GDALDataset的创建和销毁

之前在GDALDestroyDriverManager 分析中没有看到对dGDALDatasert的回收。先看一个例子程序，这个例子打开了一个tif文件，读取了一些基本信息。

为了简单示范，没有写成C++的各种类分散到各个文件中。

#include "stdafx.h"#include "gdal_priv.h"#include "cpl_conv.h" // for CPLMalloc()#include <string>#include <iostream>#include <sstream>#include <iomanip>#include <boost/cstdint.hpp>using namespace std;void print_line() {cout << "----------------------" << endl;}void printDataType(GDALDataType type) {if (type == GDALDataType::GDT_Byte) {cout << "GDALDataType: GDT_Byte" << endl;} else {cout << "GDALDataType: GDT_Unknown" << endl;}}void printAccess(GDALAccess access) {if (access == GDALAccess::GA_ReadOnly) {cout << "GDALAccess: GA_ReadOnly" << endl;} else {cout << "GDALAccess: GA_Update" << endl;}}void printCategoryNames(char** names) {if (names == NULL) {cout << "non category names" << endl;return;}size_t i = 0;char* str = names[i];while(str != "") {cout << str << endl;str = names[i];}}void printColorInterp(GDALColorInterp interp) {switch(interp) {case GDALColorInterp::GCI_AlphaBand:cout << "GDALColorInterp: GCI_AlphaBand" << endl;break;case GDALColorInterp::GCI_BlackBand:cout << "GDALColorInterp: GCI_BlackBand" << endl;break;case GDALColorInterp::GCI_RedBand:cout << "GDALColorInterp: GCI_RedBand" << endl;break;case GDALColorInterp::GCI_GreenBand:cout << "GDALColorInterp: GCI_GreenBand" << endl;break;case GDALColorInterp::GCI_BlueBand:cout << "GDALColorInterp: GCI_BlueBand" << endl;break;default:cout << "GDALColorInterp: GCI_Undefined: " << interp << endl;}}void printColorTable(GDALColorTable* table) {if (table == NULL) {cout << "color table is null" << endl;return;}cout << "ColorEntryCount: " << table->GetColorEntryCount() << endl;}string getBytesAsHexString(uint8_t * data, size_t size) {stringstream stream;stream << std::hex << std::uppercase << std::setfill('0');for (size_t i = 0; i < size; ++i) {stream <<std::setw(2) << static_cast<uint32_t>(data[i] & 0xff) << " ";}return stream.str();}void printBand(GDALRasterBand* band) {cout << "XSize: " << band->GetXSize() << endl;cout << "YSize: " << band->GetYSize() << endl;cout << "Band number(index for itself): " << band->GetBand() << endl;printDataType(band->GetRasterDataType());int x_size = 0;int y_size = 0;band->GetBlockSize(&x_size, &y_size);cout << "Band Block size, x size: " << x_size << " pixels , y size: " << y_size << " pixels" << endl;printAccess(band->GetAccess());printCategoryNames(band->GetCategoryNames());cout << "no data value: " << band->GetNoDataValue() << endl;cout << "minimum value: " << band->GetMinimum() << endl;cout << "maximum value: " << band->GetMaximum() << endl;cout << "offset value: " << band->GetOffset() << endl;cout << "scale value: " << band->GetScale() << endl;cout << "unit type: " << band->GetUnitType() << endl;printColorInterp(band->GetColorInterpretation());printColorTable(band->GetColorTable());GByte * data = static_cast<GByte*>(CPLMalloc(x_size * y_size));band->ReadBlock(5000, 3000, data);cout << "one block data: " << getBytesAsHexString(data, x_size * y_size) << endl;}void printTiffInfo(GDALDataset* set) {print_line();cout << "Tiff info " << endl;cout << "RasterXSize: " << set->GetRasterXSize() << endl;cout << "RasterYSize: " << set->GetRasterYSize() << endl;size_t band_count = set->GetRasterCount();cout << "Raster band count: " << band_count << endl;for (size_t i = 1; i <= band_count; ++i) {GDALRasterBand* band = set->GetRasterBand(i);print_line();cout << "Band " << i << " : " << endl;printBand(band);}}int _tmain(int argc, _TCHAR* argv[]){GDALAllRegister();string data_dir = "../../../study/data/";string tiffPath = data_dir + "v4_dem_gtopo30/v4_dem.tif";GDALDataset* dataset = (GDALDataset *) GDALOpen(tiffPath.c_str(), GA_ReadOnly);    if (dataset == NULL) {cout << "open ttf file in TiffCopy app failed" << endl;GDALDestroyDriverManager();exit(1);    }cout << "loading tiff file successfully" << endl;printTiffInfo(dataset);GDALClose(dataset);GDALDestroyDriverManager();return 0;}

在main函数中，用GDALOpen打开了一个tif文件，并且获得了GDALDataset对象的指针，然后用GDALClose销毁了这个对象。下面是GDALClose代码：

/** * \brief Close GDAL dataset.  * * For non-shared datasets (opened with GDALOpen()) the dataset is closed * using the C++ "delete" operator, recovering all dataset related resources.   * For shared datasets (opened with GDALOpenShared()) the dataset is  * dereferenced, and closed only if the referenced count has dropped below 1. * * @param hDS The dataset to close.  May be cast from a "GDALDataset *".  */void CPL_STDCALL GDALClose( GDALDatasetH hDS ){    VALIDATE_POINTER0( hDS, "GDALClose" );    GDALDataset *poDS = (GDALDataset *) hDS;    CPLMutexHolderD( &hDLMutex );    CPLLocaleC  oLocaleForcer;    if (poDS->GetShared())    {/* -------------------------------------------------------------------- *//*      If this file is in the shared dataset list then dereference     *//*      it, and only delete/remote it if the reference count has        *//*      dropped to zero.                                                *//* -------------------------------------------------------------------- */        if( poDS->Dereference() > 0 )            return;        delete poDS;        return;    }/* -------------------------------------------------------------------- *//*      This is not shared dataset, so directly delete it.              *//* -------------------------------------------------------------------- */    delete poDS;}

注释表明GDALDataset支持普通和引用计数管理两种生命周期管理方式。代码中表明在销毁的时候使用了互斥量，因此是线程安全的。