forked from mirrors/gecko-dev
67 lines
2.4 KiB
C++
67 lines
2.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef SizeOfState_h
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#define SizeOfState_h
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#include "mozilla/fallible.h"
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#include "mozilla/MemoryReporting.h"
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#include "mozilla/Unused.h"
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#include "nsTHashtable.h"
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#include "nsHashKeys.h"
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// This file includes types that are useful during memory reporting, but which
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// cannot be put into mfbt/MemoryReporting.h because they depend on things that
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// are not in MFBT.
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namespace mozilla {
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// A table of seen pointers. Useful when measuring structures that contain
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// nodes that may be pointed to from multiple places, e.g. via RefPtr (in C++
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// code) or Arc (in Rust code).
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class SeenPtrs : public nsTHashtable<nsPtrHashKey<const void>> {
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public:
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// Returns true if we have seen this pointer before, false otherwise. Also
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// remembers this pointer for later queries.
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bool HaveSeenPtr(const void* aPtr) {
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uint32_t oldCount = Count();
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mozilla::Unused << PutEntry(aPtr, fallible);
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// If the counts match, there are two possibilities.
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//
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// - Lookup succeeded: we've seen the pointer before, and didn't need to
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// add a new entry.
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//
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// - PutEntry() tried to add the entry and failed due to lack of memory. In
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// this case we can't tell if this pointer has been seen before (because
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// the table is in an unreliable state and may have dropped previous
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// insertions). When doing memory reporting it's better to err on the
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// side of under-reporting rather than over-reporting, so we assume we've
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// seen the pointer before.
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//
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return oldCount == Count();
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}
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};
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// Memory reporting state. Some memory measuring functions
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// (SizeOfIncludingThis(), etc.) just need a MallocSizeOf parameter, but some
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// also need a record of pointers that have been seen and should not be
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// re-measured. This class encapsulates both of those things.
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class SizeOfState {
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public:
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explicit SizeOfState(MallocSizeOf aMallocSizeOf)
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: mMallocSizeOf(aMallocSizeOf) {}
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bool HaveSeenPtr(const void* aPtr) { return mSeenPtrs.HaveSeenPtr(aPtr); }
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MallocSizeOf mMallocSizeOf;
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SeenPtrs mSeenPtrs;
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};
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} // namespace mozilla
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#endif // SizeOfState_h
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