cpython/Python/pystate.c at 8374981fb4d781d5ddbca313656bd3f32b49cef4 · python/cpython · GitHub

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

#include "Python.h"

/* --------------------------------------------------------------------------

CAUTION

Always use malloc() and free() directly in this file. A number of these

functions are advertised as safe to call when the GIL isn't held, and in

a debug build Python redirects (e.g.) PyMem_NEW (etc) to Python's debugging

obmalloc functions. Those aren't thread-safe (they rely on the GIL to avoid

the expense of doing their own locking).

-------------------------------------------------------------------------- */

#ifdef HAVE_DLOPEN

#ifdef HAVE_DLFCN_H

#include <dlfcn.h>

#endif

#ifndef RTLD_LAZY

#define RTLD_LAZY 1

#endif

#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)

#ifdef __cplusplus

extern "C" {

#endif

/* The single PyInterpreterState used by this process'

GILState implementation

static PyInterpreterState *autoInterpreterState = NULL;

static int autoTLSkey = 0;

#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;

#ifdef WITH_THREAD

static void _PyGILState_NoteThreadState(PyThreadState* tstate);

#endif

PyInterpreterState *

PyInterpreterState_New(void)

{

PyInterpreterState *interp = (PyInterpreterState *)

malloc(sizeof(PyInterpreterState));

if (interp != NULL) {

HEAD_INIT();

#ifdef WITH_THREAD

if (head_mutex == NULL)

Py_FatalError("Can't initialize threads for interpreter");

#endif

interp->modules = NULL;

interp->modules_reloading = NULL;

interp->modules_by_index = 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;

interp->codecs_initialized = 0;

#ifdef HAVE_DLOPEN

#ifdef RTLD_NOW

interp->dlopenflags = RTLD_NOW;

#else

interp->dlopenflags = RTLD_LAZY;

#endif

#ifdef WITH_TSC

interp->tscdump = 0;

#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();

Py_CLEAR(interp->codec_search_path);

Py_CLEAR(interp->codec_search_cache);

Py_CLEAR(interp->codec_error_registry);

Py_CLEAR(interp->modules);

Py_CLEAR(interp->modules_by_index);

Py_CLEAR(interp->modules_reloading);

Py_CLEAR(interp->sysdict);

Py_CLEAR(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();

free(interp);

}

/* Default implementation for _PyThreadState_GetFrame */

static struct _frame *

threadstate_getframe(PyThreadState *self)

{

return self->frame;

}

PyThreadState *

PyThreadState_New(PyInterpreterState *interp)

{

PyThreadState *tstate = (PyThreadState *)malloc(sizeof(PyThreadState));

if (_PyThreadState_GetFrame == NULL)

_PyThreadState_GetFrame = threadstate_getframe;

if (tstate != NULL) {

tstate->interp = interp;

tstate->frame = NULL;

tstate->recursion_depth = 0;

tstate->overflowed = 0;

tstate->recursion_critical = 0;

tstate->tracing = 0;

tstate->use_tracing = 0;

tstate->tick_counter = 0;

tstate->gilstate_counter = 0;

tstate->async_exc = NULL;

#ifdef WITH_THREAD

tstate->thread_id = PyThread_get_thread_ident();

#else

tstate->thread_id = 0;

#endif

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;

#ifdef WITH_THREAD

_PyGILState_NoteThreadState(tstate);

#endif

HEAD_LOCK();

tstate->next = interp->tstate_head;

interp->tstate_head = tstate;

HEAD_UNLOCK();

}

return tstate;

}

PyObject*

PyState_FindModule(struct PyModuleDef* m)

{

Py_ssize_t index = m->m_base.m_index;

PyInterpreterState *state = PyThreadState_GET()->interp;

PyObject *res;

if (index == 0)

return NULL;

if (state->modules_by_index == NULL)

return NULL;

if (index > PyList_GET_SIZE(state->modules_by_index))

return NULL;

res = PyList_GET_ITEM(state->modules_by_index, index);

return res==Py_None ? NULL : res;

}

int

_PyState_AddModule(PyObject* module, struct PyModuleDef* def)

{

PyInterpreterState *state = PyThreadState_GET()->interp;

if (!def)

return -1;

if (!state->modules_by_index) {

state->modules_by_index = PyList_New(0);

if (!state->modules_by_index)

return -1;

}

while(PyList_GET_SIZE(state->modules_by_index) <= def->m_base.m_index)

if (PyList_Append(state->modules_by_index, Py_None) < 0)

return -1;

Py_INCREF(module);

return PyList_SetItem(state->modules_by_index,

def->m_base.m_index, module);

}

void

PyThreadState_Clear(PyThreadState *tstate)

{

if (Py_VerboseFlag && tstate->frame != NULL)

fprintf(stderr,

"PyThreadState_Clear: warning: thread still has a frame\n");

Py_CLEAR(tstate->frame);

Py_CLEAR(tstate->dict);

Py_CLEAR(tstate->async_exc);

Py_CLEAR(tstate->curexc_type);

Py_CLEAR(tstate->curexc_value);

Py_CLEAR(tstate->curexc_traceback);

Py_CLEAR(tstate->exc_type);

Py_CLEAR(tstate->exc_value);

Py_CLEAR(tstate->exc_traceback);

tstate->c_profilefunc = NULL;

tstate->c_tracefunc = NULL;

Py_CLEAR(tstate->c_profileobj);

Py_CLEAR(tstate->c_traceobj);

}

/* Common code for PyThreadState_Delete() and PyThreadState_DeleteCurrent() */

static void

tstate_delete_common(PyThreadState *tstate)

{

PyInterpreterState *interp;

PyThreadState **p;

PyThreadState *prev_p = NULL;

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;

/* Sanity check. These states should never happen but if

* they do we must abort. Otherwise we'll end up spinning in

* in a tight loop with the lock held. A similar check is done

* in thread.c find_key(). */

if (*p == prev_p)

Py_FatalError(

"PyThreadState_Delete: small circular list(!)"

" and tstate not found.");

prev_p = *p;

if ((*p)->next == interp->tstate_head)

Py_FatalError(

"PyThreadState_Delete: circular list(!) and"

" tstate not found.");

}

*p = tstate->next;

HEAD_UNLOCK();

free(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

if (autoTLSkey && PyThread_get_key_value(autoTLSkey) == tstate)

PyThread_delete_key_value(autoTLSkey);

#endif /* WITH_THREAD */

}

#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);

if (autoTLSkey && PyThread_get_key_value(autoTLSkey) == tstate)

PyThread_delete_key_value(autoTLSkey);

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 *newts)

{

PyThreadState *oldts = _PyThreadState_Current;

_PyThreadState_Current = newts;

/* 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) && defined(WITH_THREAD)

if (newts) {

/* This can be called from PyEval_RestoreThread(). Similar

to it, we need to ensure errno doesn't change.

int err = errno;

PyThreadState *check = PyGILState_GetThisThreadState();

if (check && check->interp == newts->interp && check != newts)

Py_FatalError("Invalid thread state for this thread");

errno = err;

}

#endif

return oldts;

}

/* 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;

}

/* Asynchronously raise an exception in a thread.

Requested by Just van Rossum and Alex Martelli.

To prevent naive misuse, you must write your own extension

to call this, or use ctypes. Must be called with the GIL held.

Returns the number of tstates modified (normally 1, but 0 if `id` didn't

match any known thread id). Can be called with exc=NULL to clear an

existing async exception. This raises no exceptions. */

int

PyThreadState_SetAsyncExc(long id, PyObject *exc) {

PyThreadState *tstate = PyThreadState_GET();

PyInterpreterState *interp = tstate->interp;

PyThreadState *p;

/* Although the GIL is held, a few C API functions can be called

* without the GIL held, and in particular some that create and

* destroy thread and interpreter states. Those can mutate the

* list of thread states we're traversing, so to prevent that we lock

* head_mutex for the duration.

HEAD_LOCK();

for (p = interp->tstate_head; p != NULL; p = p->next) {

if (p->thread_id == id) {

/* Tricky: we need to decref the current value

* (if any) in p->async_exc, but that can in turn

* allow arbitrary Python code to run, including

* perhaps calls to this function. To prevent

* deadlock, we need to release head_mutex before

* the decref.

PyObject *old_exc = p->async_exc;

Py_XINCREF(exc);

p->async_exc = exc;

HEAD_UNLOCK();

Py_XDECREF(old_exc);

return 1;

}

HEAD_UNLOCK();

return 0;

}

/* 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;

}

/* The implementation of sys._current_frames(). This is intended to be

called with the GIL held, as it will be when called via

sys._current_frames(). It's possible it would work fine even without

the GIL held, but haven't thought enough about that.

PyObject *

_PyThread_CurrentFrames(void)

{

PyObject *result;

PyInterpreterState *i;

result = PyDict_New();

if (result == NULL)

return NULL;

/* for i in all interpreters:

* for t in all of i's thread states:

* if t's frame isn't NULL, map t's id to its frame

* Because these lists can mutute even when the GIL is held, we

* need to grab head_mutex for the duration.

HEAD_LOCK();

for (i = interp_head; i != NULL; i = i->next) {

PyThreadState *t;

for (t = i->tstate_head; t != NULL; t = t->next) {

PyObject *id;

int stat;

struct _frame *frame = t->frame;

if (frame == NULL)

continue;

id = PyLong_FromLong(t->thread_id);

if (id == NULL)

goto Fail;

stat = PyDict_SetItem(result, id, (PyObject *)frame);

Py_DECREF(id);

if (stat < 0)

goto Fail;

}

HEAD_UNLOCK();

return result;

Fail:

HEAD_UNLOCK();

Py_DECREF(result);

return NULL;

}

/* 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;

}

/* Internal initialization/finalization functions called by

Py_Initialize/Py_Finalize

void

_PyGILState_Init(PyInterpreterState *i, PyThreadState *t)

{

assert(i && t); /* must init with valid states */

autoTLSkey = PyThread_create_key();

autoInterpreterState = i;

assert(PyThread_get_key_value(autoTLSkey) == NULL);

assert(t->gilstate_counter == 0);

_PyGILState_NoteThreadState(t);

}

void

_PyGILState_Fini(void)

{

PyThread_delete_key(autoTLSkey);

autoTLSkey = 0;

autoInterpreterState = NULL;

}

/* When a thread state is created for a thread by some mechanism other than

PyGILState_Ensure, it's important that the GILState machinery knows about

it so it doesn't try to create another thread state for the thread (this is

a better fix for SF bug #1010677 than the first one attempted).

static void

_PyGILState_NoteThreadState(PyThreadState* tstate)

{

/* If autoTLSkey is 0, this must be the very first threadstate created

in Py_Initialize(). Don't do anything for now (we'll be back here

when _PyGILState_Init is called). */

if (!autoTLSkey)

return;

/* Stick the thread state for this thread in thread local storage.

The only situation where you can legitimately have more than one

thread state for an OS level thread is when there are multiple

interpreters, when:

a) You shouldn't really be using the PyGILState_ APIs anyway,

and:

b) The slightly odd way PyThread_set_key_value works (see

comments by its implementation) means that the first thread

state created for that given OS level thread will "win",

which seems reasonable behaviour.

if (PyThread_set_key_value(autoTLSkey, (void *)tstate) < 0)

Py_FatalError("Couldn't create autoTLSkey mapping");

/* PyGILState_Release must not try to delete this thread state. */

tstate->gilstate_counter = 1;

}

/* 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 = (PyThreadState *)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");

/* This is our thread state! We'll need to delete it in the

matching call to PyGILState_Release(). */

tcur->gilstate_counter = 0;

current = 0; /* new thread state is never current */

}

else

current = PyThreadState_IsCurrent(tcur);

if (current == 0)

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 = (PyThreadState *)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;

assert(tcur->gilstate_counter >= 0); /* illegal counter value */

/* If we're going to destroy this thread-state, we must

* clear it while the GIL 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);

/* Delete the thread-state. Note this releases the GIL too!

* It's vital that the GIL be held here, to avoid shutdown

* races; see bugs 225673 and 1061968 (that nasty bug has a

* habit of coming back).

PyThreadState_DeleteCurrent();

}

/* Release the lock if necessary */

else if (oldstate == PyGILState_UNLOCKED)

PyEval_SaveThread();

}

#ifdef __cplusplus

}

#endif

#endif /* WITH_THREAD */

cpython/Python/pystate.c at 8374981fb4d781d5ddbca313656bd3f32b49cef4 · python/cpython · GitHub

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