The Tor Browser: xpcom/base/nsIMemoryReporter.idl@b8a032363ba2 (annotated)

xpcom/base/nsIMemoryReporter.idl@b8a032363ba2 (annotated)

xpcom/base/nsIMemoryReporter.idl

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- 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/. */
 #include "nsISupports.idl"
 interface nsIDOMWindow;
 interface nsIRunnable;
 interface nsISimpleEnumerator;
 /*
  * Memory reporters measure Firefox's memory usage.  They are primarily used to
  * generate the about:memory page.  You should read
  * https://wiki.mozilla.org/Memory_Reporting before writing a memory
  * reporter.
  */
 [scriptable, function, uuid(3a61be3b-b93b-461a-a4f8-388214f558b1)]
 interface nsIMemoryReporterCallback : nsISupports
 {
   /*
    * The arguments to the callback are as follows.
    *
    *
    * |process|  The name of the process containing this reporter.  Each
    * reporter initially has "" in this field, indicating that it applies to the
    * current process.  (This is true even for reporters in a child process.)
    * When a reporter from a child process is copied into the main process, the
    * copy has its 'process' field set appropriately.
    *
    *
    * |path|  The path that this memory usage should be reported under.  Paths
    * are '/'-delimited, eg. "a/b/c".
    *
    * Each reporter can be viewed as representing a leaf node in a tree.
    * Internal nodes of the tree don't have reporters.  So, for example, the
    * reporters "explicit/a/b", "explicit/a/c", "explicit/d/e", and
    * "explicit/d/f" define this tree:
    *
    *   explicit
    *   |--a
    *   |  |--b [*]
    *   |  \--c [*]
    *   \--d
    *      |--e [*]
    *      \--f [*]
    *
    * Nodes marked with a [*] have a reporter.  Notice that the internal
    * nodes are implicitly defined by the paths.
    *
    * Nodes within a tree should not overlap measurements, otherwise the
    * parent node measurements will be double-counted.  So in the example
    * above, |b| should not count any allocations counted by |c|, and vice
    * versa.
    *
    * All nodes within each tree must have the same units.
    *
    * If you want to include a '/' not as a path separator, e.g. because the
    * path contains a URL, you need to convert each '/' in the URL to a '\'.
    * Consumers of the path will undo this change.  Any other '\' character
    * in a path will also be changed.  This is clumsy but hasn't caused any
    * problems so far.
    *
    * The paths of all reporters form a set of trees.  Trees can be
    * "degenerate", i.e. contain a single entry with no '/'.
    *
    *
    * |kind|  There are three kinds of memory reporters.
    *
    *  - HEAP: reporters measuring memory allocated by the heap allocator,
    *    e.g. by calling malloc, calloc, realloc, memalign, operator new, or
    *    operator new[].  Reporters in this category must have units
    *    UNITS_BYTES.
    *
    *  - NONHEAP: reporters measuring memory which the program explicitly
    *    allocated, but does not live on the heap.  Such memory is commonly
    *    allocated by calling one of the OS's memory-mapping functions (e.g.
    *    mmap, VirtualAlloc, or vm_allocate).  Reporters in this category
    *    must have units UNITS_BYTES.
    *
    *  - OTHER: reporters which don't fit into either of these categories.
    *    They can have any units.
    *
    * The kind only matters for reporters in the "explicit" tree;
    * aboutMemory.js uses it to calculate "heap-unclassified".
    *
    *
    * |units|  The units on the reporter's amount.  One of the following.
    *
    *  - BYTES: The amount contains a number of bytes.
    *
    *  - COUNT: The amount is an instantaneous count of things currently in
    *    existence.  For instance, the number of tabs currently open would have
    *    units COUNT.
    *
    *  - COUNT_CUMULATIVE: The amount contains the number of times some event
    *    has occurred since the application started up.  For instance, the
    *    number of times the user has opened a new tab would have units
    *    COUNT_CUMULATIVE.
    *
    *    The amount returned by a reporter with units COUNT_CUMULATIVE must
    *    never decrease over the lifetime of the application.
    *
    *  - PERCENTAGE: The amount contains a fraction that should be expressed as
    *    a percentage.  NOTE!  The |amount| field should be given a value 100x
    *    the actual percentage;  this number will be divided by 100 when shown.
    *    This allows a fractional percentage to be shown even though |amount| is
    *    an integer.  E.g. if the actual percentage is 12.34%, |amount| should
    *    be 1234.
    *
    *    Values greater than 100% are allowed.
    *
    *
    * |amount|  The numeric value reported by this memory reporter.  Accesses
    * can fail if something goes wrong when getting the amount.
    *
    *
    * |description|  A human-readable description of this memory usage report.
    */
   void callback(in ACString process, in AUTF8String path, in int32_t kind,
                 in int32_t units, in int64_t amount,
                 in AUTF8String description, in nsISupports data);
 };
 /*
  * An nsIMemoryReporter reports one or more memory measurements via a
  * callback function which is called once for each measurement.
  *
  * An nsIMemoryReporter that reports a single measurement is sometimes called a
  * "uni-reporter".  One that reports multiple measurements is sometimes called
  * a "multi-reporter".
  *
  * aboutMemory.js is the most important consumer of memory reports.  It
  * places the following constraints on reports.
  *
  * - All reports within a single sub-tree must have the same units.
  *
  * - There may be an "explicit" tree.  If present, it represents
  *   non-overlapping regions of memory that have been explicitly allocated with
  *   an OS-level allocation (e.g. mmap/VirtualAlloc/vm_allocate) or a
  *   heap-level allocation (e.g. malloc/calloc/operator new).  Reporters in
  *   this tree must have kind HEAP or NONHEAP, units BYTES.
  *
  * It is preferred, but not required, that report descriptions use complete
  * sentences (i.e. start with a capital letter and end with a period, or
  * similar).
  */
 [scriptable, uuid(0884cd0f-5829-4381-979b-0f53904030ed)]
 interface nsIMemoryReporter : nsISupports
 {
   /*
    * Run the reporter.
    */
   void collectReports(in nsIMemoryReporterCallback callback,
                       in nsISupports data);
   /*
    * Kinds.  See the |kind| comment in nsIMemoryReporterCallback.
    */
   const int32_t KIND_NONHEAP = 0;
   const int32_t KIND_HEAP    = 1;
   const int32_t KIND_OTHER   = 2;
   /*
    * Units.  See the |units| comment in nsIMemoryReporterCallback.
    */
   const int32_t UNITS_BYTES = 0;
   const int32_t UNITS_COUNT = 1;
   const int32_t UNITS_COUNT_CUMULATIVE = 2;
   const int32_t UNITS_PERCENTAGE = 3;
 };
 [scriptable, function, uuid(548b3909-c04d-4ca6-8466-b8bee3837457)]
 interface nsIFinishReportingCallback : nsISupports
 {
   void callback(in nsISupports data);
 };
 [scriptable, builtinclass, uuid(b6e5ec8a-71d9-48db-8ae9-68b4c5bbf2c3)]
 interface nsIMemoryReporterManager : nsISupports
 {
   /*
    * Initialize.
    */
   void init();
   /*
    * Register the given nsIMemoryReporter.  The Manager service will hold a
    * strong reference to the given reporter, and will be responsible for freeing
    * the reporter at shutdown.  You may manually unregister the reporter with
    * unregisterStrongReporter() at any point.
    */
   void registerStrongReporter(in nsIMemoryReporter reporter);
   /*
    * Like registerReporter, but the Manager service will hold a weak reference
    * via a raw pointer to the given reporter.  The reporter should be
    * unregistered before shutdown.
    * You cannot register JavaScript components with this function!  Always
    * register your JavaScript components with registerStrongReporter().
    */
   void registerWeakReporter(in nsIMemoryReporter reporter);
   /*
    * Unregister the given memory reporter, which must have been registered with
    * registerStrongReporter().  You normally don't need to unregister your
    * strong reporters, as nsIMemoryReporterManager will take care of that at
    * shutdown.
    */
   void unregisterStrongReporter(in nsIMemoryReporter reporter);
   /*
    * Unregister the given memory reporter, which must have been registered with
    * registerWeakReporter().
    */
   void unregisterWeakReporter(in nsIMemoryReporter reporter);
   /*
    * These functions should only be used for testing purposes.
    */
   void blockRegistrationAndHideExistingReporters();
   void unblockRegistrationAndRestoreOriginalReporters();
   void registerStrongReporterEvenIfBlocked(in nsIMemoryReporter aReporter);
   /*
    * Get memory reports for the current process and all child processes.
    * |handleReport| is called for each report, and |finishReporting| is called
    * once all reports have been handled.
    *
    * |finishReporting| is called even if, for example, some child processes
    * fail to report back.  However, calls to this method will silently and
    * immediately abort -- and |finishReporting| will not be called -- if a
    * previous getReports() call is still in flight, i.e. if it has not yet
    * finished invoking |finishReporting|.  The silent abort is because the
    * in-flight request will finish soon, and the caller would very likely just
    * catch and ignore any error anyway.
    */
   void getReports(in nsIMemoryReporterCallback handleReport,
                   in nsISupports handleReportData,
                   in nsIFinishReportingCallback finishReporting,
                   in nsISupports finishReportingData);
   /*
    * As above, but: If |minimizeMemoryUsage| is true, then each process will
    * minimize its memory usage (see the |minimizeMemoryUsage| method) before
    * gathering its report.  If DMD is enabled and |DMDDumpIdent| is non-empty
    * then write a DMD report to a file in the usual temporary directory (see
    * |dumpMemoryInfoToTempDir| in |nsIMemoryInfoDumper|.)
    */
   [noscript] void
     getReportsExtended(in nsIMemoryReporterCallback handleReport,
                        in nsISupports handleReportData,
                        in nsIFinishReportingCallback finishReporting,
                        in nsISupports finishReportingData,
                        in boolean minimizeMemoryUsage,
                        in AString DMDDumpIdent);
   /*
    * Get memory reports in the current process only.  |handleReport| is called
    * for each report.
    */
   void getReportsForThisProcess(in nsIMemoryReporterCallback handleReport,
                                 in nsISupports handleReportData);
   /*
    * As above, but if DMD is enabled and |DMDDumpIdent| is non-empty
    * then write a DMD report to a file in the usual temporary directory (see
    * |dumpMemoryInfoToTempDir| in |nsIMemoryInfoDumper|.)
    */
   [noscript] void
     getReportsForThisProcessExtended(in nsIMemoryReporterCallback handleReport,
                                      in nsISupports handleReportData,
                                      in AString DMDDumpIdent);
   /*
    * The memory reporter manager, for the most part, treats reporters
    * registered with it as a black box.  However, there are some
    * "distinguished" amounts (as could be reported by a memory reporter) that
    * the manager provides as attributes, because they are sufficiently
    * interesting that we want external code (e.g. telemetry) to be able to rely
    * on them.
    *
    * Note that these are not reporters and so getReports() and
    * getReportsForThisProcess() do not look at them.  However, distinguished
    * amounts can be embedded in a reporter.
    *
    * Access to these attributes can fail.  In particular, some of them are not
    * available on all platforms.
    *
    * If you add a new distinguished amount, please update
    * toolkit/components/aboutmemory/tests/test_memoryReporters.xul.
    *
    * |explicit| (UNITS_BYTES)  The total size of explicit memory allocations,
    * both at the OS-level (eg. via mmap, VirtualAlloc) and at the heap level
    * (eg. via malloc, calloc, operator new).  It covers all heap allocations,
    * but will miss any OS-level ones not covered by memory reporters.
    *
    * |vsize| (UNITS_BYTES)  The virtual size, i.e. the amount of address space
    * taken up.
    *
    * |vsizeMaxContiguous| (UNITS_BYTES)  The size of the largest contiguous
    * block of virtual memory.
    *
    * |resident| (UNITS_BYTES)  The resident size (a.k.a. RSS or physical memory
    * used).
    *
    * |residentFast| (UNITS_BYTES)  This is like |resident|, but on Mac OS
    * |resident| can purge pages, which is slow.  It also affects the result of
    * |residentFast|, and so |resident| and |residentFast| should not be used
    * together.
    *
    * |heapAllocated| (UNITS_BYTES)  Memory mapped by the heap allocator.
    *
    * |heapOverheadRatio| (UNITS_PERCENTAGE)  In the heap allocator, this is the
    * ratio of committed, unused bytes to allocated bytes.  Like all
    * UNITS_PERCENTAGE measurements, its amount is multiplied by 100x so it can
    * be represented by an int64_t.
    *
    * |JSMainRuntimeGCHeap| (UNITS_BYTES)  Size of the main JS runtime's GC
    * heap.
    *
    * |JSMainRuntimeTemporaryPeak| (UNITS_BYTES)  Peak size of the transient
    * storage in the main JSRuntime.
    *
    * |JSMainRuntimeCompartments{System,User}| (UNITS_COUNT)  The number of
    * {system,user} compartments in the main JS runtime.
    *
    * |imagesContentUsedUncompressed| (UNITS_BYTES)  Memory used for decoded
    * images in content.
    *
    * |storageSQLite| (UNITS_BYTES)  Memory used by SQLite.
    *
    * |lowMemoryEvents{Virtual,Physical}| (UNITS_COUNT_CUMULATIVE)  The number
    * of low-{virtual,physical}-memory events that have occurred since the
    * process started.
    *
    * |ghostWindows| (UNITS_COUNT)  The number of ghost windows.
    *
    * |pageFaultsHard| (UNITS_COUNT_CUMULATIVE)  The number of hard (a.k.a.
    * major) page faults that have occurred since the process started.
    */
   readonly attribute int64_t explicit;
   readonly attribute int64_t vsize;
   readonly attribute int64_t vsizeMaxContiguous;
   readonly attribute int64_t resident;
   readonly attribute int64_t residentFast;
   readonly attribute int64_t heapAllocated;
   readonly attribute int64_t heapOverheadRatio;
   readonly attribute int64_t JSMainRuntimeGCHeap;
   readonly attribute int64_t JSMainRuntimeTemporaryPeak;
   readonly attribute int64_t JSMainRuntimeCompartmentsSystem;
   readonly attribute int64_t JSMainRuntimeCompartmentsUser;
   readonly attribute int64_t imagesContentUsedUncompressed;
   readonly attribute int64_t storageSQLite;
   readonly attribute int64_t lowMemoryEventsVirtual;
   readonly attribute int64_t lowMemoryEventsPhysical;
   readonly attribute int64_t ghostWindows;
   readonly attribute int64_t pageFaultsHard;
   /*
    * This attribute indicates if moz_malloc_usable_size() works.
    */
   [infallible] readonly attribute boolean hasMozMallocUsableSize;
   /*
    * Run a series of GC/CC's in an attempt to minimize the application's memory
    * usage.  When we're finished, we invoke the given runnable if it's not
    * null.
    */
   void minimizeMemoryUsage(in nsIRunnable callback);
   /*
    * Measure the memory that is known to be owned by this tab, split up into
    * several broad categories.  Note that this will be an underestimate of the
    * true number, due to imperfect memory reporter coverage (corresponding to
    * about:memory's "heap-unclassified"), and due to some memory shared between
    * tabs not being counted.
    *
    * The time taken for the measurement (split into JS and non-JS parts) is
    * also returned.
    */
   void sizeOfTab(in nsIDOMWindow window,
                  out int64_t jsObjectsSize, out int64_t jsStringsSize,
                  out int64_t jsOtherSize, out int64_t domSize,
                  out int64_t styleSize, out int64_t otherSize,
                  out int64_t totalSize,
                  out double jsMilliseconds, out double nonJSMilliseconds);
 };
 %{C++
 #include "js/TypeDecls.h"
 #include "nsStringGlue.h"
 #include "nsTArray.h"
 #include "mozilla/Atomics.h"
 class nsPIDOMWindow;
 // nsIHandleReportCallback is a better name, but keep nsIMemoryReporterCallback
 // around for backwards compatibility.
 typedef nsIMemoryReporterCallback nsIHandleReportCallback;
 namespace mozilla {
 // Register a memory reporter.  The manager service will hold a strong
 // reference to this reporter.
 XPCOM_API(nsresult) RegisterStrongMemoryReporter(nsIMemoryReporter* aReporter);
 // Register a memory reporter.  The manager service will hold a weak reference
 // to this reporter.
 XPCOM_API(nsresult) RegisterWeakMemoryReporter(nsIMemoryReporter* aReporter);
 // Unregister a weak memory reporter.
 XPCOM_API(nsresult) UnregisterWeakMemoryReporter(nsIMemoryReporter* aReporter);
 // The memory reporter manager provides access to several distinguished
 // amounts via attributes.  Some of these amounts are provided by Gecko
 // components that cannot be accessed directly from XPCOM code.  So we provide
 // the following functions for those components to be registered with the
 // manager.
 typedef int64_t (*InfallibleAmountFn)();
 typedef nsresult (*FallibleAmountFn)(int64_t* aAmount);
 #define DECL_REGISTER_DISTINGUISHED_AMOUNT(kind, name) \
     nsresult Register##name##DistinguishedAmount(kind##AmountFn aAmountFn);
 #define DECL_UNREGISTER_DISTINGUISHED_AMOUNT(name) \
     nsresult Unregister##name##DistinguishedAmount();
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeGCHeap)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeTemporaryPeak)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeCompartmentsSystem)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, JSMainRuntimeCompartmentsUser)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, ImagesContentUsedUncompressed)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, StorageSQLite)
 DECL_UNREGISTER_DISTINGUISHED_AMOUNT(StorageSQLite)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, LowMemoryEventsVirtual)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, LowMemoryEventsPhysical)
 DECL_REGISTER_DISTINGUISHED_AMOUNT(Infallible, GhostWindows)
 #undef DECL_REGISTER_DISTINGUISHED_AMOUNT
 #undef DECL_UNREGISTER_DISTINGUISHED_AMOUNT
 // Likewise for per-tab measurement.
 typedef nsresult (*JSSizeOfTabFn)(JSObject* aObj,
                                   size_t* aJsObjectsSize,
                                   size_t* aJsStringSize,
                                   size_t* aJsPrivateSize,
                                   size_t* aJsOtherSize);
 typedef nsresult (*NonJSSizeOfTabFn)(nsPIDOMWindow* aWindow,
                                      size_t* aDomSize,
                                      size_t* aStyleSize,
                                      size_t* aOtherSize);
 nsresult RegisterJSSizeOfTab(JSSizeOfTabFn aSizeOfTabFn);
 nsresult RegisterNonJSSizeOfTab(NonJSSizeOfTabFn aSizeOfTabFn);
 }
 #if defined(MOZ_DMD)
 namespace mozilla {
 namespace dmd {
 // This runs all the memory reporters in the current process but does nothing
 // with the results;  i.e. it does the minimal amount of work possible for DMD
 // to do its thing.  It does nothing with child processes.
 void RunReportersForThisProcess();
 }
 }
 #if !defined(MOZ_MEMORY)
 #error "MOZ_DMD requires MOZ_MEMORY"
 #endif
 #include "DMD.h"
 #define MOZ_REPORT(ptr)          mozilla::dmd::Report(ptr)
 #define MOZ_REPORT_ON_ALLOC(ptr) mozilla::dmd::ReportOnAlloc(ptr)
 #else
 #define MOZ_REPORT(ptr)
 #define MOZ_REPORT_ON_ALLOC(ptr)
 #endif  // defined(MOZ_DMD)
 // Functions generated via this macro should be used by all traversal-based
 // memory reporters.  Such functions return |moz_malloc_size_of(ptr)|;  this
 // will always be zero on some obscure platforms.
 //
 // You might be wondering why we have a macro that creates multiple functions
 // that differ only in their name, instead of a single MallocSizeOf function.
 // It's mostly to help with DMD integration, though it sometimes also helps
 // with debugging and temporary ad hoc profiling.  The function name chosen
 // doesn't matter greatly, but it's best to make it similar to the path used by
 // the relevant memory reporter(s).
 #define MOZ_DEFINE_MALLOC_SIZE_OF(fn)                                         \
   static size_t fn(const void* aPtr)                                          \
   {                                                                           \
       MOZ_REPORT(aPtr);                                                       \
       return moz_malloc_size_of(aPtr);                                        \
   }
 // Functions generated by the next two macros should be used by wrapping
 // allocators that report heap blocks as soon as they are allocated and
 // unreport them as soon as they are freed.  Such allocators are used in cases
 // where we have third-party code that we cannot modify.  The two functions
 // must always be used in tandem.
 #define MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(fn)                                \
   static size_t fn(const void* aPtr)                                          \
   {                                                                           \
       MOZ_REPORT_ON_ALLOC(aPtr);                                              \
       return moz_malloc_size_of(aPtr);                                        \
   }
 #define MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(fn)                                 \
   static size_t fn(const void* aPtr)                                          \
   {                                                                           \
       return moz_malloc_size_of(aPtr);                                        \
   }
 namespace mozilla {
 // This CRTP class handles several details of wrapping allocators and should
 // be preferred to manually counting with MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC
 // and MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE.  The typical use is in a memory
 // reporter for a particular third party library:
 //
 //   class MyMemoryReporter : public CountingAllocatorBase<MyMemoryReporter>
 //   {
 //     ...
 //     NS_IMETHODIMP
 //     CollectReports(nsIHandleReportCallback* aHandleReport, nsISupports* aData)
 //     {
 //        return MOZ_COLLECT_REPORTER(
 //          "explicit/path/to/somewhere", KIND_HEAP, UNITS_BYTES,
 //          MemoryAllocated(),
 //          "A description of what we are reporting."
 //     }
 //   };
 //
 //   ...somewhere later in the code...
 //   SetThirdPartyMemoryFunctions(MyMemoryReporter::CountingAlloc,
 //                                MyMemoryReporter::CountingFree);
 template<typename T>
 class CountingAllocatorBase
 {
 public:
   CountingAllocatorBase()
   {
 #ifdef DEBUG
     // There must be only one instance of this class, due to |sAmount| being
     // static.
     static bool hasRun = false;
     MOZ_ASSERT(!hasRun);
     hasRun = true;
 #endif
   }
   static size_t
   MemoryAllocated()
   {
     return sAmount;
   }
   static void*
   CountingMalloc(size_t size)
   {
     void* p = malloc(size);
     sAmount += MallocSizeOfOnAlloc(p);
     return p;
   }
   static void*
   CountingCalloc(size_t nmemb, size_t size)
   {
     void* p = calloc(nmemb, size);
     sAmount += MallocSizeOfOnAlloc(p);
     return p;
   }
   static void*
   CountingRealloc(void* p, size_t size)
   {
     size_t oldsize = MallocSizeOfOnFree(p);
     void *pnew = realloc(p, size);
     if (pnew) {
       size_t newsize = MallocSizeOfOnAlloc(pnew);
       sAmount += newsize - oldsize;
     } else if (size == 0) {
       // We asked for a 0-sized (re)allocation of some existing pointer
       // and received NULL in return.  0-sized allocations are permitted
       // to either return NULL or to allocate a unique object per call (!).
       // For a malloc implementation that chooses the second strategy,
       // that allocation may fail (unlikely, but possible).
       //
       // Given a NULL return value and an allocation size of 0, then, we
       // don't know if that means the original pointer was freed or if
       // the allocation of the unique object failed.  If the original
       // pointer was freed, then we have nothing to do here.  If the
       // allocation of the unique object failed, the original pointer is
       // still valid and we ought to undo the decrement from above.
       // However, we have no way of knowing how the underlying realloc
       // implementation is behaving.  Assuming that the original pointer
       // was freed is the safest course of action.  We do, however, need
       // to note that we freed memory.
       sAmount -= oldsize;
     } else {
       // realloc failed.  The amount allocated hasn't changed.
     }
     return pnew;
   }
   static void
   CountingFree(void* p)
   {
     sAmount -= MallocSizeOfOnFree(p);
     free(p);
   }
 private:
   // |sAmount| can be (implicitly) accessed by multiple threads, so it
   // must be thread-safe.
   static Atomic<size_t> sAmount;
   MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(MallocSizeOfOnAlloc)
   MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(MallocSizeOfOnFree)
 };
 }
 // This macro assumes the presence of appropriate |aHandleReport| and |aData|
 // variables.
 #define MOZ_COLLECT_REPORT(path, kind, units, amount, description)            \
   aHandleReport->Callback(EmptyCString(), NS_LITERAL_CSTRING(path),           \
                           kind, units, amount,                                \
                           NS_LITERAL_CSTRING(description), aData)
 %}

The Tor Browser / annotate

xpcom/base/nsIMemoryReporter.idl@b8a032363ba2 (annotated)

xpcom/base/nsIMemoryReporter.idl