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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 http://mozilla.org/MPL/2.0/. */
#ifndef SizeOfState_h
#define SizeOfState_h
#include "mozilla/fallible.h"
#include "mozilla/MemoryReporting.h"
#include "nsTHashtable.h"
#include "nsHashKeys.h"
// This file includes types that are useful during memory reporting, but which
// cannot be put into mfbt/MemoryReporting.h because they depend on things that
// are not in MFBT.
namespace mozilla {
// A table of seen pointers. Useful when measuring structures that contain
// nodes that may be pointed to from multiple places, e.g. via RefPtr (in C++
// code) or Arc (in Rust code).
class SeenPtrs : public nsTHashtable<nsPtrHashKey<const void>> {
public:
// Returns true if we have seen this pointer before, false otherwise. Also
// remembers this pointer for later queries.
bool HaveSeenPtr(const void* aPtr) {
uint32_t oldCount = Count();
(void)PutEntry(aPtr, fallible);
// If the counts match, there are two possibilities.
//
// - Lookup succeeded: we've seen the pointer before, and didn't need to
// add a new entry.
//
// - PutEntry() tried to add the entry and failed due to lack of memory. In
// this case we can't tell if this pointer has been seen before (because
// the table is in an unreliable state and may have dropped previous
// insertions). When doing memory reporting it's better to err on the
// side of under-reporting rather than over-reporting, so we assume we've
// seen the pointer before.
//
return oldCount == Count();
}
};
// Memory reporting state. Some memory measuring functions
// (SizeOfIncludingThis(), etc.) just need a MallocSizeOf parameter, but some
// also need a record of pointers that have been seen and should not be
// re-measured. This class encapsulates both of those things.
class SizeOfState {
public:
explicit SizeOfState(MallocSizeOf aMallocSizeOf)
: mMallocSizeOf(aMallocSizeOf) {}
bool HaveSeenPtr(const void* aPtr) { return mSeenPtrs.HaveSeenPtr(aPtr); }
MallocSizeOf mMallocSizeOf;
SeenPtrs mSeenPtrs;
};
} // namespace mozilla
#endif // SizeOfState_h
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