ripple::IntrusiveRefCounts Struct Reference

Implement the strong count, weak count, and bit flags for an intrusive pointer. More...

#include <IntrusiveRefCounts.h>

Inheritance diagram for ripple::IntrusiveRefCounts:

Collaboration diagram for ripple::IntrusiveRefCounts:

Classes
struct	RefCountPair
	Unpack the count and tag fields from the packed atomic integer form. More...

Public Member Functions
virtual	~IntrusiveRefCounts () noexcept
void	addStrongRef () const noexcept
void	addWeakRef () const noexcept
ReleaseStrongRefAction	releaseStrongRef () const
ReleaseStrongRefAction	addWeakReleaseStrongRef () const
ReleaseWeakRefAction	releaseWeakRef () const
bool	checkoutStrongRefFromWeak () const noexcept
bool	expired () const noexcept
std::size_t	use_count () const noexcept

Private Types
using	CountType = std::uint16_t
using	FieldType = std::uint32_t

Private Attributes
std::atomic< FieldType >	refCounts {strongDelta}
	refCounts consists of four fields that are treated atomically:

Static Private Attributes
static constexpr size_t	StrongCountNumBits = sizeof(CountType) * 8
static constexpr size_t	WeakCountNumBits = StrongCountNumBits - 2
static constexpr size_t	FieldTypeBits = sizeof(FieldType) * 8
static constexpr FieldType	one = 1
static constexpr FieldType	strongDelta = 1
	Amount to change the strong count when adding or releasing a reference.
static constexpr FieldType	weakDelta = (one << StrongCountNumBits)
	Amount to change the weak count when adding or releasing a reference.
static constexpr FieldType	partialDestroyStartedMask
	Flag that is set when the partialDestroy function has started running (or is about to start running).
static constexpr FieldType	partialDestroyFinishedMask
	Flag that is set when the partialDestroy function has finished running.
static constexpr FieldType	tagMask
	Mask that will zero out all the count bits and leave the tag bits unchanged.
static constexpr FieldType	valueMask = ~tagMask
	Mask that will zero out the tag bits and leave the count bits unchanged.
static constexpr FieldType	strongMask
	Mask that will zero out everything except the strong count.
static constexpr FieldType	weakMask
	Mask that will zero out everything except the weak count.

Friends
template<class T >
void	partialDestructorFinished (T **o)

Detailed Description

Implement the strong count, weak count, and bit flags for an intrusive pointer.

A class can satisfy the requirements of a ripple::IntrusivePointer by inheriting from this class.

Definition at line 40 of file IntrusiveRefCounts.h.

Member Typedef Documentation

CountType

using ripple::IntrusiveRefCounts::CountType = std::uint16_t

private

Definition at line 101 of file IntrusiveRefCounts.h.

FieldType

using ripple::IntrusiveRefCounts::FieldType = std::uint32_t

private

Definition at line 104 of file IntrusiveRefCounts.h.

Constructor & Destructor Documentation

~IntrusiveRefCounts()

ripple::IntrusiveRefCounts::~IntrusiveRefCounts ( )

virtualnoexcept

Definition at line 405 of file IntrusiveRefCounts.h.

Member Function Documentation

addStrongRef()

void ripple::IntrusiveRefCounts::addStrongRef ( ) const

noexcept

Definition at line 232 of file IntrusiveRefCounts.h.

addWeakRef()

void ripple::IntrusiveRefCounts::addWeakRef ( ) const

noexcept

Definition at line 238 of file IntrusiveRefCounts.h.

releaseStrongRef()

ReleaseStrongRefAction ripple::IntrusiveRefCounts::releaseStrongRef

(

)

const

Definition at line 244 of file IntrusiveRefCounts.h.

addWeakReleaseStrongRef()

ReleaseStrongRefAction ripple::IntrusiveRefCounts::addWeakReleaseStrongRef

(

)

const

Definition at line 293 of file IntrusiveRefCounts.h.

releaseWeakRef()

ReleaseWeakRefAction ripple::IntrusiveRefCounts::releaseWeakRef

(

)

const

Definition at line 347 of file IntrusiveRefCounts.h.

checkoutStrongRefFromWeak()

bool ripple::IntrusiveRefCounts::checkoutStrongRefFromWeak ( ) const

noexcept

Definition at line 374 of file IntrusiveRefCounts.h.

expired()

bool ripple::IntrusiveRefCounts::expired ( ) const

noexcept

Definition at line 392 of file IntrusiveRefCounts.h.

use_count()

std::size_t ripple::IntrusiveRefCounts::use_count ( ) const

noexcept

Definition at line 399 of file IntrusiveRefCounts.h.

Friends And Related Symbol Documentation

partialDestructorFinished

template<class T >

void partialDestructorFinished ( T **  o )

friend

Definition at line 460 of file IntrusiveRefCounts.h.

Member Data Documentation

StrongCountNumBits

constexpr size_t ripple::IntrusiveRefCounts::StrongCountNumBits = sizeof(CountType) * 8

staticconstexprprivate

Definition at line 102 of file IntrusiveRefCounts.h.

WeakCountNumBits

constexpr size_t ripple::IntrusiveRefCounts::WeakCountNumBits = StrongCountNumBits - 2

staticconstexprprivate

Definition at line 103 of file IntrusiveRefCounts.h.

FieldTypeBits

constexpr size_t ripple::IntrusiveRefCounts::FieldTypeBits = sizeof(FieldType) * 8

staticconstexprprivate

Definition at line 105 of file IntrusiveRefCounts.h.

one

constexpr FieldType ripple::IntrusiveRefCounts::one = 1

staticconstexprprivate

Definition at line 106 of file IntrusiveRefCounts.h.

refCounts

std::atomic<FieldType> ripple::IntrusiveRefCounts::refCounts {strongDelta}

mutableprivate

refCounts consists of four fields that are treated atomically:

1. Strong count. This is a count of the number of shared pointers that hold a reference to this object. When the strong counts goes to zero, if the weak count is zero, the destructor is run. If the weak count is non-zero when the strong count goes to zero then the partialDestructor is run.
2. Weak count. This is a count of the number of weak pointer that hold a reference to this object. When the weak count goes to zero and the strong count is also zero, then the destructor is run.
3. Partial destroy started bit. This bit is set if the partialDestructor function has been started (or is about to be started). This is used to prevent the destructor from running concurrently with the partial destructor. This can easily happen when the last strong pointer release its reference in one thread and starts the partialDestructor, while in another thread the last weak pointer goes out of scope and starts the destructor while the partialDestructor is still running. Both a start and finished bit is needed to handle a corner-case where the last strong pointer goes out of scope, then then last weakPointer goes out of scope, but this happens before the partialDestructor bit is set. It would be possible to use a single bit if it could also be set atomically when the strong count goes to zero and the weak count is non-zero, but that would add complexity (and likely slow down common cases as well).
4. Partial destroy finished bit. This bit is set when the partialDestructor has finished running. See (3) above for more information.

Definition at line 141 of file IntrusiveRefCounts.h.

strongDelta

constexpr FieldType ripple::IntrusiveRefCounts::strongDelta = 1

staticconstexprprivate

Amount to change the strong count when adding or releasing a reference.

Note: The strong count is stored in the low StrongCountNumBits bits of refCounts

Definition at line 148 of file IntrusiveRefCounts.h.

weakDelta

constexpr FieldType ripple::IntrusiveRefCounts::weakDelta = (one << StrongCountNumBits)

staticconstexprprivate

Amount to change the weak count when adding or releasing a reference.

Note: The weak count is stored in the high WeakCountNumBits bits of refCounts

Definition at line 155 of file IntrusiveRefCounts.h.

partialDestroyStartedMask

constexpr FieldType ripple::IntrusiveRefCounts::partialDestroyStartedMask

staticconstexprprivate

Initial value:

=
        (one << (FieldTypeBits - 1))

Flag that is set when the partialDestroy function has started running (or is about to start running).

See description of the refCounts field for a fuller description of this field.

Definition at line 163 of file IntrusiveRefCounts.h.

partialDestroyFinishedMask

constexpr FieldType ripple::IntrusiveRefCounts::partialDestroyFinishedMask

staticconstexprprivate

Initial value:

=
        (one << (FieldTypeBits - 2))

Flag that is set when the partialDestroy function has finished running.

See description of the refCounts field for a fuller description of this field.

Definition at line 171 of file IntrusiveRefCounts.h.

tagMask

constexpr FieldType ripple::IntrusiveRefCounts::tagMask

staticconstexprprivate

Initial value:

=
        partialDestroyStartedMask | partialDestroyFinishedMask

Mask that will zero out all the count bits and leave the tag bits unchanged.

Definition at line 177 of file IntrusiveRefCounts.h.

valueMask

constexpr FieldType ripple::IntrusiveRefCounts::valueMask = ~tagMask

staticconstexprprivate

Mask that will zero out the tag bits and leave the count bits unchanged.

Definition at line 183 of file IntrusiveRefCounts.h.

strongMask

constexpr FieldType ripple::IntrusiveRefCounts::strongMask

staticconstexprprivate

Initial value:

=
        ((one << StrongCountNumBits) - 1) & valueMask

Mask that will zero out everything except the strong count.

Definition at line 187 of file IntrusiveRefCounts.h.

weakMask

constexpr FieldType ripple::IntrusiveRefCounts::weakMask

staticconstexprprivate

Initial value:

=
        (((one << WeakCountNumBits) - 1) << StrongCountNumBits) & valueMask

Mask that will zero out everything except the weak count.

Definition at line 192 of file IntrusiveRefCounts.h.