14.11. Python Hosting
Virtuoso functionality can be enhanced through external libraries by loading shared objects or DLLs. The new functions are written in a language of choice and compiled to produce a shared library appropriate to the operating system. The path to the shared library must be declared in the Virtuoso INI file and the server restarted before it can be used.
The Python language is hosted within Virtuoso in this way.
hosting_python.dll ) is the
The Python hosting module requires the Python library, version
2.2.2 or above, to build and use the module, which then must be
installed in the Plugins-Load-path defined in the Virtuoso ini
file. The source code and build script (
build.py ) for building the
hosting_python.so module are included in
the Unix distribution in the
custom/hosting/python directory. The Unix
installer will offer to build it near the end of the installation
process. The build.py is a kind of Makefile. On unix it requires
cc in the path. On windows it requires
cl.exe in the path.
The Virtuoso INI file uses a [Plugins] configuration section for listing shared libraries for the server to load upon startup. An example of this is:
[Plugins] LoadPath = /home/virtuoso/hosting Load1 = Hosting, hosting_python.so ..
The "Hosting" type defines the entry points for initialization of the runtime hosting environment, destruction of the user environment and execution of a file or string containing commands in the hosted language. It also returns a list of file extensions that it is capable of processing. Virtuoso dynamically defines memory-resident (no disk image) HTTP server handlers for each specified type.
The Python hosting plugin supports the 'py' extension. Hence,
upon initialization of the hosting plugin, Virtuoso defines the
according to the API for file type handlers in the Virtuoso HTTP
server. With this handler in place, each hit on a .py file (file
system or WebDAV) with appropriate execute permissions will cause
the HTTP server to execute the code within it and return the result
instead of simple the file contents.
The python interpreter has a global lock unrelated to the Virtuoso hosting module, thus no more than one thread can run python code at a time.
The handler will call the __hosting_http_handler VSE with a special set of parameters to represent the HTTP environment correctly. Virtuoso will, by default call the plugin to memory as required, and expel it when finished. This behavior can be controlled by the INI file parameter:
[HTTPServer] PersistentHostingModules = 1/0 default 0
PersistentHostingModules to "1" prevents
Virtuoso from removing the interpreters from the HTTP threads after