skia2/include/gpu/GrGpuResource.h

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrGpuResource_DEFINED
#define GrGpuResource_DEFINED

#include "GrResourceKey.h"
#include "GrTypesPriv.h"
#include "SkData.h"
#include "SkInstCnt.h"

class GrContext;
class GrGpu;
class GrResourceCache;

/**
 * Base class for GrGpuResource. Handles the various types of refs we need. Separated out as a base
 * class to isolate the ref-cnting behavior and provide friendship without exposing all of
 * GrGpuResource.
 *
 * Gpu resources can have three types of refs:
 *   1) Normal ref (+ by ref(), - by unref()): These are used by code that is issuing draw calls
 *      that read and write the resource via GrDrawTarget and by any object that must own a
 *      GrGpuResource and is itself owned (directly or indirectly) by Skia-client code.
 *   2) Pending read (+ by addPendingRead(), - by completedRead()): GrContext has scheduled a read
 *      of the resource by the GPU as a result of a skia API call but hasn't executed it yet.
 *   3) Pending write (+ by addPendingWrite(), - by completedWrite()): GrContext has scheduled a
 *      write to the resource by the GPU as a result of a skia API call but hasn't executed it yet.
 *
 * The latter two ref types are private and intended only for Gr core code.
 *
 * When all the ref/io counts reach zero DERIVED::notifyAllCntsAreZero() will be called (static poly
 * morphism using CRTP). Similarly when the ref (but not necessarily pending read/write) count
 * reaches 0 DERIVED::notifyRefCountIsZero() will be called. In the case when an unref() causes both
 * the ref cnt to reach zero and the other counts are zero, notifyRefCountIsZero() will be called
 * before notifyIsPurgeable(). Moreover, if notifyRefCountIsZero() returns false then
 * notifyAllRefCntsAreZero() won't be called at all. notifyRefCountIsZero() must return false if the
 * object may be deleted after notifyRefCntIsZero() returns.
 *
 * GrIORef and GrGpuResource are separate classes for organizational reasons and to be
 * able to give access via friendship to only the functions related to pending IO operations.
 */
template <typename DERIVED> class GrIORef : public SkNoncopyable {
public:
    SK_DECLARE_INST_COUNT(GrIORef)

    // Some of the signatures are written to mirror SkRefCnt so that GrGpuResource can work with
    // templated helper classes (e.g. SkAutoTUnref). However, we have different categories of
    // refs (e.g. pending reads). We also don't require thread safety as GrCacheable objects are
    // not intended to cross thread boundaries.
    void ref() const {
        this->validate();
        ++fRefCnt;
    }

    void unref() const {
        this->validate();
        
        if (!(--fRefCnt)) {
            if (!static_cast<const DERIVED*>(this)->notifyRefCountIsZero()) {
                return;
            }
        }

        this->didRemoveRefOrPendingIO(kRef_CntType);
    }

    void validate() const {
#ifdef SK_DEBUG
        SkASSERT(fRefCnt >= 0);
        SkASSERT(fPendingReads >= 0);
        SkASSERT(fPendingWrites >= 0);
        SkASSERT(fRefCnt + fPendingReads + fPendingWrites >= 0);
#endif
    }

protected:
    GrIORef() : fRefCnt(1), fPendingReads(0), fPendingWrites(0) { }

    enum CntType {
        kRef_CntType,
        kPendingRead_CntType,
        kPendingWrite_CntType,
    };

    bool isPurgeable() const { return !this->internalHasRef() && !this->internalHasPendingIO(); }

    bool internalHasPendingRead() const { return SkToBool(fPendingReads); }
    bool internalHasPendingWrite() const { return SkToBool(fPendingWrites); }
    bool internalHasPendingIO() const { return SkToBool(fPendingWrites | fPendingReads); }

    bool internalHasRef() const { return SkToBool(fRefCnt); }

private:
    void addPendingRead() const {
        this->validate();
        ++fPendingReads;
    }

    void completedRead() const {
        this->validate();
        --fPendingReads;
        this->didRemoveRefOrPendingIO(kPendingRead_CntType);
    }

    void addPendingWrite() const {
        this->validate();
        ++fPendingWrites;
    }

    void completedWrite() const {
        this->validate();
        --fPendingWrites;
        this->didRemoveRefOrPendingIO(kPendingWrite_CntType);
    }

private:
    void didRemoveRefOrPendingIO(CntType cntTypeRemoved) const {
        if (0 == fPendingReads && 0 == fPendingWrites && 0 == fRefCnt) {
            static_cast<const DERIVED*>(this)->notifyAllCntsAreZero(cntTypeRemoved);
        }
    }

    mutable int32_t fRefCnt;
    mutable int32_t fPendingReads;
    mutable int32_t fPendingWrites;

    // This class is used to manage conversion of refs to pending reads/writes.
    friend class GrGpuResourceRef;
    friend class GrResourceCache; // to check IO ref counts.

    template <typename, GrIOType> friend class GrPendingIOResource;
};

/**
 * Base class for objects that can be kept in the GrResourceCache.
 */
class SK_API GrGpuResource : public GrIORef<GrGpuResource> {
public:
    SK_DECLARE_INST_COUNT(GrGpuResource)

    enum LifeCycle {
        /**
         * The resource is cached and owned by Skia. Resources with this status may be kept alive
         * by the cache as either scratch or unique resources even when there are no refs to them.
         * The cache may release them whenever there are no refs.
         */
        kCached_LifeCycle,
        /**
         * The resource is uncached. As soon as there are no more refs to it, it is released. Under
         * the hood the cache may opaquely recycle it as a cached resource.
         */
        kUncached_LifeCycle,
        /**
         * Similar to uncached, but Skia does not manage the lifetime of the underlying backend
         * 3D API object(s). The client is responsible for freeing those. Used to inject client-
         * created GPU resources into Skia (e.g. to render to a client-created texture).
         */
        kWrapped_LifeCycle,
    };

    /**
     * Tests whether a object has been abandoned or released. All objects will
     * be in this state after their creating GrContext is destroyed or has
     * contextLost called. It's up to the client to test wasDestroyed() before
     * attempting to use an object if it holds refs on objects across
     * ~GrContext, freeResources with the force flag, or contextLost.
     *
     * @return true if the object has been released or abandoned,
     *         false otherwise.
     */
    bool wasDestroyed() const { return NULL == fGpu; }

    /**
     * Retrieves the context that owns the object. Note that it is possible for
     * this to return NULL. When objects have been release()ed or abandon()ed
     * they no longer have an owning context. Destroying a GrContext
     * automatically releases all its resources.
     */
    const GrContext* getContext() const;
    GrContext* getContext();

    /**
     * Retrieves the amount of GPU memory used by this resource in bytes. It is
     * approximate since we aren't aware of additional padding or copies made
     * by the driver.
     *
     * @return the amount of GPU memory used in bytes
     */
    size_t gpuMemorySize() const {
        if (kInvalidGpuMemorySize == fGpuMemorySize) {
            fGpuMemorySize = this->onGpuMemorySize();
            SkASSERT(kInvalidGpuMemorySize != fGpuMemorySize);
        }
        return fGpuMemorySize;
    }

    /**
     * Gets an id that is unique for this GrGpuResource object. It is static in that it does
     * not change when the content of the GrGpuResource object changes. This will never return
     * 0.
     */
    uint32_t getUniqueID() const { return fUniqueID; }

    /** Returns the current unique key for the resource. It will be invalid if the resource has no
        associated unique key. */
    const GrUniqueKey& getUniqueKey() const { return fUniqueKey; }

    /**
     * Attach a custom data object to this resource. The data will remain attached
     * for the lifetime of this resource (until it is abandoned or released).
     * Takes a ref on data. Previously attached data, if any, is unrefed.
     * Returns the data argument, for convenience.
     */
    const SkData* setCustomData(const SkData* data);

    /**
     * Returns the custom data object that was attached to this resource by
     * calling setCustomData.
     */
    const SkData* getCustomData() const { return fData.get(); }

    /**
     * Internal-only helper class used for manipulations of the resource by the cache.
     */
    class CacheAccess;
    inline CacheAccess cacheAccess();
    inline const CacheAccess cacheAccess() const;

    /**
     * Internal-only helper class used for manipulations of the resource by internal code.
     */
    class ResourcePriv;
    inline ResourcePriv resourcePriv();
    inline const ResourcePriv resourcePriv() const;

    /**
     * Removes references to objects in the underlying 3D API without freeing them.
     * Called by CacheAccess.
     * In general this method should not be called outside of skia. It was
     * made by public for a special case where it needs to be called in Blink
     * when a texture becomes unsafe to use after having been shared through
     * a texture mailbox.
     */
    void abandon();

protected:
    // This must be called by every GrGpuObject. It should be called once the object is fully
    // initialized (i.e. not in a base class constructor).
    void registerWithCache();

    GrGpuResource(GrGpu*, LifeCycle);
    virtual ~GrGpuResource();

    GrGpu* getGpu() const { return fGpu; }

    /** Overridden to free GPU resources in the backend API. */
    virtual void onRelease() { }
    /** Overridden to abandon any internal handles, ptrs, etc to backend API resources.
        This may be called when the underlying 3D context is no longer valid and so no
        backend API calls should be made. */
    virtual void onAbandon() { }

    bool isWrapped() const { return kWrapped_LifeCycle == fLifeCycle; }

    /**
     * This entry point should be called whenever gpuMemorySize() should report a different size.
     * The cache will call gpuMemorySize() to update the current size of the resource.
     */
    void didChangeGpuMemorySize() const;

    /**
     * Optionally called by the GrGpuResource subclass if the resource can be used as scratch.
     * By default resources are not usable as scratch. This should only be called once.
     **/
    void setScratchKey(const GrScratchKey& scratchKey);

private:
    /**
     * Frees the object in the underlying 3D API. Called by CacheAccess.
     */
    void release();

    virtual size_t onGpuMemorySize() const = 0;

    // See comments in CacheAccess and ResourcePriv.
    void setUniqueKey(const GrUniqueKey&);
    void removeUniqueKey();
    void notifyAllCntsAreZero(CntType) const;
    bool notifyRefCountIsZero() const;
    void removeScratchKey();
    void makeBudgeted();
    void makeUnbudgeted();

#ifdef SK_DEBUG
    friend class GrGpu; // for assert in GrGpu to access getGpu
#endif

    static uint32_t CreateUniqueID();

    // An index into a heap when this resource is purgeable or an array when not. This is maintained
    // by the cache.
    int                         fCacheArrayIndex;
    // This value reflects how recently this resource was accessed in the cache. This is maintained
    // by the cache.
    uint32_t                    fTimestamp;

    static const size_t kInvalidGpuMemorySize = ~static_cast<size_t>(0);
    GrScratchKey                fScratchKey;
    GrUniqueKey                 fUniqueKey;

    // This is not ref'ed but abandon() or release() will be called before the GrGpu object
    // is destroyed. Those calls set will this to NULL.
    GrGpu*                      fGpu;
    mutable size_t              fGpuMemorySize;

    LifeCycle                   fLifeCycle;
    const uint32_t              fUniqueID;

    SkAutoTUnref<const SkData>  fData;

    typedef GrIORef<GrGpuResource> INHERITED;
    friend class GrIORef<GrGpuResource>; // to access notifyAllCntsAreZero and notifyRefCntIsZero.
};

#endif