src/core/SkPixelRef.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
#include "SkPixelRef.h"
#include "SkFlattenableBuffers.h"
#include "SkThread.h"

SK_DEFINE_INST_COUNT(SkPixelRef)

// must be a power-of-2. undef to just use 1 mutex
#define PIXELREF_MUTEX_RING_COUNT       32

#ifdef PIXELREF_MUTEX_RING_COUNT
    static int32_t gPixelRefMutexRingIndex;
    static SK_DECLARE_MUTEX_ARRAY(gPixelRefMutexRing, PIXELREF_MUTEX_RING_COUNT);
#else
    SK_DECLARE_STATIC_MUTEX(gPixelRefMutex);
#endif

static SkBaseMutex* get_default_mutex() {
#ifdef PIXELREF_MUTEX_RING_COUNT
    // atomic_inc might be overkill here. It may be fine if once in a while
    // we hit a race-condition and two subsequent calls get the same index...
    int index = sk_atomic_inc(&gPixelRefMutexRingIndex);
    return &gPixelRefMutexRing[index & (PIXELREF_MUTEX_RING_COUNT - 1)];
#else
    return &gPixelRefMutex;
#endif
}

///////////////////////////////////////////////////////////////////////////////

int32_t SkNextPixelRefGenerationID() {
    static int32_t  gPixelRefGenerationID;
    // do a loop in case our global wraps around, as we never want to
    // return a 0
    int32_t genID;
    do {
        genID = sk_atomic_inc(&gPixelRefGenerationID) + 1;
    } while (0 == genID);
    return genID;
}

///////////////////////////////////////////////////////////////////////////////

void SkPixelRef::setMutex(SkBaseMutex* mutex) {
    if (NULL == mutex) {
        mutex = get_default_mutex();
    }
    fMutex = mutex;
}

// just need a > 0 value, so pick a funny one to aid in debugging
#define SKPIXELREF_PRELOCKED_LOCKCOUNT     123456789

SkPixelRef::SkPixelRef(SkBaseMutex* mutex) : fPreLocked(false) {
    this->setMutex(mutex);
    fPixels = NULL;
    fColorTable = NULL; // we do not track ownership of this
    fLockCount = 0;
    fGenerationID = 0;  // signal to rebuild
    fIsImmutable = false;
    fPreLocked = false;
}

SkPixelRef::SkPixelRef(SkFlattenableReadBuffer& buffer, SkBaseMutex* mutex)
        : INHERITED(buffer) {
    this->setMutex(mutex);
    fPixels = NULL;
    fColorTable = NULL; // we do not track ownership of this
    fLockCount = 0;
    fIsImmutable = buffer.readBool();
    fGenerationID = buffer.readUInt();
    fPreLocked = false;
}

void SkPixelRef::setPreLocked(void* pixels, SkColorTable* ctable) {
    // only call me in your constructor, otherwise fLockCount tracking can get
    // out of sync.
    fPixels = pixels;
    fColorTable = ctable;
    fLockCount = SKPIXELREF_PRELOCKED_LOCKCOUNT;
    fPreLocked = true;
}

void SkPixelRef::flatten(SkFlattenableWriteBuffer& buffer) const {
    this->INHERITED::flatten(buffer);
    buffer.writeBool(fIsImmutable);
    // We write the gen ID into the picture for within-process recording. This
    // is safe since the same genID will never refer to two different sets of
    // pixels (barring overflow). However, each process has its own "namespace"
    // of genIDs. So for cross-process recording we write a zero which will
    // trigger assignment of a new genID in playback.
    if (buffer.isCrossProcess()) {
        buffer.writeUInt(0);
    } else {
        buffer.writeUInt(fGenerationID);
    }
}

void SkPixelRef::lockPixels() {
    SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);

    if (!fPreLocked) {
        SkAutoMutexAcquire  ac(*fMutex);

        if (1 == ++fLockCount) {
            fPixels = this->onLockPixels(&fColorTable);
        }
    }
}

void SkPixelRef::unlockPixels() {
    SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);

    if (!fPreLocked) {
        SkAutoMutexAcquire  ac(*fMutex);

        SkASSERT(fLockCount > 0);
        if (0 == --fLockCount) {
            this->onUnlockPixels();
            fPixels = NULL;
            fColorTable = NULL;
        }
    }
}

bool SkPixelRef::lockPixelsAreWritable() const {
    return this->onLockPixelsAreWritable();
}

bool SkPixelRef::onLockPixelsAreWritable() const {
    return true;
}

uint32_t SkPixelRef::getGenerationID() const {
    if (0 == fGenerationID) {
        fGenerationID = SkNextPixelRefGenerationID();
    }
    return fGenerationID;
}

void SkPixelRef::notifyPixelsChanged() {
#ifdef SK_DEBUG
    if (fIsImmutable) {
        SkDebugf("========== notifyPixelsChanged called on immutable pixelref");
    }
#endif
    // this signals us to recompute this next time around
    fGenerationID = 0;
}

void SkPixelRef::setImmutable() {
    fIsImmutable = true;
}

bool SkPixelRef::readPixels(SkBitmap* dst, const SkIRect* subset) {
    return this->onReadPixels(dst, subset);
}

bool SkPixelRef::onReadPixels(SkBitmap* dst, const SkIRect* subset) {
    return false;
}

///////////////////////////////////////////////////////////////////////////////

#ifdef SK_BUILD_FOR_ANDROID
void SkPixelRef::globalRef(void* data) {
    this->ref();
}

void SkPixelRef::globalUnref() {
    this->unref();
}
#endif