Currently each time you instanciate a QgsOgrProvider layer, a GDAL dataset is
created. In the case of GeoPackage, this means a SQLite connection and a file
handle. As GDAL enables Spatialite function on GeoPackage connections, we are
bound to Spatialite limits, and Spatialite has a hard limit on a maximum of
64 simultaneous connections. Thus we cannot open more than 64 layers of the
same GeoPackage.
This commits enables sharing of the same GDALDataset object among several
QgsOgrProvider object. Care is made to reuse a GDALDataset object only if the
QgsOgrProvider do not point to the same layer. Mutexes are also taken to
allow safe instanciation and use of QgsOgrProvider objects from multiple
threads (but a same QgsOgrProvider should not be used by more than one thread
at a time)
With this commit, it's posssible to handle a request from a QgsProject without writing it to the disk.
```python
server = QgsServer()
project = QgsProject()
vlayer = QgsVectorLayer("/path/to/shapefile/file.shp", "layer_name_you_like", "ogr")
project.addMapLayer(vlayer)
query_string = 'https://www.qgis.org/?SERVICE=WMS&VERSION=1.3&REQUEST=GetCapabilities'
request = QgsBufferServerRequest(query_string, QgsServerRequest.GetMethod, {}, data)
response = QgsBufferServerResponse()
server.handleRequest(request, response, project)
```
See description of QgsAuthCertUtils::pkcs8PrivateKey.
This fix may be needed on other platforms (untested at this point),
because Qt5 QSslkey class *still* does not directly support creation
using non-PKCS1 PEM- or DER-encoded data, though QCA, whose qca-ossl
plugin is linked to OpenSSL, does support PKCS1 and PKCS8.
Introducing:
1. STL-style iterator: QgsAbstractGeometry::vertex_iterator
2. Java-style iterator: QgsVertexIterator (built on top of STL-style)
The iterators are modeled after Qt's STL-style and Java-style iterators,
the idea is to replace nextVertex() method and later introduce iterators
for other bits (e.g. part_iterator, ring_iterator).
So it's more inline with the std::as_const implementation which
it fills in for, and allows us to 'polyfill' other c++>11
features into the qgis:: namespace.
