libsanitizer/sanitizer_common/sanitizer_persistent_allocator.h

   1 //===-- sanitizer_persistent_allocator.h ------------------------*- C++ -*-===//
   2 //
   3 // This file is distributed under the University of Illinois Open Source
   4 // License. See LICENSE.TXT for details.
   5 //
   6 //===----------------------------------------------------------------------===//
   7 //
   8 // A fast memory allocator that does not support free() nor realloc().
   9 // All allocations are forever.
  10 //===----------------------------------------------------------------------===//
  11
  12 #ifndef SANITIZER_PERSISTENT_ALLOCATOR_H
  13 #define SANITIZER_PERSISTENT_ALLOCATOR_H
  14
  15 #include "sanitizer_internal_defs.h"
  16 #include "sanitizer_mutex.h"
  17 #include "sanitizer_atomic.h"
  18 #include "sanitizer_common.h"
  19
  20 namespace __sanitizer {
  21
  22 class PersistentAllocator {
  23  public:
  24   void *alloc(uptr size);
  25
  26  private:
  27   void *tryAlloc(uptr size);
  28   StaticSpinMutex mtx;  // Protects alloc of new blocks for region allocator.
  29   atomic_uintptr_t region_pos;  // Region allocator for Node's.
  30   atomic_uintptr_t region_end;
  31 };
  32
  33 inline void *PersistentAllocator::tryAlloc(uptr size) {
  34   // Optimisic lock-free allocation, essentially try to bump the region ptr.
  35   for (;;) {
  36     uptr cmp = atomic_load(&region_pos, memory_order_acquire);
  37     uptr end = atomic_load(&region_end, memory_order_acquire);
  38     if (cmp == 0 || cmp + size > end) return nullptr;
  39     if (atomic_compare_exchange_weak(&region_pos, &cmp, cmp + size,
  40                                      memory_order_acquire))
  41       return (void *)cmp;
  42   }
  43 }
  44
  45 inline void *PersistentAllocator::alloc(uptr size) {
  46   // First, try to allocate optimisitically.
  47   void *s = tryAlloc(size);
  48   if (s) return s;
  49   // If failed, lock, retry and alloc new superblock.
  50   SpinMutexLock l(&mtx);
  51   for (;;) {
  52     s = tryAlloc(size);
  53     if (s) return s;
  54     atomic_store(&region_pos, 0, memory_order_relaxed);
  55     uptr allocsz = 64 * 1024;
  56     if (allocsz < size) allocsz = size;
  57     uptr mem = (uptr)MmapOrDie(allocsz, "stack depot");
  58     atomic_store(&region_end, mem + allocsz, memory_order_release);
  59     atomic_store(&region_pos, mem, memory_order_release);
  60   }
  61 }
  62
  63 extern PersistentAllocator thePersistentAllocator;
  64 inline void *PersistentAlloc(uptr sz) {
  65   return thePersistentAllocator.alloc(sz);
  66 }
  67
  68 } // namespace __sanitizer
  69
  70 #endif // SANITIZER_PERSISTENT_ALLOCATOR_H