Source code
Revision control
Copy as Markdown
Other Tools
/* -*- 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
/*
* JS Atomics pseudo-module.
*
* See chapter 24.4 "The Atomics Object" and chapter 27 "Memory Model" in
* ECMAScript 2021 for the full specification.
*/
#include "builtin/AtomicsObject.h"
#include "mozilla/Atomics.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/FloatingPoint.h"
#include "mozilla/Maybe.h"
#include "mozilla/ScopeExit.h"
#include "jsnum.h"
#include "jit/AtomicOperations.h"
#include "jit/InlinableNatives.h"
#include "js/Class.h"
#include "js/friend/ErrorMessages.h" // js::GetErrorMessage, JSMSG_*
#include "js/PropertySpec.h"
#include "js/Result.h"
#include "js/WaitCallbacks.h"
#include "vm/GlobalObject.h"
#include "vm/TypedArrayObject.h"
#include "vm/Compartment-inl.h"
#include "vm/JSObject-inl.h"
using namespace js;
static bool ReportBadArrayType(JSContext* cx) {
JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
JSMSG_ATOMICS_BAD_ARRAY);
return false;
}
static bool ReportDetachedArrayBuffer(JSContext* cx) {
JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
JSMSG_TYPED_ARRAY_DETACHED);
return false;
}
static bool ReportOutOfRange(JSContext* cx) {
// Use JSMSG_BAD_INDEX here, it is what ToIndex uses for some cases that it
// reports directly.
JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_BAD_INDEX);
return false;
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.1.1 ValidateIntegerTypedArray ( typedArray [ , waitable ] )
static bool ValidateIntegerTypedArray(
JSContext* cx, HandleValue typedArray, bool waitable,
MutableHandle<TypedArrayObject*> unwrappedTypedArray) {
// Step 1 (implicit).
// Step 2.
auto* unwrapped = UnwrapAndTypeCheckValue<TypedArrayObject>(
cx, typedArray, [cx]() { ReportBadArrayType(cx); });
if (!unwrapped) {
return false;
}
if (unwrapped->hasDetachedBuffer()) {
return ReportDetachedArrayBuffer(cx);
}
// Steps 3-6.
if (waitable) {
switch (unwrapped->type()) {
case Scalar::Int32:
case Scalar::BigInt64:
break;
default:
return ReportBadArrayType(cx);
}
} else {
switch (unwrapped->type()) {
case Scalar::Int8:
case Scalar::Uint8:
case Scalar::Int16:
case Scalar::Uint16:
case Scalar::Int32:
case Scalar::Uint32:
case Scalar::BigInt64:
case Scalar::BigUint64:
break;
default:
return ReportBadArrayType(cx);
}
}
// Steps 7-9 (modified to return the TypedArray).
unwrappedTypedArray.set(unwrapped);
return true;
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.1.2 ValidateAtomicAccess ( typedArray, requestIndex )
static bool ValidateAtomicAccess(JSContext* cx,
Handle<TypedArrayObject*> typedArray,
HandleValue requestIndex, size_t* index) {
// Step 1 (implicit).
MOZ_ASSERT(!typedArray->hasDetachedBuffer());
size_t length = typedArray->length();
// Step 2.
uint64_t accessIndex;
if (!ToIndex(cx, requestIndex, &accessIndex)) {
return false;
}
// Steps 3-5.
if (accessIndex >= length) {
return ReportOutOfRange(cx);
}
// Step 6.
*index = size_t(accessIndex);
return true;
}
template <typename T>
struct ArrayOps {
using Type = T;
static JS::Result<T> convertValue(JSContext* cx, HandleValue v) {
int32_t n;
if (!ToInt32(cx, v, &n)) {
return cx->alreadyReportedError();
}
return static_cast<T>(n);
}
static JS::Result<T> convertValue(JSContext* cx, HandleValue v,
MutableHandleValue result) {
double d;
if (!ToInteger(cx, v, &d)) {
return cx->alreadyReportedError();
}
result.setNumber(d);
return static_cast<T>(JS::ToInt32(d));
}
static JS::Result<> storeResult(JSContext* cx, T v,
MutableHandleValue result) {
result.setInt32(v);
return Ok();
}
};
template <>
JS::Result<> ArrayOps<uint32_t>::storeResult(JSContext* cx, uint32_t v,
MutableHandleValue result) {
// Always double typed so that the JITs can assume the types are stable.
result.setDouble(v);
return Ok();
}
template <>
struct ArrayOps<int64_t> {
using Type = int64_t;
static JS::Result<int64_t> convertValue(JSContext* cx, HandleValue v) {
BigInt* bi = ToBigInt(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
return BigInt::toInt64(bi);
}
static JS::Result<int64_t> convertValue(JSContext* cx, HandleValue v,
MutableHandleValue result) {
BigInt* bi = ToBigInt(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
result.setBigInt(bi);
return BigInt::toInt64(bi);
}
static JS::Result<> storeResult(JSContext* cx, int64_t v,
MutableHandleValue result) {
BigInt* bi = BigInt::createFromInt64(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
result.setBigInt(bi);
return Ok();
}
};
template <>
struct ArrayOps<uint64_t> {
using Type = uint64_t;
static JS::Result<uint64_t> convertValue(JSContext* cx, HandleValue v) {
BigInt* bi = ToBigInt(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
return BigInt::toUint64(bi);
}
static JS::Result<uint64_t> convertValue(JSContext* cx, HandleValue v,
MutableHandleValue result) {
BigInt* bi = ToBigInt(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
result.setBigInt(bi);
return BigInt::toUint64(bi);
}
static JS::Result<> storeResult(JSContext* cx, uint64_t v,
MutableHandleValue result) {
BigInt* bi = BigInt::createFromUint64(cx, v);
if (!bi) {
return cx->alreadyReportedError();
}
result.setBigInt(bi);
return Ok();
}
};
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.1.11 AtomicReadModifyWrite ( typedArray, index, value, op ), steps 1-2.
// 24.4.1.12 AtomicLoad ( typedArray, index ), steps 1-2.
// 24.4.4 Atomics.compareExchange ( typedArray, index, ... ), steps 1-2.
// 24.4.9 Atomics.store ( typedArray, index, value ), steps 1-2.
template <typename Op>
bool AtomicAccess(JSContext* cx, HandleValue obj, HandleValue index, Op op) {
// Step 1.
Rooted<TypedArrayObject*> unwrappedTypedArray(cx);
if (!ValidateIntegerTypedArray(cx, obj, false, &unwrappedTypedArray)) {
return false;
}
// Step 2.
size_t intIndex;
if (!ValidateAtomicAccess(cx, unwrappedTypedArray, index, &intIndex)) {
return false;
}
switch (unwrappedTypedArray->type()) {
case Scalar::Int8:
return op(ArrayOps<int8_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Uint8:
return op(ArrayOps<uint8_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Int16:
return op(ArrayOps<int16_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Uint16:
return op(ArrayOps<uint16_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Int32:
return op(ArrayOps<int32_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Uint32:
return op(ArrayOps<uint32_t>{}, unwrappedTypedArray, intIndex);
case Scalar::BigInt64:
return op(ArrayOps<int64_t>{}, unwrappedTypedArray, intIndex);
case Scalar::BigUint64:
return op(ArrayOps<uint64_t>{}, unwrappedTypedArray, intIndex);
case Scalar::Float32:
case Scalar::Float64:
case Scalar::Uint8Clamped:
case Scalar::MaxTypedArrayViewType:
case Scalar::Int64:
case Scalar::Simd128:
break;
}
MOZ_CRASH("Unsupported TypedArray type");
}
template <typename T>
static SharedMem<T*> TypedArrayData(JSContext* cx, TypedArrayObject* typedArray,
size_t index) {
if (typedArray->hasDetachedBuffer()) {
ReportDetachedArrayBuffer(cx);
return {};
}
SharedMem<void*> typedArrayData = typedArray->dataPointerEither();
return typedArrayData.cast<T*>() + index;
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.4 Atomics.compareExchange ( typedArray, index, expectedValue,
// replacementValue )
static bool atomics_compareExchange(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue typedArray = args.get(0);
HandleValue index = args.get(1);
return AtomicAccess(
cx, typedArray, index,
[cx, &args](auto ops, Handle<TypedArrayObject*> unwrappedTypedArray,
size_t index) {
using T = typename decltype(ops)::Type;
HandleValue expectedValue = args.get(2);
HandleValue replacementValue = args.get(3);
T oldval;
JS_TRY_VAR_OR_RETURN_FALSE(cx, oldval,
ops.convertValue(cx, expectedValue));
T newval;
JS_TRY_VAR_OR_RETURN_FALSE(cx, newval,
ops.convertValue(cx, replacementValue));
SharedMem<T*> addr = TypedArrayData<T>(cx, unwrappedTypedArray, index);
if (!addr) {
return false;
}
oldval =
jit::AtomicOperations::compareExchangeSeqCst(addr, oldval, newval);
JS_TRY_OR_RETURN_FALSE(cx, ops.storeResult(cx, oldval, args.rval()));
return true;
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.7 Atomics.load ( typedArray, index )
static bool atomics_load(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue typedArray = args.get(0);
HandleValue index = args.get(1);
return AtomicAccess(
cx, typedArray, index,
[cx, &args](auto ops, Handle<TypedArrayObject*> unwrappedTypedArray,
size_t index) {
using T = typename decltype(ops)::Type;
SharedMem<T*> addr = TypedArrayData<T>(cx, unwrappedTypedArray, index);
if (!addr) {
return false;
}
T v = jit::AtomicOperations::loadSeqCst(addr);
JS_TRY_OR_RETURN_FALSE(cx, ops.storeResult(cx, v, args.rval()));
return true;
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.9 Atomics.store ( typedArray, index, value )
static bool atomics_store(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue typedArray = args.get(0);
HandleValue index = args.get(1);
return AtomicAccess(
cx, typedArray, index,
[cx, &args](auto ops, Handle<TypedArrayObject*> unwrappedTypedArray,
size_t index) {
using T = typename decltype(ops)::Type;
HandleValue value = args.get(2);
T v;
JS_TRY_VAR_OR_RETURN_FALSE(cx, v,
ops.convertValue(cx, value, args.rval()));
SharedMem<T*> addr = TypedArrayData<T>(cx, unwrappedTypedArray, index);
if (!addr) {
return false;
}
jit::AtomicOperations::storeSeqCst(addr, v);
return true;
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.1.11 AtomicReadModifyWrite ( typedArray, index, value, op )
template <typename AtomicOp>
static bool AtomicReadModifyWrite(JSContext* cx, const CallArgs& args,
AtomicOp op) {
HandleValue typedArray = args.get(0);
HandleValue index = args.get(1);
return AtomicAccess(
cx, typedArray, index,
[cx, &args, op](auto ops, Handle<TypedArrayObject*> unwrappedTypedArray,
size_t index) {
using T = typename decltype(ops)::Type;
HandleValue value = args.get(2);
T v;
JS_TRY_VAR_OR_RETURN_FALSE(cx, v, ops.convertValue(cx, value));
SharedMem<T*> addr = TypedArrayData<T>(cx, unwrappedTypedArray, index);
if (!addr) {
return false;
}
v = op(addr, v);
JS_TRY_OR_RETURN_FALSE(cx, ops.storeResult(cx, v, args.rval()));
return true;
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.5 Atomics.exchange ( typedArray, index, value )
static bool atomics_exchange(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::exchangeSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.2 Atomics.add ( typedArray, index, value )
static bool atomics_add(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::fetchAddSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.10 Atomics.sub ( typedArray, index, value )
static bool atomics_sub(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::fetchSubSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.3 Atomics.and ( typedArray, index, value )
static bool atomics_and(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::fetchAndSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.8 Atomics.or ( typedArray, index, value )
static bool atomics_or(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::fetchOrSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.13 Atomics.xor ( typedArray, index, value )
static bool atomics_xor(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
return AtomicReadModifyWrite(cx, args, [](auto addr, auto val) {
return jit::AtomicOperations::fetchXorSeqCst(addr, val);
});
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.6 Atomics.isLockFree ( size )
static bool atomics_isLockFree(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue v = args.get(0);
// Step 1.
int32_t size;
if (v.isInt32()) {
size = v.toInt32();
} else {
double dsize;
if (!ToInteger(cx, v, &dsize)) {
return false;
}
// Step 7 (non-integer case only).
if (!mozilla::NumberEqualsInt32(dsize, &size)) {
args.rval().setBoolean(false);
return true;
}
}
// Steps 2-7.
args.rval().setBoolean(jit::AtomicOperations::isLockfreeJS(size));
return true;
}
namespace js {
// Represents one waiting worker.
//
// The type is declared opaque in SharedArrayObject.h. Instances of
// js::FutexWaiter are stack-allocated and linked onto a list across a
// call to FutexThread::wait().
//
// The 'waiters' field of the SharedArrayRawBuffer points to the highest
// priority waiter in the list, and lower priority nodes are linked through
// the 'lower_pri' field. The 'back' field goes the other direction.
// The list is circular, so the 'lower_pri' field of the lowest priority
// node points to the first node in the list. The list has no dedicated
// header node.
class FutexWaiter {
public:
FutexWaiter(size_t offset, JSContext* cx)
: offset(offset), cx(cx), lower_pri(nullptr), back(nullptr) {}
size_t offset; // int32 element index within the SharedArrayBuffer
JSContext* cx; // The waiting thread
FutexWaiter* lower_pri; // Lower priority nodes in circular doubly-linked
// list of waiters
FutexWaiter* back; // Other direction
};
class AutoLockFutexAPI {
// We have to wrap this in a Maybe because of the way loading
// mozilla::Atomic pointers works.
mozilla::Maybe<js::UniqueLock<js::Mutex>> unique_;
public:
AutoLockFutexAPI() {
js::Mutex* lock = FutexThread::lock_;
unique_.emplace(*lock);
}
~AutoLockFutexAPI() { unique_.reset(); }
js::UniqueLock<js::Mutex>& unique() { return *unique_; }
};
} // namespace js
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.11 Atomics.wait ( typedArray, index, value, timeout ), steps 8-9, 14-25.
template <typename T>
static FutexThread::WaitResult AtomicsWait(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, T value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout) {
// Validation and other guards should ensure that this does not happen.
MOZ_ASSERT(sarb, "wait is only applicable to shared memory");
// Steps 8-9.
if (!cx->fx.canWait()) {
JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
JSMSG_ATOMICS_WAIT_NOT_ALLOWED);
return FutexThread::WaitResult::Error;
}
SharedMem<T*> addr =
sarb->dataPointerShared().cast<T*>() + (byteOffset / sizeof(T));
// Steps 15 (reordered), 17.a and 23 (through destructor).
// This lock also protects the "waiters" field on SharedArrayRawBuffer,
// and it provides the necessary memory fence.
AutoLockFutexAPI lock;
// Steps 16-17.
if (jit::AtomicOperations::loadSafeWhenRacy(addr) != value) {
return FutexThread::WaitResult::NotEqual;
}
// Steps 14, 18-22.
FutexWaiter w(byteOffset, cx);
if (FutexWaiter* waiters = sarb->waiters()) {
w.lower_pri = waiters;
w.back = waiters->back;
waiters->back->lower_pri = &w;
waiters->back = &w;
} else {
w.lower_pri = w.back = &w;
sarb->setWaiters(&w);
}
FutexThread::WaitResult retval = cx->fx.wait(cx, lock.unique(), timeout);
if (w.lower_pri == &w) {
sarb->setWaiters(nullptr);
} else {
w.lower_pri->back = w.back;
w.back->lower_pri = w.lower_pri;
if (sarb->waiters() == &w) {
sarb->setWaiters(w.lower_pri);
}
}
// Steps 24-25.
return retval;
}
FutexThread::WaitResult js::atomics_wait_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int32_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout) {
return AtomicsWait(cx, sarb, byteOffset, value, timeout);
}
FutexThread::WaitResult js::atomics_wait_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int64_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout) {
return AtomicsWait(cx, sarb, byteOffset, value, timeout);
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.11 Atomics.wait ( typedArray, index, value, timeout ), steps 6-25.
template <typename T>
static bool DoAtomicsWait(JSContext* cx,
Handle<TypedArrayObject*> unwrappedTypedArray,
size_t index, T value, HandleValue timeoutv,
MutableHandleValue r) {
mozilla::Maybe<mozilla::TimeDuration> timeout;
if (!timeoutv.isUndefined()) {
// Step 6.
double timeout_ms;
if (!ToNumber(cx, timeoutv, &timeout_ms)) {
return false;
}
// Step 7.
if (!std::isnan(timeout_ms)) {
if (timeout_ms < 0) {
timeout = mozilla::Some(mozilla::TimeDuration::FromSeconds(0.0));
} else if (!std::isinf(timeout_ms)) {
timeout =
mozilla::Some(mozilla::TimeDuration::FromMilliseconds(timeout_ms));
}
}
}
// Step 10.
Rooted<SharedArrayBufferObject*> unwrappedSab(
cx, unwrappedTypedArray->bufferShared());
// Step 11.
size_t offset = unwrappedTypedArray->byteOffset();
// Steps 12-13.
// The computation will not overflow because range checks have been
// performed.
size_t indexedPosition = index * sizeof(T) + offset;
// Steps 8-9, 14-25.
switch (atomics_wait_impl(cx, unwrappedSab->rawBufferObject(),
indexedPosition, value, timeout)) {
case FutexThread::WaitResult::NotEqual:
r.setString(cx->names().futexNotEqual);
return true;
case FutexThread::WaitResult::OK:
r.setString(cx->names().futexOK);
return true;
case FutexThread::WaitResult::TimedOut:
r.setString(cx->names().futexTimedOut);
return true;
case FutexThread::WaitResult::Error:
return false;
default:
MOZ_CRASH("Should not happen");
}
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.11 Atomics.wait ( typedArray, index, value, timeout )
static bool atomics_wait(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue objv = args.get(0);
HandleValue index = args.get(1);
HandleValue valv = args.get(2);
HandleValue timeoutv = args.get(3);
MutableHandleValue r = args.rval();
// Step 1.
Rooted<TypedArrayObject*> unwrappedTypedArray(cx);
if (!ValidateIntegerTypedArray(cx, objv, true, &unwrappedTypedArray)) {
return false;
}
MOZ_ASSERT(unwrappedTypedArray->type() == Scalar::Int32 ||
unwrappedTypedArray->type() == Scalar::BigInt64);
if (!unwrappedTypedArray->isSharedMemory()) {
return ReportBadArrayType(cx);
}
// Step 2.
size_t intIndex;
if (!ValidateAtomicAccess(cx, unwrappedTypedArray, index, &intIndex)) {
return false;
}
if (unwrappedTypedArray->type() == Scalar::Int32) {
// Step 5.
int32_t value;
if (!ToInt32(cx, valv, &value)) {
return false;
}
// Steps 6-25.
return DoAtomicsWait(cx, unwrappedTypedArray, intIndex, value, timeoutv, r);
}
MOZ_ASSERT(unwrappedTypedArray->type() == Scalar::BigInt64);
// Step 4.
RootedBigInt value(cx, ToBigInt(cx, valv));
if (!value) {
return false;
}
// Steps 6-25.
return DoAtomicsWait(cx, unwrappedTypedArray, intIndex,
BigInt::toInt64(value), timeoutv, r);
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.12 Atomics.notify ( typedArray, index, count ), steps 10-16.
int64_t js::atomics_notify_impl(SharedArrayRawBuffer* sarb, size_t byteOffset,
int64_t count) {
// Validation should ensure this does not happen.
MOZ_ASSERT(sarb, "notify is only applicable to shared memory");
// Steps 12 (reordered), 15 (through destructor).
AutoLockFutexAPI lock;
// Step 11 (reordered).
int64_t woken = 0;
// Steps 10, 13-14.
FutexWaiter* waiters = sarb->waiters();
if (waiters && count) {
FutexWaiter* iter = waiters;
do {
FutexWaiter* c = iter;
iter = iter->lower_pri;
if (c->offset != byteOffset || !c->cx->fx.isWaiting()) {
continue;
}
c->cx->fx.notify(FutexThread::NotifyExplicit);
// Overflow will be a problem only in two cases:
// (1) 128-bit systems with substantially more than 2^64 bytes of
// memory per process, and a very lightweight
// Atomics.waitAsync(). Obviously a future problem.
// (2) Bugs.
MOZ_RELEASE_ASSERT(woken < INT64_MAX);
++woken;
if (count > 0) {
--count;
}
} while (count && iter != waiters);
}
// Step 16.
return woken;
}
// ES2021 draft rev bd868f20b8c574ad6689fba014b62a1dba819e56
// 24.4.12 Atomics.notify ( typedArray, index, count )
static bool atomics_notify(JSContext* cx, unsigned argc, Value* vp) {
CallArgs args = CallArgsFromVp(argc, vp);
HandleValue objv = args.get(0);
HandleValue index = args.get(1);
HandleValue countv = args.get(2);
MutableHandleValue r = args.rval();
// Step 1.
Rooted<TypedArrayObject*> unwrappedTypedArray(cx);
if (!ValidateIntegerTypedArray(cx, objv, true, &unwrappedTypedArray)) {
return false;
}
MOZ_ASSERT(unwrappedTypedArray->type() == Scalar::Int32 ||
unwrappedTypedArray->type() == Scalar::BigInt64);
// Step 2.
size_t intIndex;
if (!ValidateAtomicAccess(cx, unwrappedTypedArray, index, &intIndex)) {
return false;
}
// Steps 3-4.
int64_t count;
if (countv.isUndefined()) {
count = -1;
} else {
double dcount;
if (!ToInteger(cx, countv, &dcount)) {
return false;
}
if (dcount < 0.0) {
dcount = 0.0;
}
count = dcount < double(1ULL << 63) ? int64_t(dcount) : -1;
}
if (!unwrappedTypedArray->isSharedMemory()) {
r.setInt32(0);
return true;
}
// Step 5.
Rooted<SharedArrayBufferObject*> unwrappedSab(
cx, unwrappedTypedArray->bufferShared());
// Step 6.
size_t offset = unwrappedTypedArray->byteOffset();
// Steps 7-9.
// The computation will not overflow because range checks have been
// performed.
size_t elementSize = Scalar::byteSize(unwrappedTypedArray->type());
size_t indexedPosition = intIndex * elementSize + offset;
// Steps 10-16.
r.setNumber(double(atomics_notify_impl(unwrappedSab->rawBufferObject(),
indexedPosition, count)));
return true;
}
/* static */
bool js::FutexThread::initialize() {
MOZ_ASSERT(!lock_);
lock_ = js_new<js::Mutex>(mutexid::FutexThread);
return lock_ != nullptr;
}
/* static */
void js::FutexThread::destroy() {
if (lock_) {
js::Mutex* lock = lock_;
js_delete(lock);
lock_ = nullptr;
}
}
/* static */
void js::FutexThread::lock() {
// Load the atomic pointer.
js::Mutex* lock = lock_;
lock->lock();
}
/* static */ mozilla::Atomic<js::Mutex*, mozilla::SequentiallyConsistent>
FutexThread::lock_;
/* static */
void js::FutexThread::unlock() {
// Load the atomic pointer.
js::Mutex* lock = lock_;
lock->unlock();
}
js::FutexThread::FutexThread()
: cond_(nullptr), state_(Idle), canWait_(false) {}
bool js::FutexThread::initInstance() {
MOZ_ASSERT(lock_);
cond_ = js_new<js::ConditionVariable>();
return cond_ != nullptr;
}
void js::FutexThread::destroyInstance() {
if (cond_) {
js_delete(cond_);
}
}
bool js::FutexThread::isWaiting() {
// When a worker is awoken for an interrupt it goes into state
// WaitingNotifiedForInterrupt for a short time before it actually
// wakes up and goes into WaitingInterrupted. In those states the
// worker is still waiting, and if an explicit notify arrives the
// worker transitions to Woken. See further comments in
// FutexThread::wait().
return state_ == Waiting || state_ == WaitingInterrupted ||
state_ == WaitingNotifiedForInterrupt;
}
FutexThread::WaitResult js::FutexThread::wait(
JSContext* cx, js::UniqueLock<js::Mutex>& locked,
const mozilla::Maybe<mozilla::TimeDuration>& timeout) {
MOZ_ASSERT(&cx->fx == this);
MOZ_ASSERT(cx->fx.canWait());
MOZ_ASSERT(state_ == Idle || state_ == WaitingInterrupted);
// Disallow waiting when a runtime is processing an interrupt.
// See explanation below.
if (state_ == WaitingInterrupted) {
UnlockGuard<Mutex> unlock(locked);
JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr,
JSMSG_ATOMICS_WAIT_NOT_ALLOWED);
return WaitResult::Error;
}
// Go back to Idle after returning.
auto onFinish = mozilla::MakeScopeExit([&] { state_ = Idle; });
const bool isTimed = timeout.isSome();
auto finalEnd = timeout.map([](const mozilla::TimeDuration& timeout) {
return mozilla::TimeStamp::Now() + timeout;
});
// 4000s is about the longest timeout slice that is guaranteed to
// work cross-platform.
auto maxSlice = mozilla::TimeDuration::FromSeconds(4000.0);
for (;;) {
// If we are doing a timed wait, calculate the end time for this wait
// slice.
auto sliceEnd = finalEnd.map([&](mozilla::TimeStamp& finalEnd) {
auto sliceEnd = mozilla::TimeStamp::Now() + maxSlice;
if (finalEnd < sliceEnd) {
sliceEnd = finalEnd;
}
return sliceEnd;
});
state_ = Waiting;
MOZ_ASSERT((cx->runtime()->beforeWaitCallback == nullptr) ==
(cx->runtime()->afterWaitCallback == nullptr));
mozilla::DebugOnly<bool> callbacksPresent =
cx->runtime()->beforeWaitCallback != nullptr;
void* cookie = nullptr;
uint8_t clientMemory[JS::WAIT_CALLBACK_CLIENT_MAXMEM];
if (cx->runtime()->beforeWaitCallback) {
cookie = (*cx->runtime()->beforeWaitCallback)(clientMemory);
}
if (isTimed) {
(void)cond_->wait_until(locked, *sliceEnd);
} else {
cond_->wait(locked);
}
MOZ_ASSERT((cx->runtime()->afterWaitCallback != nullptr) ==
callbacksPresent);
if (cx->runtime()->afterWaitCallback) {
(*cx->runtime()->afterWaitCallback)(cookie);
}
switch (state_) {
case FutexThread::Waiting:
// Timeout or spurious wakeup.
if (isTimed) {
auto now = mozilla::TimeStamp::Now();
if (now >= *finalEnd) {
return WaitResult::TimedOut;
}
}
break;
case FutexThread::Woken:
return WaitResult::OK;
case FutexThread::WaitingNotifiedForInterrupt:
// The interrupt handler may reenter the engine. In that case
// there are two complications:
//
// - The waiting thread is not actually waiting on the
// condition variable so we have to record that it
// should be woken when the interrupt handler returns.
// To that end, we flag the thread as interrupted around
// the interrupt and check state_ when the interrupt
// handler returns. A notify() call that reaches the
// runtime during the interrupt sets state_ to Woken.
//
// - It is in principle possible for wait() to be
// reentered on the same thread/runtime and waiting on the
// same location and to yet again be interrupted and enter
// the interrupt handler. In this case, it is important
// that when another agent notifies waiters, all waiters using
// the same runtime on the same location are woken in LIFO
// order; FIFO may be the required order, but FIFO would
// fail to wake up the innermost call. Interrupts are
// outside any spec anyway. Also, several such suspended
// waiters may be woken at a time.
//
// For the time being we disallow waiting from within code
// that runs from within an interrupt handler; this may
// occasionally (very rarely) be surprising but is
// expedient. Other solutions exist, see bug #1131943. The
// code that performs the check is above, at the head of
// this function.
state_ = WaitingInterrupted;
{
UnlockGuard<Mutex> unlock(locked);
if (!cx->handleInterrupt()) {
return WaitResult::Error;
}
}
if (state_ == Woken) {
return WaitResult::OK;
}
break;
default:
MOZ_CRASH("Bad FutexState in wait()");
}
}
}
void js::FutexThread::notify(NotifyReason reason) {
MOZ_ASSERT(isWaiting());
if ((state_ == WaitingInterrupted || state_ == WaitingNotifiedForInterrupt) &&
reason == NotifyExplicit) {
state_ = Woken;
return;
}
switch (reason) {
case NotifyExplicit:
state_ = Woken;
break;
case NotifyForJSInterrupt:
if (state_ == WaitingNotifiedForInterrupt) {
return;
}
state_ = WaitingNotifiedForInterrupt;
break;
default:
MOZ_CRASH("bad NotifyReason in FutexThread::notify()");
}
cond_->notify_all();
}
const JSFunctionSpec AtomicsMethods[] = {
JS_INLINABLE_FN("compareExchange", atomics_compareExchange, 4, 0,
AtomicsCompareExchange),
JS_INLINABLE_FN("load", atomics_load, 2, 0, AtomicsLoad),
JS_INLINABLE_FN("store", atomics_store, 3, 0, AtomicsStore),
JS_INLINABLE_FN("exchange", atomics_exchange, 3, 0, AtomicsExchange),
JS_INLINABLE_FN("add", atomics_add, 3, 0, AtomicsAdd),
JS_INLINABLE_FN("sub", atomics_sub, 3, 0, AtomicsSub),
JS_INLINABLE_FN("and", atomics_and, 3, 0, AtomicsAnd),
JS_INLINABLE_FN("or", atomics_or, 3, 0, AtomicsOr),
JS_INLINABLE_FN("xor", atomics_xor, 3, 0, AtomicsXor),
JS_INLINABLE_FN("isLockFree", atomics_isLockFree, 1, 0, AtomicsIsLockFree),
JS_FN("wait", atomics_wait, 4, 0),
JS_FN("notify", atomics_notify, 3, 0),
JS_FN("wake", atomics_notify, 3, 0), // Legacy name
JS_FS_END};
static const JSPropertySpec AtomicsProperties[] = {
JS_STRING_SYM_PS(toStringTag, "Atomics", JSPROP_READONLY), JS_PS_END};
static JSObject* CreateAtomicsObject(JSContext* cx, JSProtoKey key) {
RootedObject proto(cx, &cx->global()->getObjectPrototype());
return NewTenuredObjectWithGivenProto(cx, &AtomicsObject::class_, proto);
}
static const ClassSpec AtomicsClassSpec = {CreateAtomicsObject, nullptr,
AtomicsMethods, AtomicsProperties};
const JSClass AtomicsObject::class_ = {
"Atomics", JSCLASS_HAS_CACHED_PROTO(JSProto_Atomics), JS_NULL_CLASS_OPS,
&AtomicsClassSpec};