Python/pystate.c

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

#include "Python.h"

#ifdef HAVE_DLOPEN
#ifdef HAVE_DLFCN_H
#include <dlfcn.h>
#endif
#ifndef RTLD_LAZY
#define RTLD_LAZY 1
#endif
#endif


#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;
PyThreadFrameGetter _PyThreadState_GetFrame = 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->tstate_head = NULL;
		interp->codec_search_path = NULL;
		interp->codec_search_cache = NULL;
		interp->codec_error_registry = NULL;
#ifdef HAVE_DLOPEN
#ifdef RTLD_NOW
                interp->dlopenflags = RTLD_NOW;
#else
		interp->dlopenflags = RTLD_LAZY;
#endif
#endif

		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->codec_search_path);
	ZAP(interp->codec_search_cache);
	ZAP(interp->codec_error_registry);
	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);
}


/* Default implementation for _PyThreadState_GetFrame */
static struct _frame *
threadstate_getframe(PyThreadState *self)
{
	return self->frame;
}

PyThreadState *
PyThreadState_New(PyInterpreterState *interp)
{
	PyThreadState *tstate = PyMem_NEW(PyThreadState, 1);
	if (_PyThreadState_GetFrame == NULL)
		_PyThreadState_GetFrame = threadstate_getframe;

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

		tstate->frame = NULL;
		tstate->recursion_depth = 0;
		tstate->tracing = 0;
		tstate->use_tracing = 0;
		tstate->tick_counter = 0;
		tstate->gilstate_counter = 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->c_profilefunc = NULL;
		tstate->c_tracefunc = NULL;
		tstate->c_profileobj = NULL;
		tstate->c_traceobj = 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);

	tstate->c_profilefunc = NULL;
	tstate->c_tracefunc = NULL;
	ZAP(tstate->c_profileobj);
	ZAP(tstate->c_traceobj);
}


/* Common code for PyThreadState_Delete() and PyThreadState_DeleteCurrent() */
static void
tstate_delete_common(PyThreadState *tstate)
{
	PyInterpreterState *interp;
	PyThreadState **p;
	if (tstate == NULL)
		Py_FatalError("PyThreadState_Delete: NULL tstate");
	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);
}


void
PyThreadState_Delete(PyThreadState *tstate)
{
	if (tstate == _PyThreadState_Current)
		Py_FatalError("PyThreadState_Delete: tstate is still current");
	tstate_delete_common(tstate);
}


#ifdef WITH_THREAD
void
PyThreadState_DeleteCurrent()
{
	PyThreadState *tstate = _PyThreadState_Current;
	if (tstate == NULL)
		Py_FatalError(
			"PyThreadState_DeleteCurrent: no current tstate");
	_PyThreadState_Current = NULL;
	tstate_delete_common(tstate);
	PyEval_ReleaseLock();
}
#endif /* WITH_THREAD */


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;
	/* It should not be possible for more than one thread state
	   to be used for a thread.  Check this the best we can in debug 
	   builds.
	*/
#if defined(Py_DEBUG)
	if (new) {
		PyThreadState *check = PyGILState_GetThisThreadState();
		if (check && check != new)
			Py_FatalError("Invalid thread state for this thread");
	}
#endif
	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 *not* been raised
   and the caller should assume no per-thread state is available. */

PyObject *
PyThreadState_GetDict(void)
{
	if (_PyThreadState_Current == NULL)
		return NULL;

	if (_PyThreadState_Current->dict == NULL) {
		PyObject *d;
		_PyThreadState_Current->dict = d = PyDict_New();
		if (d == NULL)
			PyErr_Clear();
	}
	return _PyThreadState_Current->dict;
}


/* Routines for advanced debuggers, requested by David Beazley.
   Don't use unless you know what you are doing! */

PyInterpreterState *
PyInterpreterState_Head(void)
{
	return interp_head;
}

PyInterpreterState *
PyInterpreterState_Next(PyInterpreterState *interp) {
	return interp->next;
}

PyThreadState *
PyInterpreterState_ThreadHead(PyInterpreterState *interp) {
	return interp->tstate_head;
}

PyThreadState *
PyThreadState_Next(PyThreadState *tstate) {
	return tstate->next;
}

/* Python "auto thread state" API. */
#ifdef WITH_THREAD

/* Keep this as a static, as it is not reliable!  It can only
   ever be compared to the state for the *current* thread.
   * If not equal, then it doesn't matter that the actual
     value may change immediately after comparison, as it can't
     possibly change to the current thread's state.
   * If equal, then the current thread holds the lock, so the value can't
     change until we yield the lock.
*/
static int
PyThreadState_IsCurrent(PyThreadState *tstate)
{
	/* Must be the tstate for this thread */
	assert(PyGILState_GetThisThreadState()==tstate);
	/* On Windows at least, simple reads and writes to 32 bit values
	   are atomic.
	*/
	return tstate == _PyThreadState_Current;
}

/* The single PyInterpreterState used by this process'
   GILState implementation
*/
static PyInterpreterState *autoInterpreterState = NULL;
static int autoTLSkey = 0;

/* Internal initialization/finalization functions called by 
   Py_Initialize/Py_Finalize 
*/
void _PyGILState_Init(PyInterpreterState *i, PyThreadState *t)
{
	assert(i && t); /* must init with a valid states */
	autoTLSkey = PyThread_create_key();
	autoInterpreterState = i;
	/* Now stash the thread state for this thread in TLS */
	PyThread_set_key_value(autoTLSkey, (void *)t);
	assert(t->gilstate_counter==0); /* must be a new thread state */
	t->gilstate_counter = 1;
}

void _PyGILState_Fini(void)
{
	PyThread_delete_key(autoTLSkey);
	autoTLSkey = 0;
	autoInterpreterState = NULL;;
}

/* The public functions */
PyThreadState *PyGILState_GetThisThreadState(void)
{
	if (autoInterpreterState==NULL || autoTLSkey==0)
		return NULL;
	return (PyThreadState *) PyThread_get_key_value(autoTLSkey);
}

PyGILState_STATE PyGILState_Ensure(void)
{
	int current;
	PyThreadState *tcur;
	/* Note that we do not auto-init Python here - apart from 
	   potential races with 2 threads auto-initializing, pep-311 
	   spells out other issues.  Embedders are expected to have
	   called Py_Initialize() and usually PyEval_InitThreads().
	*/
	assert(autoInterpreterState); /* Py_Initialize() hasn't been called! */
	tcur = PyThread_get_key_value(autoTLSkey);
	if (tcur==NULL) {
		/* Create a new thread state for this thread */
		tcur = PyThreadState_New(autoInterpreterState);
		if (tcur==NULL)
			Py_FatalError("Couldn't create thread-state for new thread");
		PyThread_set_key_value(autoTLSkey, (void *)tcur);
		current = 0; /* new thread state is never current */
	} else
		current = PyThreadState_IsCurrent(tcur);
	if (!current)
		PyEval_RestoreThread(tcur);
	/* Update our counter in the thread-state - no need for locks:
	   - tcur will remain valid as we hold the GIL.
	   - the counter is safe as we are the only thread "allowed" 
	     to modify this value
	*/
	tcur->gilstate_counter++;
	return current ? PyGILState_LOCKED : PyGILState_UNLOCKED;
}

void PyGILState_Release(PyGILState_STATE oldstate)
{
	PyThreadState *tcur = PyThread_get_key_value(autoTLSkey);
	if (tcur==NULL)
		Py_FatalError("auto-releasing thread-state, "
		              "but no thread-state for this thread");
	/* We must hold the GIL and have our thread state current */
	/* XXX - remove the check - the assert should be fine,
	   but while this is very new (April 2003), the extra check 
	   by release-only users can't hurt.
	*/
	if (!PyThreadState_IsCurrent(tcur))
		Py_FatalError("This thread state must be current when releasing");
	assert (PyThreadState_IsCurrent(tcur));
	tcur->gilstate_counter -= 1;
	assert (tcur->gilstate_counter >= 0); /* illegal counter value */

	/* If we are about to destroy this thread-state, we must 
	   clear it while the lock is held, as destructors may run
	*/
	if (tcur->gilstate_counter==0) {
		/* can't have been locked when we created it */
		assert(oldstate==PyGILState_UNLOCKED);
		PyThreadState_Clear(tcur);
	}

	/* Release the lock if necessary */
	if (oldstate==PyGILState_UNLOCKED)
		PyEval_ReleaseThread(tcur);

	/* Now complete destruction of the thread if necessary */
	if (tcur->gilstate_counter==0) {
		/* Delete this thread from our TLS */
		PyThread_delete_key_value(autoTLSkey);
		/* Delete the thread-state */
		PyThreadState_Delete(tcur);
	}
}
#endif /* WITH_THREAD */