added DropCache to GDALDataset

gcore/gdal.h

@@ -1191,6 +1191,7 @@ CPLErr CPL_DLL CPL_STDCALL GDALBuildOverviewsEx(
 void CPL_DLL CPL_STDCALL GDALGetOpenDatasets(GDALDatasetH **hDS, int *pnCount);
 int CPL_DLL CPL_STDCALL GDALGetAccess(GDALDatasetH hDS);
 CPLErr CPL_DLL CPL_STDCALL GDALFlushCache(GDALDatasetH hDS);
+CPLErr CPL_DLL CPL_STDCALL GDALDropCache(GDALDatasetH hDS);
 
 CPLErr CPL_DLL CPL_STDCALL GDALCreateDatasetMaskBand(GDALDatasetH hDS,
                                                      int nFlags);
@@ -1545,6 +1546,7 @@ CPLErr CPL_DLL CPL_STDCALL GDALComputeRasterMinMax(GDALRasterBandH hBand,
                                                    int bApproxOK,
                                                    double adfMinMax[2]);
 CPLErr CPL_DLL CPL_STDCALL GDALFlushRasterCache(GDALRasterBandH hBand);
+CPLErr CPL_DLL CPL_STDCALL GDALDropRasterCache(GDALRasterBandH hBand);
 CPLErr CPL_DLL CPL_STDCALL GDALGetRasterHistogram(
     GDALRasterBandH hBand, double dfMin, double dfMax, int nBuckets,
     int *panHistogram, int bIncludeOutOfRange, int bApproxOK,

gcore/gdal_priv.h

@@ -537,6 +537,7 @@ class CPL_DLL GDALDataset : public GDALMajorObject
     Bands GetBands();
 
     virtual CPLErr FlushCache(bool bAtClosing = false);
+    virtual CPLErr DropCache();
 
     virtual GIntBig GetEstimatedRAMUsage();
 
@@ -1188,7 +1189,7 @@ class GDALAbstractBandBlockCache
 
     int m_nInitialDirtyBlocksInFlushCache = 0;
     int m_nLastTick = -1;
-    bool m_bWriteDirtyBlocks = true;
+    size_t m_bWriteDirtyBlocksDisabled = 0;
 
     void FreeDanglingBlocks();
     void UnreferenceBlockBase();
@@ -1205,9 +1206,13 @@ class GDALAbstractBandBlockCache
     void AddBlockToFreeList(GDALRasterBlock *);
     void IncDirtyBlocks(int nInc);
     void WaitCompletionPendingTasks();
+    void EnableDirtyBlockWriting()
+    {
+        --m_bWriteDirtyBlocksDisabled;
+    }
     void DisableDirtyBlockWriting()
     {
-        m_bWriteDirtyBlocks = false;
+        ++m_bWriteDirtyBlocksDisabled;
     }
     bool HasDirtyBlocks() const
     {
@@ -1412,6 +1417,7 @@ class CPL_DLL GDALRasterBand : public GDALMajorObject
     // New OpengIS CV_SampleDimension stuff.
 
     virtual CPLErr FlushCache(bool bAtClosing = false);
+    virtual CPLErr DropCache();
     virtual char **GetCategoryNames();
     virtual double GetNoDataValue(int *pbSuccess = nullptr);
     virtual int64_t GetNoDataValueAsInt64(int *pbSuccess = nullptr);

gcore/gdalarraybandblockcache.cpp

@@ -442,7 +442,7 @@ CPLErr GDALArrayBandBlockCache::FlushBlock(int nXBlockOff, int nYBlockOff,
 
     CPLErr eErr = CE_None;
 
-    if (m_bWriteDirtyBlocks && bWriteDirtyBlock && poBlock->GetDirty())
+    if (!m_bWriteDirtyBlocksDisabled && bWriteDirtyBlock && poBlock->GetDirty())
     {
         UpdateDirtyBlockFlushingLog();
 

gcore/gdaldataset.cpp

@@ -613,6 +613,59 @@ CPLErr CPL_STDCALL GDALFlushCache(GDALDatasetH hDS)
     return GDALDataset::FromHandle(hDS)->FlushCache(false);
 }
 
+/************************************************************************/
+/*                             DropCache()                              */
+/************************************************************************/
+
+/**
+* \brief Drop all write cached data
+*
+* This method is the same as the C function GDALDropCache().
+*
+* @return CE_None in case of success
+*/
+
+CPLErr GDALDataset::DropCache()
+
+{
+    CPLErr eErr = CE_None;
+    // This sometimes happens if a dataset is destroyed before completely
+    // built.
+
+    if (papoBands)
+    {
+        for (int i = 0; i < nBands; ++i)
+        {
+            if (papoBands[i])
+            {
+                if (papoBands[i]->DropCache() != CE_None)
+                    eErr = CE_Failure;
+            }
+        }
+    }
+
+    return eErr;
+}
+
+/************************************************************************/
+/*                           GDALDropCache()                           */
+/************************************************************************/
+
+/**
+* \brief Drop all write cached data
+*
+* @see GDALDataset::DropCache().
+* @return CE_None in case of success
+*/
+
+CPLErr CPL_STDCALL GDALDropCache(GDALDatasetH hDS)
+
+{
+    VALIDATE_POINTER1(hDS, "GDALDropCache", CE_Failure);
+
+    return GDALDataset::FromHandle(hDS)->DropCache();
+}
+
 /************************************************************************/
 /*                      GetEstimatedRAMUsage()                          */
 /************************************************************************/

gcore/gdalhashsetbandblockcache.cpp

@@ -170,7 +170,7 @@ CPLErr GDALHashSetBandBlockCache::FlushCache()
         {
             CPLErr eErr = CE_None;
 
-            if (m_bWriteDirtyBlocks && eGlobalErr == CE_None &&
+            if (!m_bWriteDirtyBlocksDisabled && eGlobalErr == CE_None &&
                 poBlock->GetDirty())
             {
                 UpdateDirtyBlockFlushingLog();
@@ -227,7 +227,7 @@ CPLErr GDALHashSetBandBlockCache::FlushBlock(int nXBlockOff, int nYBlockOff,
 
     CPLErr eErr = CE_None;
 
-    if (m_bWriteDirtyBlocks && bWriteDirtyBlock && poBlock->GetDirty())
+    if (!m_bWriteDirtyBlocksDisabled && bWriteDirtyBlock && poBlock->GetDirty())
         eErr = poBlock->Write();
 
     delete poBlock;

gcore/gdalrasterband.cpp

@@ -1140,6 +1140,68 @@ CPLErr CPL_STDCALL GDALFlushRasterCache(GDALRasterBandH hBand)
     return GDALRasterBand::FromHandle(hBand)->FlushCache(false);
 }
 
+/************************************************************************/
+/*                             DropCache()                              */
+/************************************************************************/
+
+/**
+* \brief Drop raster data cache : data in cache will be lost.
+*
+* This call will recover memory used to cache data blocks for this raster
+* band, and ensure that new requests are referred to the underlying driver.
+*
+* This method is the same as the C function GDALDropRasterCache().
+*
+* @return CE_None on success.
+*/
+
+CPLErr GDALRasterBand::DropCache()
+
+{
+    CPLErr result = CE_None;
+
+    if (poBandBlockCache)
+        poBandBlockCache->DisableDirtyBlockWriting();
+
+    CPLErr eGlobalErr = eFlushBlockErr;
+
+    if (eFlushBlockErr != CE_None)
+    {
+        ReportError(
+            eFlushBlockErr, CPLE_AppDefined,
+            "An error occurred while writing a dirty block from DropCache");
+        eFlushBlockErr = CE_None;
+    }
+
+    if (poBandBlockCache == nullptr || !poBandBlockCache->IsInitOK())
+        result = eGlobalErr;
+    else
+        result = poBandBlockCache->FlushCache();
+
+    if (poBandBlockCache)
+        poBandBlockCache->EnableDirtyBlockWriting();
+
+    return result;
+}
+
+/************************************************************************/
+/*                        GDALDropRasterCache()                         */
+/************************************************************************/
+
+/**
+* \brief Drop raster data cache.
+*
+* @see GDALRasterBand::DropCache()
+*/
+
+CPLErr CPL_STDCALL GDALDropRasterCache(GDALRasterBandH hBand)
+
+{
+    VALIDATE_POINTER1(hBand, "GDALDropRasterCache", CE_Failure);
+
+    return GDALRasterBand::FromHandle(hBand)->DropCache();
+}
+
 /************************************************************************/
 /*                        UnreferenceBlock()                            */
 /*                                                                      */