I'm unclear on why the sub-interpreter API exists and why it's used in modules such as the mod_wsgi apache module. Is it mainly used for creating a security sandbox for different applications running within the same process, or is it a way to allow concurrency with multiple threads? Maybe both? Are there other purposes?
I imagine the purpose is to create separate python execution environments. For instance, mod_wsgi (Apache Python module) hosts a single python interpreter and then hosts multiple applications within sub-interpreters (in the default configuration).
Some key points from the documentation:
- This is an (almost) totally separate environment for the execution of Python code. In particular, the new interpreter has separate, independent versions of all imported modules, including the fundamental modules
__builtin__,__main__andsys. - The table of loaded modules (sys.modules) and the module search path (sys.path) are also separate.
- Because sub-interpreters (and the main interpreter) are part of the same process, the insulation between them isn’t perfect — for example, using low-level file operations like os.close() they can (accidentally or maliciously) affect each other’s open files.
- Because of the way extensions are shared between (sub-)interpreters, some extensions may not work properly; this is especially likely when the extension makes use of (static) global variables, or when the extension manipulates its module’s dictionary after its initialization.
As I understood it last, the idea was to be able to execute multiple applications as well as multiple copies of the same application within the same process.
This is a feature found in other scripting languages (e.g. TCL), and is of particular use to gui builders, web servers, etc.
It breaks in python because many extensions are not multiple-interpreter safe, so one interpreter's actions could affect the variables in another interpreter.
来源：https://stackoverflow.com/questions/755070/what-is-the-purpose-of-the-sub-interpreter-api-in-cpython