JavaScriptCore/wtf/TCPageMap.h

// Copyright (c) 2005, Google Inc.
// All rights reserved.
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// ---
// Author: Sanjay Ghemawat <opensource@google.com>
//
// A data structure used by the caching malloc.  It maps from page# to
// a pointer that contains info about that page.  We use two
// representations: one for 32-bit addresses, and another for 64 bit
// addresses.  Both representations provide the same interface.  The
// first representation is implemented as a flat array, the seconds as
// a three-level radix tree that strips away approximately 1/3rd of
// the bits every time.
//
// The BITS parameter should be the number of bits required to hold
// a page number.  E.g., with 32 bit pointers and 4K pages (i.e.,
// page offset fits in lower 12 bits), BITS == 20.

#ifndef TCMALLOC_PAGEMAP_H__
#define TCMALLOC_PAGEMAP_H__

#include "config.h"

#if HAVE(STDINT_H)
#include <stdint.h>
#elif HAVE(INTTYPES_H)
#include <inttypes.h>
#else
#include <sys/types.h>
#endif

#include <string.h>

#include "Assertions.h"

// Single-level array
template <int BITS>
class TCMalloc_PageMap1 {
 private:
  void** array_;

 public:
  typedef uintptr_t Number;

  void init(void* (*allocator)(size_t)) {
    array_ = reinterpret_cast<void**>((*allocator)(sizeof(void*) << BITS));
    memset(array_, 0, sizeof(void*) << BITS);
  }

  // Ensure that the map contains initialized entries "x .. x+n-1".
  // Returns true if successful, false if we could not allocate memory.
  bool Ensure(Number x, size_t n) {
    // Nothing to do since flat array was allocate at start
    return true;
  }

  // REQUIRES "k" is in range "[0,2^BITS-1]".
  // REQUIRES "k" has been ensured before.
  //
  // Return the current value for KEY.  Returns "Value()" if not
  // yet set.
  void* get(Number k) const {
    return array_[k];
  }

  // REQUIRES "k" is in range "[0,2^BITS-1]".
  // REQUIRES "k" has been ensured before.
  //
  // Sets the value for KEY.
  void set(Number k, void* v) {
    array_[k] = v;
  }
};

// Two-level radix tree
template <int BITS>
class TCMalloc_PageMap2 {
 private:
  // Put 32 entries in the root and (2^BITS)/32 entries in each leaf.
  static const int ROOT_BITS = 5;
  static const int ROOT_LENGTH = 1 << ROOT_BITS;

  static const int LEAF_BITS = BITS - ROOT_BITS;
  static const int LEAF_LENGTH = 1 << LEAF_BITS;

  // Leaf node
  struct Leaf {
    void* values[LEAF_LENGTH];
  };

  Leaf* root_[ROOT_LENGTH];             // Pointers to 32 child nodes
  void* (*allocator_)(size_t);          // Memory allocator

 public:
  typedef uintptr_t Number;

  void init(void* (*allocator)(size_t)) {
    allocator_ = allocator;
    memset(root_, 0, sizeof(root_));
  }

  void* get(Number k) const {
    ASSERT(k >> BITS == 0);
    const Number i1 = k >> LEAF_BITS;
    const Number i2 = k & (LEAF_LENGTH-1);
    return root_[i1]->values[i2];
  }

  void set(Number k, void* v) {
    ASSERT(k >> BITS == 0);
    const Number i1 = k >> LEAF_BITS;
    const Number i2 = k & (LEAF_LENGTH-1);
    root_[i1]->values[i2] = v;
  }

  bool Ensure(Number start, size_t n) {
    for (Number key = start; key <= start + n - 1; ) {
      const Number i1 = key >> LEAF_BITS;

      // Make 2nd level node if necessary
      if (root_[i1] == NULL) {
        Leaf* leaf = reinterpret_cast<Leaf*>((*allocator_)(sizeof(Leaf)));
        if (leaf == NULL) return false;
        memset(leaf, 0, sizeof(*leaf));
        root_[i1] = leaf;
      }

      // Advance key past whatever is covered by this leaf node
      key = ((key >> LEAF_BITS) + 1) << LEAF_BITS;
    }
    return true;
  }

#ifdef WTF_CHANGES
  template<class Visitor, class MemoryReader>
  void visit(const Visitor& visitor, const MemoryReader& reader)
  {
    for (int i = 0; i < ROOT_LENGTH; i++) {
      if (!root_[i])
        continue;

      Leaf* l = reader(reinterpret_cast<Leaf*>(root_[i]));
      for (int j = 0; j < LEAF_LENGTH; j += visitor.visit(l->values[j]))
        ;
    }
  }
#endif
};

// Three-level radix tree
template <int BITS>
class TCMalloc_PageMap3 {
 private:
  // How many bits should we consume at each interior level
  static const int INTERIOR_BITS = (BITS + 2) / 3; // Round-up
  static const int INTERIOR_LENGTH = 1 << INTERIOR_BITS;

  // How many bits should we consume at leaf level
  static const int LEAF_BITS = BITS - 2*INTERIOR_BITS;
  static const int LEAF_LENGTH = 1 << LEAF_BITS;

  // Interior node
  struct Node {
    Node* ptrs[INTERIOR_LENGTH];
  };

  // Leaf node
  struct Leaf {
    void* values[LEAF_LENGTH];
  };

  Node* root_;                          // Root of radix tree
  void* (*allocator_)(size_t);          // Memory allocator

  Node* NewNode() {
    Node* result = reinterpret_cast<Node*>((*allocator_)(sizeof(Node)));
    if (result != NULL) {
      memset(result, 0, sizeof(*result));
    }
    return result;
  }

 public:
  typedef uintptr_t Number;

  void init(void* (*allocator)(size_t)) {
    allocator_ = allocator;
    root_ = NewNode();
  }

  void* get(Number k) const {
    ASSERT(k >> BITS == 0);
    const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
    const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
    const Number i3 = k & (LEAF_LENGTH-1);
    return reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3];
  }

  void set(Number k, void* v) {
    ASSERT(k >> BITS == 0);
    const Number i1 = k >> (LEAF_BITS + INTERIOR_BITS);
    const Number i2 = (k >> LEAF_BITS) & (INTERIOR_LENGTH-1);
    const Number i3 = k & (LEAF_LENGTH-1);
    reinterpret_cast<Leaf*>(root_->ptrs[i1]->ptrs[i2])->values[i3] = v;
  }

  bool Ensure(Number start, size_t n) {
    for (Number key = start; key <= start + n - 1; ) {
      const Number i1 = key >> (LEAF_BITS + INTERIOR_BITS);
      const Number i2 = (key >> LEAF_BITS) & (INTERIOR_LENGTH-1);

      // Make 2nd level node if necessary
      if (root_->ptrs[i1] == NULL) {
        Node* n = NewNode();
        if (n == NULL) return false;
        root_->ptrs[i1] = n;
      }

      // Make leaf node if necessary
      if (root_->ptrs[i1]->ptrs[i2] == NULL) {
        Leaf* leaf = reinterpret_cast<Leaf*>((*allocator_)(sizeof(Leaf)));
        if (leaf == NULL) return false;
        memset(leaf, 0, sizeof(*leaf));
        root_->ptrs[i1]->ptrs[i2] = reinterpret_cast<Node*>(leaf);
      }

      // Advance key past whatever is covered by this leaf node
      key = ((key >> LEAF_BITS) + 1) << LEAF_BITS;
    }
    return true;
  }

#ifdef WTF_CHANGES
  template<class Visitor, class MemoryReader>
  void visit(const Visitor& visitor, const MemoryReader& reader) {
    Node* root = reader(root_);
    for (int i = 0; i < INTERIOR_LENGTH; i++) {
      if (!root->ptrs[i])
        continue;

      Node* n = reader(root->ptrs[i]);
      for (int j = 0; j < INTERIOR_LENGTH; j++) {
        if (!n->ptrs[j])
          continue;

        Leaf* l = reader(reinterpret_cast<Leaf*>(n->ptrs[j]));
        for (int k = 0; k < LEAF_LENGTH; k += visitor.visit(l->values[k]))
          ;
      }
    }
  }
#endif
};

#endif  // TCMALLOC_PAGEMAP_H__