| Graham Dumpleton (JIRA) 2005-09-06, 2:46 am |
| [ http://issues.apache.org/jira/brows...action_12322710 ]
Graham Dumpleton commented on MODPYTHON-77:
-------------------------------------------
I worked out what was going on a few days ago, but first time with Internet access since. :-(
I agree that what is being proposed is reasonable provided that correct changes which will work for any version of 2.3 or later versions of Python.
Some further clarification on the issue.
1. The new API does not really break the concept of multiple interpreters. What it means is that if someone is lazy enough to use the new API they limit their extension to only being usable with the first created interpreter. Someone can still use the exi
sting APIs and write the extension to work in a multi interpreter context.
2. Even with the patches, an extension will still not work properly. In order to work it is important that PythonImport and
PythonInterpreter be used as appropriate and that "main_interpreter" be explicitly specified. This means that one can't have multiple interpreters for different virtual hosts or applications which is a big shortcoming.
In short, extensions writers should be discouraged from using the new API if want to work with mod_python.
Out ot time, gotta go.
> The multiple interpreter concept of mod_python is broken for Python extension modules since Python 2.3
> ------------------------------------------------------------------------------------------------------
>
> Key: MODPYTHON-77
> URL: http://issues.apache.org/jira/browse/MODPYTHON-77
> Project: mod_python
> Type: Bug
> Components: core
> Versions: 3.1.4
> Environment: Python >= 2.3
> Reporter: Boyan Boyadjiev
> Attachments: diff.txt, diff2.txt, diff3.txt, gil_test.c, mod_python.c, mod_python.c.diff, mod_python.h.diff, src.zip
>
> The multiple interpreter concept of mod_python is broken for Python extension modules since Python 2.3 because of the PEP 311 (Simplified Global Interpreter Lock Acquisition for Extensions):
> ...
> Limitations and Exclusions
> This proposal identifies a solution for extension authors with
> complex multi-threaded requirements, but that only require a
> single "PyInterpreterState". There is no attempt to cater for
> extensions that require multiple interpreter states. At the time
> of writing, no extension has been identified that requires
> multiple PyInterpreterStates, and indeed it is not clear if that
> facility works correctly in Python itself.
> ...
> For mod_python this means, that complex Python extensions won't work any more with Python >= 2.3, because they are supposed to work only with the first interpreter state initialized for the current process (a problem we experienced). The first interpret
er state is not used by mod_python after the python_init is called.
> One solution, which works fine for me, is to save the first interpreter state into the "interpreters" dictionary in the function python_init (MAIN_INTERPRETER is used as a key):
> static int python_init(apr_pool_t *p, apr_pool_t *ptemp,
> apr_pool_t *plog, server_rec *s)
> {
> ...
> /* initialize global Python interpreter if necessary */
> if (! Py_IsInitialized())
> {
> /* initialze the interpreter */
> Py_Initialize();
> #ifdef WITH_THREAD
> /* create and acquire the interpreter lock */
> PyEval_InitThreads();
> #endif
> /* create the obCallBack dictionary */
> interpreters = PyDict_New();
> if (! interpreters) {
> ap_log_error(APLOG_MARK, APLOG_NOERRNO|APLOG_ERR, 0, s,
> "python_init: PyDict_New() failed! No more memory?");
> exit(1);
> }
> {
> /*
> Workaround PEP 311 - Simplified Global Interpreter Lock Acquisition for Extensions
> BEGIN
> */
> PyObject *p = 0;
> interpreterdata * idata = (interpreterdata *)malloc(sizeof(interpreterdata));
> PyThreadState* currentThreadState = PyThreadState_Get();
> PyInterpreterState *istate = currentThreadState->interp;
> idata->istate = istate;
> /* obcallback will be created on first use */
> idata->obcallback = NULL;
> p = PyCObject_FromVoidPtr((void ) idata, NULL); /*p->refcout = 1*/
> PyDict_SetItemString(interpreters, MAIN_INTERPRETER, p); /*p->refcout = 2*/
> Py_DECREF(p); /*p->refcout = 1*/
> /*
> END
> Workaround PEP 311 - Simplified Global Interpreter Lock Acquisition for Extensions
> */
> }
> /* Release the thread state because we will never use
> * the main interpreter, only sub interpreters created later. */
> PyThreadState_Swap(NULL);
> #ifdef WITH_THREAD
> /* release the lock; now other threads can run */
> PyEval_ReleaseLock();
> #endif
> }
> return OK;
> }
> Another change I've made in the attached file is to Py_DECREF(p) in get_interpreter, which will remove leaky reference to the PyCObject with the interpreter data. This was not a real problem, but now I see fewer leaks in BoundsChecker :-).
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