src/page_heap_allocator.h

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
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// ---
// Author: Sanjay Ghemawat <opensource@google.com>

#ifndef TCMALLOC_PAGE_HEAP_ALLOCATOR_H_
#define TCMALLOC_PAGE_HEAP_ALLOCATOR_H_

#include <stddef.h>                     // for NULL, size_t

#include "common.h"            // for MetaDataAlloc
#include "internal_logging.h"  // for ASSERT

namespace tcmalloc {

// Simple allocator for objects of a specified type.  External locking
// is required before accessing one of these objects.
template <class T>
class PageHeapAllocator {
 public:
  // We use an explicit Init function because these variables are statically
  // allocated and their constructors might not have run by the time some
  // other static variable tries to allocate memory.
  void Init() {
    ASSERT(sizeof(T) <= kAllocIncrement);
    inuse_ = 0;
    free_area_ = NULL;
    free_avail_ = 0;
    free_list_ = NULL;
    // Reserve some space at the beginning to avoid fragmentation.
    Delete(New());
  }

  T* New() {
    // Consult free list
    void* result;
    if (free_list_ != NULL) {
      result = free_list_;
      free_list_ = *(reinterpret_cast<void**>(result));
    } else {
      if (free_avail_ < sizeof(T)) {
        // Need more room. We assume that MetaDataAlloc returns
        // suitably aligned memory.
        free_area_ = reinterpret_cast<char*>(MetaDataAlloc(kAllocIncrement));
        if (free_area_ == NULL) {
          Log(kCrash, __FILE__, __LINE__,
              "FATAL ERROR: Out of memory trying to allocate internal "
              "tcmalloc data (bytes, object-size)",
              kAllocIncrement, sizeof(T));
        }
        free_avail_ = kAllocIncrement;
      }
      result = free_area_;
      free_area_ += sizeof(T);
      free_avail_ -= sizeof(T);
    }
    inuse_++;
    return reinterpret_cast<T*>(result);
  }

  void Delete(T* p) {
    *(reinterpret_cast<void**>(p)) = free_list_;
    free_list_ = p;
    inuse_--;
  }

  int inuse() const { return inuse_; }

 private:
  // How much to allocate from system at a time
  static const int kAllocIncrement = 128 << 10;

  // Free area from which to carve new objects
  char* free_area_;
  size_t free_avail_;

  // Free list of already carved objects
  void* free_list_;

  // Number of allocated but unfreed objects
  int inuse_;
};

}  // namespace tcmalloc

#endif  // TCMALLOC_PAGE_HEAP_ALLOCATOR_H_