// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// 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 "free_list.h"          // for FL_Push/FL_Pop
#include "internal_logging.h"  // for ASSERT
#include "system-alloc.h"      // for TCMalloc_SystemAddGuard

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 = FL_Pop(&free_list_);
    } 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));
        }

        // This guard page protects the metadata from being corrupted by a
        // buffer overrun. We currently have no mechanism for freeing it, since
        // we never release the metadata buffer. If that changes we'll need to
        // add something like TCMalloc_SystemRemoveGuard.
        size_t guard_size = TCMalloc_SystemAddGuard(free_area_,
                                                    kAllocIncrement);
        free_area_ += guard_size;
        free_avail_ = kAllocIncrement - guard_size;
        if (free_avail_ < sizeof(T)) {
          Log(kCrash, __FILE__, __LINE__,
              "FATAL ERROR: Insufficient memory to guard internal tcmalloc "
              "data (%d bytes, object-size %d, guard-size %d)\n",
              kAllocIncrement, static_cast<int>(sizeof(T)), guard_size);
        }
      }
      result = free_area_;
      free_area_ += sizeof(T);
      free_avail_ -= sizeof(T);
    }
    inuse_++;
    return reinterpret_cast<T*>(result);
  }

  void Delete(T* p) {
    FL_Push(&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_