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 #ifndef SANITIZER_PERSISTENT_ALLOCATOR_H
  12 #define SANITIZER_PERSISTENT_ALLOCATOR_H
  13
  14 #include "sanitizer_internal_defs.h"
  15 #include "sanitizer_mutex.h"
  16 #include "sanitizer_atomic.h"
  17 #include "sanitizer_common.h"
  18
  19 namespace __sanitizer {
  20
  21 class PersistentAllocator {
  22  public:
  23   void *alloc(uptr size);
  24
  25  private:
  26   void *tryAlloc(uptr size);
  27   StaticSpinMutex mtx;  // Protects alloc of new blocks for region allocator.
  28   atomic_uintptr_t region_pos;  // Region allocator for Node's.
  29   atomic_uintptr_t region_end;
  30 };
  31
  32 inline void *PersistentAllocator::tryAlloc(uptr size) {
  33   // Optimisic lock-free allocation, essentially try to bump the region ptr.
  34   for (;;) {
  35     uptr cmp = atomic_load(&region_pos, memory_order_acquire);
  36     uptr end = atomic_load(&region_end, memory_order_acquire);
  37     if (cmp == 0 || cmp + size > end) return 0;
  38     if (atomic_compare_exchange_weak(&region_pos, &cmp, cmp + size,
  39                                      memory_order_acquire))
  40       return (void *)cmp;
  41   }
  42 }
  43
  44 inline void *PersistentAllocator::alloc(uptr size) {
  45   // First, try to allocate optimisitically.
  46   void *s = tryAlloc(size);
  47   if (s) return s;
  48   // If failed, lock, retry and alloc new superblock.
  49   SpinMutexLock l(&mtx);
  50   for (;;) {
  51     s = tryAlloc(size);
  52     if (s) return s;
  53     atomic_store(&region_pos, 0, memory_order_relaxed);
  54     uptr allocsz = 64 * 1024;
  55     if (allocsz < size) allocsz = size;
  56     uptr mem = (uptr)MmapOrDie(allocsz, "stack depot");
  57     atomic_store(&region_end, mem + allocsz, memory_order_release);
  58     atomic_store(&region_pos, mem, memory_order_release);
  59   }
  60 }
  61
  62 extern PersistentAllocator thePersistentAllocator;
  63 inline void *PersistentAlloc(uptr sz) {
  64   return thePersistentAllocator.alloc(sz);
  65 }
  66
  67 } // namespace __sanitizer
  68
  69 #endif  // SANITIZER_PERSISTENT_ALLOCATOR_H