Persistent open-addressing hash table mapping UUIDs to integers. More...

#include "MMappedUUIDHashTable.h"

Collaboration diagram for MMappedUUIDHashTable:

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Classes
struct	value_t
	One slot in the hash table: a UUID key and its associated integer value. More...
struct	table_t
	On-disk layout of the hash table stored in the mmap file. More...

Public Member Functions
	MMappedUUIDHashTable (const char *filename, bool read_only, uint64_t magic)
	Open (or create) the mmap-backed hash table.
	~MMappedUUIDHashTable ()
	Sync and unmap the file.
bool	uncleanShutdown () const
	Whether this file still had `FLAG_DIRTY` set when it was opened, i.e.
unsigned long	operator[] (pg_uuid_t u) const
	Look up the integer index for UUID `u`.
std::pair< unsigned long, bool >	add (pg_uuid_t u)
	Insert UUID `u`, assigning it the next available integer.
std::pair< unsigned long, bool >	publish (pg_uuid_t u, unsigned long value)
	Insert UUID `u` with a caller-chosen value.
unsigned long	nextValue () const
	The value the next `add` would assign.
unsigned long	capacity () const
	The number of slots the table currently has.
unsigned long	slotValue (unsigned long k) const
	The `k-th` slot's value, or `NOTHING` when the slot is empty.
pg_uuid_t	slotKey (unsigned long k) const
	The `k-th` slot's key; only meaningful when `slotValue(k)` is not `NOTHING`.
unsigned long	nbElements () const
	Return the number of UUID→integer pairs currently stored.
void	sync ()
	Flush the backing region to its file (`MappedRegion::sync()`).
void	flush ()
	Force the backing file to stable storage (`MappedRegion::flush()`).

Static Public Attributes
static constexpr unsigned long	NOTHING =static_cast<unsigned long>(-1)
	Sentinel returned by `operator[]()` when the UUID is not present.
static constexpr uint32_t	FLAG_DIRTY = 1u
	Bit of `table_t::flags` set while the file is open for writing.

Private Member Functions
unsigned long	hash (pg_uuid_t u) const
	Compute the starting slot index for UUID `u`.
unsigned long	find (pg_uuid_t u) const
	Find the slot index of `u`, or `NOTHING` if absent.
void	grow ()
	Double the table capacity and rehash all existing entries.

Private Attributes
MappedRegion	region
	Backing storage (shared mmap, or heap buffer).
table_t *	table
	Typed view of `region.base()`.
std::string	path_
	Backing file, for the atomic rehash in `grow()`.
bool	read_only_ = false
	Mapped read-only: the header must not be written.
bool	unclean_ = false
	The previous run left the dirty bit set.

Static Private Attributes
static constexpr unsigned	STARTING_LOG_SIZE =16
	Initial log2 capacity (65 536 slots).
static constexpr double	MAXIMUM_LOAD_FACTOR =.5
	Rehash when this fraction of slots is occupied.

Detailed Description

Persistent open-addressing hash table mapping UUIDs to integers.

Definition at line 41 of file MMappedUUIDHashTable.h.

Constructor & Destructor Documentation

◆ MMappedUUIDHashTable()

MMappedUUIDHashTable::MMappedUUIDHashTable	(	const char *	filename,
		bool	read_only,
		uint64_t	magic )

Open (or create) the mmap-backed hash table.

Parameters

filename	Path to the backing file (created if absent).
read_only	If `true`, map the file read-only (no new entries can be inserted).
magic	Expected magic value for format validation.

Definition at line 34 of file MMappedUUIDHashTable.cpp.

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◆ ~MMappedUUIDHashTable()

MMappedUUIDHashTable::~MMappedUUIDHashTable ( )

Sync and unmap the file.

Definition at line 119 of file MMappedUUIDHashTable.cpp.

Member Function Documentation

◆ add()

std::pair< unsigned long, bool > MMappedUUIDHashTable::add ( pg_uuid_t u )

Insert UUID u, assigning it the next available integer.

If u is already present the existing value is returned without modification.

Parameters

u	UUID to insert.

Returns: A pair {value, inserted} where inserted is true if a new entry was created.

Definition at line 144 of file MMappedUUIDHashTable.cpp.

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◆ capacity()

unsigned long MMappedUUIDHashTable::capacity ( ) const

inline

The number of slots the table currently has.

Definition at line 206 of file MMappedUUIDHashTable.h.

◆ find()

unsigned long MMappedUUIDHashTable::find ( pg_uuid_t u ) const

private

Find the slot index of u, or NOTHING if absent.

Parameters

u	UUID to look up.

Returns: Slot index, or NOTHING if u is not in the table.

Definition at line 126 of file MMappedUUIDHashTable.cpp.

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◆ flush()

void MMappedUUIDHashTable::flush ( )

Force the backing file to stable storage (MappedRegion::flush()).

Definition at line 179 of file MMappedUUIDHashTable.cpp.

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◆ grow()

void MMappedUUIDHashTable::grow ( )

private

Double the table capacity and rehash all existing entries.

Definition at line 86 of file MMappedUUIDHashTable.cpp.

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◆ hash()

unsigned long MMappedUUIDHashTable::hash ( pg_uuid_t u ) const

inlineprivate

Compute the starting slot index for UUID u.

Reinterprets the first 8 bytes of u as a 64-bit integer and takes it modulo the current capacity.

Parameters

u	UUID to hash.

Returns: Slot index in [0, capacity).

Definition at line 116 of file MMappedUUIDHashTable.h.

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◆ nbElements()

unsigned long MMappedUUIDHashTable::nbElements ( ) const

inline

Return the number of UUID→integer pairs currently stored.

Returns: Element count.

Definition at line 226 of file MMappedUUIDHashTable.h.

◆ nextValue()

unsigned long MMappedUUIDHashTable::nextValue ( ) const

inline

The value the next add would assign.

Kept equal to the number of gate records by MMappedCircuit.

Definition at line 201 of file MMappedUUIDHashTable.h.

◆ operator[]()

unsigned long MMappedUUIDHashTable::operator[] ( pg_uuid_t u ) const

Look up the integer index for UUID u.

Parameters

u	The UUID to look up.

Returns: The associated integer, or NOTHING if u is absent.

Definition at line 137 of file MMappedUUIDHashTable.cpp.

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◆ publish()

std::pair< unsigned long, bool > MMappedUUIDHashTable::publish	(	pg_uuid_t	u,
		unsigned long	value )

Insert UUID u with a caller-chosen value.

Lets the caller build the record value indexes before the key that points at it becomes visible, so that a process killed between the two leaves an unreferenced record rather than a mapping entry pointing past the end of the record vector – which would shift every later gate for the rest of the store's life. The slot's value field is written last, and an aligned 8-byte store is atomic on the supported platforms, so a reader sees either NOTHING or the complete entry.

Parameters

u	UUID to insert.
value	Value to associate with it.

Returns: A pair {value, inserted}; inserted is false (and the existing value returned) when u was already there.

Definition at line 152 of file MMappedUUIDHashTable.cpp.

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◆ slotKey()

pg_uuid_t MMappedUUIDHashTable::slotKey ( unsigned long k ) const

inline

The k-th slot's key; only meaningful when slotValue(k) is not NOTHING.

Definition at line 218 of file MMappedUUIDHashTable.h.

◆ slotValue()

unsigned long MMappedUUIDHashTable::slotValue ( unsigned long k ) const

inline

The k-th slot's value, or NOTHING when the slot is empty.

For consistency checks and for the clean-up's mark phase.

Definition at line 212 of file MMappedUUIDHashTable.h.

◆ sync()

void MMappedUUIDHashTable::sync ( )

Flush the backing region to its file (MappedRegion::sync()).

Definition at line 174 of file MMappedUUIDHashTable.cpp.

◆ uncleanShutdown()

bool MMappedUUIDHashTable::uncleanShutdown ( ) const

inline

Whether this file still had FLAG_DIRTY set when it was opened, i.e.

whoever wrote it last did not close it.

Definition at line 157 of file MMappedUUIDHashTable.h.

Member Data Documentation

◆ FLAG_DIRTY

uint32_t MMappedUUIDHashTable::FLAG_DIRTY = 1u

staticconstexpr

Bit of table_t::flags set while the file is open for writing.

Cleared on a clean close, so a file found with it still set was left behind by a process that died (or by an immediate shutdown). Reported by uncleanShutdown; the header layout is unchanged, since the bit lives in what used to be reserved padding.

Definition at line 153 of file MMappedUUIDHashTable.h.

◆ MAXIMUM_LOAD_FACTOR

double MMappedUUIDHashTable::MAXIMUM_LOAD_FACTOR =.5

staticconstexprprivate

Rehash when this fraction of slots is occupied.

Definition at line 106 of file MMappedUUIDHashTable.h.

◆ NOTHING

unsigned long MMappedUUIDHashTable::NOTHING =static_cast<unsigned long>(-1)

staticconstexpr

Sentinel returned by operator[]() when the UUID is not present.

Definition at line 131 of file MMappedUUIDHashTable.h.

◆ path_

std::string MMappedUUIDHashTable::path_

private

Backing file, for the atomic rehash in grow().

Definition at line 99 of file MMappedUUIDHashTable.h.

◆ read_only_

bool MMappedUUIDHashTable::read_only_ = false

private

Mapped read-only: the header must not be written.

Definition at line 100 of file MMappedUUIDHashTable.h.

◆ region

MappedRegion MMappedUUIDHashTable::region

private

Backing storage (shared mmap, or heap buffer).

Definition at line 97 of file MMappedUUIDHashTable.h.

◆ STARTING_LOG_SIZE

unsigned MMappedUUIDHashTable::STARTING_LOG_SIZE =16

staticconstexprprivate

Initial log2 capacity (65 536 slots).

Definition at line 104 of file MMappedUUIDHashTable.h.

◆ table

table_t* MMappedUUIDHashTable::table

private

Typed view of region.base().

Definition at line 98 of file MMappedUUIDHashTable.h.

◆ unclean_

bool MMappedUUIDHashTable::unclean_ = false

private

The previous run left the dirty bit set.

Definition at line 101 of file MMappedUUIDHashTable.h.

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

/home/senellar/git/software/provsql/src/MMappedUUIDHashTable.h
/home/senellar/git/software/provsql/src/MMappedUUIDHashTable.cpp

Classes

Public Member Functions

Static Public Attributes

Private Member Functions

Private Attributes

Static Private Attributes

Detailed Description

Constructor & Destructor Documentation

◆ MMappedUUIDHashTable()

◆ ~MMappedUUIDHashTable()

Member Function Documentation

◆ add()

◆ capacity()

◆ find()

◆ flush()

◆ grow()

◆ hash()

◆ nbElements()

◆ nextValue()

◆ operator[]()

◆ publish()

◆ slotKey()

◆ slotValue()

◆ sync()

◆ uncleanShutdown()

Member Data Documentation

◆ FLAG_DIRTY

◆ MAXIMUM_LOAD_FACTOR

◆ NOTHING

◆ path_

◆ read_only_

◆ region

◆ STARTING_LOG_SIZE

◆ table

◆ unclean_