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/*
* Copyright (C) 2015-2019 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include "JSScope.h"
#include "VM.h"
namespace JSC {
template<typename JSCellType>
class InferredValue {
WTF_MAKE_NONCOPYABLE(InferredValue);
WTF_MAKE_NONMOVABLE(InferredValue);
public:
// For the purpose of deciding whether or not to watch this variable, you only need
// to inspect inferredValue(). If this returns something other than the empty
// value, then it means that at all future safepoints, this watchpoint set will be
// in one of these states:
//
// IsWatched: in this case, the variable's value must still be the
// inferredValue.
//
// IsInvalidated: in this case the variable's value may be anything but you'll
// either notice that it's invalidated and not install the watchpoint, or
// you will have been notified that the watchpoint was fired.
JSCellType* inferredValue()
{
uintptr_t data = m_data;
if (isFat(data))
return fat(data)->inferredValue();
return bitwise_cast<JSCellType*>(data & ValueMask);
}
explicit InferredValue()
: m_data(encodeState(ClearWatchpoint))
{
ASSERT(inferredValue() == nullptr);
}
~InferredValue()
{
if (isThin())
return;
freeFat();
}
// Fast way of getting the state, which only works from the main thread.
WatchpointState stateOnJSThread() const
{
uintptr_t data = m_data;
if (isFat(data))
return fat(data)->stateOnJSThread();
return decodeState(data);
}
// It is safe to call this from another thread. It may return a prior state,
// but that should be fine since you should only perform actions based on the
// state if you also add a watchpoint.
WatchpointState state() const
{
WTF::loadLoadFence();
uintptr_t data = m_data;
WTF::loadLoadFence();
if (isFat(data))
return fat(data)->state();
return decodeState(data);
}
// It is safe to call this from another thread. It may return false
// even if the set actually had been invalidated, but that ought to happen
// only in the case of races, and should be rare.
bool hasBeenInvalidated() const
{
return state() == IsInvalidated;
}
// Like hasBeenInvalidated(), may be called from another thread.
bool isStillValid() const
{
return !hasBeenInvalidated();
}
void add(Watchpoint*);
void invalidate(VM& vm, const FireDetail& detail)
{
if (isFat())
fat()->invalidate(vm, detail);
else
m_data = encodeState(IsInvalidated);
}
bool isBeingWatched() const
{
if (isFat())
return fat()->isBeingWatched();
return false;
}
void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
{
if (LIKELY(stateOnJSThread() == IsInvalidated))
return;
notifyWriteSlow(vm, owner, value, detail);
}
void notifyWrite(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
{
if (LIKELY(stateOnJSThread() == IsInvalidated))
return;
notifyWriteSlow(vm, owner, value, reason);
}
void finalizeUnconditionally(VM&);
private:
class InferredValueWatchpointSet final : public WatchpointSet {
public:
InferredValueWatchpointSet(WatchpointState state, JSCellType* value)
: WatchpointSet(state)
, m_value(value)
{
}
JSCellType* inferredValue() const { return m_value; }
void invalidate(VM& vm, const FireDetail& detail)
{
m_value = nullptr;
WatchpointSet::invalidate(vm, detail);
}
void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);
private:
JSCellType* m_value;
};
static constexpr uintptr_t IsThinFlag = 1;
static constexpr uintptr_t StateMask = 6;
static constexpr uintptr_t StateShift = 1;
static constexpr uintptr_t ValueMask = ~static_cast<uintptr_t>(IsThinFlag | StateMask);
static bool isThin(uintptr_t data) { return data & IsThinFlag; }
static bool isFat(uintptr_t data) { return !isThin(data); }
static WatchpointState decodeState(uintptr_t data)
{
ASSERT(isThin(data));
return static_cast<WatchpointState>((data & StateMask) >> StateShift);
}
static uintptr_t encodeState(WatchpointState state)
{
return (static_cast<uintptr_t>(state) << StateShift) | IsThinFlag;
}
bool isThin() const { return isThin(m_data); }
bool isFat() const { return isFat(m_data); };
static InferredValueWatchpointSet* fat(uintptr_t data)
{
return bitwise_cast<InferredValueWatchpointSet*>(data);
}
InferredValueWatchpointSet* fat()
{
ASSERT(isFat());
return fat(m_data);
}
const InferredValueWatchpointSet* fat() const
{
ASSERT(isFat());
return fat(m_data);
}
InferredValueWatchpointSet* inflate()
{
if (LIKELY(isFat()))
return fat();
return inflateSlow();
}
InferredValueWatchpointSet* inflateSlow();
void freeFat();
void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const FireDetail&);
void notifyWriteSlow(VM&, JSCell* owner, JSCellType*, const char* reason);
uintptr_t m_data;
};
template<typename JSCellType>
void InferredValue<JSCellType>::InferredValueWatchpointSet::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
{
switch (state()) {
case ClearWatchpoint:
m_value = value;
vm.heap.writeBarrier(owner, value);
startWatching();
return;
case IsWatched:
ASSERT(!!m_value);
if (m_value == value)
return;
invalidate(vm, detail);
return;
case IsInvalidated:
ASSERT_NOT_REACHED();
return;
}
ASSERT_NOT_REACHED();
}
template<typename JSCellType>
void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const FireDetail& detail)
{
uintptr_t data = m_data;
if (isFat(data)) {
fat(data)->notifyWriteSlow(vm, owner, value, detail);
return;
}
switch (state()) {
case ClearWatchpoint:
ASSERT(decodeState(m_data) != IsInvalidated);
m_data = (bitwise_cast<uintptr_t>(value) & ValueMask) | encodeState(IsWatched);
vm.heap.writeBarrier(owner, value);
return;
case IsWatched:
ASSERT(!!inferredValue());
if (inferredValue() == value)
return;
invalidate(vm, detail);
return;
case IsInvalidated:
ASSERT_NOT_REACHED();
return;
}
ASSERT_NOT_REACHED();
}
template<typename JSCellType>
void InferredValue<JSCellType>::notifyWriteSlow(VM& vm, JSCell* owner, JSCellType* value, const char* reason)
{
notifyWriteSlow(vm, owner, value, StringFireDetail(reason));
}
template<typename JSCellType>
void InferredValue<JSCellType>::add(Watchpoint* watchpoint)
{
inflate()->add(watchpoint);
}
template<typename JSCellType>
auto InferredValue<JSCellType>::inflateSlow() -> InferredValueWatchpointSet*
{
ASSERT(isThin());
ASSERT(!isCompilationThread());
uintptr_t data = m_data;
InferredValueWatchpointSet* fat = adoptRef(new InferredValueWatchpointSet(decodeState(m_data), bitwise_cast<JSCellType*>(data & ValueMask))).leakRef();
WTF::storeStoreFence();
m_data = bitwise_cast<uintptr_t>(fat);
return fat;
}
template<typename JSCellType>
void InferredValue<JSCellType>::freeFat()
{
ASSERT(isFat());
fat()->deref();
}
} // namespace JSC