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bugfix(audio): Prevent race condition when accessing deleted drawables from audio thread #461

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bugfix(audio): Prevent race condition when accessing deleted drawables from audio thread #461

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21 changes: 15 additions & 6 deletions Core/GameEngine/Source/Common/Audio/AudioEventRTS.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,7 @@

#include "GameClient/Drawable.h" // For getPosition
#include "GameClient/GameClient.h" // For getDrawableByID
#include "Common/ScopedMutex.h" // For ScopedMutex


//-------------------------------------------------------------------------------------------------
Expand Down Expand Up @@ -741,13 +742,21 @@ const Coord3D *AudioEventRTS::getCurrentPosition()
return &m_positionOfAudio;

case OT_Drawable:
if (Drawable *draw = TheGameClient->findDrawableByID(m_drawableID))
{
m_positionOfAudio.set( draw->getPosition() );
}
else
{
m_ownerType = OT_Dead;
// Hold the drawable lookup mutex for the duration of the find-and-read to prevent
// the main thread from destroying the drawable (and freeing its memory) between
// findDrawableByID() returning a non-null pointer and getPosition() being called.
// This function can be invoked from the Miles audio background thread via
// notifyOfAudioCompletion(), so the mutex is needed to close this race window.
ScopedMutex mut(TheGameClient->getDrawableLookupMutex());
if (Drawable *draw = TheGameClient->findDrawableByID(m_drawableID))
{
m_positionOfAudio.set( draw->getPosition() );
}
else
{
m_ownerType = OT_Dead;
}
}
return &m_positionOfAudio;

Expand Down
3 changes: 3 additions & 0 deletions Generals/Code/GameEngine/Include/GameClient/GameClient.h
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Original file line number Diff line number Diff line change
Expand Up @@ -99,6 +99,8 @@ class GameClient : public SubsystemInterface,

virtual Drawable *findDrawableByID( const DrawableID id ); ///< Given an ID, return the associated drawable

HANDLE getDrawableLookupMutex() const { return m_drawableLookupMutex; } ///< Returns the mutex that guards drawable hash access and drawable lifetime

void setDrawableIDCounter( DrawableID nextDrawableID ) { m_nextDrawableID = nextDrawableID; }
DrawableID getDrawableIDCounter() { return m_nextDrawableID; }

Expand Down Expand Up @@ -160,6 +162,7 @@ class GameClient : public SubsystemInterface,

Drawable *m_drawableList; ///< All of the drawables in the world
DrawablePtrHash m_drawableHash; ///< Used for DrawableID lookups
HANDLE m_drawableLookupMutex; ///< Guards drawable hash access and drawable lifetime against concurrent audio thread access

DrawableID m_nextDrawableID; ///< For allocating drawable id's
DrawableID allocDrawableID(); ///< Returns a new unique drawable id
Expand Down
18 changes: 13 additions & 5 deletions Generals/Code/GameEngine/Source/GameClient/GameClient.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@

// USER INCLUDES //////////////////////////////////////////////////////////////
#include "Common/ActionManager.h"
#include "Common/ScopedMutex.h"
#include "Common/GameEngine.h"
#include "Common/GameState.h"
#include "Common/GameUtility.h"
Expand Down Expand Up @@ -107,6 +108,8 @@ GameClient::GameClient()

m_nextDrawableID = (DrawableID)1;
TheDrawGroupInfo = new DrawGroupInfo;

m_drawableLookupMutex = CreateMutex(nullptr, FALSE, nullptr);
}

//std::vector<std::string> preloadTextureNamesGlobalHack;
Expand Down Expand Up @@ -223,6 +226,9 @@ GameClient::~GameClient()
delete TheEva;
TheEva = nullptr;

CloseHandle(m_drawableLookupMutex);
m_drawableLookupMutex = nullptr;

}

//-------------------------------------------------------------------------------------------------
Expand Down Expand Up @@ -821,11 +827,13 @@ void GameClient::destroyDrawable( Drawable *draw )

}

// remove the drawable from our hash of drawables
removeDrawableFromLookupTable( draw );

// free storage
deleteInstance(draw);
// Remove from hash and free storage under the mutex so that audio threads looking up
// drawables by ID cannot observe a drawable pointer after its memory has been freed.
{
ScopedMutex mut(m_drawableLookupMutex);
removeDrawableFromLookupTable( draw );
deleteInstance(draw);
}

}

Expand Down
3 changes: 3 additions & 0 deletions GeneralsMD/Code/GameEngine/Include/GameClient/GameClient.h
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,8 @@ class GameClient : public SubsystemInterface,

virtual Drawable *findDrawableByID( const DrawableID id ); ///< Given an ID, return the associated drawable

HANDLE getDrawableLookupMutex() const { return m_drawableLookupMutex; } ///< Returns the mutex that guards drawable lookup access and drawable lifetime

void setDrawableIDCounter( DrawableID nextDrawableID ) { m_nextDrawableID = nextDrawableID; }
DrawableID getDrawableIDCounter() { return m_nextDrawableID; }

Expand Down Expand Up @@ -181,6 +183,7 @@ class GameClient : public SubsystemInterface,
Drawable *m_drawableList; ///< All of the drawables in the world
// DrawablePtrHash m_drawableHash; ///< Used for DrawableID lookups
DrawablePtrVector m_drawableVector;
HANDLE m_drawableLookupMutex; ///< Guards drawable lookup access and drawable lifetime against concurrent audio thread access

DrawableID m_nextDrawableID; ///< For allocating drawable id's
DrawableID allocDrawableID(); ///< Returns a new unique drawable id
Expand Down
18 changes: 13 additions & 5 deletions GeneralsMD/Code/GameEngine/Source/GameClient/GameClient.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,7 @@

// USER INCLUDES //////////////////////////////////////////////////////////////
#include "Common/ActionManager.h"
#include "Common/ScopedMutex.h"
#include "Common/GameEngine.h"
#include "Common/GameState.h"
#include "Common/GameUtility.h"
Expand Down Expand Up @@ -119,6 +120,8 @@ GameClient::GameClient()

m_nextDrawableID = (DrawableID)1;
TheDrawGroupInfo = new DrawGroupInfo;

m_drawableLookupMutex = CreateMutex(nullptr, FALSE, nullptr);
}

//std::vector<std::string> preloadTextureNamesGlobalHack;
Expand Down Expand Up @@ -241,6 +244,9 @@ GameClient::~GameClient()
delete TheSnowManager;
TheSnowManager = nullptr;

CloseHandle(m_drawableLookupMutex);
m_drawableLookupMutex = nullptr;

}

//-------------------------------------------------------------------------------------------------
Expand Down Expand Up @@ -884,11 +890,13 @@ void GameClient::destroyDrawable( Drawable *draw )

}

// remove the drawable from our hash of drawables
removeDrawableFromLookupTable( draw );

// free storage
deleteInstance(draw);
// Remove from lookup and free storage under the mutex so that audio threads looking up
// drawables by ID cannot observe a drawable pointer after its memory has been freed.
{
ScopedMutex mut(m_drawableLookupMutex);
removeDrawableFromLookupTable( draw );
deleteInstance(draw);
}

}

Expand Down
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