
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std::mutex mWorkersDoneMutex;
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mutable std::shared_mutex mSimulationMutex;
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mutable std::shared_mutex mCollisionWorldMutex;
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mutable std::shared_mutex mLOSCacheMutex;
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