xpcom/base/CountingAllocatorBase.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef CountingAllocatorBase_h
   8 #define CountingAllocatorBase_h
   9
  10 #include <cstdlib>
  11 #include "mozilla/Assertions.h"
  12 #include "mozilla/Atomics.h"
  13 #include "mozilla/mozalloc.h"
  14 #include "nsIMemoryReporter.h"
  15
  16 namespace mozilla {
  17
  18 // This CRTP class handles several details of wrapping allocators and should
  19 // be preferred to manually counting with MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC
  20 // and MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE.  The typical use is in a memory
  21 // reporter for a particular third party library:
  22 //
  23 //   class MyMemoryReporter : public CountingAllocatorBase<MyMemoryReporter>
  24 //   {
  25 //     ...
  26 //     NS_IMETHOD
  27 //     CollectReports(nsIHandleReportCallback* aHandleReport,
  28 //                    nsISupports* aData, bool aAnonymize) override
  29 //     {
  30 //        MOZ_COLLECT_REPORT(
  31 //          "explicit/path/to/somewhere", KIND_HEAP, UNITS_BYTES,
  32 //          MemoryAllocated(),
  33 //          "A description of what we are reporting.");
  34 //
  35 //        return NS_OK;
  36 //     }
  37 //   };
  38 //
  39 //   ...somewhere later in the code...
  40 //   SetThirdPartyMemoryFunctions(MyMemoryReporter::CountingAlloc,
  41 //                                MyMemoryReporter::CountingFree);
  42 template <typename T>
  43 class CountingAllocatorBase {
  44  public:
  45   CountingAllocatorBase() {
  46 #ifdef DEBUG
  47     // There must be only one instance of this class, due to |sAmount| being
  48     // static.
  49     static bool hasRun = false;
  50     MOZ_ASSERT(!hasRun);
  51     hasRun = true;
  52 #endif
  53   }
  54
  55   static size_t MemoryAllocated() { return sAmount; }
  56
  57   static void* CountingMalloc(size_t size) {
  58     void* p = malloc(size);
  59     sAmount += MallocSizeOfOnAlloc(p);
  60     return p;
  61   }
  62
  63   static void* CountingCalloc(size_t nmemb, size_t size) {
  64     void* p = calloc(nmemb, size);
  65     sAmount += MallocSizeOfOnAlloc(p);
  66     return p;
  67   }
  68
  69   static void* CountingRealloc(void* p, size_t size) {
  70     size_t oldsize = MallocSizeOfOnFree(p);
  71     void* pnew = realloc(p, size);
  72     if (pnew) {
  73       size_t newsize = MallocSizeOfOnAlloc(pnew);
  74       sAmount += newsize - oldsize;
  75     } else if (size == 0) {
  76       // We asked for a 0-sized (re)allocation of some existing pointer
  77       // and received NULL in return.  0-sized allocations are permitted
  78       // to either return NULL or to allocate a unique object per call (!).
  79       // For a malloc implementation that chooses the second strategy,
  80       // that allocation may fail (unlikely, but possible).
  81       //
  82       // Given a NULL return value and an allocation size of 0, then, we
  83       // don't know if that means the original pointer was freed or if
  84       // the allocation of the unique object failed.  If the original
  85       // pointer was freed, then we have nothing to do here.  If the
  86       // allocation of the unique object failed, the original pointer is
  87       // still valid and we ought to undo the decrement from above.
  88       // However, we have no way of knowing how the underlying realloc
  89       // implementation is behaving.  Assuming that the original pointer
  90       // was freed is the safest course of action.  We do, however, need
  91       // to note that we freed memory.
  92       sAmount -= oldsize;
  93     } else {
  94       // realloc failed.  The amount allocated hasn't changed.
  95     }
  96     return pnew;
  97   }
  98
  99   // Some library code expects that realloc(x, 0) will free x, which is not
 100   // the behavior of the version of jemalloc we're using, so this wrapped
 101   // version of realloc is needed.
 102   static void* CountingFreeingRealloc(void* p, size_t size) {
 103     if (size == 0) {
 104       CountingFree(p);
 105       return nullptr;
 106     }
 107     return CountingRealloc(p, size);
 108   }
 109
 110   static void CountingFree(void* p) {
 111     sAmount -= MallocSizeOfOnFree(p);
 112     free(p);
 113   }
 114
 115   // Infallible-allocation wrappers for the counting malloc/calloc/realloc
 116   // functions, for clients that don't safely handle allocation failures
 117   // themselves.
 118   static void* InfallibleCountingMalloc(size_t size) {
 119     void* p = moz_xmalloc(size);
 120     sAmount += MallocSizeOfOnAlloc(p);
 121     return p;
 122   }
 123
 124   static void* InfallibleCountingCalloc(size_t nmemb, size_t size) {
 125     void* p = moz_xcalloc(nmemb, size);
 126     sAmount += MallocSizeOfOnAlloc(p);
 127     return p;
 128   }
 129
 130   static void* InfallibleCountingRealloc(void* p, size_t size) {
 131     size_t oldsize = MallocSizeOfOnFree(p);
 132     void* pnew = moz_xrealloc(p, size);
 133     if (pnew) {
 134       size_t newsize = MallocSizeOfOnAlloc(pnew);
 135       sAmount += newsize - oldsize;
 136     } else if (size == 0) {
 137       // See comment in CountingRealloc above.
 138       sAmount -= oldsize;
 139     } else {
 140       // realloc failed.  The amount allocated hasn't changed.
 141     }
 142     return pnew;
 143   }
 144
 145  private:
 146   // |sAmount| can be (implicitly) accessed by multiple threads, so it
 147   // must be thread-safe. It may be written during GC, so accesses are not
 148   // recorded.
 149   typedef Atomic<size_t, SequentiallyConsistent> AmountType;
 150   static AmountType sAmount;
 151
 152   MOZ_DEFINE_MALLOC_SIZE_OF_ON_ALLOC(MallocSizeOfOnAlloc)
 153   MOZ_DEFINE_MALLOC_SIZE_OF_ON_FREE(MallocSizeOfOnFree)
 154 };
 155
 156 }  // namespace mozilla
 157
 158 #endif  // CountingAllocatorBase_h