libsanitizer/sanitizer_common/sanitizer_persistent_allocator.h

   1 //===-- sanitizer_persistent_allocator.h ------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // A fast memory allocator that does not support free() nor realloc().
  10 // All allocations are forever.
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef SANITIZER_PERSISTENT_ALLOCATOR_H
  14 #define SANITIZER_PERSISTENT_ALLOCATOR_H
  15
  16 #include "sanitizer_internal_defs.h"
  17 #include "sanitizer_mutex.h"
  18 #include "sanitizer_atomic.h"
  19 #include "sanitizer_common.h"
  20
  21 namespace __sanitizer {
  22
  23 class PersistentAllocator {
  24  public:
  25   void *alloc(uptr size);
  26
  27  private:
  28   void *tryAlloc(uptr size);
  29   StaticSpinMutex mtx;  // Protects alloc of new blocks for region allocator.
  30   atomic_uintptr_t region_pos;  // Region allocator for Node's.
  31   atomic_uintptr_t region_end;
  32 };
  33
  34 inline void *PersistentAllocator::tryAlloc(uptr size) {
  35   // Optimisic lock-free allocation, essentially try to bump the region ptr.
  36   for (;;) {
  37     uptr cmp = atomic_load(&region_pos, memory_order_acquire);
  38     uptr end = atomic_load(&region_end, memory_order_acquire);
  39     if (cmp == 0 || cmp + size > end) return nullptr;
  40     if (atomic_compare_exchange_weak(&region_pos, &cmp, cmp + size,
  41                                      memory_order_acquire))
  42       return (void *)cmp;
  43   }
  44 }
  45
  46 inline void *PersistentAllocator::alloc(uptr size) {
  47   // First, try to allocate optimisitically.
  48   void *s = tryAlloc(size);
  49   if (s) return s;
  50   // If failed, lock, retry and alloc new superblock.
  51   SpinMutexLock l(&mtx);
  52   for (;;) {
  53     s = tryAlloc(size);
  54     if (s) return s;
  55     atomic_store(&region_pos, 0, memory_order_relaxed);
  56     uptr allocsz = 64 * 1024;
  57     if (allocsz < size) allocsz = size;
  58     uptr mem = (uptr)MmapOrDie(allocsz, "stack depot");
  59     atomic_store(&region_end, mem + allocsz, memory_order_release);
  60     atomic_store(&region_pos, mem, memory_order_release);
  61   }
  62 }
  63
  64 extern PersistentAllocator thePersistentAllocator;
  65 inline void *PersistentAlloc(uptr sz) {
  66   return thePersistentAllocator.alloc(sz);
  67 }
  68
  69 } // namespace __sanitizer
  70
  71 #endif // SANITIZER_PERSISTENT_ALLOCATOR_H