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/*
* Copyright (C) 2022 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. AND ITS CONTRIBUTORS ``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 ITS 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 "IPCTester.h"
#include "ObjectIdentifierReferenceTracker.h"
#include <wtf/Condition.h>
#include <wtf/HashMap.h>
#include <wtf/Lock.h>
#include <wtf/ThreadAssertions.h>
namespace WebKit {
// Container that holds identifier -> object mapping between two processes.
// Used in scenarios where the holder process processes messages with the object references in multiple
// threads. `ThreadSafeObjectHeap` tracks the read and write references to the content pointed
// by a particular identifier.
// Pending reads may block new writes. Alternatively new writes can skip ahead of the reads,
// for example in copy-on-write scenarios.
// Pending writes block reads.
// Currently implemented only for read-only (create-read-destroy) or copy-on-write types,
// e.g. no two-phase get() operations are not implemented yet.
template<typename Identifier, typename HeldType>
class ThreadSafeObjectHeap {
public:
using ReadReference = typename ObjectIdentifierReferenceTracker<Identifier>::ReadReference;
using WriteReference = typename ObjectIdentifierReferenceTracker<Identifier>::WriteReference;
using Reference = typename ObjectIdentifierReferenceTracker<Identifier>::Reference;
virtual ~ThreadSafeObjectHeap() = default;
void add(Identifier, HeldType&&);
// Waits until a write creates the reference and then retires the read or
// times out.
HeldType retire(ReadReference&&, IPC::Timeout);
// Inserts a new version of the object or removes an old one and then retires the write or
// times out.
// If timeout is passed, waits until pending reads are done.
// It is a caller error to not wait and mutate the old object.
void retire(WriteReference&&, std::optional<HeldType>&& newObject, std::optional<IPC::Timeout>);
void retireRemove(WriteReference&&);
void clear();
private:
Lock m_objectsLock;
Condition m_objectsCondition;
struct ReferenceState {
uint64_t retiredReads { 0 };
std::optional<uint64_t> finalRead; // Remove after `finalRead` reads.
std::optional<HeldType> object; // Object or tombstone.
ReferenceState() = default;
explicit ReferenceState(HeldType&& object)
: object(WTFMove(object))
{
}
// Tombstone constructor.
explicit ReferenceState(uint64_t finalRead)
: finalRead(finalRead)
{
}
};
HashMap<Reference, ReferenceState> m_objects WTF_GUARDED_BY_LOCK(m_objectsLock);
};
template<typename Identifier, typename HeldType>
HeldType ThreadSafeObjectHeap<Identifier, HeldType>::retire(ReadReference&& read, IPC::Timeout timeout)
{
Locker locker { m_objectsLock };
do {
auto it = m_objects.find(read.reference());
if (it != m_objects.end()) {
auto& state = it->value;
if (state.object) {
HeldType result = *state.object;
state.retiredReads++;
if (state.finalRead) {
ASSERT(state.finalRead >= state.retiredReads); // Trusted assert because this is ensured on `finalRead` assignment.
if (state.finalRead == state.retiredReads)
m_objects.remove(it);
}
m_objectsCondition.notifyAll();
return result;
}
}
if (!m_objectsCondition.waitUntil(m_objectsLock, timeout.deadline()))
break;
} while (true);
return nullptr;
}
template<typename Identifier, typename HeldType>
void ThreadSafeObjectHeap<Identifier, HeldType>::retire(WriteReference&& write, std::optional<HeldType>&& object, std::optional<IPC::Timeout> timeout)
{
const bool waitForPendingReads = timeout.has_value();
Locker locker { m_objectsLock };
do {
auto it = m_objects.find(write.reference());
if (it != m_objects.end()) {
auto& state = it->value;
if (state.finalRead && state.object) {
// Write replay: `finalRead` is assigned on write. Cannot have the same version with writes.
ASSERT_IS_TESTING_IPC();
return;
}
if (state.retiredReads > write.pendingReads()) {
// Write underflow: more reads have been done than the sender claims is the maximum.
ASSERT_IS_TESTING_IPC();
return;
}
// It is likely a caller error to try to add a new reference with the same client object without
// waiting for pending reads on the old reference.
ASSERT(waitForPendingReads || !state.object || *state.object != object);
if (state.retiredReads == write.pendingReads() || !waitForPendingReads) {
if (state.retiredReads < write.pendingReads())
state.finalRead = write.pendingReads();
else if (state.retiredReads == write.pendingReads())
m_objects.remove(it);
if (object) {
auto addResult = m_objects.add(WTFMove(write).retiredReference(), ReferenceState { WTFMove(*object) });
if (!addResult.isNewEntry) {
auto& newState = addResult.iterator->value;
// Entry was a tombstone.
if (newState.finalRead && !*newState.finalRead) {
m_objects.remove(addResult.iterator);
} else if (!newState.object) {
newState.object = WTFMove(*object);
} else if (newState.object) {
// Write replay: the retired write already exists, the entry was not a tombstone.
ASSERT_IS_TESTING_IPC();
return;
}
}
m_objectsCondition.notifyAll();
}
return;
}
} else if (!waitForPendingReads || !write.pendingReads()) {
// Write the tombstone.
m_objects.add(write.reference(), ReferenceState { write.pendingReads() });
if (object)
m_objects.add(WTFMove(write).retiredReference(), ReferenceState { WTFMove(*object) });
m_objectsCondition.notifyAll();
return;
}
ASSERT(timeout);
if (!m_objectsCondition.waitUntil(m_objectsLock, timeout->deadline()))
break;
} while (true);
}
template<typename Identifier, typename HeldType>
void ThreadSafeObjectHeap<Identifier, HeldType>::retireRemove(WriteReference&& object)
{
retire(WTFMove(object), std::nullopt, std::nullopt);
}
template<typename Identifier, typename HeldType>
void ThreadSafeObjectHeap<Identifier, HeldType>::clear()
{
Locker locker { m_objectsLock };
m_objects.clear();
}
template<typename Identifier, typename HeldType>
void ThreadSafeObjectHeap<Identifier, HeldType>::add(Identifier identifier, HeldType&& object)
{
Reference reference { identifier, 0 };
Locker locker { m_objectsLock };
ASSERT(!m_objects.contains(reference));
m_objects.add(reference, ReferenceState { WTFMove(object) });
}
}
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