folly::hazptr_obj_linked< Atom > Class Template Reference

#include <Hazptr-fwd.h>

Inheritance diagram for folly::hazptr_obj_linked< Atom >:

Public Member Functions
void	acquire_link () noexcept
void	acquire_link_safe () noexcept
void	acquire_ref () noexcept
void	acquire_ref_safe () noexcept
Public Member Functions inherited from folly::hazptr_obj< Atom >
	hazptr_obj () noexcept
	hazptr_obj (const hazptr_obj< Atom > &) noexcept
	hazptr_obj (hazptr_obj< Atom > &&) noexcept
hazptr_obj< Atom > &	operator= (const hazptr_obj< Atom > &) noexcept
hazptr_obj< Atom > &	operator= (hazptr_obj< Atom > &&) noexcept

Private Types
using	Count = uint32_t

Private Member Functions
Count	count () const noexcept
void	count_set (Count val) noexcept
void	count_inc (Count add) noexcept
void	count_inc_safe (Count add) noexcept
bool	count_cas (Count &oldval, Count newval) noexcept
bool	release_link () noexcept
bool	release_ref () noexcept
bool	downgrade_link () noexcept

Private Attributes
Atom< Count >	count_ {0}

Static Private Attributes
static constexpr Count	kRef = 1u
static constexpr Count	kLink = 1u << 16
static constexpr Count	kRefMask = kLink - 1u
static constexpr Count	kLinkMask = ~kRefMask

Friends
template<typename , template< typename > class, typename >
class	hazptr_obj_base_linked

Detailed Description

template<template< typename > class Atom>
class folly::hazptr_obj_linked< Atom >

hazptr_obj_linked

hazptr_obj_linked

Base class template for link counted objects. Supports:

• Protecting descendants of protected objects.
• One-pass reclamation of long immutable chains of objects.
• Automatic reclamation of acyclic structures.

Two inbound link counts are maintained per object:

• Link count: Represents the number of links from mutable paths.
• Ref count: Represents the number of links from immutable paths. [Note: The ref count is one less than such links plus one if the object hasn't gone through matching with hazard pointers without finding a match. That is, a new object without inbound links has a ref count of 0 and an about-to-be-reclaimed object can be viewed to have a ref count of -1.]

User code can increment the link and ref counts by calling acquire_link and acquire_ref or their variants that require the user to guarantee thread safety. There are no public functions to decrement the counts explicitly. Counts are decremented implicitly as described in hazptr_obj_base_linked.

Definition at line 79 of file Hazptr-fwd.h.

Member Typedef Documentation

template<template< typename > class Atom>

using folly::hazptr_obj_linked< Atom >::Count = uint32_t

private

Definition at line 92 of file HazptrObjLinked.h.

Member Function Documentation

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::acquire_link ( )

inlinenoexcept

Definition at line 102 of file HazptrObjLinked.h.

                               {
    count_inc(kLink);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::acquire_link_safe ( )

inlinenoexcept

Definition at line 106 of file HazptrObjLinked.h.

Referenced by auto_retire_test(), and basic_objects_test().

                                    {
    count_inc_safe(kLink);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::acquire_ref ( )

inlinenoexcept

Definition at line 110 of file HazptrObjLinked.h.

                              {
    count_inc(kRef);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::acquire_ref_safe ( )

inlinenoexcept

Definition at line 114 of file HazptrObjLinked.h.

                                   {
    count_inc_safe(kRef);
  }

template<template< typename > class Atom>

Count folly::hazptr_obj_linked< Atom >::count ( ) const

inlineprivatenoexcept

Definition at line 122 of file HazptrObjLinked.h.

                               {
    return count_.load(std::memory_order_acquire);
  }

template<template< typename > class Atom>

bool folly::hazptr_obj_linked< Atom >::count_cas ( Count &  oldval, Count  newval  )

inlineprivatenoexcept

Definition at line 143 of file HazptrObjLinked.h.

                                                       {
    return count_.compare_exchange_weak(
        oldval, newval, std::memory_order_acq_rel, std::memory_order_acquire);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::count_inc ( Count  add )

inlineprivatenoexcept

Definition at line 130 of file HazptrObjLinked.h.

References add.

                                     {
    auto oldval = count_.fetch_add(add, std::memory_order_acq_rel);
    DCHECK_LT(oldval & kLinkMask, kLinkMask);
    DCHECK_LT(oldval & kRefMask, kRefMask);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::count_inc_safe ( Count  add )

inlineprivatenoexcept

Definition at line 136 of file HazptrObjLinked.h.

References add, and count.

                                          {
    auto oldval = count();
    count_set(oldval + add);
    DCHECK_LT(oldval & kLinkMask, kLinkMask);
    DCHECK_LT(oldval & kRefMask, kRefMask);
  }

template<template< typename > class Atom>

void folly::hazptr_obj_linked< Atom >::count_set ( Count  val )

inlineprivatenoexcept

Definition at line 126 of file HazptrObjLinked.h.

References val.

                                     {
    count_.store(val, std::memory_order_release);
  }

template<template< typename > class Atom>

bool folly::hazptr_obj_linked< Atom >::downgrade_link ( )

inlineprivatenoexcept

Definition at line 180 of file HazptrObjLinked.h.

References Atom, count, D, and folly::gen::sub().

                                 {
    auto oldval = count();
    auto sub = kLink - kRef;
    while (true) {
      if (oldval == kLink) {
        count_set(kRef);
        return true;
      }
      if (count_cas(oldval, oldval - sub)) {
        return (oldval & kLinkMask) == kLink;
      }
    }
  }

template<template< typename > class Atom>

bool folly::hazptr_obj_linked< Atom >::release_link ( )

inlineprivatenoexcept

Definition at line 148 of file HazptrObjLinked.h.

References count, and folly::gen::sub().

                               {
    auto sub = kLink;
    auto oldval = count();
    while (true) {
      DCHECK_GT(oldval & kLinkMask, 0u);
      if (oldval == kLink) {
        count_set(0u);
        return true;
      }
      if (count_cas(oldval, oldval - sub)) {
        return false;
      }
    }
  }

template<template< typename > class Atom>

bool folly::hazptr_obj_linked< Atom >::release_ref ( )

inlineprivatenoexcept

Definition at line 163 of file HazptrObjLinked.h.

References count, folly::kIsDebug, and folly::gen::sub().

                              {
    auto sub = kRef;
    auto oldval = count();
    while (true) {
      if (oldval == 0u) {
        if (kIsDebug) {
          count_set(kRefMask);
        }
        return true;
      }
      DCHECK_GT(oldval & kRefMask, 0u);
      if (count_cas(oldval, oldval - sub)) {
        return false;
      }
    }
  }

Friends And Related Function Documentation

template<template< typename > class Atom>

template<typename , template< typename > class, typename >

friend class hazptr_obj_base_linked

friend

Definition at line 120 of file HazptrObjLinked.h.

Member Data Documentation

template<template< typename > class Atom>

Atom<Count> folly::hazptr_obj_linked< Atom >::count_ {0}

private

Definition at line 99 of file HazptrObjLinked.h.

template<template< typename > class Atom>

constexpr Count folly::hazptr_obj_linked< Atom >::kLink = 1u << 16

staticprivate

Definition at line 95 of file HazptrObjLinked.h.

template<template< typename > class Atom>

constexpr Count folly::hazptr_obj_linked< Atom >::kLinkMask = ~kRefMask

staticprivate

Definition at line 97 of file HazptrObjLinked.h.

template<template< typename > class Atom>

constexpr Count folly::hazptr_obj_linked< Atom >::kRef = 1u

staticprivate

Definition at line 94 of file HazptrObjLinked.h.

template<template< typename > class Atom>

constexpr Count folly::hazptr_obj_linked< Atom >::kRefMask = kLink - 1u

staticprivate

Definition at line 96 of file HazptrObjLinked.h.

---

The documentation for this class was generated from the following files:

• proxygen/folly/folly/synchronization/Hazptr-fwd.h
• proxygen/folly/folly/synchronization/HazptrObjLinked.h