#include "Python.h"

#include "pycore_call.h" // _PyObject_VectorcallTstate()

#include "pycore_context.h"

#include "pycore_freelist.h" // _Py_FREELIST_FREE(), _Py_FREELIST_POP()

#include "pycore_gc.h" // _PyObject_GC_MAY_BE_TRACKED()

#include "pycore_hamt.h"

#include "pycore_initconfig.h" // _PyStatus_OK()

#include "pycore_object.h"

#include "pycore_pyerrors.h"

#include "pycore_pystate.h" // _PyThreadState_GET()

#include "clinic/context.c.h"

/*[clinic input]

module _contextvars

[clinic start generated code]*/

/*[clinic end generated code: output=da39a3ee5e6b4b0d input=a0955718c8b8cea6]*/

#define ENSURE_Context(o, err_ret) \

if (!PyContext_CheckExact(o)) { \

PyErr_SetString(PyExc_TypeError, \

"an instance of Context was expected"); \

return err_ret; \

}

#define ENSURE_ContextVar(o, err_ret) \

if (!PyContextVar_CheckExact(o)) { \

PyErr_SetString(PyExc_TypeError, \

"an instance of ContextVar was expected"); \

return err_ret; \

}

#define ENSURE_ContextToken(o, err_ret) \

if (!PyContextToken_CheckExact(o)) { \

PyErr_SetString(PyExc_TypeError, \

"an instance of Token was expected"); \

return err_ret; \

}

/////////////////////////// Context API

static PyContext *

context_new_empty(void);

static PyContext *

context_new_from_vars(PyHamtObject *vars);

static inline PyContext *

context_get(void);

static PyContextToken *

token_new(PyContext *ctx, PyContextVar *var, PyObject *val);

static PyContextVar *

contextvar_new(PyObject *name, PyObject *def);

static int

contextvar_set(PyContextVar *var, PyObject *val);

static int

contextvar_del(PyContextVar *var);

PyObject *

_PyContext_NewHamtForTests(void)

{

return (PyObject *)_PyHamt_New();

}

PyObject *

PyContext_New(void)

{

return (PyObject *)context_new_empty();

}

PyObject *

PyContext_Copy(PyObject * octx)

{

ENSURE_Context(octx, NULL)

PyContext *ctx = (PyContext *)octx;

return (PyObject *)context_new_from_vars(ctx->ctx_vars);

}

PyObject *

PyContext_CopyCurrent(void)

{

PyContext *ctx = context_get();

if (ctx == NULL) {

return NULL;

}

return (PyObject *)context_new_from_vars(ctx->ctx_vars);

}

static const char *

context_event_name(PyContextEvent event) {

switch (event) {

case Py_CONTEXT_EVENT_ENTER:

return "Py_CONTEXT_EVENT_ENTER";

case Py_CONTEXT_EVENT_EXIT:

return "Py_CONTEXT_EVENT_EXIT";

default:

return "?";

}

Py_UNREACHABLE();

}

static void notify_context_watchers(PyContextEvent event, PyContext *ctx, PyThreadState *ts)

{

assert(Py_REFCNT(ctx) > 0);

PyInterpreterState *interp = ts->interp;

assert(interp->_initialized);

uint8_t bits = interp->active_context_watchers;

int i = 0;

while (bits) {

assert(i < CONTEXT_MAX_WATCHERS);

if (bits & 1) {

PyContext_WatchCallback cb = interp->context_watchers[i];

assert(cb != NULL);

if (cb(event, ctx) < 0) {

PyErr_FormatUnraisable(

"Exception ignored in %s watcher callback for %R",

context_event_name(event), ctx);

}

}

i++;

bits >>= 1;

}

}

int

PyContext_AddWatcher(PyContext_WatchCallback callback)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->_initialized);

for (int i = 0; i < CONTEXT_MAX_WATCHERS; i++) {

if (!interp->context_watchers[i]) {

interp->context_watchers[i] = callback;

interp->active_context_watchers |= (1 << i);

return i;

}

}

PyErr_SetString(PyExc_RuntimeError, "no more context watcher IDs available");

return -1;

}

int

PyContext_ClearWatcher(int watcher_id)

{

PyInterpreterState *interp = _PyInterpreterState_GET();

assert(interp->_initialized);

if (watcher_id < 0 || watcher_id >= CONTEXT_MAX_WATCHERS) {

PyErr_Format(PyExc_ValueError, "Invalid context watcher ID %d", watcher_id);

return -1;

}

if (!interp->context_watchers[watcher_id]) {

PyErr_Format(PyExc_ValueError, "No context watcher set for ID %d", watcher_id);

return -1;

}

interp->context_watchers[watcher_id] = NULL;

interp->active_context_watchers &= ~(1 << watcher_id);

return 0;

}

static int

_PyContext_Enter(PyThreadState *ts, PyObject *octx)

{

ENSURE_Context(octx, -1)

PyContext *ctx = (PyContext *)octx;

if (ctx->ctx_entered) {

_PyErr_Format(ts, PyExc_RuntimeError,

"cannot enter context: %R is already entered", ctx);

return -1;

}

ctx->ctx_prev = (PyContext *)ts->context; /* borrow */

ctx->ctx_entered = 1;

ts->context = Py_NewRef(ctx);

ts->context_ver++;

notify_context_watchers(Py_CONTEXT_EVENT_ENTER, ctx, ts);

return 0;

}

int

PyContext_Enter(PyObject *octx)

{

PyThreadState *ts = _PyThreadState_GET();

assert(ts != NULL);

return _PyContext_Enter(ts, octx);

}

static int

_PyContext_Exit(PyThreadState *ts, PyObject *octx)

{

ENSURE_Context(octx, -1)

PyContext *ctx = (PyContext *)octx;

if (!ctx->ctx_entered) {

PyErr_Format(PyExc_RuntimeError,

"cannot exit context: %R has not been entered", ctx);

return -1;

}

if (ts->context != (PyObject *)ctx) {

/* Can only happen if someone misuses the C API */

PyErr_SetString(PyExc_RuntimeError,

"cannot exit context: thread state references "

"a different context object");

return -1;

}

notify_context_watchers(Py_CONTEXT_EVENT_EXIT, ctx, ts);

Py_SETREF(ts->context, (PyObject *)ctx->ctx_prev);

ts->context_ver++;

ctx->ctx_prev = NULL;

ctx->ctx_entered = 0;

return 0;

}

int

PyContext_Exit(PyObject *octx)

{

PyThreadState *ts = _PyThreadState_GET();

assert(ts != NULL);

return _PyContext_Exit(ts, octx);

}

PyObject *

PyContextVar_New(const char *name, PyObject *def)

{

PyObject *pyname = PyUnicode_FromString(name);

if (pyname == NULL) {

return NULL;

}

PyContextVar *var = contextvar_new(pyname, def);

Py_DECREF(pyname);

return (PyObject *)var;

}

int

PyContextVar_Get(PyObject *ovar, PyObject *def, PyObject **val)

{

ENSURE_ContextVar(ovar, -1)

PyContextVar *var = (PyContextVar *)ovar;

PyThreadState *ts = _PyThreadState_GET();

assert(ts != NULL);

if (ts->context == NULL) {

goto not_found;

}

#ifndef Py_GIL_DISABLED

if (var->var_cached != NULL &&

var->var_cached_tsid == ts->id &&

var->var_cached_tsver == ts->context_ver)

{

*val = var->var_cached;

goto found;

}

#endif

assert(PyContext_CheckExact(ts->context));

PyHamtObject *vars = ((PyContext *)ts->context)->ctx_vars;

PyObject *found = NULL;

int res = _PyHamt_Find(vars, (PyObject*)var, &found);

if (res < 0) {

goto error;

}

if (res == 1) {

assert(found != NULL);

#ifndef Py_GIL_DISABLED

var->var_cached = found; /* borrow */

var->var_cached_tsid = ts->id;

var->var_cached_tsver = ts->context_ver;

#endif

*val = found;

goto found;

}

not_found:

if (def == NULL) {

if (var->var_default != NULL) {

*val = var->var_default;

goto found;

}

*val = NULL;

goto found;

}

else {

*val = def;

goto found;

}

found:

Py_XINCREF(*val);

return 0;

error:

*val = NULL;

return -1;

}

PyObject *

PyContextVar_Set(PyObject *ovar, PyObject *val)

{

ENSURE_ContextVar(ovar, NULL)

PyContextVar *var = (PyContextVar *)ovar;

if (!PyContextVar_CheckExact(var)) {

PyErr_SetString(

PyExc_TypeError, "an instance of ContextVar was expected");

return NULL;

}

PyContext *ctx = context_get();

if (ctx == NULL) {

return NULL;

}

PyObject *old_val = NULL;

int found = _PyHamt_Find(ctx->ctx_vars, (PyObject *)var, &old_val);

if (found < 0) {

return NULL;

}

Py_XINCREF(old_val);

PyContextToken *tok = token_new(ctx, var, old_val);

Py_XDECREF(old_val);

if (contextvar_set(var, val)) {

Py_DECREF(tok);

return NULL;

}

return (PyObject *)tok;

}

int

PyContextVar_Reset(PyObject *ovar, PyObject *otok)

{

ENSURE_ContextVar(ovar, -1)

ENSURE_ContextToken(otok, -1)

PyContextVar *var = (PyContextVar *)ovar;

PyContextToken *tok = (PyContextToken *)otok;

if (tok->tok_used) {

PyErr_Format(PyExc_RuntimeError,

"%R has already been used once", tok);

return -1;

}

if (var != tok->tok_var) {

PyErr_Format(PyExc_ValueError,

"%R was created by a different ContextVar", tok);

return -1;

}

PyContext *ctx = context_get();

if (ctx != tok->tok_ctx) {

PyErr_Format(PyExc_ValueError,

"%R was created in a different Context", tok);

return -1;

}

tok->tok_used = 1;

if (tok->tok_oldval == NULL) {

return contextvar_del(var);

}

else {

return contextvar_set(var, tok->tok_oldval);

}

}

/////////////////////////// PyContext

/*[clinic input]

class _contextvars.Context "PyContext *" "&PyContext_Type"

[clinic start generated code]*/

/*[clinic end generated code: output=da39a3ee5e6b4b0d input=bdf87f8e0cb580e8]*/

static inline PyContext *

_context_alloc(void)

{

PyContext *ctx = _Py_FREELIST_POP(PyContext, contexts);

if (ctx == NULL) {

ctx = PyObject_GC_New(PyContext, &PyContext_Type);

if (ctx == NULL) {

return NULL;

}

}

ctx->ctx_vars = NULL;

ctx->ctx_prev = NULL;

ctx->ctx_entered = 0;

ctx->ctx_weakreflist = NULL;

return ctx;

}

static PyContext *

context_new_empty(void)

{

PyContext *ctx = _context_alloc();

if (ctx == NULL) {

return NULL;

}

ctx->ctx_vars = _PyHamt_New();

if (ctx->ctx_vars == NULL) {

Py_DECREF(ctx);

return NULL;

}

_PyObject_GC_TRACK(ctx);

return ctx;

}

static PyContext *

context_new_from_vars(PyHamtObject *vars)

{

PyContext *ctx = _context_alloc();

if (ctx == NULL) {

return NULL;

}

ctx->ctx_vars = (PyHamtObject*)Py_NewRef(vars);

_PyObject_GC_TRACK(ctx);

return ctx;

}

static inline PyContext *

context_get(void)

{

PyThreadState *ts = _PyThreadState_GET();

assert(ts != NULL);

PyContext *current_ctx = (PyContext *)ts->context;

if (current_ctx == NULL) {

current_ctx = context_new_empty();

if (current_ctx == NULL) {

return NULL;

}

ts->context = (PyObject *)current_ctx;

}

return current_ctx;

}

static int

context_check_key_type(PyObject *key)

{

if (!PyContextVar_CheckExact(key)) {

// abort();

PyErr_Format(PyExc_TypeError,

"a ContextVar key was expected, got %R", key);

return -1;

}

return 0;

}

static PyObject *

context_tp_new(PyTypeObject *type, PyObject *args, PyObject *kwds)

{

if (PyTuple_Size(args) || (kwds != NULL && PyDict_Size(kwds))) {

PyErr_SetString(

PyExc_TypeError, "Context() does not accept any arguments");

return NULL;

}

return PyContext_New();

}

static int

context_tp_clear(PyContext *self)

{

Py_CLEAR(self->ctx_prev);

Py_CLEAR(self->ctx_vars);

return 0;

}

static int

context_tp_traverse(PyContext *self, visitproc visit, void *arg)

{

Py_VISIT(self->ctx_prev);

Py_VISIT(self->ctx_vars);

return 0;

}

static void

context_tp_dealloc(PyContext *self)

{

_PyObject_GC_UNTRACK(self);

if (self->ctx_weakreflist != NULL) {

PyObject_ClearWeakRefs((PyObject*)self);

}

(void)context_tp_clear(self);

_Py_FREELIST_FREE(contexts, self, Py_TYPE(self)->tp_free);

}

static PyObject *

context_tp_iter(PyContext *self)

{

return _PyHamt_NewIterKeys(self->ctx_vars);

}

static PyObject *

context_tp_richcompare(PyObject *v, PyObject *w, int op)

{

if (!PyContext_CheckExact(v) || !PyContext_CheckExact(w) ||

(op != Py_EQ && op != Py_NE))

{

Py_RETURN_NOTIMPLEMENTED;

}

int res = _PyHamt_Eq(

((PyContext *)v)->ctx_vars, ((PyContext *)w)->ctx_vars);

if (res < 0) {

return NULL;

}

if (op == Py_NE) {

res = !res;

}

if (res) {

Py_RETURN_TRUE;

}

else {

Py_RETURN_FALSE;

}

}

static Py_ssize_t

context_tp_len(PyContext *self)

{

return _PyHamt_Len(self->ctx_vars);

}

static PyObject *

context_tp_subscript(PyContext *self, PyObject *key)

{

if (context_check_key_type(key)) {

return NULL;

}

PyObject *val = NULL;

int found = _PyHamt_Find(self->ctx_vars, key, &val);

if (found < 0) {

return NULL;

}

if (found == 0) {

PyErr_SetObject(PyExc_KeyError, key);

return NULL;

}

return Py_NewRef(val);

}

static int

context_tp_contains(PyContext *self, PyObject *key)

{

if (context_check_key_type(key)) {

return -1;

}

PyObject *val = NULL;

return _PyHamt_Find(self->ctx_vars, key, &val);

}

/*[clinic input]

_contextvars.Context.get

key: object

default: object = None

/

Return the value for `key` if `key` has the value in the context object.

If `key` does not exist, return `default`. If `default` is not given,

return None.

[clinic start generated code]*/

static PyObject *

_contextvars_Context_get_impl(PyContext *self, PyObject *key,

PyObject *default_value)

/*[clinic end generated code: output=0c54aa7664268189 input=c8eeb81505023995]*/

{

if (context_check_key_type(key)) {

return NULL;

}

PyObject *val = NULL;

int found = _PyHamt_Find(self->ctx_vars, key, &val);

if (found < 0) {

return NULL;

}

if (found == 0) {

return Py_NewRef(default_value);

}

return Py_NewRef(val);

}

/*[clinic input]

_contextvars.Context.items

Return all variables and their values in the context object.

The result is returned as a list of 2-tuples (variable, value).

[clinic start generated code]*/

static PyObject *

_contextvars_Context_items_impl(PyContext *self)

/*[clinic end generated code: output=fa1655c8a08502af input=00db64ae379f9f42]*/

{

return _PyHamt_NewIterItems(self->ctx_vars);

}

/*[clinic input]

_contextvars.Context.keys

Return a list of all variables in the context object.

[clinic start generated code]*/

static PyObject *

_contextvars_Context_keys_impl(PyContext *self)

/*[clinic end generated code: output=177227c6b63ec0e2 input=114b53aebca3449c]*/

{

return _PyHamt_NewIterKeys(self->ctx_vars);

}

/*[clinic input]

_contextvars.Context.values

Return a list of all variables' values in the context object.

[clinic start generated code]*/

static PyObject *

_contextvars_Context_values_impl(PyContext *self)

/*[clinic end generated code: output=d286dabfc8db6dde input=ce8075d04a6ea526]*/

{

return _PyHamt_NewIterValues(self->ctx_vars);

}

/*[clinic input]

_contextvars.Context.copy

Return a shallow copy of the context object.

[clinic start generated code]*/

static PyObject *

_contextvars_Context_copy_impl(PyContext *self)

/*[clinic end generated code: output=30ba8896c4707a15 input=ebafdbdd9c72d592]*/

{

return (PyObject *)context_new_from_vars(self->ctx_vars);

}

static PyObject *

context_run(PyContext *self, PyObject *const *args,

Py_ssize_t nargs, PyObject *kwnames)

{

PyThreadState *ts = _PyThreadState_GET();

if (nargs < 1) {

_PyErr_SetString(ts, PyExc_TypeError,

"run() missing 1 required positional argument");

return NULL;

}

if (_PyContext_Enter(ts, (PyObject *)self)) {

return NULL;

}

PyObject *call_result = _PyObject_VectorcallTstate(

ts, args[0], args + 1, nargs - 1, kwnames);

if (_PyContext_Exit(ts, (PyObject *)self)) {

Py_XDECREF(call_result);

return NULL;

}

return call_result;

}

static PyMethodDef PyContext_methods[] = {

_CONTEXTVARS_CONTEXT_GET_METHODDEF

_CONTEXTVARS_CONTEXT_ITEMS_METHODDEF

_CONTEXTVARS_CONTEXT_KEYS_METHODDEF

_CONTEXTVARS_CONTEXT_VALUES_METHODDEF

_CONTEXTVARS_CONTEXT_COPY_METHODDEF

{"run", _PyCFunction_CAST(context_run), METH_FASTCALL | METH_KEYWORDS, NULL},

{NULL, NULL}

};

static PySequenceMethods PyContext_as_sequence = {

0, /* sq_length */

0, /* sq_concat */

0, /* sq_repeat */

0, /* sq_item */

0, /* sq_slice */

0, /* sq_ass_item */

0, /* sq_ass_slice */

(objobjproc)context_tp_contains, /* sq_contains */

0, /* sq_inplace_concat */

0, /* sq_inplace_repeat */

};

static PyMappingMethods PyContext_as_mapping = {

(lenfunc)context_tp_len, /* mp_length */

(binaryfunc)context_tp_subscript, /* mp_subscript */

};

PyTypeObject PyContext_Type = {

PyVarObject_HEAD_INIT(&PyType_Type, 0)

"_contextvars.Context",

sizeof(PyContext),

.tp_methods = PyContext_methods,

.tp_as_mapping = &PyContext_as_mapping,

.tp_as_sequence = &PyContext_as_sequence,

.tp_iter = (getiterfunc)context_tp_iter,

.tp_dealloc = (destructor)context_tp_dealloc,

.tp_getattro = PyObject_GenericGetAttr,

.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,

.tp_richcompare = context_tp_richcompare,

.tp_traverse = (traverseproc)context_tp_traverse,

.tp_clear = (inquiry)context_tp_clear,

.tp_new = context_tp_new,

.tp_weaklistoffset = offsetof(PyContext, ctx_weakreflist),

.tp_hash = PyObject_HashNotImplemented,

};

/////////////////////////// ContextVar

static int

contextvar_set(PyContextVar *var, PyObject *val)

{

#ifndef Py_GIL_DISABLED

var->var_cached = NULL;

PyThreadState *ts = _PyThreadState_GET();

#endif

PyContext *ctx = context_get();

if (ctx == NULL) {

return -1;

}

PyHamtObject *new_vars = _PyHamt_Assoc(

ctx->ctx_vars, (PyObject *)var, val);

if (new_vars == NULL) {

return -1;

}

Py_SETREF(ctx->ctx_vars, new_vars);

#ifndef Py_GIL_DISABLED

var->var_cached = val; /* borrow */

var->var_cached_tsid = ts->id;

var->var_cached_tsver = ts->context_ver;

#endif

return 0;

}

static int

contextvar_del(PyContextVar *var)

{

#ifndef Py_GIL_DISABLED

var->var_cached = NULL;

#endif

PyContext *ctx = context_get();

if (ctx == NULL) {

return -1;

}

PyHamtObject *vars = ctx->ctx_vars;

PyHamtObject *new_vars = _PyHamt_Without(vars, (PyObject *)var);

if (new_vars == NULL) {

return -1;

}

if (vars == new_vars) {

Py_DECREF(new_vars);

PyErr_SetObject(PyExc_LookupError, (PyObject *)var);

return -1;

}

Py_SETREF(ctx->ctx_vars, new_vars);

return 0;

}

static Py_hash_t

contextvar_generate_hash(void *addr, PyObject *name)

{

/* Take hash of `name` and XOR it with the object's addr.

The structure of the tree is encoded in objects' hashes, which

means that sufficiently similar hashes would result in tall trees

with many Collision nodes. Which would, in turn, result in slower

get and set operations.

The XORing helps to ensure that:

(1) sequentially allocated ContextVar objects have

different hashes;

(2) context variables with equal names have

different hashes.

*/

Py_hash_t name_hash = PyObject_Hash(name);

if (name_hash == -1) {

return -1;

}

Py_hash_t res = _Py_HashPointer(addr) ^ name_hash;

return res == -1 ? -2 : res;

}

static PyContextVar *

contextvar_new(PyObject *name, PyObject *def)

{

if (!PyUnicode_Check(name)) {

PyErr_SetString(PyExc_TypeError,

"context variable name must be a str");

return NULL;

}

PyContextVar *var = PyObject_GC_New(PyContextVar, &PyContextVar_Type);

if (var == NULL) {

return NULL;

}

var->var_hash = contextvar_generate_hash(var, name);

if (var->var_hash == -1) {

Py_DECREF(var);

return NULL;

}

var->var_name = Py_NewRef(name);

var->var_default = Py_XNewRef(def);

#ifndef Py_GIL_DISABLED

var->var_cached = NULL;

var->var_cached_tsid = 0;

var->var_cached_tsver = 0;

#endif

if (_PyObject_GC_MAY_BE_TRACKED(name) ||

(def != NULL && _PyObject_GC_MAY_BE_TRACKED(def)))

{

PyObject_GC_Track(var);

}

return var;

}

/*[clinic input]

class _contextvars.ContextVar "PyContextVar *" "&PyContextVar_Type"

[clinic start generated code]*/

/*[clinic end generated code: output=da39a3ee5e6b4b0d input=445da935fa8883c3]*/

static PyObject *

contextvar_tp_new(PyTypeObject *type, PyObject *args, PyObject *kwds)

{

static char *kwlist[] = {"", "default", NULL};

PyObject *name;

PyObject *def = NULL;

if (!PyArg_ParseTupleAndKeywords(

args, kwds, "O|$O:ContextVar", kwlist, &name, &def))

{

return NULL;

}

return (PyObject *)contextvar_new(name, def);

}

static int

contextvar_tp_clear(PyContextVar *self)

{

Py_CLEAR(self->var_name);

Py_CLEAR(self->var_default);

#ifndef Py_GIL_DISABLED

self->var_cached = NULL;

self->var_cached_tsid = 0;

self->var_cached_tsver = 0;

#endif

return 0;

}

static int

contextvar_tp_traverse(PyContextVar *self, visitproc visit, void *arg)

{

Py_VISIT(self->var_name);

Py_VISIT(self->var_default);

return 0;

}

static void

contextvar_tp_dealloc(PyContextVar *self)

{

PyObject_GC_UnTrack(self);

(void)contextvar_tp_clear(self);

Py_TYPE(self)->tp_free(self);

}

static Py_hash_t

contextvar_tp_hash(PyContextVar *self)

{

return self->var_hash;

}

static PyObject *

contextvar_tp_repr(PyContextVar *self)

{

// Estimation based on the shortest name and default value,

// but maximize the pointer size.

// "<ContextVar name='a' at 0x1234567812345678>"

// "<ContextVar name='a' default=1 at 0x1234567812345678>"

Py_ssize_t estimate = self->var_default ? 53 : 43;

PyUnicodeWriter *writer = PyUnicodeWriter_Create(estimate);

if (writer == NULL) {

return NULL;

}

if (PyUnicodeWriter_WriteUTF8(writer, "<ContextVar name=", 17) < 0) {

goto error;

}

if (PyUnicodeWriter_WriteRepr(writer, self->var_name) < 0) {

goto error;

}

if (self->var_default != NULL) {

if (PyUnicodeWriter_WriteUTF8(writer, " default=", 9) < 0) {

goto error;

}

if (PyUnicodeWriter_WriteRepr(writer, self->var_default) < 0) {

goto error;

}

}

if (PyUnicodeWriter_Format(writer, " at %p>", self) < 0) {

goto error;

}

return PyUnicodeWriter_Finish(writer);

error:

PyUnicodeWriter_Discard(writer);

return NULL;

}

/*[clinic input]

_contextvars.ContextVar.get

default: object = NULL

/

Return a value for the context variable for the current context.

If there is no value for the variable in the current context, the method will:

* return the value of the default argument of the method, if provided; or

* return the default value for the context variable, if it was created