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      1 //===-- tsan_dense_alloc.h --------------------------------------*- C++ -*-===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file is a part of ThreadSanitizer (TSan), a race detector.
     11 //
     12 // A DenseSlabAlloc is a freelist-based allocator of fixed-size objects.
     13 // DenseSlabAllocCache is a thread-local cache for DenseSlabAlloc.
     14 // The only difference with traditional slab allocators is that DenseSlabAlloc
     15 // allocates/free indices of objects and provide a functionality to map
     16 // the index onto the real pointer. The index is u32, that is, 2 times smaller
     17 // than uptr (hense the Dense prefix).
     18 //===----------------------------------------------------------------------===//
     19 #ifndef TSAN_DENSE_ALLOC_H
     20 #define TSAN_DENSE_ALLOC_H
     21 
     22 #include "sanitizer_common/sanitizer_common.h"
     23 #include "tsan_defs.h"
     24 #include "tsan_mutex.h"
     25 
     26 namespace __tsan {
     27 
     28 class DenseSlabAllocCache {
     29   static const uptr kSize = 128;
     30   typedef u32 IndexT;
     31   uptr pos;
     32   IndexT cache[kSize];
     33   template<typename T, uptr kL1Size, uptr kL2Size> friend class DenseSlabAlloc;
     34 };
     35 
     36 template<typename T, uptr kL1Size, uptr kL2Size>
     37 class DenseSlabAlloc {
     38  public:
     39   typedef DenseSlabAllocCache Cache;
     40   typedef typename Cache::IndexT IndexT;
     41 
     42   DenseSlabAlloc() {
     43     // Check that kL1Size and kL2Size are sane.
     44     CHECK_EQ(kL1Size & (kL1Size - 1), 0);
     45     CHECK_EQ(kL2Size & (kL2Size - 1), 0);
     46     CHECK_GE(1ull << (sizeof(IndexT) * 8), kL1Size * kL2Size);
     47     // Check that it makes sense to use the dense alloc.
     48     CHECK_GE(sizeof(T), sizeof(IndexT));
     49     internal_memset(map_, 0, sizeof(map_));
     50     freelist_ = 0;
     51     fillpos_ = 0;
     52   }
     53 
     54   ~DenseSlabAlloc() {
     55     for (uptr i = 0; i < kL1Size; i++) {
     56       if (map_[i] != 0)
     57         UnmapOrDie(map_[i], kL2Size * sizeof(T));
     58     }
     59   }
     60 
     61   IndexT Alloc(Cache *c) {
     62     if (c->pos == 0)
     63       Refill(c);
     64     return c->cache[--c->pos];
     65   }
     66 
     67   void Free(Cache *c, IndexT idx) {
     68     if (c->pos == Cache::kSize)
     69       Drain(c);
     70     c->cache[c->pos++] = idx;
     71   }
     72 
     73   T *Map(IndexT idx) {
     74     DCHECK_NE(idx, 0);
     75     DCHECK_LE(idx, kL1Size * kL2Size);
     76     return &map_[idx / kL2Size][idx % kL2Size];
     77   }
     78 
     79   void FlushCache(Cache *c) {
     80     SpinMutexLock lock(&mtx_);
     81     while (c->pos) {
     82       IndexT idx = c->cache[--c->pos];
     83       *(IndexT*)Map(idx) = freelist_;
     84       freelist_ = idx;
     85     }
     86   }
     87 
     88   void InitCache(Cache *c) {
     89     c->pos = 0;
     90     internal_memset(c->cache, 0, sizeof(c->cache));
     91   }
     92 
     93  private:
     94   T *map_[kL1Size];
     95   SpinMutex mtx_;
     96   IndexT freelist_;
     97   uptr fillpos_;
     98 
     99   void Refill(Cache *c) {
    100     SpinMutexLock lock(&mtx_);
    101     if (freelist_ == 0) {
    102       if (fillpos_ == kL1Size) {
    103         Printf("ThreadSanitizer: DenseSlabAllocator overflow. Dying.\n");
    104         Die();
    105       }
    106       T *batch = (T*)MmapOrDie(kL2Size * sizeof(T), "DenseSlabAllocator");
    107       // Reserve 0 as invalid index.
    108       IndexT start = fillpos_ == 0 ? 1 : 0;
    109       for (IndexT i = start; i < kL2Size; i++) {
    110         new(batch + i) T();
    111         *(IndexT*)(batch + i) = i + 1 + fillpos_ * kL2Size;
    112       }
    113       *(IndexT*)(batch + kL2Size - 1) = 0;
    114       freelist_ = fillpos_ * kL2Size + start;
    115       map_[fillpos_++] = batch;
    116     }
    117     for (uptr i = 0; i < Cache::kSize / 2 && freelist_ != 0; i++) {
    118       IndexT idx = freelist_;
    119       c->cache[c->pos++] = idx;
    120       freelist_ = *(IndexT*)Map(idx);
    121     }
    122   }
    123 
    124   void Drain(Cache *c) {
    125     SpinMutexLock lock(&mtx_);
    126     for (uptr i = 0; i < Cache::kSize / 2; i++) {
    127       IndexT idx = c->cache[--c->pos];
    128       *(IndexT*)Map(idx) = freelist_;
    129       freelist_ = idx;
    130     }
    131   }
    132 };
    133 
    134 }  // namespace __tsan
    135 
    136 #endif  // TSAN_DENSE_ALLOC_H
    137