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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#ifndef vm_GeneratorObject_h
#define vm_GeneratorObject_h
#include "frontend/ParserAtom.h" // frontend::TaggedParserAtomIndex
#include "js/Class.h"
#include "vm/ArgumentsObject.h"
#include "vm/ArrayObject.h"
#include "vm/BytecodeUtil.h"
#include "vm/GeneratorResumeKind.h" // GeneratorResumeKind
#include "vm/JSContext.h"
#include "vm/JSObject.h"
#include "vm/Stack.h"
namespace js {
extern const JSClass GeneratorFunctionClass;
class AbstractGeneratorObject : public NativeObject {
// Magic value stored in the resumeIndex slot when the generator is
// running or closing. See the resumeIndex comment below.
static const int32_t RESUME_INDEX_RUNNING = INT32_MAX;
enum {
// Maximum number of fixed stack slots in a generator or async function
// script. If a script would have more, we instead store some variables in
// heap EnvironmentObjects.
// This limit is a performance heuristic. Stack slots reduce allocations,
// and `Local` opcodes are a bit faster than `AliasedVar` ones; but at each
// `yield` or `await` the stack slots must be memcpy'd into a
// GeneratorObject. At some point the memcpy is too much. The limit is
// plenty for typical human-authored code.
static constexpr uint32_t FixedSlotLimit = 256;
static JSObject* createModuleGenerator(JSContext* cx, AbstractFramePtr frame);
static JSObject* createFromFrame(JSContext* cx, AbstractFramePtr frame);
static AbstractGeneratorObject* create(JSContext* cx, HandleFunction callee,
HandleScript script,
HandleObject environmentChain,
Handle<ArgumentsObject*> argsObject);
static bool resume(JSContext* cx, InterpreterActivation& activation,
Handle<AbstractGeneratorObject*> genObj, HandleValue arg,
HandleValue resumeKind);
static bool suspend(JSContext* cx, HandleObject obj, AbstractFramePtr frame,
jsbytecode* pc, unsigned nvalues);
static void finalSuspend(HandleObject obj);
JSFunction& callee() const {
return getFixedSlot(CALLEE_SLOT).toObject().as<JSFunction>();
void setCallee(JSFunction& callee) {
setFixedSlot(CALLEE_SLOT, ObjectValue(callee));
JSObject& environmentChain() const {
return getFixedSlot(ENV_CHAIN_SLOT).toObject();
void setEnvironmentChain(JSObject& envChain) {
setFixedSlot(ENV_CHAIN_SLOT, ObjectValue(envChain));
bool hasArgsObj() const { return getFixedSlot(ARGS_OBJ_SLOT).isObject(); }
ArgumentsObject& argsObj() const {
return getFixedSlot(ARGS_OBJ_SLOT).toObject().as<ArgumentsObject>();
void setArgsObj(ArgumentsObject& argsObj) {
setFixedSlot(ARGS_OBJ_SLOT, ObjectValue(argsObj));
bool hasStackStorage() const {
return getFixedSlot(STACK_STORAGE_SLOT).isObject();
bool isStackStorageEmpty() const {
return stackStorage().getDenseInitializedLength() == 0;
ArrayObject& stackStorage() const {
return getFixedSlot(STACK_STORAGE_SLOT).toObject().as<ArrayObject>();
void setStackStorage(ArrayObject& stackStorage) {
setFixedSlot(STACK_STORAGE_SLOT, ObjectValue(stackStorage));
// Access stack storage. Requires `hasStackStorage() && isSuspended()`.
// `slot` is the index of the desired local in the stack frame when this
// generator is *not* suspended.
const Value& getUnaliasedLocal(uint32_t slot) const;
void setUnaliasedLocal(uint32_t slot, const Value& value);
// The resumeIndex slot is abused for a few purposes. It's undefined if
// it hasn't been set yet (before the initial yield), and null if the
// generator is closed. If the generator is running, the resumeIndex is
// If the generator is suspended, it's the resumeIndex (stored as
// JSOp::InitialYield/JSOp::Yield/JSOp::Await operand) of the yield
// instruction that suspended the generator. The resumeIndex can be mapped to
// the bytecode offset (interpreter) or to the native code offset (JIT).
bool isBeforeInitialYield() const {
return getFixedSlot(RESUME_INDEX_SLOT).isUndefined();
bool isRunning() const {
return getFixedSlot(RESUME_INDEX_SLOT) == Int32Value(RESUME_INDEX_RUNNING);
bool isSuspended() const {
// Note: also update Baseline's IsSuspendedGenerator code if this
// changes.
Value resumeIndex = getFixedSlot(RESUME_INDEX_SLOT);
return resumeIndex.isInt32() &&
resumeIndex.toInt32() < RESUME_INDEX_RUNNING;
void setRunning() {
void setResumeIndex(jsbytecode* pc) {
MOZ_ASSERT(JSOp(*pc) == JSOp::InitialYield || JSOp(*pc) == JSOp::Yield ||
JSOp(*pc) == JSOp::Await);
MOZ_ASSERT_IF(JSOp(*pc) == JSOp::InitialYield,
MOZ_ASSERT_IF(JSOp(*pc) != JSOp::InitialYield, isRunning());
uint32_t resumeIndex = GET_UINT24(pc);
MOZ_ASSERT(resumeIndex < uint32_t(RESUME_INDEX_RUNNING));
setFixedSlot(RESUME_INDEX_SLOT, Int32Value(resumeIndex));
void setResumeIndex(int32_t resumeIndex) {
setFixedSlot(RESUME_INDEX_SLOT, Int32Value(resumeIndex));
uint32_t resumeIndex() const {
return getFixedSlot(RESUME_INDEX_SLOT).toInt32();
bool isClosed() const { return getFixedSlot(CALLEE_SLOT).isNull(); }
void setClosed() {
setFixedSlot(CALLEE_SLOT, NullValue());
setFixedSlot(ENV_CHAIN_SLOT, NullValue());
setFixedSlot(ARGS_OBJ_SLOT, NullValue());
setFixedSlot(STACK_STORAGE_SLOT, NullValue());
setFixedSlot(RESUME_INDEX_SLOT, NullValue());
bool isAfterYield();
bool isAfterAwait();
bool isAfterYieldOrAwait(JSOp op);
void trace(JSTracer* trc);
static size_t offsetOfCalleeSlot() { return getFixedSlotOffset(CALLEE_SLOT); }
static size_t offsetOfEnvironmentChainSlot() {
return getFixedSlotOffset(ENV_CHAIN_SLOT);
static size_t offsetOfArgsObjSlot() {
return getFixedSlotOffset(ARGS_OBJ_SLOT);
static size_t offsetOfResumeIndexSlot() {
return getFixedSlotOffset(RESUME_INDEX_SLOT);
static size_t offsetOfStackStorageSlot() {
return getFixedSlotOffset(STACK_STORAGE_SLOT);
static size_t calleeSlot() { return CALLEE_SLOT; }
static size_t envChainSlot() { return ENV_CHAIN_SLOT; }
static size_t argsObjectSlot() { return ARGS_OBJ_SLOT; }
static size_t stackStorageSlot() { return STACK_STORAGE_SLOT; }
static size_t resumeIndexSlot() { return RESUME_INDEX_SLOT; }
#ifdef DEBUG
void dump() const;
class GeneratorObject : public AbstractGeneratorObject {
enum { RESERVED_SLOTS = AbstractGeneratorObject::RESERVED_SLOTS };
static const JSClass class_;
static const JSClassOps classOps_;
static GeneratorObject* create(JSContext* cx, HandleFunction fun);
bool GeneratorThrowOrReturn(JSContext* cx, AbstractFramePtr frame,
Handle<AbstractGeneratorObject*> obj,
HandleValue val, GeneratorResumeKind resumeKind);
* Return the generator object associated with the given frame. The frame must
* be a call frame for a generator.
* This may return nullptr at certain points in the generator lifecycle:
* - While a generator call evaluates default argument values and performs
* destructuring, which occurs before the generator object is created.
* - Between the `Generator` instruction and the `SetAliasedVar .generator`
* instruction, at which point the generator object does exist, but is held
* only on the stack, and not the `.generator` pseudo-variable this function
* consults.
AbstractGeneratorObject* GetGeneratorObjectForFrame(JSContext* cx,
AbstractFramePtr frame);
* If `env` or any enclosing environment is a `CallObject` associated with a
* generator object, return the generator.
* Otherwise `env` is not in a generator or async function, or the generator
* object hasn't been created yet; return nullptr with no pending exception.
AbstractGeneratorObject* GetGeneratorObjectForEnvironment(JSContext* cx,
HandleObject env);
GeneratorResumeKind ParserAtomToResumeKind(
JSContext* cx, frontend::TaggedParserAtomIndex atom);
JSAtom* ResumeKindToAtom(JSContext* cx, GeneratorResumeKind kind);
} // namespace js
template <>
bool JSObject::is<js::AbstractGeneratorObject>() const;
#endif /* vm_GeneratorObject_h */