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/* -*- indent-tabs-mode: nil; tab-width: 4; -*- */
/**
* Implementation of greenlet::UserGreenlet.
*
* 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"
*/
#ifndef T_USER_GREENLET_CPP
#define T_USER_GREENLET_CPP
#include "greenlet_internal.hpp"
#include "TGreenlet.hpp"
#include "TThreadStateDestroy.cpp"
namespace greenlet {
using greenlet::refs::BorrowedMainGreenlet;
greenlet::PythonAllocator<UserGreenlet> UserGreenlet::allocator;
void* UserGreenlet::operator new(size_t UNUSED(count))
{
return allocator.allocate(1);
}
void UserGreenlet::operator delete(void* ptr)
{
return allocator.deallocate(static_cast<UserGreenlet*>(ptr),
1);
}
UserGreenlet::UserGreenlet(PyGreenlet* p, BorrowedGreenlet the_parent)
: Greenlet(p), _parent(the_parent)
{
}
UserGreenlet::~UserGreenlet()
{
// Python 3.11: If we don't clear out the raw frame datastack
// when deleting an unfinished greenlet,
// TestLeaks.test_untracked_memory_doesnt_increase_unfinished_thread_dealloc_in_main fails.
this->python_state.did_finish(nullptr);
this->tp_clear();
}
const BorrowedMainGreenlet
UserGreenlet::main_greenlet() const
{
return this->_main_greenlet;
}
BorrowedMainGreenlet
UserGreenlet::find_main_greenlet_in_lineage() const
{
if (this->started()) {
assert(this->_main_greenlet);
return BorrowedMainGreenlet(this->_main_greenlet);
}
if (!this->_parent) {
/* garbage collected greenlet in chain */
// XXX: WHAT?
return BorrowedMainGreenlet(nullptr);
}
return this->_parent->find_main_greenlet_in_lineage();
}
/**
* CAUTION: This will allocate memory and may trigger garbage
* collection and arbitrary Python code.
*/
OwnedObject
UserGreenlet::throw_GreenletExit_during_dealloc(const ThreadState& current_thread_state)
{
/* The dying greenlet cannot be a parent of ts_current
because the 'parent' field chain would hold a
reference */
UserGreenlet::ParentIsCurrentGuard with_current_parent(this, current_thread_state);
// We don't care about the return value, only whether an
// exception happened. Whether or not an exception happens,
// we need to restore the parent in case the greenlet gets
// resurrected.
return Greenlet::throw_GreenletExit_during_dealloc(current_thread_state);
}
ThreadState*
UserGreenlet::thread_state() const noexcept
{
// TODO: maybe make this throw, if the thread state isn't there?
// if (!this->main_greenlet) {
// throw std::runtime_error("No thread state"); // TODO: Better exception
// }
if (!this->_main_greenlet) {
return nullptr;
}
return this->_main_greenlet->thread_state();
}
bool
UserGreenlet::was_running_in_dead_thread() const noexcept
{
return this->_main_greenlet && !this->thread_state();
}
OwnedObject
UserGreenlet::g_switch()
{
assert(this->args() || PyErr_Occurred());
try {
this->check_switch_allowed();
}
catch (const PyErrOccurred&) {
this->release_args();
throw;
}
// Switching greenlets used to attempt to clean out ones that need
// deleted *if* we detected a thread switch. Should it still do
// that?
// An issue is that if we delete a greenlet from another thread,
// it gets queued to this thread, and ``kill_greenlet()`` switches
// back into the greenlet
/* find the real target by ignoring dead greenlets,
and if necessary starting a greenlet. */
switchstack_result_t err;
Greenlet* target = this;
// TODO: probably cleaner to handle the case where we do
// switch to ourself separately from the other cases.
// This can probably even further be simplified if we keep
// track of the switching_state we're going for and just call
// into g_switch() if it's not ourself. The main problem with that
// is that we would be using more stack space.
bool target_was_me = true;
bool was_initial_stub = false;
while (target) {
if (target->active()) {
if (!target_was_me) {
target->args() <<= this->args();
assert(!this->args());
}
err = target->g_switchstack();
break;
}
if (!target->started()) {
// We never encounter a main greenlet that's not started.
assert(!target->main());
UserGreenlet* real_target = static_cast<UserGreenlet*>(target);
assert(real_target);
void* dummymarker;
was_initial_stub = true;
if (!target_was_me) {
target->args() <<= this->args();
assert(!this->args());
}
try {
// This can only throw back to us while we're
// still in this greenlet. Once the new greenlet
// is bootstrapped, it has its own exception state.
err = real_target->g_initialstub(&dummymarker);
}
catch (const PyErrOccurred&) {
this->release_args();
throw;
}
catch (const GreenletStartedWhileInPython&) {
// The greenlet was started sometime before this
// greenlet actually switched to it, i.e.,
// "concurrent" calls to switch() or throw().
// We need to retry the switch.
// Note that the current greenlet has been reset
// to this one (or we wouldn't be running!)
continue;
}
break;
}
target = target->parent();
target_was_me = false;
}
// The ``this`` pointer and all other stack or register based
// variables are invalid now, at least where things succeed
// above.
// But this one, probably not so much? It's not clear if it's
// safe to throw an exception at this point.
if (err.status < 0) {
// 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.
return this->on_switchstack_or_initialstub_failure(target, err, target_was_me, was_initial_stub);
}
// err.the_new_current_greenlet would be the same as ``target``,
// if target wasn't probably corrupt.
return err.the_new_current_greenlet->g_switch_finish(err);
}
Greenlet::switchstack_result_t
UserGreenlet::g_initialstub(void* mark)
{
OwnedObject run;
// We need to grab a reference to the current switch arguments
// in case we're entered concurrently during the call to
// GetAttr() and have to try again.
// We'll restore them when we return in that case.
// Scope them tightly to avoid ref leaks.
{
SwitchingArgs args(this->args());
/* save exception in case getattr clears it */
PyErrPieces saved;
/*
self.run is the object to call in the new greenlet.
This could run arbitrary python code and switch greenlets!
*/
run = this->self().PyRequireAttr(mod_globs->str_run);
/* restore saved exception */
saved.PyErrRestore();
/* recheck that it's safe to switch in case greenlet reparented anywhere above */
this->check_switch_allowed();
/* by the time we got here another start could happen elsewhere,
* that means it should now be a regular switch.
* This can happen if the Python code is a subclass that implements
* __getattribute__ or __getattr__, or makes ``run`` a descriptor;
* all of those can run arbitrary code that switches back into
* this greenlet.
*/
if (this->stack_state.started()) {
// the successful switch cleared these out, we need to
// restore our version. They will be copied on up to the
// next target.
assert(!this->args());
this->args() <<= args;
throw GreenletStartedWhileInPython();
}
}
// Sweet, if we got here, we have the go-ahead and will switch
// greenlets.
// Nothing we do from here on out should allow for a thread or
// greenlet switch: No arbitrary calls to Python, including
// decref'ing
#if GREENLET_USE_CFRAME
/* OK, we need it, we're about to switch greenlets, save the state. */
/*
See green_new(). This is a stack-allocated variable used
while *self* is in PyObject_Call().
We want to defer copying the state info until we're sure
we need it and are in a stable place to do so.
*/
_PyCFrame trace_info;
this->python_state.set_new_cframe(trace_info);
#endif
/* start the greenlet */
ThreadState& thread_state = GET_THREAD_STATE().state();
this->stack_state = StackState(mark,
thread_state.borrow_current()->stack_state);
this->python_state.set_initial_state(PyThreadState_GET());
this->exception_state.clear();
this->_main_greenlet = thread_state.get_main_greenlet();
/* perform the initial switch */
switchstack_result_t err = this->g_switchstack();
/* returns twice!
The 1st time with ``err == 1``: we are in the new greenlet.
This one owns a greenlet that used to be current.
The 2nd time with ``err <= 0``: back in the caller's
greenlet; this happens if the child finishes or switches
explicitly to us. Either way, the ``err`` variable is
created twice at the same memory location, but possibly
having different ``origin`` values. Note that it's not
constructed for the second time until the switch actually happens.
*/
if (err.status == 1) {
// In the new greenlet.
// This never returns! Calling inner_bootstrap steals
// the contents of our run object within this stack frame, so
// it is not valid to do anything with it.
try {
this->inner_bootstrap(err.origin_greenlet.relinquish_ownership(),
run.relinquish_ownership());
}
// Getting a C++ exception here isn't good. It's probably a
// bug in the underlying greenlet, meaning it's probably a
// C++ extension. We're going to abort anyway, but try to
// display some nice information *if* possible. Some obscure
// platforms don't properly support this (old 32-bit Arm, see see
// https://github.com/python-greenlet/greenlet/issues/385); that's not
// great, but should usually be OK because, as mentioned above, we're
// terminating anyway.
//
// The catching is tested by
// ``test_cpp.CPPTests.test_unhandled_exception_in_greenlet_aborts``.
//
// PyErrOccurred can theoretically be thrown by
// inner_bootstrap() -> g_switch_finish(), but that should
// never make it back to here. It is a std::exception and
// would be caught if it is.
catch (const std::exception& e) {
std::string base = "greenlet: Unhandled C++ exception: ";
base += e.what();
Py_FatalError(base.c_str());
}
catch (...) {
// Some compilers/runtimes use exceptions internally.
// It appears that GCC on Linux with libstdc++ throws an
// exception internally at process shutdown time to unwind
// stacks and clean up resources. Depending on exactly
// where we are when the process exits, that could result
// in an unknown exception getting here. If we
// Py_FatalError() or abort() here, we interfere with
// orderly process shutdown. Throwing the exception on up
// is the right thing to do.
//
// gevent's ``examples/dns_mass_resolve.py`` demonstrates this.
#ifndef NDEBUG
fprintf(stderr,
"greenlet: inner_bootstrap threw unknown exception; "
"is the process terminating?\n");
#endif
throw;
}
Py_FatalError("greenlet: inner_bootstrap returned with no exception.\n");
}
// In contrast, notice that we're keeping the origin greenlet
// around as an owned reference; we need it to call the trace
// function for the switch back into the parent. It was only
// captured at the time the switch actually happened, though,
// so we haven't been keeping an extra reference around this
// whole time.
/* back in the parent */
if (err.status < 0) {
/* start failed badly, restore greenlet state */
this->stack_state = StackState();
this->_main_greenlet.CLEAR();
// CAUTION: This may run arbitrary Python code.
run.CLEAR(); // inner_bootstrap didn't run, we own the reference.
}
// In the success case, the spawned code (inner_bootstrap) will
// take care of decrefing this, so we relinquish ownership so as
// to not double-decref.
run.relinquish_ownership();
return err;
}
void
UserGreenlet::inner_bootstrap(PyGreenlet* origin_greenlet, PyObject* run)
{
// The arguments here would be another great place for move.
// As it is, we take them as a reference so that when we clear
// them we clear what's on the stack above us. Do that NOW, and
// without using a C++ RAII object,
// so there's no way that exiting the parent frame can clear it,
// or we clear it unexpectedly. This arises in the context of the
// interpreter shutting down. See https://github.com/python-greenlet/greenlet/issues/325
//PyObject* run = _run.relinquish_ownership();
/* in the new greenlet */
assert(this->thread_state()->borrow_current() == BorrowedGreenlet(this->_self));
// C++ exceptions cannot propagate to the parent greenlet from
// here. (TODO: Do we need a catch(...) clause, perhaps on the
// function itself? ALl we could do is terminate the program.)
// NOTE: On 32-bit Windows, the call chain is extremely
// important here in ways that are subtle, having to do with
// the depth of the SEH list. The call to restore it MUST NOT
// add a new SEH handler to the list, or we'll restore it to
// the wrong thing.
this->thread_state()->restore_exception_state();
/* stack variables from above are no good and also will not unwind! */
// EXCEPT: That can't be true, we access run, among others, here.
this->stack_state.set_active(); /* running */
// We're about to possibly run Python code again, which
// could switch back/away to/from us, so we need to grab the
// arguments locally.
SwitchingArgs args;
args <<= this->args();
assert(!this->args());
// XXX: We could clear this much earlier, right?
// Or would that introduce the possibility of running Python
// code when we don't want to?
// CAUTION: This may run arbitrary Python code.
this->_run_callable.CLEAR();
// The first switch we need to manually call the trace
// function here instead of in g_switch_finish, because we
// never return there.
if (OwnedObject tracefunc = this->thread_state()->get_tracefunc()) {
OwnedGreenlet trace_origin;
trace_origin = origin_greenlet;
try {
g_calltrace(tracefunc,
args ? mod_globs->event_switch : mod_globs->event_throw,
trace_origin,
this->_self);
}
catch (const PyErrOccurred&) {
/* Turn trace errors into switch throws */
args.CLEAR();
}
}
// We no longer need the origin, it was only here for
// tracing.
// We may never actually exit this stack frame so we need
// to explicitly clear it.
// This could run Python code and switch.
Py_CLEAR(origin_greenlet);
OwnedObject result;
if (!args) {
/* pending exception */
result = NULL;
}
else {
/* call g.run(*args, **kwargs) */
// This could result in further switches
try {
//result = run.PyCall(args.args(), args.kwargs());
// CAUTION: Just invoking this, before the function even
// runs, may cause memory allocations, which may trigger
// GC, which may run arbitrary Python code.
result = OwnedObject::consuming(PyObject_Call(run, args.args().borrow(), args.kwargs().borrow()));
}
catch (...) {
// Unhandled C++ exception!
// If we declare ourselves as noexcept, if we don't catch
// this here, most platforms will just abort() the
// process. But on 64-bit Windows with older versions of
// the C runtime, this can actually corrupt memory and
// just return. We see this when compiling with the
// Windows 7.0 SDK targeting Windows Server 2008, but not
// when using the Appveyor Visual Studio 2019 image. So
// this currently only affects Python 2.7 on Windows 64.
// That is, the tests pass and the runtime aborts
// everywhere else.
//
// However, if we catch it and try to continue with a
// Python error, then all Windows 64 bit platforms corrupt
// memory. So all we can do is manually abort, hopefully
// with a good error message. (Note that the above was
// tested WITHOUT the `/EHr` switch being used at compile
// time, so MSVC may have "optimized" out important
// checking. Using that switch, we may be in a better
// place in terms of memory corruption.) But sometimes it
// can't be caught here at all, which is confusing but not
// terribly surprising; so again, the G_NOEXCEPT_WIN32
// plus "/EHr".
//
// Hopefully the basic C stdlib is still functional enough
// for us to at least print an error.
//
// It gets more complicated than that, though, on some
// platforms, specifically at least Linux/gcc/libstdc++. They use
// an exception to unwind the stack when a background
// thread exits. (See comments about noexcept.) So this
// may not actually represent anything untoward. On those
// platforms we allow throws of this to propagate, or
// attempt to anyway.
# if defined(WIN32) || defined(_WIN32)
Py_FatalError(
"greenlet: Unhandled C++ exception from a greenlet run function. "
"Because memory is likely corrupted, terminating process.");
std::abort();
#else
throw;
#endif
}
}
// These lines may run arbitrary code
args.CLEAR();
Py_CLEAR(run);
if (!result
&& mod_globs->PyExc_GreenletExit.PyExceptionMatches()
&& (this->args())) {
// This can happen, for example, if our only reference
// goes away after we switch back to the parent.
// See test_dealloc_switch_args_not_lost
PyErrPieces clear_error;
result <<= this->args();
result = single_result(result);
}
this->release_args();
this->python_state.did_finish(PyThreadState_GET());
result = g_handle_exit(result);
assert(this->thread_state()->borrow_current() == this->_self);
/* jump back to parent */
this->stack_state.set_inactive(); /* dead */
// TODO: Can we decref some things here? Release our main greenlet
// and maybe parent?
for (Greenlet* parent = this->_parent;
parent;
parent = parent->parent()) {
// We need to somewhere consume a reference to
// the result; in most cases we'll never have control
// back in this stack frame again. Calling
// green_switch actually adds another reference!
// This would probably be clearer with a specific API
// to hand results to the parent.
parent->args() <<= result;
assert(!result);
// The parent greenlet now owns the result; in the
// typical case we'll never get back here to assign to
// result and thus release the reference.
try {
result = parent->g_switch();
}
catch (const PyErrOccurred&) {
// Ignore, keep passing the error on up.
}
/* Return here means switch to parent failed,
* in which case we throw *current* exception
* to the next parent in chain.
*/
assert(!result);
}
/* We ran out of parents, cannot continue */
PyErr_WriteUnraisable(this->self().borrow_o());
Py_FatalError("greenlet: ran out of parent greenlets while propagating exception; "
"cannot continue");
std::abort();
}
void
UserGreenlet::run(const BorrowedObject nrun)
{
if (this->started()) {
throw AttributeError(
"run cannot be set "
"after the start of the greenlet");
}
this->_run_callable = nrun;
}
const OwnedGreenlet
UserGreenlet::parent() const
{
return this->_parent;
}
void
UserGreenlet::parent(const BorrowedObject raw_new_parent)
{
if (!raw_new_parent) {
throw AttributeError("can't delete attribute");
}
BorrowedMainGreenlet main_greenlet_of_new_parent;
BorrowedGreenlet new_parent(raw_new_parent.borrow()); // could
// throw
// TypeError!
for (BorrowedGreenlet p = new_parent; p; p = p->parent()) {
if (p == this->self()) {
throw ValueError("cyclic parent chain");
}
main_greenlet_of_new_parent = p->main_greenlet();
}
if (!main_greenlet_of_new_parent) {
throw ValueError("parent must not be garbage collected");
}
if (this->started()
&& this->_main_greenlet != main_greenlet_of_new_parent) {
throw ValueError("parent cannot be on a different thread");
}
this->_parent = new_parent;
}
void
UserGreenlet::murder_in_place()
{
this->_main_greenlet.CLEAR();
Greenlet::murder_in_place();
}
bool
UserGreenlet::belongs_to_thread(const ThreadState* thread_state) const
{
return Greenlet::belongs_to_thread(thread_state) && this->_main_greenlet == thread_state->borrow_main_greenlet();
}
int
UserGreenlet::tp_traverse(visitproc visit, void* arg)
{
Py_VISIT(this->_parent.borrow_o());
Py_VISIT(this->_main_greenlet.borrow_o());
Py_VISIT(this->_run_callable.borrow_o());
return Greenlet::tp_traverse(visit, arg);
}
int
UserGreenlet::tp_clear()
{
Greenlet::tp_clear();
this->_parent.CLEAR();
this->_main_greenlet.CLEAR();
this->_run_callable.CLEAR();
return 0;
}
UserGreenlet::ParentIsCurrentGuard::ParentIsCurrentGuard(UserGreenlet* p,
const ThreadState& thread_state)
: oldparent(p->_parent),
greenlet(p)
{
p->_parent = thread_state.get_current();
}
UserGreenlet::ParentIsCurrentGuard::~ParentIsCurrentGuard()
{
this->greenlet->_parent = oldparent;
oldparent.CLEAR();
}
}; //namespace greenlet
#endif