/**************************************************************************** ** ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** ** This file is part of the examples of the Qt Toolkit. ** ** $QT_BEGIN_LICENSE:LGPL$ ** No Commercial Usage ** This file contains pre-release code and may not be distributed. ** You may use this file in accordance with the terms and conditions ** contained in the Technology Preview License Agreement accompanying ** this package. ** ** GNU Lesser General Public License Usage ** Alternatively, this file may be used under the terms of the GNU Lesser ** General Public License version 2.1 as published by the Free Software ** Foundation and appearing in the file LICENSE.LGPL included in the ** packaging of this file. Please review the following information to ** ensure the GNU Lesser General Public License version 2.1 requirements ** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html. ** ** In addition, as a special exception, Nokia gives you certain additional ** rights. These rights are described in the Nokia Qt LGPL Exception ** version 1.1, included in the file LGPL_EXCEPTION.txt in this package. ** ** If you have questions regarding the use of this file, please contact ** Nokia at qt-info@nokia.com. ** ** ** ** ** ** ** ** ** $QT_END_LICENSE$ ** ****************************************************************************/ #include "environment.h" #include "qcontext2dcanvas.h" #include "context2d.h" #include #include struct FakeDomEvent { enum KeyCodes { DOM_VK_UNDEFINED = 0x0, DOM_VK_RIGHT_ALT = 0x12, DOM_VK_LEFT_ALT = 0x12, DOM_VK_LEFT_CONTROL = 0x11, DOM_VK_RIGHT_CONTROL = 0x11, DOM_VK_LEFT_SHIFT = 0x10, DOM_VK_RIGHT_SHIFT = 0x10, DOM_VK_META = 0x9D, DOM_VK_BACK_SPACE = 0x08, DOM_VK_CAPS_LOCK = 0x14, DOM_VK_DELETE = 0x7F, DOM_VK_END = 0x23, DOM_VK_ENTER = 0x0D, DOM_VK_ESCAPE = 0x1B, DOM_VK_HOME = 0x24, DOM_VK_NUM_LOCK = 0x90, DOM_VK_PAUSE = 0x13, DOM_VK_PRINTSCREEN = 0x9A, DOM_VK_SCROLL_LOCK = 0x91, DOM_VK_SPACE = 0x20, DOM_VK_TAB = 0x09, DOM_VK_LEFT = 0x25, DOM_VK_RIGHT = 0x27, DOM_VK_UP = 0x26, DOM_VK_DOWN = 0x28, DOM_VK_PAGE_DOWN = 0x22, DOM_VK_PAGE_UP = 0x21, DOM_VK_F1 = 0x70, DOM_VK_F2 = 0x71, DOM_VK_F3 = 0x72, DOM_VK_F4 = 0x73, DOM_VK_F5 = 0x74, DOM_VK_F6 = 0x75, DOM_VK_F7 = 0x76, DOM_VK_F8 = 0x77, DOM_VK_F9 = 0x78, DOM_VK_F10 = 0x79, DOM_VK_F11 = 0x7A, DOM_VK_F12 = 0x7B, DOM_VK_F13 = 0xF000, DOM_VK_F14 = 0xF001, DOM_VK_F15 = 0xF002, DOM_VK_F16 = 0xF003, DOM_VK_F17 = 0xF004, DOM_VK_F18 = 0xF005, DOM_VK_F19 = 0xF006, DOM_VK_F20 = 0xF007, DOM_VK_F21 = 0xF008, DOM_VK_F22 = 0xF009, DOM_VK_F23 = 0xF00A, DOM_VK_F24 = 0xF00B }; static int qtToDomKey(int keyCode); }; int FakeDomEvent::qtToDomKey(int keyCode) { switch (keyCode) { case Qt::Key_Backspace: return DOM_VK_BACK_SPACE; case Qt::Key_Enter: return DOM_VK_ENTER; case Qt::Key_Return: return DOM_VK_ENTER; case Qt::Key_NumLock: return DOM_VK_NUM_LOCK; case Qt::Key_Alt: return DOM_VK_RIGHT_ALT; case Qt::Key_Control: return DOM_VK_LEFT_CONTROL; case Qt::Key_Shift: return DOM_VK_LEFT_SHIFT; case Qt::Key_Meta: return DOM_VK_META; case Qt::Key_CapsLock: return DOM_VK_CAPS_LOCK; case Qt::Key_Delete: return DOM_VK_DELETE; case Qt::Key_End: return DOM_VK_END; case Qt::Key_Escape: return DOM_VK_ESCAPE; case Qt::Key_Home: return DOM_VK_HOME; case Qt::Key_Pause: return DOM_VK_PAUSE; case Qt::Key_Print: return DOM_VK_PRINTSCREEN; case Qt::Key_ScrollLock: return DOM_VK_SCROLL_LOCK; case Qt::Key_Left: return DOM_VK_LEFT; case Qt::Key_Right: return DOM_VK_RIGHT; case Qt::Key_Up: return DOM_VK_UP; case Qt::Key_Down: return DOM_VK_DOWN; case Qt::Key_PageDown: return DOM_VK_PAGE_DOWN; case Qt::Key_PageUp: return DOM_VK_PAGE_UP; case Qt::Key_F1: return DOM_VK_F1; case Qt::Key_F2: return DOM_VK_F2; case Qt::Key_F3: return DOM_VK_F3; case Qt::Key_F4: return DOM_VK_F4; case Qt::Key_F5: return DOM_VK_F5; case Qt::Key_F6: return DOM_VK_F6; case Qt::Key_F7: return DOM_VK_F7; case Qt::Key_F8: return DOM_VK_F8; case Qt::Key_F9: return DOM_VK_F9; case Qt::Key_F10: return DOM_VK_F10; case Qt::Key_F11: return DOM_VK_F11; case Qt::Key_F12: return DOM_VK_F12; case Qt::Key_F13: return DOM_VK_F13; case Qt::Key_F14: return DOM_VK_F14; case Qt::Key_F15: return DOM_VK_F15; case Qt::Key_F16: return DOM_VK_F16; case Qt::Key_F17: return DOM_VK_F17; case Qt::Key_F18: return DOM_VK_F18; case Qt::Key_F19: return DOM_VK_F19; case Qt::Key_F20: return DOM_VK_F20; case Qt::Key_F21: return DOM_VK_F21; case Qt::Key_F22: return DOM_VK_F22; case Qt::Key_F23: return DOM_VK_F23; case Qt::Key_F24: return DOM_VK_F24; } return keyCode; } //! [0] Environment::Environment(QObject *parent) : QObject(parent) { m_engine = new QScriptEngine(this); m_document = m_engine->newQObject( new Document(this), QScriptEngine::QtOwnership, QScriptEngine::ExcludeSuperClassContents); CanvasGradientPrototype::setup(m_engine); m_originalGlobalObject = m_engine->globalObject(); reset(); } //! [0] Environment::~Environment() { } QScriptEngine *Environment::engine() const { return m_engine; } QScriptValue Environment::document() const { return m_document; } int Environment::setTimeout(const QScriptValue &expression, int delay) { if (expression.isString() || expression.isFunction()) { int timerId = startTimer(delay); m_timeoutHash.insert(timerId, expression); return timerId; } return -1; } void Environment::clearTimeout(int timerId) { killTimer(timerId); m_timeoutHash.remove(timerId); } //! [1] int Environment::setInterval(const QScriptValue &expression, int delay) { if (expression.isString() || expression.isFunction()) { int timerId = startTimer(delay); m_intervalHash.insert(timerId, expression); return timerId; } return -1; } void Environment::clearInterval(int timerId) { killTimer(timerId); m_intervalHash.remove(timerId); } void Environment::timerEvent(QTimerEvent *event) { int id = event->timerId(); QScriptValue expression = m_intervalHash.value(id); if (!expression.isValid()) { expression = m_timeoutHash.value(id); if (expression.isValid()) killTimer(id); } if (expression.isString()) { evaluate(expression.toString()); } else if (expression.isFunction()) { expression.call(); } maybeEmitScriptError(); } //! [1] //! [5] void Environment::addCanvas(QContext2DCanvas *canvas) { m_canvases.append(canvas); } QContext2DCanvas *Environment::canvasByName(const QString &name) const { for (int i = 0; i < m_canvases.size(); ++i) { QContext2DCanvas *canvas = m_canvases.at(i); if (canvas->objectName() == name) return canvas; } return 0; } //! [5] QList Environment::canvases() const { return m_canvases; } void Environment::reset() { if (m_engine->isEvaluating()) m_engine->abortEvaluation(); { QHash::const_iterator it; for (it = m_intervalHash.constBegin(); it != m_intervalHash.constEnd(); ++it) killTimer(it.key()); m_intervalHash.clear(); for (it = m_timeoutHash.constBegin(); it != m_timeoutHash.constEnd(); ++it) killTimer(it.key()); m_timeoutHash.clear(); } for (int i = 0; i < m_canvases.size(); ++i) m_canvases.at(i)->reset(); QScriptValue self = m_engine->newQObject( this, QScriptEngine::QtOwnership, QScriptEngine::ExcludeSuperClassContents); { QScriptValueIterator it(m_originalGlobalObject); while (it.hasNext()) { it.next(); self.setProperty(it.scriptName(), it.value(), it.flags()); } } self.setProperty("self", self); self.setProperty("window", self); QScriptValue navigator = m_engine->newObject(); navigator.setProperty("appCodeName", "context2d"); navigator.setProperty("appMinorVersion", 1); navigator.setProperty("appVersion", 1); navigator.setProperty("browserLanguage", "en_US"); navigator.setProperty("cookieEnabled", false); navigator.setProperty("cpuClass", "i686"); navigator.setProperty("onLine", false); navigator.setProperty("platform", "bogus OS"); navigator.setProperty("systemLanguage", "en_US"); navigator.setProperty("userAgent", "Context2D/1.1"); navigator.setProperty("userLanguage", "en_US"); self.setProperty("navigator", navigator); m_engine->setGlobalObject(self); m_engine->collectGarbage(); } QScriptValue Environment::evaluate(const QString &code, const QString &fileName) { return m_engine->evaluate(code, fileName); } //! [2] QScriptValue Environment::toWrapper(QObject *object) { return m_engine->newQObject(object, QScriptEngine::QtOwnership, QScriptEngine::PreferExistingWrapperObject | QScriptEngine::ExcludeSuperClassContents); } //! [2] //! [3] void Environment::handleEvent(QContext2DCanvas *canvas, QMouseEvent *e) { QString type; switch (e->type()) { case QEvent::MouseButtonPress: type = "mousedown"; break; case QEvent::MouseButtonRelease: type = "mouseup"; break; case QEvent::MouseMove: type = "mousemove"; break; default: break; } if (type.isEmpty()) return; QScriptValue handlerObject; QScriptValue handler = eventHandler(canvas, type, &handlerObject); if (!handler.isFunction()) return; QScriptValue scriptEvent = newFakeDomEvent(type, toWrapper(canvas)); // MouseEvent scriptEvent.setProperty("screenX", e->globalX(), QScriptValue::ReadOnly); scriptEvent.setProperty("screenY", e->globalY(), QScriptValue::ReadOnly); scriptEvent.setProperty("clientX", e->x(), QScriptValue::ReadOnly); scriptEvent.setProperty("clientY", e->y(), QScriptValue::ReadOnly); scriptEvent.setProperty("layerX", e->x(), QScriptValue::ReadOnly); scriptEvent.setProperty("layerY", e->y(), QScriptValue::ReadOnly); scriptEvent.setProperty("pageX", e->x(), QScriptValue::ReadOnly); scriptEvent.setProperty("pageY", e->y(), QScriptValue::ReadOnly); scriptEvent.setProperty("altKey", (e->modifiers() & Qt::AltModifier) != 0, QScriptValue::ReadOnly); scriptEvent.setProperty("ctrlKey", (e->modifiers() & Qt::ControlModifier) != 0, QScriptValue::ReadOnly); scriptEvent.setProperty("metaKey", (e->modifiers() & Qt::MetaModifier) != 0, QScriptValue::ReadOnly); scriptEvent.setProperty("shiftKey", (e->modifiers() & Qt::ShiftModifier) != 0, QScriptValue::ReadOnly); int button = 0; if (e->button() == Qt::RightButton) button = 2; else if (e->button() == Qt::MidButton) button = 1; scriptEvent.setProperty("button", button); scriptEvent.setProperty("relatedTarget", m_engine->nullValue(), QScriptValue::ReadOnly); handler.call(handlerObject, QScriptValueList() << scriptEvent); maybeEmitScriptError(); } //! [3] void Environment::handleEvent(QContext2DCanvas *canvas, QKeyEvent *e) { QString type; switch (e->type()) { case QEvent::KeyPress: type = "keydown"; break; case QEvent::KeyRelease: type = "keyup"; break; default: break; } if (type.isEmpty()) return; QScriptValue handlerObject; QScriptValue handler = eventHandler(canvas, type, &handlerObject); if (!handler.isFunction()) return; QScriptValue scriptEvent = newFakeDomEvent(type, toWrapper(canvas)); // KeyEvent scriptEvent.setProperty("isChar", !e->text().isEmpty()); scriptEvent.setProperty("charCode", e->text()); scriptEvent.setProperty("keyCode", FakeDomEvent::qtToDomKey(e->key())); scriptEvent.setProperty("which", e->key()); handler.call(handlerObject, QScriptValueList() << scriptEvent); maybeEmitScriptError(); } QScriptValue Environment::eventHandler(QContext2DCanvas *canvas, const QString &type, QScriptValue *who) { QString handlerName = "on" + type; QScriptValue obj = toWrapper(canvas); QScriptValue handler = obj.property(handlerName); if (!handler.isValid()) { obj = m_document; handler = obj.property(handlerName); } if (who && handler.isFunction()) *who = obj; return handler; } //! [4] QScriptValue Environment::newFakeDomEvent(const QString &type, const QScriptValue &target) { QScriptValue e = m_engine->newObject(); // Event e.setProperty("type", type, QScriptValue::ReadOnly); e.setProperty("bubbles", true, QScriptValue::ReadOnly); e.setProperty("cancelable", false, QScriptValue::ReadOnly); e.setProperty("target", target, QScriptValue::ReadOnly); e.setProperty("currentTarget", target, QScriptValue::ReadOnly); e.setProperty("eventPhase", 3); // bubbling e.setProperty("timeStamp", QDateTime::currentDateTime().toTime_t()); // UIEvent e.setProperty("detail", 0, QScriptValue::ReadOnly); e.setProperty("view", m_engine->globalObject(), QScriptValue::ReadOnly); return e; } //! [4] void Environment::maybeEmitScriptError() { if (m_engine->hasUncaughtException()) emit scriptError(m_engine->uncaughtException()); } Document::Document(Environment *env) : QObject(env) { } Document::~Document() { } QScriptValue Document::getElementById(const QString &id) const { Environment *env = qobject_cast(parent()); QContext2DCanvas *canvas = env->canvasByName(id); if (!canvas) return QScriptValue(); return env->toWrapper(canvas); } QScriptValue Document::getElementsByTagName(const QString &name) const { if (name != "canvas") return QScriptValue(); Environment *env = qobject_cast(parent()); QList list = env->canvases(); QScriptValue result = env->engine()->newArray(list.size()); for (int i = 0; i < list.size(); ++i) result.setProperty(i, env->toWrapper(list.at(i))); return result; } void Document::addEventListener(const QString &type, const QScriptValue &listener, bool useCapture) { Q_UNUSED(useCapture); if (listener.isFunction()) { Environment *env = qobject_cast(parent()); QScriptValue self = env->toWrapper(this); self.setProperty("on" + type, listener); } } QColor colorFromString(const QString &name); CanvasGradientPrototype::CanvasGradientPrototype(QObject *parent) : QObject(parent) { } void CanvasGradientPrototype::addColorStop(qreal offset, const QString &color) { CanvasGradient *self = qscriptvalue_cast(thisObject()); if (!self || (self->value.type() == QGradient::NoGradient)) return; self->value.setColorAt(offset, colorFromString(color)); } void CanvasGradientPrototype::setup(QScriptEngine *engine) { CanvasGradientPrototype *proto = new CanvasGradientPrototype(); engine->setDefaultPrototype(qMetaTypeId(), engine->newQObject(proto, QScriptEngine::ScriptOwnership, QScriptEngine::ExcludeSuperClassContents)); } href='#n417'>417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 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// Cyclic garbage collector implementation for free-threaded build.
#include "Python.h"
#include "pycore_brc.h"           // struct _brc_thread_state
#include "pycore_ceval.h"         // _Py_set_eval_breaker_bit()
#include "pycore_context.h"
#include "pycore_dict.h"          // _PyDict_MaybeUntrack()
#include "pycore_initconfig.h"
#include "pycore_interp.h"        // PyInterpreterState.gc
#include "pycore_object.h"
#include "pycore_object_alloc.h"  // _PyObject_MallocWithType()
#include "pycore_object_stack.h"
#include "pycore_pyerrors.h"
#include "pycore_pystate.h"       // _PyThreadState_GET()
#include "pycore_time.h"          // _PyTime_GetPerfCounter()
#include "pycore_tstate.h"        // _PyThreadStateImpl
#include "pycore_weakref.h"       // _PyWeakref_ClearRef()
#include "pydtrace.h"

#ifdef Py_GIL_DISABLED

typedef struct _gc_runtime_state GCState;

#ifdef Py_DEBUG
#  define GC_DEBUG
#endif

// Each thread buffers the count of allocated objects in a thread-local
// variable up to +/- this amount to reduce the overhead of updating
// the global count.
#define LOCAL_ALLOC_COUNT_THRESHOLD 512

// Automatically choose the generation that needs collecting.
#define GENERATION_AUTO (-1)

// A linked list of objects using the `ob_tid` field as the next pointer.
// The linked list pointers are distinct from any real thread ids, because the
// thread ids returned by _Py_ThreadId() are also pointers to distinct objects.
// No thread will confuse its own id with a linked list pointer.
struct worklist {
    uintptr_t head;
};

struct worklist_iter {
    uintptr_t *ptr;   // pointer to current object
    uintptr_t *next;  // next value of ptr
};

struct visitor_args {
    size_t offset;  // offset of PyObject from start of block
};

// Per-collection state
struct collection_state {
    struct visitor_args base;
    PyInterpreterState *interp;
    GCState *gcstate;
    Py_ssize_t collected;
    Py_ssize_t uncollectable;
    Py_ssize_t long_lived_total;
    struct worklist unreachable;
    struct worklist legacy_finalizers;
    struct worklist wrcb_to_call;
    struct worklist objs_to_decref;
};

// iterate over a worklist
#define WORKSTACK_FOR_EACH(stack, op) \
    for ((op) = (PyObject *)(stack)->head; (op) != NULL; (op) = (PyObject *)(op)->ob_tid)

// iterate over a worklist with support for removing the current object
#define WORKSTACK_FOR_EACH_ITER(stack, iter, op) \
    for (worklist_iter_init((iter), &(stack)->head), (op) = (PyObject *)(*(iter)->ptr); \
         (op) != NULL; \
         worklist_iter_init((iter), (iter)->next), (op) = (PyObject *)(*(iter)->ptr))

static void
worklist_push(struct worklist *worklist, PyObject *op)
{
    assert(op->ob_tid == 0);
    op->ob_tid = worklist->head;
    worklist->head = (uintptr_t)op;
}

static PyObject *
worklist_pop(struct worklist *worklist)
{
    PyObject *op = (PyObject *)worklist->head;
    if (op != NULL) {
        worklist->head = op->ob_tid;
        op->ob_tid = 0;
    }
    return op;
}

static void
worklist_iter_init(struct worklist_iter *iter, uintptr_t *next)
{
    iter->ptr = next;
    PyObject *op = (PyObject *)*(iter->ptr);
    if (op) {
        iter->next = &op->ob_tid;
    }
}

static void
worklist_remove(struct worklist_iter *iter)
{
    PyObject *op = (PyObject *)*(iter->ptr);
    *(iter->ptr) = op->ob_tid;
    op->ob_tid = 0;
    iter->next = iter->ptr;
}

static inline int
gc_is_unreachable(PyObject *op)
{
    return (op->ob_gc_bits & _PyGC_BITS_UNREACHABLE) != 0;
}

static void
gc_set_unreachable(PyObject *op)
{
    op->ob_gc_bits |= _PyGC_BITS_UNREACHABLE;
}

static void
gc_clear_unreachable(PyObject *op)
{
    op->ob_gc_bits &= ~_PyGC_BITS_UNREACHABLE;
}

// Initialize the `ob_tid` field to zero if the object is not already
// initialized as unreachable.
static void
gc_maybe_init_refs(PyObject *op)
{
    if (!gc_is_unreachable(op)) {
        gc_set_unreachable(op);
        op->ob_tid = 0;
    }
}

static inline Py_ssize_t
gc_get_refs(PyObject *op)
{
    return (Py_ssize_t)op->ob_tid;
}

static inline void
gc_add_refs(PyObject *op, Py_ssize_t refs)
{
    assert(_PyObject_GC_IS_TRACKED(op));
    op->ob_tid += refs;
}

static inline void
gc_decref(PyObject *op)
{
    op->ob_tid -= 1;
}

static Py_ssize_t
merge_refcount(PyObject *op, Py_ssize_t extra)
{
    assert(_PyInterpreterState_GET()->stoptheworld.world_stopped);

    Py_ssize_t refcount = Py_REFCNT(op);
    refcount += extra;

#ifdef Py_REF_DEBUG
    _Py_AddRefTotal(_PyInterpreterState_GET(), extra);
#endif

    // No atomics necessary; all other threads in this interpreter are paused.
    op->ob_tid = 0;
    op->ob_ref_local = 0;
    op->ob_ref_shared = _Py_REF_SHARED(refcount, _Py_REF_MERGED);
    return refcount;
}

static void
gc_restore_tid(PyObject *op)
{
    mi_segment_t *segment = _mi_ptr_segment(op);
    if (_Py_REF_IS_MERGED(op->ob_ref_shared)) {
        op->ob_tid = 0;
    }
    else {
        // NOTE: may change ob_tid if the object was re-initialized by
        // a different thread or its segment was abandoned and reclaimed.
        // The segment thread id might be zero, in which case we should
        // ensure the refcounts are now merged.
        op->ob_tid = segment->thread_id;
        if (op->ob_tid == 0) {
            merge_refcount(op, 0);
        }
    }
}

static void
gc_restore_refs(PyObject *op)
{
    if (gc_is_unreachable(op)) {
        gc_restore_tid(op);
        gc_clear_unreachable(op);
    }
}

// Given a mimalloc memory block return the PyObject stored in it or NULL if
// the block is not allocated or the object is not tracked or is immortal.
static PyObject *
op_from_block(void *block, void *arg, bool include_frozen)
{
    struct visitor_args *a = arg;
    if (block == NULL) {
        return NULL;
    }
    PyObject *op = (PyObject *)((char*)block + a->offset);
    assert(PyObject_IS_GC(op));
    if (!_PyObject_GC_IS_TRACKED(op)) {
        return NULL;
    }
    if (!include_frozen && (op->ob_gc_bits & _PyGC_BITS_FROZEN) != 0) {
        return NULL;
    }
    return op;
}

static int
gc_visit_heaps_lock_held(PyInterpreterState *interp, mi_block_visit_fun *visitor,
                         struct visitor_args *arg)
{
    // Offset of PyObject header from start of memory block.
    Py_ssize_t offset_base = 0;
    if (_PyMem_DebugEnabled()) {
        // The debug allocator adds two words at the beginning of each block.
        offset_base += 2 * sizeof(size_t);
    }

    // Objects with Py_TPFLAGS_PREHEADER have two extra fields
    Py_ssize_t offset_pre = offset_base + 2 * sizeof(PyObject*);

    // visit each thread's heaps for GC objects
    for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
        struct _mimalloc_thread_state *m = &((_PyThreadStateImpl *)p)->mimalloc;

        arg->offset = offset_base;
        if (!mi_heap_visit_blocks(&m->heaps[_Py_MIMALLOC_HEAP_GC], true,
                                  visitor, arg)) {
            return -1;
        }
        arg->offset = offset_pre;
        if (!mi_heap_visit_blocks(&m->heaps[_Py_MIMALLOC_HEAP_GC_PRE], true,
                                  visitor, arg)) {
            return -1;
        }
    }

    // visit blocks in the per-interpreter abandoned pool (from dead threads)
    mi_abandoned_pool_t *pool = &interp->mimalloc.abandoned_pool;
    arg->offset = offset_base;
    if (!_mi_abandoned_pool_visit_blocks(pool, _Py_MIMALLOC_HEAP_GC, true,
                                         visitor, arg)) {
        return -1;
    }
    arg->offset = offset_pre;
    if (!_mi_abandoned_pool_visit_blocks(pool, _Py_MIMALLOC_HEAP_GC_PRE, true,
                                         visitor, arg)) {
        return -1;
    }
    return 0;
}

// Visits all GC objects in the interpreter's heaps.
// NOTE: It is not safe to allocate or free any mimalloc managed memory while
// this function is running.
static int
gc_visit_heaps(PyInterpreterState *interp, mi_block_visit_fun *visitor,
               struct visitor_args *arg)
{
    // Other threads in the interpreter must be paused so that we can safely
    // traverse their heaps.
    assert(interp->stoptheworld.world_stopped);

    int err;
    HEAD_LOCK(&_PyRuntime);
    err = gc_visit_heaps_lock_held(interp, visitor, arg);
    HEAD_UNLOCK(&_PyRuntime);
    return err;
}

static void
merge_queued_objects(_PyThreadStateImpl *tstate, struct collection_state *state)
{
    struct _brc_thread_state *brc = &tstate->brc;
    _PyObjectStack_Merge(&brc->local_objects_to_merge, &brc->objects_to_merge);

    PyObject *op;
    while ((op = _PyObjectStack_Pop(&brc->local_objects_to_merge)) != NULL) {
        // Subtract one when merging because the queue had a reference.
        Py_ssize_t refcount = merge_refcount(op, -1);

        if (!_PyObject_GC_IS_TRACKED(op) && refcount == 0) {
            // GC objects with zero refcount are handled subsequently by the
            // GC as if they were cyclic trash, but we have to handle dead
            // non-GC objects here. Add one to the refcount so that we can
            // decref and deallocate the object once we start the world again.
            op->ob_ref_shared += (1 << _Py_REF_SHARED_SHIFT);
#ifdef Py_REF_DEBUG
            _Py_IncRefTotal(_PyInterpreterState_GET());
#endif
            worklist_push(&state->objs_to_decref, op);
        }
    }
}

static void
merge_all_queued_objects(PyInterpreterState *interp, struct collection_state *state)
{
    HEAD_LOCK(&_PyRuntime);
    for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
        merge_queued_objects((_PyThreadStateImpl *)p, state);
    }
    HEAD_UNLOCK(&_PyRuntime);
}

static void
process_delayed_frees(PyInterpreterState *interp)
{
    // In STW status, we can observe the latest write sequence by
    // advancing the write sequence immediately.
    _Py_qsbr_advance(&interp->qsbr);
    _PyThreadStateImpl *current_tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
    _Py_qsbr_quiescent_state(current_tstate->qsbr);
    HEAD_LOCK(&_PyRuntime);
    PyThreadState *tstate = interp->threads.head;
    while (tstate != NULL) {
        _PyMem_ProcessDelayed(tstate);
        tstate = (PyThreadState *)tstate->next;
    }
    HEAD_UNLOCK(&_PyRuntime);
}

// Subtract an incoming reference from the computed "gc_refs" refcount.
static int
visit_decref(PyObject *op, void *arg)
{
    if (_PyObject_GC_IS_TRACKED(op) && !_Py_IsImmortal(op)) {
        // If update_refs hasn't reached this object yet, mark it
        // as (tentatively) unreachable and initialize ob_tid to zero.
        gc_maybe_init_refs(op);
        gc_decref(op);
    }
    return 0;
}

// Compute the number of external references to objects in the heap
// by subtracting internal references from the refcount. The difference is
// computed in the ob_tid field (we restore it later).
static bool
update_refs(const mi_heap_t *heap, const mi_heap_area_t *area,
            void *block, size_t block_size, void *args)
{
    PyObject *op = op_from_block(block, args, false);
    if (op == NULL) {
        return true;
    }

    // Exclude immortal objects from garbage collection
    if (_Py_IsImmortal(op)) {
        op->ob_tid = 0;
        _PyObject_GC_UNTRACK(op);
        gc_clear_unreachable(op);
        return true;
    }

    // Untrack tuples and dicts as necessary in this pass.
    if (PyTuple_CheckExact(op)) {
        _PyTuple_MaybeUntrack(op);
        if (!_PyObject_GC_IS_TRACKED(op)) {
            gc_restore_refs(op);
            return true;
        }
    }
    else if (PyDict_CheckExact(op)) {
        _PyDict_MaybeUntrack(op);
        if (!_PyObject_GC_IS_TRACKED(op)) {
            gc_restore_refs(op);
            return true;
        }
    }

    Py_ssize_t refcount = Py_REFCNT(op);
    _PyObject_ASSERT(op, refcount >= 0);

    // We repurpose ob_tid to compute "gc_refs", the number of external
    // references to the object (i.e., from outside the GC heaps). This means
    // that ob_tid is no longer a valid thread id until it is restored by
    // scan_heap_visitor(). Until then, we cannot use the standard reference
    // counting functions or allow other threads to run Python code.
    gc_maybe_init_refs(op);

    // Add the actual refcount to ob_tid.
    gc_add_refs(op, refcount);

    // Subtract internal references from ob_tid. Objects with ob_tid > 0
    // are directly reachable from outside containers, and so can't be
    // collected.
    Py_TYPE(op)->tp_traverse(op, visit_decref, NULL);
    return true;
}

static int
visit_clear_unreachable(PyObject *op, _PyObjectStack *stack)
{
    if (gc_is_unreachable(op)) {
        _PyObject_ASSERT(op, _PyObject_GC_IS_TRACKED(op));
        gc_clear_unreachable(op);
        return _PyObjectStack_Push(stack, op);
    }
    return 0;
}

// Transitively clear the unreachable bit on all objects reachable from op.
static int
mark_reachable(PyObject *op)
{
    _PyObjectStack stack = { NULL };
    do {
        traverseproc traverse = Py_TYPE(op)->tp_traverse;
        if (traverse(op, (visitproc)&visit_clear_unreachable, &stack) < 0) {
            _PyObjectStack_Clear(&stack);
            return -1;
        }
        op = _PyObjectStack_Pop(&stack);
    } while (op != NULL);
    return 0;
}

#ifdef GC_DEBUG
static bool
validate_gc_objects(const mi_heap_t *heap, const mi_heap_area_t *area,
                    void *block, size_t block_size, void *args)
{
    PyObject *op = op_from_block(block, args, false);
    if (op == NULL) {
        return true;
    }

    _PyObject_ASSERT(op, gc_is_unreachable(op));
    _PyObject_ASSERT_WITH_MSG(op, gc_get_refs(op) >= 0,
                                  "refcount is too small");
    return true;
}
#endif

static bool
mark_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
                  void *block, size_t block_size, void *args)
{
    PyObject *op = op_from_block(block, args, false);
    if (op == NULL) {
        return true;
    }

    if (gc_is_unreachable(op) && gc_get_refs(op) != 0) {
        // Object is reachable but currently marked as unreachable.
        // Mark it as reachable and traverse its pointers to find
        // any other object that may be directly reachable from it.
        gc_clear_unreachable(op);

        // Transitively mark reachable objects by clearing the unreachable flag.
        if (mark_reachable(op) < 0) {
            return false;
        }
    }

    return true;
}

/* Return true if object has a pre-PEP 442 finalization method. */
static int
has_legacy_finalizer(PyObject *op)
{
    return Py_TYPE(op)->tp_del != NULL;
}

static bool
scan_heap_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
                  void *block, size_t block_size, void *args)
{
    PyObject *op = op_from_block(block, args, false);
    if (op == NULL) {
        return true;
    }

    struct collection_state *state = (struct collection_state *)args;
    if (gc_is_unreachable(op)) {
        // Merge and add one to the refcount to prevent deallocation while we
        // are holding on to it in a worklist.
        merge_refcount(op, 1);

        if (has_legacy_finalizer(op)) {
            // would be unreachable, but has legacy finalizer
            gc_clear_unreachable(op);
            worklist_push(&state->legacy_finalizers, op);
        }
        else {
            worklist_push(&state->unreachable, op);
        }
    }
    else {
        // object is reachable, restore `ob_tid`; we're done with these objects
        gc_restore_tid(op);
        state->long_lived_total++;
    }

    return true;
}

static int
move_legacy_finalizer_reachable(struct collection_state *state);

static int
deduce_unreachable_heap(PyInterpreterState *interp,
                        struct collection_state *state)
{
    // Identify objects that are directly reachable from outside the GC heap
    // by computing the difference between the refcount and the number of
    // incoming references.
    gc_visit_heaps(interp, &update_refs, &state->base);

#ifdef GC_DEBUG
    // Check that all objects are marked as unreachable and that the computed
    // reference count difference (stored in `ob_tid`) is non-negative.
    gc_visit_heaps(interp, &validate_gc_objects, &state->base);
#endif

    // Transitively mark reachable objects by clearing the
    // _PyGC_BITS_UNREACHABLE flag.
    if (gc_visit_heaps(interp, &mark_heap_visitor, &state->base) < 0) {
        return -1;
    }

    // Identify remaining unreachable objects and push them onto a stack.
    // Restores ob_tid for reachable objects.
    gc_visit_heaps(interp, &scan_heap_visitor, &state->base);

    if (state->legacy_finalizers.head) {
        // There may be objects reachable from legacy finalizers that are in
        // the unreachable set. We need to mark them as reachable.
        if (move_legacy_finalizer_reachable(state) < 0) {
            return -1;
        }
    }

    return 0;
}

static int
move_legacy_finalizer_reachable(struct collection_state *state)
{
    // Clear the reachable bit on all objects transitively reachable
    // from the objects with legacy finalizers.
    PyObject *op;
    WORKSTACK_FOR_EACH(&state->legacy_finalizers, op) {
        if (mark_reachable(op) < 0) {
            return -1;
        }
    }

    // Move the reachable objects from the unreachable worklist to the legacy
    // finalizer worklist.
    struct worklist_iter iter;
    WORKSTACK_FOR_EACH_ITER(&state->unreachable, &iter, op) {
        if (!gc_is_unreachable(op)) {
            worklist_remove(&iter);
            worklist_push(&state->legacy_finalizers, op);
        }
    }

    return 0;
}

// Clear all weakrefs to unreachable objects. Weakrefs with callbacks are
// enqueued in `wrcb_to_call`, but not invoked yet.
static void
clear_weakrefs(struct collection_state *state)
{
    PyObject *op;
    WORKSTACK_FOR_EACH(&state->unreachable, op) {
        if (PyWeakref_Check(op)) {
            // Clear weakrefs that are themselves unreachable to ensure their
            // callbacks will not be executed later from a `tp_clear()`
            // inside delete_garbage(). That would be unsafe: it could
            // resurrect a dead object or access a an already cleared object.
            // See bpo-38006 for one example.
            _PyWeakref_ClearRef((PyWeakReference *)op);
        }

        if (!_PyType_SUPPORTS_WEAKREFS(Py_TYPE(op))) {
            continue;
        }

        // NOTE: This is never triggered for static types so we can avoid the
        // (slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR().
        PyWeakReference **wrlist = _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(op);

        // `op` may have some weakrefs.  March over the list, clear
        // all the weakrefs, and enqueue the weakrefs with callbacks
        // that must be called into wrcb_to_call.
        for (PyWeakReference *wr = *wrlist; wr != NULL; wr = *wrlist) {
            // _PyWeakref_ClearRef clears the weakref but leaves
            // the callback pointer intact.  Obscure: it also
            // changes *wrlist.
            _PyObject_ASSERT((PyObject *)wr, wr->wr_object == op);
            _PyWeakref_ClearRef(wr);
            _PyObject_ASSERT((PyObject *)wr, wr->wr_object == Py_None);

            // We do not invoke callbacks for weakrefs that are themselves
            // unreachable. This is partly for historical reasons: weakrefs
            // predate safe object finalization, and a weakref that is itself
            // unreachable may have a callback that resurrects other
            // unreachable objects.
            if (wr->wr_callback == NULL || gc_is_unreachable((PyObject *)wr)) {
                continue;
            }

            // Create a new reference so that wr can't go away before we can
            // process it again.
            merge_refcount((PyObject *)wr, 1);

            // Enqueue weakref to be called later.
            worklist_push(&state->wrcb_to_call, (PyObject *)wr);
        }
    }
}

static void
call_weakref_callbacks(struct collection_state *state)
{
    // Invoke the callbacks we decided to honor.
    PyObject *op;
    while ((op = worklist_pop(&state->wrcb_to_call)) != NULL) {
        _PyObject_ASSERT(op, PyWeakref_Check(op));

        PyWeakReference *wr = (PyWeakReference *)op;
        PyObject *callback = wr->wr_callback;
        _PyObject_ASSERT(op, callback != NULL);

        /* copy-paste of weakrefobject.c's handle_callback() */
        PyObject *temp = PyObject_CallOneArg(callback, (PyObject *)wr);
        if (temp == NULL) {
            PyErr_WriteUnraisable(callback);
        }
        else {
            Py_DECREF(temp);
        }

        gc_restore_tid(op);
        Py_DECREF(op);  // drop worklist reference
    }
}


static GCState *
get_gc_state(void)
{
    PyInterpreterState *interp = _PyInterpreterState_GET();
    return &interp->gc;
}


void
_PyGC_InitState(GCState *gcstate)
{
    // TODO: move to pycore_runtime_init.h once the incremental GC lands.
    gcstate->generations[0].threshold = 2000;
}


PyStatus
_PyGC_Init(PyInterpreterState *interp)
{
    GCState *gcstate = &interp->gc;

    gcstate->garbage = PyList_New(0);
    if (gcstate->garbage == NULL) {
        return _PyStatus_NO_MEMORY();
    }

    gcstate->callbacks = PyList_New(0);
    if (gcstate->callbacks == NULL) {
        return _PyStatus_NO_MEMORY();
    }

    return _PyStatus_OK();
}

static void
debug_cycle(const char *msg, PyObject *op)
{
    PySys_FormatStderr("gc: %s <%s %p>\n",
                       msg, Py_TYPE(op)->tp_name, op);
}

/* Run first-time finalizers (if any) on all the objects in collectable.
 * Note that this may remove some (or even all) of the objects from the
 * list, due to refcounts falling to 0.
 */
static void
finalize_garbage(struct collection_state *state)
{
    // NOTE: the unreachable worklist holds a strong reference to the object
    // to prevent it from being deallocated while we are holding on to it.
    PyObject *op;
    WORKSTACK_FOR_EACH(&state->unreachable, op) {
        if (!_PyGC_FINALIZED(op)) {
            destructor finalize = Py_TYPE(op)->tp_finalize;
            if (finalize != NULL) {
                _PyGC_SET_FINALIZED(op);
                finalize(op);
                assert(!_PyErr_Occurred(_PyThreadState_GET()));
            }
        }
    }
}

// Break reference cycles by clearing the containers involved.
static void
delete_garbage(struct collection_state *state)
{
    PyThreadState *tstate = _PyThreadState_GET();
    GCState *gcstate = state->gcstate;

    assert(!_PyErr_Occurred(tstate));

    PyObject *op;
    while ((op = worklist_pop(&state->objs_to_decref)) != NULL) {
        Py_DECREF(op);
    }

    while ((op = worklist_pop(&state->unreachable)) != NULL) {
        _PyObject_ASSERT(op, gc_is_unreachable(op));

        // Clear the unreachable flag.
        gc_clear_unreachable(op);

        if (!_PyObject_GC_IS_TRACKED(op)) {
            // Object might have been untracked by some other tp_clear() call.
            Py_DECREF(op);  // drop the reference from the worklist
            continue;
        }

        state->collected++;

        if (gcstate->debug & _PyGC_DEBUG_SAVEALL) {
            assert(gcstate->garbage != NULL);
            if (PyList_Append(gcstate->garbage, op) < 0) {
                _PyErr_Clear(tstate);
            }
        }
        else {
            inquiry clear = Py_TYPE(op)->tp_clear;
            if (clear != NULL) {
                (void) clear(op);
                if (_PyErr_Occurred(tstate)) {
                    PyErr_FormatUnraisable("Exception ignored in tp_clear of %s",
                                           Py_TYPE(op)->tp_name);
                }
            }
        }

        Py_DECREF(op);  // drop the reference from the worklist
    }
}

static void
handle_legacy_finalizers(struct collection_state *state)
{
    GCState *gcstate = state->gcstate;
    assert(gcstate->garbage != NULL);

    PyObject *op;
    while ((op = worklist_pop(&state->legacy_finalizers)) != NULL) {
        state->uncollectable++;

        if (gcstate->debug & _PyGC_DEBUG_UNCOLLECTABLE) {
            debug_cycle("uncollectable", op);
        }