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// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_PERSISTENT_NODE_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_HEAP_PERSISTENT_NODE_H_
#include <memory>
#include "third_party/blink/renderer/platform/heap/process_heap.h"
#include "third_party/blink/renderer/platform/heap/thread_state.h"
#include "third_party/blink/renderer/platform/platform_export.h"
#include "third_party/blink/renderer/platform/wtf/allocator.h"
#include "third_party/blink/renderer/platform/wtf/assertions.h"
#include "third_party/blink/renderer/platform/wtf/threading_primitives.h"
namespace blink {
class CrossThreadPersistentRegion;
class PersistentNode final {
DISALLOW_NEW();
public:
PersistentNode() : self_(nullptr), trace_(nullptr) { DCHECK(IsUnused()); }
#if DCHECK_IS_ON()
~PersistentNode() {
// If you hit this assert, it means that the thread finished
// without clearing persistent handles that the thread created.
// We don't enable the assert for the main thread because the
// main thread finishes without clearing all persistent handles.
DCHECK(IsMainThread() || IsUnused());
}
#endif
// It is dangerous to copy the PersistentNode because it breaks the
// free list.
PersistentNode& operator=(const PersistentNode& otherref) = delete;
// Ideally the trace method should be virtual and automatically dispatch
// to the most specific implementation. However having a virtual method
// on PersistentNode leads to too eager template instantiation with MSVC
// which leads to include cycles.
// Instead we call the constructor with a TraceCallback which knows the
// type of the most specific child and calls trace directly. See
// TraceMethodDelegate in Visitor.h for how this is done.
void TracePersistentNode(Visitor* visitor) {
DCHECK(!IsUnused());
DCHECK(trace_);
trace_(visitor, self_);
}
void Initialize(void* self, TraceCallback trace) {
DCHECK(IsUnused());
self_ = self;
trace_ = trace;
}
void SetFreeListNext(PersistentNode* node) {
DCHECK(!node || node->IsUnused());
self_ = node;
trace_ = nullptr;
DCHECK(IsUnused());
}
PersistentNode* FreeListNext() {
DCHECK(IsUnused());
PersistentNode* node = reinterpret_cast<PersistentNode*>(self_);
DCHECK(!node || node->IsUnused());
return node;
}
bool IsUnused() const { return !trace_; }
void* Self() const { return self_; }
private:
// If this PersistentNode is in use:
// - m_self points to the corresponding Persistent handle.
// - m_trace points to the trace method.
// If this PersistentNode is freed:
// - m_self points to the next freed PersistentNode.
// - m_trace is nullptr.
void* self_;
TraceCallback trace_;
};
struct PersistentNodeSlots final {
USING_FAST_MALLOC(PersistentNodeSlots);
private:
static const int kSlotCount = 256;
PersistentNodeSlots* next_;
PersistentNode slot_[kSlotCount];
friend class PersistentRegion;
friend class CrossThreadPersistentRegion;
};
// PersistentRegion provides a region of PersistentNodes. PersistentRegion
// holds a linked list of PersistentNodeSlots, each of which stores
// a predefined number of PersistentNodes. You can call allocatePersistentNode/
// freePersistentNode to allocate/free a PersistentNode on the region.
class PLATFORM_EXPORT PersistentRegion final {
USING_FAST_MALLOC(PersistentRegion);
public:
PersistentRegion()
: free_list_head_(nullptr),
slots_(nullptr)
#if DCHECK_IS_ON()
,
persistent_count_(0)
#endif
{
}
~PersistentRegion();
PersistentNode* AllocatePersistentNode(void* self, TraceCallback trace) {
#if DCHECK_IS_ON()
++persistent_count_;
#endif
if (UNLIKELY(!free_list_head_))
EnsurePersistentNodeSlots(self, trace);
DCHECK(free_list_head_);
PersistentNode* node = free_list_head_;
free_list_head_ = free_list_head_->FreeListNext();
node->Initialize(self, trace);
DCHECK(!node->IsUnused());
return node;
}
void FreePersistentNode(PersistentNode* persistent_node) {
#if DCHECK_IS_ON()
DCHECK_GT(persistent_count_, 0);
#endif
persistent_node->SetFreeListNext(free_list_head_);
free_list_head_ = persistent_node;
#if DCHECK_IS_ON()
--persistent_count_;
#endif
}
static bool ShouldTracePersistentNode(Visitor*, PersistentNode*) {
return true;
}
void ReleasePersistentNode(PersistentNode*,
ThreadState::PersistentClearCallback);
using ShouldTraceCallback = bool (*)(Visitor*, PersistentNode*);
void TracePersistentNodes(
Visitor*,
ShouldTraceCallback = PersistentRegion::ShouldTracePersistentNode);
int NumberOfPersistents();
void PrepareForThreadStateTermination();
private:
friend CrossThreadPersistentRegion;
void EnsurePersistentNodeSlots(void*, TraceCallback);
PersistentNode* free_list_head_;
PersistentNodeSlots* slots_;
#if DCHECK_IS_ON()
int persistent_count_;
#endif
};
// Protected by ProcessHeap::CrossThreadPersistentMutex.
class CrossThreadPersistentRegion final {
USING_FAST_MALLOC(CrossThreadPersistentRegion);
public:
void AllocatePersistentNode(PersistentNode*& persistent_node,
void* self,
TraceCallback trace) {
#if DCHECK_IS_ON()
DCHECK(ProcessHeap::CrossThreadPersistentMutex().Locked());
#endif
PersistentNode* node =
persistent_region_.AllocatePersistentNode(self, trace);
ReleaseStore(reinterpret_cast<void* volatile*>(&persistent_node), node);
}
void FreePersistentNode(PersistentNode*& persistent_node) {
#if DCHECK_IS_ON()
DCHECK(ProcessHeap::CrossThreadPersistentMutex().Locked());
#endif
// When the thread that holds the heap object that the cross-thread
// persistent shuts down, prepareForThreadStateTermination() will clear out
// the associated CrossThreadPersistent<> and PersistentNode so as to avoid
// unsafe access. This can overlap with a holder of the
// CrossThreadPersistent<> also clearing the persistent and freeing the
// PersistentNode.
//
// The lock ensures the updating is ordered, but by the time lock has been
// acquired the PersistentNode reference may have been cleared out already;
// check for this.
if (!persistent_node)
return;
persistent_region_.FreePersistentNode(persistent_node);
ReleaseStore(reinterpret_cast<void* volatile*>(&persistent_node), nullptr);
}
void TracePersistentNodes(Visitor* visitor) {
// If this assert triggers, you're tracing without being in a LockScope.
#if DCHECK_IS_ON()
DCHECK(ProcessHeap::CrossThreadPersistentMutex().Locked());
#endif
persistent_region_.TracePersistentNodes(
visitor, CrossThreadPersistentRegion::ShouldTracePersistentNode);
}
void PrepareForThreadStateTermination(ThreadState*);
NO_SANITIZE_ADDRESS
static bool ShouldTracePersistentNode(Visitor*, PersistentNode*);
#if defined(ADDRESS_SANITIZER)
void UnpoisonCrossThreadPersistents();
#endif
private:
// We don't make CrossThreadPersistentRegion inherit from PersistentRegion
// because we don't want to virtualize performance-sensitive methods
// such as PersistentRegion::allocate/freePersistentNode.
PersistentRegion persistent_region_;
};
} // namespace blink
#endif
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