/src/gdal/gcore/gdalrasterblock.cpp

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/******************************************************************************
 *
 * Project:  GDAL Core
 * Purpose:  Implementation of GDALRasterBlock class and related global
 *           raster block cache management.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 **********************************************************************
 * Copyright (c) 1998, Frank Warmerdam <warmerdam@pobox.com>
 * Copyright (c) 2008-2013, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "cpl_port.h"
#include "gdal.h"
#include "gdal_priv.h"

#include <algorithm>
#include <climits>
#include <cstring>
#include <mutex>

#include "cpl_atomic_ops.h"
#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_multiproc.h"
#include "cpl_string.h"
#include "cpl_vsi.h"

// Will later be overridden by the default 5% if GDAL_CACHEMAX not defined.
static GIntBig nCacheMax = 40 * 1024 * 1024;
static GIntBig nCacheUsed = 0;

static GDALRasterBlock *poOldest = nullptr;  // Tail.
static GDALRasterBlock *poNewest = nullptr;  // Head.

static int nDisableDirtyBlockFlushCounter = 0;

#if 0
static CPLMutex *hRBLock = nullptr;
#define INITIALIZE_LOCK CPLMutexHolderD(&hRBLock)
#define TAKE_LOCK CPLMutexHolderOptionalLockD(hRBLock)
#define DESTROY_LOCK CPLDestroyMutex(hRBLock)
#else

static CPLLock *hRBLock = nullptr;
static bool bDebugContention = false;
static bool bSleepsForBockCacheDebug = false;

static CPLLockType GetLockType()
{
    static int nLockType = -1;
    if (nLockType < 0)
    {
        const char *pszLockType =
            CPLGetConfigOption("GDAL_RB_LOCK_TYPE", "ADAPTIVE");
        if (EQUAL(pszLockType, "ADAPTIVE"))
            nLockType = LOCK_ADAPTIVE_MUTEX;
        else if (EQUAL(pszLockType, "RECURSIVE"))
            nLockType = LOCK_RECURSIVE_MUTEX;
        else if (EQUAL(pszLockType, "SPIN"))
            nLockType = LOCK_SPIN;
        else
        {
            CPLError(
                CE_Warning, CPLE_NotSupported,
                "GDAL_RB_LOCK_TYPE=%s not supported. Falling back to ADAPTIVE",
                pszLockType);
            nLockType = LOCK_ADAPTIVE_MUTEX;
        }
        bDebugContention = CPLTestBool(
            CPLGetConfigOption("GDAL_RB_LOCK_DEBUG_CONTENTION", "NO"));
    }
    return static_cast<CPLLockType>(nLockType);
}

#define INITIALIZE_LOCK                                                        \
    CPLLockHolderD(&hRBLock, GetLockType());                                   \
    CPLLockSetDebugPerf(hRBLock, bDebugContention)
#define TAKE_LOCK CPLLockHolderOptionalLockD(hRBLock)
#define DESTROY_LOCK CPLDestroyLock(hRBLock)

#endif

// #define ENABLE_DEBUG

/************************************************************************/
/*                          GDALSetCacheMax()                           */
/************************************************************************/

/**
 * \brief Set maximum cache memory.
 *
 * This function sets the maximum amount of memory that GDAL is permitted
 * to use for GDALRasterBlock caching. The unit of the value is bytes.
 *
 * The maximum value is 2GB, due to the use of a signed 32 bit integer.
 * Use GDALSetCacheMax64() to be able to set a higher value.
 *
 * @param nNewSizeInBytes the maximum number of bytes for caching.
 */

void CPL_STDCALL GDALSetCacheMax(int nNewSizeInBytes)

{
    GDALSetCacheMax64(nNewSizeInBytes);
}

/************************************************************************/
/*                        GDALSetCacheMax64()                           */
/************************************************************************/

/**
 * \brief Set maximum cache memory.
 *
 * This function sets the maximum amount of memory that GDAL is permitted
 * to use for GDALRasterBlock caching. The unit of the value is bytes.
 *
 * Note: On 32 bit platforms, the maximum amount of memory that can be addressed
 * by a process might be 2 GB or 3 GB, depending on the operating system
 * capabilities. This function will not make any attempt to check the
 * consistency of the passed value with the effective capabilities of the OS.
 *
 * @param nNewSizeInBytes the maximum number of bytes for caching.
 *
 * @since GDAL 1.8.0
 */

void CPL_STDCALL GDALSetCacheMax64(GIntBig nNewSizeInBytes)

{
#if 0
    if( nNewSizeInBytes == 12346789 )
    {
        GDALRasterBlock::DumpAll();
        return;
    }
#endif

    // To force one-time initialization of nCacheMax if not already done
    GDALGetCacheMax64();
    nCacheMax = nNewSizeInBytes;

    /* -------------------------------------------------------------------- */
    /*      Flush blocks till we are under the new limit or till we         */
    /*      can't seem to flush anymore.                                    */
    /* -------------------------------------------------------------------- */
    while (nCacheUsed > nCacheMax)
    {
        const GIntBig nOldCacheUsed = nCacheUsed;

        GDALFlushCacheBlock();

        if (nCacheUsed == nOldCacheUsed)
            break;
    }
}

/************************************************************************/
/*                          GDALGetCacheMax()                           */
/************************************************************************/

/**
 * \brief Get maximum cache memory.
 *
 * Gets the maximum amount of memory available to the GDALRasterBlock
 * caching system for caching GDAL read/write imagery.
 *
 * The first type this function is called, it will read the GDAL_CACHEMAX
 * configuration option to initialize the maximum cache memory.
 * Starting with GDAL 2.1, the value can be expressed as x% of the usable
 * physical RAM (which may potentially be used by other processes). Otherwise
 * it is expected to be a value in MB.
 *
 * This function cannot return a value higher than 2 GB. Use
 * GDALGetCacheMax64() to get a non-truncated value.
 *
 * @return maximum in bytes.
 */

int CPL_STDCALL GDALGetCacheMax()
{
    GIntBig nRes = GDALGetCacheMax64();
    if (nRes > INT_MAX)
    {
        CPLErrorOnce(CE_Warning, CPLE_AppDefined,
                     "Cache max value doesn't fit on a 32 bit integer. "
                     "Call GDALGetCacheMax64() instead");
        nRes = INT_MAX;
    }
    return static_cast<int>(nRes);
}

/************************************************************************/
/*                         GDALGetCacheMax64()                          */
/************************************************************************/

/**
 * \brief Get maximum cache memory.
 *
 * Gets the maximum amount of memory available to the GDALRasterBlock
 * caching system for caching GDAL read/write imagery.
 *
 * The first time this function is called, it will read the GDAL_CACHEMAX
 * configuration option to initialize the maximum cache memory.
 * Starting with GDAL 2.1, the value can be expressed as x% of the usable
 * physical RAM (which may potentially be used by other processes). Starting
 * with GDAL 3.11, the value can include units of memory. If not units are
 * provided the value is assumed to be in MB.
 *
 * @return maximum in bytes.
 *
 * @since GDAL 1.8.0
 */

GIntBig CPL_STDCALL GDALGetCacheMax64()
{
    static std::once_flag flagSetupGDALGetCacheMax64;
    std::call_once(
        flagSetupGDALGetCacheMax64,
        []()
        {
            {
                INITIALIZE_LOCK;
            }
            bSleepsForBockCacheDebug =
                CPLTestBool(CPLGetConfigOption("GDAL_DEBUG_BLOCK_CACHE", "NO"));

            const char *pszCacheMax = CPLGetConfigOption("GDAL_CACHEMAX", "5%");
            GIntBig nNewCacheMax;
            bool bUnitSpecified = false;

            if (CPLParseMemorySize(pszCacheMax, &nNewCacheMax,
                                   &bUnitSpecified) != CE_None)
            {
                CPLError(CE_Failure, CPLE_NotSupported,
                         "Invalid value for GDAL_CACHEMAX. "
                         "Using default value.");
                if (CPLParseMemorySize("5%", &nNewCacheMax, &bUnitSpecified) !=
                    CE_None)
                {
                    // This means that usable physical RAM could not be determined.
                    nNewCacheMax = nCacheMax;
                }
            }

            if (!bUnitSpecified && nNewCacheMax < 100000)
            {
                // Assume MB
                nNewCacheMax *= (1024 * 1024);
            }

            nCacheMax = nNewCacheMax;
            CPLDebug("GDAL", "GDAL_CACHEMAX = " CPL_FRMT_GIB " MB",
                     nCacheMax / (1024 * 1024));
        });

    return nCacheMax;
}

/************************************************************************/
/*                          GDALGetCacheUsed()                          */
/************************************************************************/

/**
 * \brief Get cache memory used.
 *
 * @return the number of bytes of memory currently in use by the
 * GDALRasterBlock memory caching.
 */

int CPL_STDCALL GDALGetCacheUsed()
{
    if (nCacheUsed > INT_MAX)
    {
        CPLErrorOnce(CE_Warning, CPLE_AppDefined,
                     "Cache used value doesn't fit on a 32 bit integer. "
                     "Call GDALGetCacheUsed64() instead");
        return INT_MAX;
    }
    return static_cast<int>(nCacheUsed);
}

/************************************************************************/
/*                        GDALGetCacheUsed64()                          */
/************************************************************************/

/**
 * \brief Get cache memory used.
 *
 * @return the number of bytes of memory currently in use by the
 * GDALRasterBlock memory caching.
 *
 * @since GDAL 1.8.0
 */

GIntBig CPL_STDCALL GDALGetCacheUsed64()
{
    return nCacheUsed;
}

/************************************************************************/
/*                        GDALFlushCacheBlock()                         */
/*                                                                      */
/*      The workhorse of cache management!                              */
/************************************************************************/

/**
 * \brief Try to flush one cached raster block
 *
 * This function will search the first unlocked raster block and will
 * flush it to release the associated memory.
 *
 * @return TRUE if one block was flushed, FALSE if there are no cached blocks
 *         or if they are currently locked.
 */
int CPL_STDCALL GDALFlushCacheBlock()

{
    return GDALRasterBlock::FlushCacheBlock();
}

/************************************************************************/
/* ==================================================================== */
/*                           GDALRasterBlock                            */
/* ==================================================================== */
/************************************************************************/

/**
 * \class GDALRasterBlock "gdal_priv.h"
 *
 * GDALRasterBlock objects hold one block of raster data for one band
 * that is currently stored in the GDAL raster cache.  The cache holds
 * some blocks of raster data for zero or more GDALRasterBand objects
 * across zero or more GDALDataset objects in a global raster cache with
 * a least recently used (LRU) list and an upper cache limit (see
 * GDALSetCacheMax()) under which the cache size is normally kept.
 *
 * Some blocks in the cache may be modified relative to the state on disk
 * (they are marked "Dirty") and must be flushed to disk before they can
 * be discarded.  Other (Clean) blocks may just be discarded if their memory
 * needs to be recovered.
 *
 * In normal situations applications do not interact directly with the
 * GDALRasterBlock - instead it it utilized by the RasterIO() interfaces
 * to implement caching.
 *
 * Some driver classes are implemented in a fashion that completely avoids
 * use of the GDAL raster cache (and GDALRasterBlock) though this is not very
 * common.
 */

/************************************************************************/
/*                          FlushCacheBlock()                           */
/*                                                                      */
/*      Note, if we have a lot of blocks locked for a long time, this    */
/*      method is going to get slow because it will have to traverse    */
/*      the linked list a long ways looking for a flushing              */
/*      candidate.   It might help to re-touch locked blocks to push    */
/*      them to the top of the list.                                    */
/************************************************************************/

/**
 * \brief Attempt to flush at least one block from the cache.
 *
 * This static method is normally used to recover memory when a request
 * for a new cache block would put cache memory use over the established
 * limit.
 *
 * C++ analog to the C function GDALFlushCacheBlock().
 *
 * @param bDirtyBlocksOnly Only flushes dirty blocks.
 * @return TRUE if successful or FALSE if no flushable block is found.
 */

int GDALRasterBlock::FlushCacheBlock(int bDirtyBlocksOnly)

{
    GDALRasterBlock *poTarget;

    {
        INITIALIZE_LOCK;
        poTarget = poOldest;

        while (poTarget != nullptr)
        {
            if (!bDirtyBlocksOnly ||
                (poTarget->GetDirty() && nDisableDirtyBlockFlushCounter == 0))
            {
                if (CPLAtomicCompareAndExchange(&(poTarget->nLockCount), 0, -1))
                    break;
            }
            poTarget = poTarget->poPrevious;
        }

        if (poTarget == nullptr)
            return FALSE;
#ifndef __COVERITY__
        // Disabled to avoid complains about sleeping under locks, that
        // are only true for debug/testing code
        if (bSleepsForBockCacheDebug)
        {
            const double dfDelay = CPLAtof(CPLGetConfigOption(
                "GDAL_RB_FLUSHBLOCK_SLEEP_AFTER_DROP_LOCK", "0"));
            if (dfDelay > 0)
                CPLSleep(dfDelay);
        }
#endif

        poTarget->Detach_unlocked();
        poTarget->GetBand()->UnreferenceBlock(poTarget);
    }

#ifndef __COVERITY__
    // Disabled to avoid complains about sleeping under locks, that
    // are only true for debug/testing code
    if (bSleepsForBockCacheDebug)
    {
        const double dfDelay = CPLAtof(
            CPLGetConfigOption("GDAL_RB_FLUSHBLOCK_SLEEP_AFTER_RB_LOCK", "0"));
        if (dfDelay > 0)
            CPLSleep(dfDelay);
    }
#endif

    if (poTarget->GetDirty())
    {
        const CPLErr eErr = poTarget->Write();
        if (eErr != CE_None)
        {
            // Save the error for later reporting.
            poTarget->GetBand()->SetFlushBlockErr(eErr);
        }
    }

    VSIFreeAligned(poTarget->pData);
    poTarget->pData = nullptr;
    poTarget->GetBand()->AddBlockToFreeList(poTarget);

    return TRUE;
}

/************************************************************************/
/*                          FlushDirtyBlocks()                          */
/************************************************************************/

/**
 * \brief Flush all dirty blocks from cache.
 *
 * This static method is normally used to recover memory and is especially
 * useful when doing multi-threaded code that can trigger the block cache.
 *
 * Due to the current design of the block cache, dirty blocks belonging to a
 * same dataset could be pushed simultaneously to the IWriteBlock() method of
 * that dataset from different threads, causing races.
 *
 * Calling this method before that code can help workarounding that issue,
 * in a multiple readers, one writer scenario.
 *
 * @since GDAL 2.0
 */

void GDALRasterBlock::FlushDirtyBlocks()

{
    while (FlushCacheBlock(TRUE))
    {
        /* go on */
    }
}

/************************************************************************/
/*                      EnterDisableDirtyBlockFlush()                   */
/************************************************************************/

/**
 * \brief Starts preventing dirty blocks from being flushed
 *
 * This static method is used to prevent dirty blocks from being flushed.
 * This might be useful when in a IWriteBlock() method, whose implementation
 * can directly/indirectly cause the block cache to evict new blocks, to
 * be recursively called on the same dataset.
 *
 * This method implements a reference counter and is thread-safe.
 *
 * This call must be paired with a corresponding LeaveDisableDirtyBlockFlush().
 *
 * @since GDAL 2.2.2
 */

void GDALRasterBlock::EnterDisableDirtyBlockFlush()
{
    CPLAtomicInc(&nDisableDirtyBlockFlushCounter);
}

/************************************************************************/
/*                      LeaveDisableDirtyBlockFlush()                   */
/************************************************************************/

/**
 * \brief Ends preventing dirty blocks from being flushed.
 *
 * Undoes the effect of EnterDisableDirtyBlockFlush().
 *
 * @since GDAL 2.2.2
 */

void GDALRasterBlock::LeaveDisableDirtyBlockFlush()
{
    CPLAtomicDec(&nDisableDirtyBlockFlushCounter);
}

/************************************************************************/
/*                          GDALRasterBlock()                           */
/************************************************************************/

/**
 * @brief GDALRasterBlock Constructor
 *
 * Normally only called from GDALRasterBand::GetLockedBlockRef().
 *
 * @param poBandIn the raster band used as source of raster block
 * being constructed.
 *
 * @param nXOffIn the horizontal block offset, with zero indicating
 * the left most block, 1 the next block and so forth.
 *
 * @param nYOffIn the vertical block offset, with zero indicating
 * the top most block, 1 the next block and so forth.
 */

GDALRasterBlock::GDALRasterBlock(GDALRasterBand *poBandIn, int nXOffIn,
                                 int nYOffIn)
    : eType(poBandIn->GetRasterDataType()), bDirty(false), nLockCount(0),
      nXOff(nXOffIn), nYOff(nYOffIn), nXSize(0), nYSize(0), pData(nullptr),
      poBand(poBandIn), poNext(nullptr), poPrevious(nullptr), bMustDetach(true)
{
    if (!hRBLock)
    {
        // Needed for scenarios where GDALAllRegister() is called after
        // GDALDestroyDriverManager()
        INITIALIZE_LOCK;
    }

    CPLAssert(poBandIn != nullptr);
    poBand->GetBlockSize(&nXSize, &nYSize);
}

/************************************************************************/
/*                          GDALRasterBlock()                           */
/************************************************************************/

/**
 * @brief GDALRasterBlock Constructor (for GDALHashSetBandBlockAccess purpose)
 *
 * Normally only called from GDALHashSetBandBlockAccess class. Such a block
 * is completely non functional and only meant as being used to do a look-up
 * in the hash set of GDALHashSetBandBlockAccess
 *
 * @param nXOffIn the horizontal block offset, with zero indicating
 * the left most block, 1 the next block and so forth.
 *
 * @param nYOffIn the vertical block offset, with zero indicating
 * the top most block, 1 the next block and so forth.
 */

GDALRasterBlock::GDALRasterBlock(int nXOffIn, int nYOffIn)
    : eType(GDT_Unknown), bDirty(false), nLockCount(0), nXOff(nXOffIn),
      nYOff(nYOffIn), nXSize(0), nYSize(0), pData(nullptr), poBand(nullptr),
      poNext(nullptr), poPrevious(nullptr), bMustDetach(false)
{
}

/************************************************************************/
/*                                  RecycleFor()                        */
/************************************************************************/

/**
 * Recycle an existing block (of the same band)
 *
 * Normally called from GDALAbstractBandBlockCache::CreateBlock().
 */

void GDALRasterBlock::RecycleFor(int nXOffIn, int nYOffIn)
{
    CPLAssert(pData == nullptr);
    pData = nullptr;
    bDirty = false;
    nLockCount = 0;

    poNext = nullptr;
    poPrevious = nullptr;

    nXOff = nXOffIn;
    nYOff = nYOffIn;
    bMustDetach = true;
}

/************************************************************************/
/*                          ~GDALRasterBlock()                          */
/************************************************************************/

/**
 * Block destructor.
 *
 * Normally called from GDALRasterBand::FlushBlock().
 */

GDALRasterBlock::~GDALRasterBlock()

{
    Detach();

    if (pData != nullptr)
    {
        VSIFreeAligned(pData);
    }

    CPLAssert(nLockCount <= 0);

#ifdef ENABLE_DEBUG
    Verify();
#endif
}

/************************************************************************/
/*                        GetEffectiveBlockSize()                       */
/************************************************************************/

static size_t GetEffectiveBlockSize(GPtrDiff_t nBlockSize)
{
    // The real cost of a block allocation is more than just nBlockSize
    // As we allocate with 64-byte alignment, use 64 as a multiple.
    // We arbitrarily add 2 * sizeof(GDALRasterBlock) to account for that
    return static_cast<size_t>(
        std::min(static_cast<GUIntBig>(UINT_MAX),
                 static_cast<GUIntBig>(DIV_ROUND_UP(nBlockSize, 64)) * 64 +
                     2 * sizeof(GDALRasterBlock)));
}

/************************************************************************/
/*                               Detach()                               */
/************************************************************************/

/**
 * Remove block from cache.
 *
 * This method removes the current block from the linked list used to keep
 * track of all cached blocks in order of age.  It does not affect whether
 * the block is referenced by a GDALRasterBand nor does it destroy or flush
 * the block.
 */

void GDALRasterBlock::Detach()

{
    if (bMustDetach)
    {
        TAKE_LOCK;
        Detach_unlocked();
    }
}

void GDALRasterBlock::Detach_unlocked()
{
    if (poOldest == this)
        poOldest = poPrevious;

    if (poNewest == this)
    {
        poNewest = poNext;
    }

    if (poPrevious != nullptr)
        poPrevious->poNext = poNext;

    if (poNext != nullptr)
        poNext->poPrevious = poPrevious;

    poPrevious = nullptr;
    poNext = nullptr;
    bMustDetach = false;

    if (pData)
        nCacheUsed -= GetEffectiveBlockSize(GetBlockSize());

#ifdef ENABLE_DEBUG
    Verify();
#endif
}

/************************************************************************/
/*                               Verify()                               */
/************************************************************************/

/**
 * Confirms (via assertions) that the block cache linked list is in a
 * consistent state.
 */

#ifdef ENABLE_DEBUG
void GDALRasterBlock::Verify()

{
    TAKE_LOCK;

    CPLAssert((poNewest == nullptr && poOldest == nullptr) ||
              (poNewest != nullptr && poOldest != nullptr));

    if (poNewest != nullptr)
    {
        CPLAssert(poNewest->poPrevious == nullptr);
        CPLAssert(poOldest->poNext == nullptr);

        GDALRasterBlock *poLast = nullptr;
        for (GDALRasterBlock *poBlock = poNewest; poBlock != nullptr;
             poBlock = poBlock->poNext)
        {
            CPLAssert(poBlock->poPrevious == poLast);

            poLast = poBlock;
        }

        CPLAssert(poOldest == poLast);
    }
}

#else
void GDALRasterBlock::Verify()
{
}
#endif

#ifdef notdef
void GDALRasterBlock::CheckNonOrphanedBlocks(GDALRasterBand *poBand)
{
    TAKE_LOCK;
    for (GDALRasterBlock *poBlock = poNewest; poBlock != nullptr;
         poBlock = poBlock->poNext)
    {
        if (poBlock->GetBand() == poBand)
        {
            printf("Cache has still blocks of band %p\n", poBand); /*ok*/
            printf("Band : %d\n", poBand->GetBand());              /*ok*/
            printf("nRasterXSize = %d\n", poBand->GetXSize());     /*ok*/
            printf("nRasterYSize = %d\n", poBand->GetYSize());     /*ok*/
            int nBlockXSize, nBlockYSize;
            poBand->GetBlockSize(&nBlockXSize, &nBlockYSize);
            printf("nBlockXSize = %d\n", nBlockXSize);      /*ok*/
            printf("nBlockYSize = %d\n", nBlockYSize);      /*ok*/
            printf("Dataset : %p\n", poBand->GetDataset()); /*ok*/
            if (poBand->GetDataset())
                printf("Dataset : %s\n", /*ok*/
                       poBand->GetDataset()->GetDescription());
        }
    }
}
#endif

/************************************************************************/
/*                               Write()                                */
/************************************************************************/

/**
 * Force writing of the current block, if dirty.
 *
 * The block is written using GDALRasterBand::IWriteBlock() on its
 * corresponding band object.  Even if the write fails the block will
 * be marked clean.
 *
 * @return CE_None otherwise the error returned by IWriteBlock().
 */

CPLErr GDALRasterBlock::Write()

{
    if (!GetDirty())
        return CE_None;

    if (poBand == nullptr)
        return CE_Failure;

    MarkClean();

    if (poBand->eFlushBlockErr == CE_None)
    {
        int bCallLeaveReadWrite = poBand->EnterReadWrite(GF_Write);
        CPLErr eErr = poBand->IWriteBlock(nXOff, nYOff, pData);
        if (bCallLeaveReadWrite)
            poBand->LeaveReadWrite();
        return eErr;
    }
    else
        return poBand->eFlushBlockErr;
}

/************************************************************************/
/*                               Touch()                                */
/************************************************************************/

/**
 * Push block to top of LRU (least-recently used) list.
 *
 * This method is normally called when a block is used to keep track
 * that it has been recently used.
 */

void GDALRasterBlock::Touch()

{
    // Can be safely tested outside the lock
    if (poNewest == this)
        return;

    TAKE_LOCK;
    Touch_unlocked();
}

void GDALRasterBlock::Touch_unlocked()

{
    // Could happen even if tested in Touch() before taking the lock
    // Scenario would be :
    // 0. this is the second block (the one pointed by poNewest->poNext)
    // 1. Thread 1 calls Touch() and poNewest != this at that point
    // 2. Thread 2 detaches poNewest
    // 3. Thread 1 arrives here
    if (poNewest == this)
        return;

    // We should not try to touch a block that has been detached.
    // If that happen, corruption has already occurred.
    CPLAssert(bMustDetach);

    if (poOldest == this)
        poOldest = this->poPrevious;

    if (poPrevious != nullptr)
        poPrevious->poNext = poNext;

    if (poNext != nullptr)
        poNext->poPrevious = poPrevious;

    poPrevious = nullptr;
    poNext = poNewest;

    if (poNewest != nullptr)
    {
        CPLAssert(poNewest->poPrevious == nullptr);
        poNewest->poPrevious = this;
    }
    poNewest = this;

    if (poOldest == nullptr)
    {
        CPLAssert(poPrevious == nullptr && poNext == nullptr);
        poOldest = this;
    }
#ifdef ENABLE_DEBUG
    Verify();
#endif
}

/************************************************************************/
/*                            Internalize()                             */
/************************************************************************/

/**
 * Allocate memory for block.
 *
 * This method allocates memory for the block, and attempts to flush other
 * blocks, if necessary, to bring the total cache size back within the limits.
 * The newly allocated block is touched and will be considered most recently
 * used in the LRU list.
 *
 * @return CE_None on success or CE_Failure if memory allocation fails.
 */

CPLErr GDALRasterBlock::Internalize()

{
    CPLAssert(pData == nullptr);

    void *pNewData = nullptr;

    // This call will initialize the hRBLock mutex. Other call places can
    // only be called if we have go through there.
    const GIntBig nCurCacheMax = GDALGetCacheMax64();

    // No risk of overflow as it is checked in GDALRasterBand::InitBlockInfo().
    const auto nSizeInBytes = GetBlockSize();

    /* -------------------------------------------------------------------- */
    /*      Flush old blocks if we are nearing our memory limit.            */
    /* -------------------------------------------------------------------- */
    bool bFirstIter = true;
    bool bLoopAgain = false;
    GDALDataset *poThisDS = poBand->GetDataset();
    do
    {
        bLoopAgain = false;
        GDALRasterBlock *apoBlocksToFree[64] = {nullptr};
        int nBlocksToFree = 0;
        {
            TAKE_LOCK;

            if (bFirstIter)
                nCacheUsed += GetEffectiveBlockSize(nSizeInBytes);
            GDALRasterBlock *poTarget = poOldest;
            while (nCacheUsed > nCurCacheMax)
            {
                GDALRasterBlock *poDirtyBlockOtherDataset = nullptr;
                // In this first pass, only discard dirty blocks of this
                // dataset. We do this to decrease significantly the likelihood
                // of the following weakness of the block cache design:
                // 1. Thread 1 fills block B with ones
                // 2. Thread 2 evicts this dirty block, while thread 1 almost
                //    at the same time (but slightly after) tries to reacquire
                //    this block. As it has been removed from the block cache
                //    array/set, thread 1 now tries to read block B from disk,
                //    so gets the old value.
                while (poTarget != nullptr)
                {
                    if (!poTarget->GetDirty())
                    {
                        if (CPLAtomicCompareAndExchange(&(poTarget->nLockCount),
                                                        0, -1))
                            break;
                    }
                    else if (nDisableDirtyBlockFlushCounter == 0)
                    {
                        if (poTarget->poBand->GetDataset() == poThisDS)
                        {
                            if (CPLAtomicCompareAndExchange(
                                    &(poTarget->nLockCount), 0, -1))
                                break;
                        }
                        else if (poDirtyBlockOtherDataset == nullptr)
                        {
                            poDirtyBlockOtherDataset = poTarget;
                        }
                    }
                    poTarget = poTarget->poPrevious;
                }
                if (poTarget == nullptr && poDirtyBlockOtherDataset)
                {
                    if (CPLAtomicCompareAndExchange(
                            &(poDirtyBlockOtherDataset->nLockCount), 0, -1))
                    {
                        CPLDebug("GDAL",
                                 "Evicting dirty block of another dataset");
                        poTarget = poDirtyBlockOtherDataset;
                    }
                    else
                    {
                        poTarget = poOldest;
                        while (poTarget != nullptr)
                        {
                            if (CPLAtomicCompareAndExchange(
                                    &(poTarget->nLockCount), 0, -1))
                            {
                                CPLDebug(
                                    "GDAL",
                                    "Evicting dirty block of another dataset");
                                break;
                            }
                            poTarget = poTarget->poPrevious;
                        }
                    }
                }

                if (poTarget != nullptr)
                {
#ifndef __COVERITY__
                    // Disabled to avoid complains about sleeping under locks,
                    // that are only true for debug/testing code
                    if (bSleepsForBockCacheDebug)
                    {
                        const double dfDelay = CPLAtof(CPLGetConfigOption(
                            "GDAL_RB_INTERNALIZE_SLEEP_AFTER_DROP_LOCK", "0"));
                        if (dfDelay > 0)
                            CPLSleep(dfDelay);
                    }
#endif

                    GDALRasterBlock *_poPrevious = poTarget->poPrevious;

                    poTarget->Detach_unlocked();
                    poTarget->GetBand()->UnreferenceBlock(poTarget);

                    apoBlocksToFree[nBlocksToFree++] = poTarget;
                    if (poTarget->GetDirty())
                    {
                        // Only free one dirty block at a time so that
                        // other dirty blocks of other bands with the same
                        // coordinates can be found with TryGetLockedBlock()
                        bLoopAgain = nCacheUsed > nCurCacheMax;
                        break;
                    }
                    if (nBlocksToFree == 64)
                    {
                        bLoopAgain = (nCacheUsed > nCurCacheMax);
                        break;
                    }

                    poTarget = _poPrevious;
                }
                else
                {
                    break;
                }
            }

            /* ------------------------------------------------------------------
             */
            /*      Add this block to the list. */
            /* ------------------------------------------------------------------
             */
            if (!bLoopAgain)
                Touch_unlocked();
        }

        bFirstIter = false;

        // Now free blocks we have detached and removed from their band.
        for (int i = 0; i < nBlocksToFree; ++i)
        {
            GDALRasterBlock *const poBlock = apoBlocksToFree[i];

            if (poBlock->GetDirty())
            {
#ifndef __COVERITY__
                // Disabled to avoid complains about sleeping under locks, that
                // are only true for debug/testing code
                if (bSleepsForBockCacheDebug)
                {
                    const double dfDelay = CPLAtof(CPLGetConfigOption(
                        "GDAL_RB_INTERNALIZE_SLEEP_AFTER_DETACH_BEFORE_WRITE",
                        "0"));
                    if (dfDelay > 0)
                        CPLSleep(dfDelay);
                }
#endif

                CPLErr eErr = poBlock->Write();
                if (eErr != CE_None)
                {
                    // Save the error for later reporting.
                    poBlock->GetBand()->SetFlushBlockErr(eErr);
                }
            }

            // Try to recycle the data of an existing block.
            void *pDataBlock = poBlock->pData;
            if (pNewData == nullptr && pDataBlock != nullptr &&
                poBlock->GetBlockSize() == nSizeInBytes)
            {
                pNewData = pDataBlock;
            }
            else
            {
                VSIFreeAligned(poBlock->pData);
            }
            poBlock->pData = nullptr;

            poBlock->GetBand()->AddBlockToFreeList(poBlock);
        }
    } while (bLoopAgain);

    if (pNewData == nullptr)
    {
        pNewData = VSI_MALLOC_ALIGNED_AUTO_VERBOSE(nSizeInBytes);
        if (pNewData == nullptr)
        {
            return (CE_Failure);
        }
    }

    pData = pNewData;

    return CE_None;
}

/************************************************************************/
/*                             MarkDirty()                              */
/************************************************************************/

/**
 * Mark the block as modified.
 *
 * A dirty block is one that has been modified and will need to be written
 * to disk before it can be flushed.
 */

void GDALRasterBlock::MarkDirty()
{
    if (poBand)
    {
        poBand->InitRWLock();
        if (!bDirty)
            poBand->IncDirtyBlocks(1);
    }
    bDirty = true;
}

/************************************************************************/
/*                             MarkClean()                              */
/************************************************************************/

/**
 * Mark the block as unmodified.
 *
 * A dirty block is one that has been modified and will need to be written
 * to disk before it can be flushed.
 */

void GDALRasterBlock::MarkClean()
{
    if (bDirty && poBand)
        poBand->IncDirtyBlocks(-1);
    bDirty = false;
}

/************************************************************************/
/*                          DestroyRBMutex()                           */
/************************************************************************/

/*! @cond Doxygen_Suppress */
void GDALRasterBlock::DestroyRBMutex()
{
    if (hRBLock != nullptr)
        DESTROY_LOCK;
    hRBLock = nullptr;
}

/*! @endcond */

/************************************************************************/
/*                              TakeLock()                              */
/************************************************************************/

/**
 * Take a lock and Touch().
 *
 * Should only be used by GDALArrayBandBlockCache::TryGetLockedBlockRef()
 * and GDALHashSetBandBlockCache::TryGetLockedBlockRef()
 *
 * @return TRUE if the lock has been successfully acquired. If FALSE, the
 *         block is being evicted by another thread, and so should be
 *         considered as invalid.
 */

int GDALRasterBlock::TakeLock()
{
    const int nLockVal = AddLock();
    CPLAssert(nLockVal >= 0);
#ifndef __COVERITY__
    // Disabled to avoid complains about sleeping under locks, that
    // are only true for debug/testing code
    if (bSleepsForBockCacheDebug)
    {
        const double dfDelay = CPLAtof(
            CPLGetConfigOption("GDAL_RB_TRYGET_SLEEP_AFTER_TAKE_LOCK", "0"));
        if (dfDelay > 0)
            CPLSleep(dfDelay);
    }
#endif

    if (nLockVal == 0)
    {
        // The block is being evicted by GDALRasterBlock::Internalize()
        // or FlushCacheBlock()

#ifdef DEBUG
        CPLDebug(
            "GDAL",
            "TakeLock(%p): Block(%d,%d,%p) is being evicted while trying to "
            "reacquire it.",
            reinterpret_cast<void *>(CPLGetPID()), nXOff, nYOff, poBand);
#endif
        DropLock();

        return FALSE;
    }
    Touch();
    return TRUE;
}

/************************************************************************/
/*                      DropLockForRemovalFromStorage()                 */
/************************************************************************/

/**
 * Drop a lock before removing the block from the band storage.
 *
 * Should only be used by GDALArrayBandBlockCache::FlushBlock()
 * and GDALHashSetBandBlockCache::FlushBlock()
 *
 * @return TRUE if the lock has been successfully dropped.
 */

int GDALRasterBlock::DropLockForRemovalFromStorage()
{
    // Detect potential conflict with GDALRasterBlock::Internalize()
    // or FlushCacheBlock()
    if (CPLAtomicCompareAndExchange(&nLockCount, 0, -1))
        return TRUE;
#ifdef DEBUG
    CPLDebug("GDAL",
             "DropLockForRemovalFromStorage(%p): Block(%d,%d,%p) was attempted "
             "to be flushed from band but it is flushed by global cache.",
             reinterpret_cast<void *>(CPLGetPID()), nXOff, nYOff, poBand);
#endif

    // Wait for the block for having been unreferenced.
    TAKE_LOCK;

    return FALSE;
}

#if 0
void GDALRasterBlock::DumpAll()
{
    int iBlock = 0;
    for( GDALRasterBlock *poBlock = poNewest;
         poBlock != nullptr;
         poBlock = poBlock->poNext )
    {
        printf("Block %d\n", iBlock);/*ok*/
        poBlock->DumpBlock();
        printf("\n");/*ok*/
        iBlock++;
    }
}

void GDALRasterBlock::DumpBlock()
{
    printf("  Lock count = %d\n", nLockCount);/*ok*/
    printf("  bDirty = %d\n", static_cast<int>(bDirty));/*ok*/
    printf("  nXOff = %d\n", nXOff);/*ok*/
    printf("  nYOff = %d\n", nYOff);/*ok*/
    printf("  nXSize = %d\n", nXSize);/*ok*/
    printf("  nYSize = %d\n", nYSize);/*ok*/
    printf("  eType = %d\n", eType);/*ok*/
    printf("  Band %p\n", GetBand());/*ok*/
    printf("  Band %d\n", GetBand()->GetBand());/*ok*/
    if( GetBand()->GetDataset() )
        printf("  Dataset = %s\n",/*ok*/
               GetBand()->GetDataset()->GetDescription());
}
#endif  // if 0

Coverage Report

Created: 2025-06-13 06:29