• Tim Peters's avatar
    PyInterpreterState_New is not thread-safe, and the recent fix to _PyPclose · 412f2460
    Tim Peters yazdı
    can cause it to get called by multiple threads simultaneously.
    
    Ditto for PyInterpreterState_Delete.
    
    Of the former, the docs say "The interpreter lock need not be held, but may
    be held if it is necessary to serialize calls to this function".  This
    kinda implies it both is and isn't thread-safe.
    
    Of the latter, the docs merely say "The interpreter lock need not be
    held.", and the clause about serializing is absent.
    
    I expect it was *believed* these are both thread-safe, and the bit about
    serializing via the global lock was meant as a permission rather than a
    caution.
    
    I also expect we've never seen a problem here because the Python core
    (prior to the _PyPclose fix) only calls these functions once per run.
    The Py_NewInterpreter subsystem exposed by the C API (but not used by
    Python itself) also calls them, but that subsystem appears to be very
    rarely used.
    
    Whatever, they're both thread-safe now.
    412f2460
pystate.c 4.73 KB

/* Thread and interpreter state structures and their interfaces */

#include "Python.h"

#define ZAP(x) { \
	PyObject *tmp = (PyObject *)(x); \
	(x) = NULL; \
	Py_XDECREF(tmp); \
}


#ifdef WITH_THREAD
#include "pythread.h"
static PyThread_type_lock head_mutex = NULL; /* Protects interp->tstate_head */
#define HEAD_INIT() (void)(head_mutex || (head_mutex = PyThread_allocate_lock()))
#define HEAD_LOCK() PyThread_acquire_lock(head_mutex, WAIT_LOCK)
#define HEAD_UNLOCK() PyThread_release_lock(head_mutex)
#else
#define HEAD_INIT() /* Nothing */
#define HEAD_LOCK() /* Nothing */
#define HEAD_UNLOCK() /* Nothing */
#endif

static PyInterpreterState *interp_head = NULL;

PyThreadState *_PyThreadState_Current = NULL;


PyInterpreterState *
PyInterpreterState_New(void)
{
	PyInterpreterState *interp = PyMem_NEW(PyInterpreterState, 1);

	if (interp != NULL) {
		HEAD_INIT();
		interp->modules = NULL;
		interp->sysdict = NULL;
		interp->builtins = NULL;
		interp->checkinterval = 10;
		interp->tstate_head = NULL;

		HEAD_LOCK();
		interp->next = interp_head;
		interp_head = interp;
		HEAD_UNLOCK();
	}

	return interp;
}


void
PyInterpreterState_Clear(PyInterpreterState *interp)
{
	PyThreadState *p;
	HEAD_LOCK();
	for (p = interp->tstate_head; p != NULL; p = p->next)
		PyThreadState_Clear(p);
	HEAD_UNLOCK();
	ZAP(interp->modules);
	ZAP(interp->sysdict);
	ZAP(interp->builtins);
}


static void
zapthreads(PyInterpreterState *interp)
{
	PyThreadState *p;
	/* No need to lock the mutex here because this should only happen
	   when the threads are all really dead (XXX famous last words). */
	while ((p = interp->tstate_head) != NULL) {
		PyThreadState_Delete(p);
	}
}


void
PyInterpreterState_Delete(PyInterpreterState *interp)
{
	PyInterpreterState **p;
	zapthreads(interp);
	HEAD_LOCK();
	for (p = &interp_head; ; p = &(*p)->next) {
		if (*p == NULL)
			Py_FatalError(
				"PyInterpreterState_Delete: invalid interp");
		if (*p == interp)
			break;
	}
	if (interp->tstate_head != NULL)
		Py_FatalError("PyInterpreterState_Delete: remaining threads");
	*p = interp->next;
	HEAD_UNLOCK();
	PyMem_DEL(interp);
}


PyThreadState *
PyThreadState_New(PyInterpreterState *interp)
{
	PyThreadState *tstate = PyMem_NEW(PyThreadState, 1);

	if (tstate != NULL) {
		tstate->interp = interp;

		tstate->frame = NULL;
		tstate->recursion_depth = 0;
		tstate->ticker = 0;
		tstate->tracing = 0;

		tstate->dict = NULL;

		tstate->curexc_type = NULL;
		tstate->curexc_value = NULL;
		tstate->curexc_traceback = NULL;

		tstate->exc_type = NULL;
		tstate->exc_value = NULL;
		tstate->exc_traceback = NULL;

		tstate->sys_profilefunc = NULL;
		tstate->sys_tracefunc = NULL;

		HEAD_LOCK();
		tstate->next = interp->tstate_head;
		interp->tstate_head = tstate;
		HEAD_UNLOCK();
	}

	return tstate;
}


void
PyThreadState_Clear(PyThreadState *tstate)
{
	if (Py_VerboseFlag && tstate->frame != NULL)
		fprintf(stderr,
		  "PyThreadState_Clear: warning: thread still has a frame\n");

	ZAP(tstate->frame);

	ZAP(tstate->dict);

	ZAP(tstate->curexc_type);
	ZAP(tstate->curexc_value);
	ZAP(tstate->curexc_traceback);

	ZAP(tstate->exc_type);
	ZAP(tstate->exc_value);
	ZAP(tstate->exc_traceback);

	ZAP(tstate->sys_profilefunc);
	ZAP(tstate->sys_tracefunc);
}


void
PyThreadState_Delete(PyThreadState *tstate)
{
	PyInterpreterState *interp;
	PyThreadState **p;
	if (tstate == NULL)
		Py_FatalError("PyThreadState_Delete: NULL tstate");
	if (tstate == _PyThreadState_Current)
		Py_FatalError("PyThreadState_Delete: tstate is still current");
	interp = tstate->interp;
	if (interp == NULL)
		Py_FatalError("PyThreadState_Delete: NULL interp");
	HEAD_LOCK();
	for (p = &interp->tstate_head; ; p = &(*p)->next) {
		if (*p == NULL)
			Py_FatalError(
				"PyThreadState_Delete: invalid tstate");
		if (*p == tstate)
			break;
	}
	*p = tstate->next;
	HEAD_UNLOCK();
	PyMem_DEL(tstate);
}


PyThreadState *
PyThreadState_Get(void)
{
	if (_PyThreadState_Current == NULL)
		Py_FatalError("PyThreadState_Get: no current thread");

	return _PyThreadState_Current;
}


PyThreadState *
PyThreadState_Swap(PyThreadState *new)
{
	PyThreadState *old = _PyThreadState_Current;

	_PyThreadState_Current = new;

	return old;
}

/* An extension mechanism to store arbitrary additional per-thread state.
   PyThreadState_GetDict() returns a dictionary that can be used to hold such
   state; the caller should pick a unique key and store its state there.  If
   PyThreadState_GetDict() returns NULL, an exception has been raised (most
   likely MemoryError) and the caller should pass on the exception. */

PyObject *
PyThreadState_GetDict(void)
{
	if (_PyThreadState_Current == NULL)
		Py_FatalError("PyThreadState_GetDict: no current thread");

	if (_PyThreadState_Current->dict == NULL)
		_PyThreadState_Current->dict = PyDict_New();
	return _PyThreadState_Current->dict;
}