as_gc.h

/*
   AngelCode Scripting Library
   Copyright (c) 2003-2018 Andreas Jonsson

   This software is provided 'as-is', without any express or implied
   warranty. In no event will the authors be held liable for any
   damages arising from the use of this software.

   Permission is granted to anyone to use this software for any
   purpose, including commercial applications, and to alter it and
   redistribute it freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you
      must not claim that you wrote the original software. If you use
      this software in a product, an acknowledgment in the product
      documentation would be appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and
      must not be misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
      distribution.

   The original version of this library can be located at:
   http://www.angelcode.com/angelscript/

   Andreas Jonsson
   andreas@angelcode.com
*/


//
// as_gc.h
//
// The garbage collector is used to resolve cyclic references
//



#ifndef AS_GC_H
#define AS_GC_H

#include "as_config.h"
#include "as_memory.h"
#include "as_map.h"
#include "as_thread.h"

BEGIN_AS_NAMESPACE

class asCScriptEngine;
class asCObjectType;

class asCGarbageCollector {
public:
    asCGarbageCollector();
    ~asCGarbageCollector();

    int    GarbageCollect(asDWORD flags, asUINT iterations);
    void   GetStatistics(asUINT *currentSize, asUINT *totalDestroyed, asUINT *totalDetected, asUINT *newObjects, asUINT *totalNewDestroyed) const;
    void   GCEnumCallback(void *reference);
    int    AddScriptObjectToGC(void *obj, asCObjectType *objType);
    int    GetObjectInGC(asUINT idx, asUINT *seqNbr, void **obj, asITypeInfo **type);

    int    ReportAndReleaseUndestroyedObjects();

    asCScriptEngine *engine;

    // Callback for when circular reference are detected
    asCIRCULARREFFUNC_t circularRefDetectCallbackFunc;
    void               *circularRefDetectCallbackParam;

protected:
    struct asSObjTypePair {
        void *obj;
        asCObjectType *type;
        asUINT seqNbr;
    };
    struct asSIntTypePair {
        int i;
        asCObjectType *type;
    };
    typedef asSMapNode<void *, asSIntTypePair> asSMapNode_t;

    enum egcDestroyState {
        destroyGarbage_init = 0,
        destroyGarbage_loop,
        destroyGarbage_haveMore
    };

    enum egcDetectState {
        clearCounters_init = 0,
        clearCounters_loop,
        buildMap_init,
        buildMap_loop,
        countReferences_init,
        countReferences_loop,
        detectGarbage_init,
        detectGarbage_loop1,
        detectGarbage_loop2,
        verifyUnmarked_init,
        verifyUnmarked_loop,
        breakCircles_init,
        breakCircles_loop,
        breakCircles_haveGarbage
    };

    int            DestroyNewGarbage();
    int            DestroyOldGarbage();
    int            IdentifyGarbageWithCyclicRefs();
    asSObjTypePair GetNewObjectAtIdx(int idx);
    asSObjTypePair GetOldObjectAtIdx(int idx);
    void           RemoveNewObjectAtIdx(int idx);
    void           RemoveOldObjectAtIdx(int idx);
    void           MoveObjectToOldList(int idx);
    void           MoveAllObjectsToOldList();

    // Holds all the objects known by the garbage collector
    asCArray<asSObjTypePair>           gcNewObjects;
    asCArray<asSObjTypePair>           gcOldObjects;

    // This array temporarily holds references to objects known to be live objects
    asCArray<void *>                    liveObjects;

    // This map holds objects currently being searched for cyclic references, it also holds a
    // counter that gives the number of references to the object that the GC can't reach
    asCMap<void *, asSIntTypePair>      gcMap;

    // State variables
    egcDestroyState                    destroyNewState;
    egcDestroyState                    destroyOldState;
    asUINT                             destroyNewIdx;
    asUINT                             destroyOldIdx;
    asUINT                             numDestroyed;
    asUINT                             numNewDestroyed;
    egcDetectState                     detectState;
    asUINT                             detectIdx;
    asUINT                             numDetected;
    asUINT                             numAdded;
    asUINT                             seqAtSweepStart[3];
    asSMapNode_t                      *gcMapCursor;
    bool                               isProcessing;

    // We'll keep a pool of nodes to avoid allocating memory all the time
    asSMapNode_t            *GetNode(void *obj, asSIntTypePair it);
    void                     ReturnNode(asSMapNode_t *node);
    asCArray<asSMapNode_t *>  freeNodes;

    // Critical section for multithreaded access
    DECLARECRITICALSECTION(gcCritical)   // Used for adding/removing objects
    DECLARECRITICALSECTION(gcCollecting) // Used for processing
};

END_AS_NAMESPACE

#endif