venv

1 files changed, 714 insertions, 0 deletions

diff --git a/venv/lib/python3.11/site-packages/greenlet/TGreenlet.cpp b/venv/lib/python3.11/site-packages/greenlet/TGreenlet.cpp
new file mode 100644
index 0000000..51f8995
--- /dev/null
+++ b/venv/lib/python3.11/site-packages/greenlet/TGreenlet.cpp
@@ -0,0 +1,714 @@
+/* -*- indent-tabs-mode: nil; tab-width: 4; -*- */
+/**
+ * Implementation of greenlet::Greenlet.
+ *
+ * Format with:
+ *  clang-format -i --style=file src/greenlet/greenlet.c
+ *
+ *
+ * Fix missing braces with:
+ *   clang-tidy src/greenlet/greenlet.c -fix -checks="readability-braces-around-statements"
+*/
+
+#include "greenlet_internal.hpp"
+#include "greenlet_greenlet.hpp"
+#include "greenlet_thread_state.hpp"
+
+#include "TGreenletGlobals.cpp"
+#include "TThreadStateDestroy.cpp"
+
+namespace greenlet {
+
+Greenlet::Greenlet(PyGreenlet* p)
+{
+    p ->pimpl = this;
+}
+
+Greenlet::~Greenlet()
+{
+    // XXX: Can't do this. tp_clear is a virtual function, and by the
+    // time we're here, we've sliced off our child classes.
+    //this->tp_clear();
+}
+
+Greenlet::Greenlet(PyGreenlet* p, const StackState& initial_stack)
+    : stack_state(initial_stack)
+{
+    // can't use a delegating constructor because of
+    // MSVC for Python 2.7
+    p->pimpl = this;
+}
+
+bool
+Greenlet::force_slp_switch_error() const noexcept
+{
+    return false;
+}
+
+void
+Greenlet::release_args()
+{
+    this->switch_args.CLEAR();
+}
+
+/**
+ * CAUTION: This will allocate memory and may trigger garbage
+ * collection and arbitrary Python code.
+ */
+OwnedObject
+Greenlet::throw_GreenletExit_during_dealloc(const ThreadState& UNUSED(current_thread_state))
+{
+    // If we're killed because we lost all references in the
+    // middle of a switch, that's ok. Don't reset the args/kwargs,
+    // we still want to pass them to the parent.
+    PyErr_SetString(mod_globs->PyExc_GreenletExit,
+                    "Killing the greenlet because all references have vanished.");
+    // To get here it had to have run before
+    return this->g_switch();
+}
+
+inline void
+Greenlet::slp_restore_state() noexcept
+{
+#ifdef SLP_BEFORE_RESTORE_STATE
+    SLP_BEFORE_RESTORE_STATE();
+#endif
+    this->stack_state.copy_heap_to_stack(
+           this->thread_state()->borrow_current()->stack_state);
+}
+
+
+inline int
+Greenlet::slp_save_state(char *const stackref) noexcept
+{
+    // XXX: This used to happen in the middle, before saving, but
+    // after finding the next owner. Does that matter? This is
+    // only defined for Sparc/GCC where it flushes register
+    // windows to the stack (I think)
+#ifdef SLP_BEFORE_SAVE_STATE
+    SLP_BEFORE_SAVE_STATE();
+#endif
+    return this->stack_state.copy_stack_to_heap(stackref,
+                                                this->thread_state()->borrow_current()->stack_state);
+}
+
+/**
+ * CAUTION: This will allocate memory and may trigger garbage
+ * collection and arbitrary Python code.
+ */
+OwnedObject
+Greenlet::on_switchstack_or_initialstub_failure(
+    Greenlet* target,
+    const Greenlet::switchstack_result_t& err,
+    const bool target_was_me,
+    const bool was_initial_stub)
+{
+    // If we get here, either g_initialstub()
+    // failed, or g_switchstack() failed. Either one of those
+    // cases SHOULD leave us in the original greenlet with a valid stack.
+    if (!PyErr_Occurred()) {
+        PyErr_SetString(
+            PyExc_SystemError,
+            was_initial_stub
+            ? "Failed to switch stacks into a greenlet for the first time."
+            : "Failed to switch stacks into a running greenlet.");
+    }
+    this->release_args();
+
+    if (target && !target_was_me) {
+        target->murder_in_place();
+    }
+
+    assert(!err.the_new_current_greenlet);
+    assert(!err.origin_greenlet);
+    return OwnedObject();
+
+}
+
+OwnedGreenlet
+Greenlet::g_switchstack_success() noexcept
+{
+    PyThreadState* tstate = PyThreadState_GET();
+    // restore the saved state
+    this->python_state >> tstate;
+    this->exception_state >> tstate;
+
+    // The thread state hasn't been changed yet.
+    ThreadState* thread_state = this->thread_state();
+    OwnedGreenlet result(thread_state->get_current());
+    thread_state->set_current(this->self());
+    //assert(thread_state->borrow_current().borrow() == this->_self);
+    return result;
+}
+
+Greenlet::switchstack_result_t
+Greenlet::g_switchstack(void)
+{
+    // if any of these assertions fail, it's likely because we
+    // switched away and tried to switch back to us. Early stages of
+    // switching are not reentrant because we re-use ``this->args()``.
+    // Switching away would happen if we trigger a garbage collection
+    // (by just using some Python APIs that happen to allocate Python
+    // objects) and some garbage had weakref callbacks or __del__ that
+    // switches (people don't write code like that by hand, but with
+    // gevent it's possible without realizing it)
+    assert(this->args() || PyErr_Occurred());
+    { /* save state */
+        if (this->thread_state()->is_current(this->self())) {
+            // Hmm, nothing to do.
+            // TODO: Does this bypass trace events that are
+            // important?
+            return switchstack_result_t(0,
+                                        this, this->thread_state()->borrow_current());
+        }
+        BorrowedGreenlet current = this->thread_state()->borrow_current();
+        PyThreadState* tstate = PyThreadState_GET();
+
+        current->python_state << tstate;
+        current->exception_state << tstate;
+        this->python_state.will_switch_from(tstate);
+        switching_thread_state = this;
+        current->expose_frames();
+    }
+    assert(this->args() || PyErr_Occurred());
+    // If this is the first switch into a greenlet, this will
+    // return twice, once with 1 in the new greenlet, once with 0
+    // in the origin.
+    int err;
+    if (this->force_slp_switch_error()) {
+        err = -1;
+    }
+    else {
+        err = slp_switch();
+    }
+
+    if (err < 0) { /* error */
+        // Tested by
+        // test_greenlet.TestBrokenGreenlets.test_failed_to_slp_switch_into_running
+        //
+        // It's not clear if it's worth trying to clean up and
+        // continue here. Failing to switch stacks is a big deal which
+        // may not be recoverable (who knows what state the stack is in).
+        // Also, we've stolen references in preparation for calling
+        // ``g_switchstack_success()`` and we don't have a clean
+        // mechanism for backing that all out.
+        Py_FatalError("greenlet: Failed low-level slp_switch(). The stack is probably corrupt.");
+    }
+
+    // No stack-based variables are valid anymore.
+
+    // But the global is volatile so we can reload it without the
+    // compiler caching it from earlier.
+    Greenlet* greenlet_that_switched_in = switching_thread_state; // aka this
+    switching_thread_state = nullptr;
+    // except that no stack variables are valid, we would:
+    // assert(this == greenlet_that_switched_in);
+
+    // switchstack success is where we restore the exception state,
+    // etc. It returns the origin greenlet because its convenient.
+
+    OwnedGreenlet origin = greenlet_that_switched_in->g_switchstack_success();
+    assert(greenlet_that_switched_in->args() || PyErr_Occurred());
+    return switchstack_result_t(err, greenlet_that_switched_in, origin);
+}
+
+
+inline void
+Greenlet::check_switch_allowed() const
+{
+    // TODO: Make this take a parameter of the current greenlet,
+    // or current main greenlet, to make the check for
+    // cross-thread switching cheaper. Surely somewhere up the
+    // call stack we've already accessed the thread local variable.
+
+    // We expect to always have a main greenlet now; accessing the thread state
+    // created it. However, if we get here and cleanup has already
+    // begun because we're a greenlet that was running in a
+    // (now dead) thread, these invariants will not hold true. In
+    // fact, accessing `this->thread_state` may not even be possible.
+
+    // If the thread this greenlet was running in is dead,
+    // we'll still have a reference to a main greenlet, but the
+    // thread state pointer we have is bogus.
+    // TODO: Give the objects an API to determine if they belong
+    // to a dead thread.
+
+    const BorrowedMainGreenlet main_greenlet = this->find_main_greenlet_in_lineage();
+
+    if (!main_greenlet) {
+        throw PyErrOccurred(mod_globs->PyExc_GreenletError,
+                            "cannot switch to a garbage collected greenlet");
+    }
+
+    if (!main_greenlet->thread_state()) {
+        throw PyErrOccurred(mod_globs->PyExc_GreenletError,
+                            "cannot switch to a different thread (which happens to have exited)");
+    }
+
+    // The main greenlet we found was from the .parent lineage.
+    // That may or may not have any relationship to the main
+    // greenlet of the running thread. We can't actually access
+    // our this->thread_state members to try to check that,
+    // because it could be in the process of getting destroyed,
+    // but setting the main_greenlet->thread_state member to NULL
+    // may not be visible yet. So we need to check against the
+    // current thread state (once the cheaper checks are out of
+    // the way)
+    const BorrowedMainGreenlet current_main_greenlet = GET_THREAD_STATE().state().borrow_main_greenlet();
+    if (
+        // lineage main greenlet is not this thread's greenlet
+        current_main_greenlet != main_greenlet
+        || (
+            // atteched to some thread
+            this->main_greenlet()
+            // XXX: Same condition as above. Was this supposed to be
+            // this->main_greenlet()?
+            && current_main_greenlet != main_greenlet)
+        // switching into a known dead thread (XXX: which, if we get here,
+        // is bad, because we just accessed the thread state, which is
+        // gone!)
+        || (!current_main_greenlet->thread_state())) {
+        // CAUTION: This may trigger memory allocations, gc, and
+        // arbitrary Python code.
+        throw PyErrOccurred(mod_globs->PyExc_GreenletError,
+                            "cannot switch to a different thread");
+    }
+}
+
+const OwnedObject
+Greenlet::context() const
+{
+    using greenlet::PythonStateContext;
+    OwnedObject result;
+
+    if (this->is_currently_running_in_some_thread()) {
+        /* Currently running greenlet: context is stored in the thread state,
+           not the greenlet object. */
+        if (GET_THREAD_STATE().state().is_current(this->self())) {
+            result = PythonStateContext::context(PyThreadState_GET());
+        }
+        else {
+            throw ValueError(
+                            "cannot get context of a "
+                            "greenlet that is running in a different thread");
+        }
+    }
+    else {
+        /* Greenlet is not running: just return context. */
+        result = this->python_state.context();
+    }
+    if (!result) {
+        result = OwnedObject::None();
+    }
+    return result;
+}
+
+
+void
+Greenlet::context(BorrowedObject given)
+{
+    using greenlet::PythonStateContext;
+    if (!given) {
+        throw AttributeError("can't delete context attribute");
+    }
+    if (given.is_None()) {
+        /* "Empty context" is stored as NULL, not None. */
+        given = nullptr;
+    }
+
+    //checks type, incrs refcnt
+    greenlet::refs::OwnedContext context(given);
+    PyThreadState* tstate = PyThreadState_GET();
+
+    if (this->is_currently_running_in_some_thread()) {
+        if (!GET_THREAD_STATE().state().is_current(this->self())) {
+            throw ValueError("cannot set context of a greenlet"
+                             " that is running in a different thread");
+        }
+
+        /* Currently running greenlet: context is stored in the thread state,
+           not the greenlet object. */
+        OwnedObject octx = OwnedObject::consuming(PythonStateContext::context(tstate));
+        PythonStateContext::context(tstate, context.relinquish_ownership());
+    }
+    else {
+        /* Greenlet is not running: just set context. Note that the
+           greenlet may be dead.*/
+        this->python_state.context() = context;
+    }
+}
+
+/**
+ * CAUTION: May invoke arbitrary Python code.
+ *
+ * Figure out what the result of ``greenlet.switch(arg, kwargs)``
+ * should be and transfers ownership of it to the left-hand-side.
+ *
+ * If switch() was just passed an arg tuple, then we'll just return that.
+ * If only keyword arguments were passed, then we'll pass the keyword
+ * argument dict. Otherwise, we'll create a tuple of (args, kwargs) and
+ * return both.
+ *
+ * CAUTION: This may allocate a new tuple object, which may
+ * cause the Python garbage collector to run, which in turn may
+ * run arbitrary Python code that switches.
+ */
+OwnedObject& operator<<=(OwnedObject& lhs, greenlet::SwitchingArgs& rhs) noexcept
+{
+    // Because this may invoke arbitrary Python code, which could
+    // result in switching back to us, we need to get the
+    // arguments locally on the stack.
+    assert(rhs);
+    OwnedObject args = rhs.args();
+    OwnedObject kwargs = rhs.kwargs();
+    rhs.CLEAR();
+    // We shouldn't be called twice for the same switch.
+    assert(args || kwargs);
+    assert(!rhs);
+
+    if (!kwargs) {
+        lhs = args;
+    }
+    else if (!PyDict_Size(kwargs.borrow())) {
+        lhs = args;
+    }
+    else if (!PySequence_Length(args.borrow())) {
+        lhs = kwargs;
+    }
+    else {
+        // PyTuple_Pack allocates memory, may GC, may run arbitrary
+        // Python code.
+        lhs = OwnedObject::consuming(PyTuple_Pack(2, args.borrow(), kwargs.borrow()));
+    }
+    return lhs;
+}
+
+static OwnedObject
+g_handle_exit(const OwnedObject& greenlet_result)
+{
+    if (!greenlet_result && mod_globs->PyExc_GreenletExit.PyExceptionMatches()) {
+        /* catch and ignore GreenletExit */
+        PyErrFetchParam val;
+        PyErr_Fetch(PyErrFetchParam(), val, PyErrFetchParam());
+        if (!val) {
+            return OwnedObject::None();
+        }
+        return OwnedObject(val);
+    }
+
+    if (greenlet_result) {
+        // package the result into a 1-tuple
+        // PyTuple_Pack increments the reference of its arguments,
+        // so we always need to decref the greenlet result;
+        // the owner will do that.
+        return OwnedObject::consuming(PyTuple_Pack(1, greenlet_result.borrow()));
+    }
+
+    return OwnedObject();
+}
+
+
+
+/**
+ * May run arbitrary Python code.
+ */
+OwnedObject
+Greenlet::g_switch_finish(const switchstack_result_t& err)
+{
+    assert(err.the_new_current_greenlet == this);
+
+    ThreadState& state = *this->thread_state();
+    // Because calling the trace function could do arbitrary things,
+    // including switching away from this greenlet and then maybe
+    // switching back, we need to capture the arguments now so that
+    // they don't change.
+    OwnedObject result;
+    if (this->args()) {
+        result <<= this->args();
+    }
+    else {
+        assert(PyErr_Occurred());
+    }
+    assert(!this->args());
+    try {
+        // Our only caller handles the bad error case
+        assert(err.status >= 0);
+        assert(state.borrow_current() == this->self());
+        if (OwnedObject tracefunc = state.get_tracefunc()) {
+            assert(result || PyErr_Occurred());
+            g_calltrace(tracefunc,
+                        result ? mod_globs->event_switch : mod_globs->event_throw,
+                        err.origin_greenlet,
+                        this->self());
+        }
+        // The above could have invoked arbitrary Python code, but
+        // it couldn't switch back to this object and *also*
+        // throw an exception, so the args won't have changed.
+
+        if (PyErr_Occurred()) {
+            // We get here if we fell of the end of the run() function
+            // raising an exception. The switch itself was
+            // successful, but the function raised.
+            // valgrind reports that memory allocated here can still
+            // be reached after a test run.
+            throw PyErrOccurred::from_current();
+        }
+        return result;
+    }
+    catch (const PyErrOccurred&) {
+        /* Turn switch errors into switch throws */
+        /* Turn trace errors into switch throws */
+        this->release_args();
+        throw;
+    }
+}
+
+void
+Greenlet::g_calltrace(const OwnedObject& tracefunc,
+                      const greenlet::refs::ImmortalEventName& event,
+                      const BorrowedGreenlet& origin,
+                      const BorrowedGreenlet& target)
+{
+    PyErrPieces saved_exc;
+    try {
+        TracingGuard tracing_guard;
+        // TODO: We have saved the active exception (if any) that's
+        // about to be raised. In the 'throw' case, we could provide
+        // the exception to the tracefunction, which seems very helpful.
+        tracing_guard.CallTraceFunction(tracefunc, event, origin, target);
+    }
+    catch (const PyErrOccurred&) {
+        // In case of exceptions trace function is removed,
+        // and any existing exception is replaced with the tracing
+        // exception.
+        GET_THREAD_STATE().state().set_tracefunc(Py_None);
+        throw;
+    }
+
+    saved_exc.PyErrRestore();
+    assert(
+        (event == mod_globs->event_throw && PyErr_Occurred())
+        || (event == mod_globs->event_switch && !PyErr_Occurred())
+    );
+}
+
+void
+Greenlet::murder_in_place()
+{
+    if (this->active()) {
+        assert(!this->is_currently_running_in_some_thread());
+        this->deactivate_and_free();
+    }
+}
+
+inline void
+Greenlet::deactivate_and_free()
+{
+    if (!this->active()) {
+        return;
+    }
+    // Throw away any saved stack.
+    this->stack_state = StackState();
+    assert(!this->stack_state.active());
+    // Throw away any Python references.
+    // We're holding a borrowed reference to the last
+    // frame we executed. Since we borrowed it, the
+    // normal traversal, clear, and dealloc functions
+    // ignore it, meaning it leaks. (The thread state
+    // object can't find it to clear it when that's
+    // deallocated either, because by definition if we
+    // got an object on this list, it wasn't
+    // running and the thread state doesn't have
+    // this frame.)
+    // So here, we *do* clear it.
+    this->python_state.tp_clear(true);
+}
+
+bool
+Greenlet::belongs_to_thread(const ThreadState* thread_state) const
+{
+    if (!this->thread_state() // not running anywhere, or thread
+                              // exited
+        || !thread_state) { // same, or there is no thread state.
+        return false;
+    }
+    return true;
+}
+
+
+void
+Greenlet::deallocing_greenlet_in_thread(const ThreadState* current_thread_state)
+{
+    /* Cannot raise an exception to kill the greenlet if
+       it is not running in the same thread! */
+    if (this->belongs_to_thread(current_thread_state)) {
+        assert(current_thread_state);
+        // To get here it had to have run before
+        /* Send the greenlet a GreenletExit exception. */
+
+        // We don't care about the return value, only whether an
+        // exception happened.
+        this->throw_GreenletExit_during_dealloc(*current_thread_state);
+        return;
+    }
+
+    // Not the same thread! Temporarily save the greenlet
+    // into its thread's deleteme list, *if* it exists.
+    // If that thread has already exited, and processed its pending
+    // cleanup, we'll never be able to clean everything up: we won't
+    // be able to raise an exception.
+    // That's mostly OK! Since we can't add it to a list, our refcount
+    // won't increase, and we'll go ahead with the DECREFs later.
+    ThreadState *const  thread_state = this->thread_state();
+    if (thread_state) {
+        thread_state->delete_when_thread_running(this->self());
+    }
+    else {
+        // The thread is dead, we can't raise an exception.
+        // We need to make it look non-active, though, so that dealloc
+        // finishes killing it.
+        this->deactivate_and_free();
+    }
+    return;
+}
+
+
+int
+Greenlet::tp_traverse(visitproc visit, void* arg)
+{
+
+    int result;
+    if ((result = this->exception_state.tp_traverse(visit, arg)) != 0) {
+        return result;
+    }
+    //XXX: This is ugly. But so is handling everything having to do
+    //with the top frame.
+    bool visit_top_frame = this->was_running_in_dead_thread();
+    // When true, the thread is dead. Our implicit weak reference to the
+    // frame is now all that's left; we consider ourselves to
+    // strongly own it now.
+    if ((result = this->python_state.tp_traverse(visit, arg, visit_top_frame)) != 0) {
+        return result;
+    }
+    return 0;
+}
+
+int
+Greenlet::tp_clear()
+{
+    bool own_top_frame = this->was_running_in_dead_thread();
+    this->exception_state.tp_clear();
+    this->python_state.tp_clear(own_top_frame);
+    return 0;
+}
+
+bool Greenlet::is_currently_running_in_some_thread() const
+{
+    return this->stack_state.active() && !this->python_state.top_frame();
+}
+
+#if GREENLET_PY312
+void GREENLET_NOINLINE(Greenlet::expose_frames)()
+{
+    if (!this->python_state.top_frame()) {
+        return;
+    }
+
+    _PyInterpreterFrame* last_complete_iframe = nullptr;
+    _PyInterpreterFrame* iframe = this->python_state.top_frame()->f_frame;
+    while (iframe) {
+        // We must make a copy before looking at the iframe contents,
+        // since iframe might point to a portion of the greenlet's C stack
+        // that was spilled when switching greenlets.
+        _PyInterpreterFrame iframe_copy;
+        this->stack_state.copy_from_stack(&iframe_copy, iframe, sizeof(*iframe));
+        if (!_PyFrame_IsIncomplete(&iframe_copy)) {
+            // If the iframe were OWNED_BY_CSTACK then it would always be
+            // incomplete. Since it's not incomplete, it's not on the C stack
+            // and we can access it through the original `iframe` pointer
+            // directly.  This is important since GetFrameObject might
+            // lazily _create_ the frame object and we don't want the
+            // interpreter to lose track of it.
+            assert(iframe_copy.owner != FRAME_OWNED_BY_CSTACK);
+
+            // We really want to just write:
+            //     PyFrameObject* frame = _PyFrame_GetFrameObject(iframe);
+            // but _PyFrame_GetFrameObject calls _PyFrame_MakeAndSetFrameObject
+            // which is not a visible symbol in libpython. The easiest
+            // way to get a public function to call it is using
+            // PyFrame_GetBack, which is defined as follows:
+            //     assert(frame != NULL);
+            //     assert(!_PyFrame_IsIncomplete(frame->f_frame));
+            //     PyFrameObject *back = frame->f_back;
+            //     if (back == NULL) {
+            //         _PyInterpreterFrame *prev = frame->f_frame->previous;
+            //         prev = _PyFrame_GetFirstComplete(prev);
+            //         if (prev) {
+            //             back = _PyFrame_GetFrameObject(prev);
+            //         }
+            //     }
+            //     return (PyFrameObject*)Py_XNewRef(back);
+            if (!iframe->frame_obj) {
+                PyFrameObject dummy_frame;
+                _PyInterpreterFrame dummy_iframe;
+                dummy_frame.f_back = nullptr;
+                dummy_frame.f_frame = &dummy_iframe;
+                // force the iframe to be considered complete without
+                // needing to check its code object:
+                dummy_iframe.owner = FRAME_OWNED_BY_GENERATOR;
+                dummy_iframe.previous = iframe;
+                assert(!_PyFrame_IsIncomplete(&dummy_iframe));
+                // Drop the returned reference immediately; the iframe
+                // continues to hold a strong reference
+                Py_XDECREF(PyFrame_GetBack(&dummy_frame));
+                assert(iframe->frame_obj);
+            }
+
+            // This is a complete frame, so make the last one of those we saw
+            // point at it, bypassing any incomplete frames (which may have
+            // been on the C stack) in between the two. We're overwriting
+            // last_complete_iframe->previous and need that to be reversible,
+            // so we store the original previous ptr in the frame object
+            // (which we must have created on a previous iteration through
+            // this loop). The frame object has a bunch of storage that is
+            // only used when its iframe is OWNED_BY_FRAME_OBJECT, which only
+            // occurs when the frame object outlives the frame's execution,
+            // which can't have happened yet because the frame is currently
+            // executing as far as the interpreter is concerned. So, we can
+            // reuse it for our own purposes.
+            assert(iframe->owner == FRAME_OWNED_BY_THREAD
+                   || iframe->owner == FRAME_OWNED_BY_GENERATOR);
+            if (last_complete_iframe) {
+                assert(last_complete_iframe->frame_obj);
+                memcpy(&last_complete_iframe->frame_obj->_f_frame_data[0],
+                       &last_complete_iframe->previous, sizeof(void *));
+                last_complete_iframe->previous = iframe;
+            }
+            last_complete_iframe = iframe;
+        }
+        // Frames that are OWNED_BY_FRAME_OBJECT are linked via the
+        // frame's f_back while all others are linked via the iframe's
+        // previous ptr. Since all the frames we traverse are running
+        // as far as the interpreter is concerned, we don't have to
+        // worry about the OWNED_BY_FRAME_OBJECT case.
+        iframe = iframe_copy.previous;
+    }
+
+    // Give the outermost complete iframe a null previous pointer to
+    // account for any potential incomplete/C-stack iframes between it
+    // and the actual top-of-stack
+    if (last_complete_iframe) {
+        assert(last_complete_iframe->frame_obj);
+        memcpy(&last_complete_iframe->frame_obj->_f_frame_data[0],
+               &last_complete_iframe->previous, sizeof(void *));
+        last_complete_iframe->previous = nullptr;
+    }
+}
+#else
+void Greenlet::expose_frames()
+{
+
+}
+#endif
+
+}; // namespace greenlet