1 files changed, 67 insertions, 0 deletions
diff --git a/xpcom/base/SizeOfState.h b/xpcom/base/SizeOfState.h
new file mode 100644
index 0000000000..2df0b24e93
--- /dev/null
+++ b/xpcom/base/SizeOfState.h
@@ -0,0 +1,67 @@
+/* -*- 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 "mozilla/Unused.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();
+
+    mozilla::Unused << 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