third_party/gperftools/src/span.h

// -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*-
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// ---
// Author: Sanjay Ghemawat <opensource@google.com>
//
// A Span is a contiguous run of pages.

#ifndef TCMALLOC_SPAN_H_
#define TCMALLOC_SPAN_H_

#include <config.h>
#include "common.h"

namespace tcmalloc {

// Information kept for a span (a contiguous run of pages).
struct Span {
  PageID        start;          // Starting page number
  Length        length;         // Number of pages in span
  Span*         next;           // Used when in link list
  Span*         prev;           // Used when in link list
  void*         objects;        // Linked list of free objects
  unsigned int  refcount : 16;  // Number of non-free objects
  unsigned int  sizeclass : 8;  // Size-class for small objects (or 0)
  unsigned int  location : 2;   // Is the span on a freelist, and if so, which?
  unsigned int  sample : 1;     // Sampled object?

#undef SPAN_HISTORY
#ifdef SPAN_HISTORY
  // For debugging, we can keep a log events per span
  int nexthistory;
  char history[64];
  int value[64];
#endif

  // What freelist the span is on: IN_USE if on none, or normal or returned
  enum { IN_USE, ON_NORMAL_FREELIST, ON_RETURNED_FREELIST };
};

#ifdef SPAN_HISTORY
void Event(Span* span, char op, int v = 0);
#else
#define Event(s,o,v) ((void) 0)
#endif

// Allocator/deallocator for spans
Span* NewSpan(PageID p, Length len);
void DeleteSpan(Span* span);

// -------------------------------------------------------------------------
// Doubly linked list of spans.
// -------------------------------------------------------------------------

// Initialize *list to an empty list.
void DLL_Init(Span* list);

// Remove 'span' from the linked list in which it resides, updating the
// pointers of adjacent Spans and setting span's next and prev to NULL.
void DLL_Remove(Span* span);

// Return true iff "list" is empty.
inline bool DLL_IsEmpty(const Span* list) {
  return list->next == list;
}

// Add span to the front of list.
void DLL_Prepend(Span* list, Span* span);

// Return the length of the linked list. O(n)
int DLL_Length(const Span* list);

}  // namespace tcmalloc

#endif  // TCMALLOC_SPAN_H_