mysql::scheduler::Sharded_counter Class Reference

Concurrent counter, relaxing contention on atomic counter when being updated by different threads. More...

#include <sharded_counter.h>

Public Member Functions
long long	get (std::size_t thread_id) const
	Obtains value for specific thread id. More...
long long	get () const
	Coalescing get operation, available only for integer type. More...
void	store (long long arg, std::size_t thread_id=0)
	Stores value for specific thread id. More...
void	add (long long arg, std::size_t thread_id=0)
	Updates value (add operation) for specific thread id. More...
void	init (std::size_t num_threads, bool enabled=true)
	Initializes this counter for requested number of threads, starting with thread id equal to 0, up to num_threads-1. More...
void	start_time (std::size_t thread_id=0)
	Special function to handle timer (helper for add/get when builing a timer over a concurrent counter). More...
void	stop_time (std::size_t thread_id=0)
	Special function to handle timer (helper for add/get when builing a timer over a concurrent counter). More...
long long	get_timer (std::size_t thread_id) const
	Special function to handle timer (helper for add/get when builing a timer over a concurrent counter). More...
long long	get_timer () const
	Special function to handle timer (helper for add/get when builing a timer over a concurrent counter). More...
void	reset ()
	Sets the internal value to 0. More...

Protected Types
using	Map_value_type = std::atomic< long long >

Protected Attributes
std::unordered_map< long long, Map_value_type >	m_value
	Keeps mapping between thread id and value of the counter for this thread id. More...
bool	m_enabled {true}
	Flag specifying whether this statistic is enabled, when false, methods are noop and return default values. More...

Detailed Description

Concurrent counter, relaxing contention on atomic counter when being updated by different threads.

The caller is able to get a value for specific thread, and store the value held by a specific thread (get, store). In addition to that, the caller can extract cumulative value for all of the threads (via get), atomically increment the counter by a specific value, or use helper time counters (start_timer, stop_timer, get_timer).

Member Typedef Documentation

Map_value_type

using mysql::scheduler::Sharded_counter::Map_value_type = std::atomic<long long>

protected

Member Function Documentation

add()

void mysql::scheduler::Sharded_counter::add	(	long long	arg,
		std::size_t	thread_id = 0
	)

Updates value (add operation) for specific thread id.

Parameters

arg	Update op argument
thread_id	Requested thread id

get() [1/2]

long long mysql::scheduler::Sharded_counter::get

(

)

const

Coalescing get operation, available only for integer type.

get() [2/2]

long long mysql::scheduler::Sharded_counter::get

(

std::size_t

thread_id

)

const

Obtains value for specific thread id.

Parameters

thread_id

Requested thread id

get_timer() [1/2]

long long mysql::scheduler::Sharded_counter::get_timer

(

)

const

Special function to handle timer (helper for add/get when builing a timer over a concurrent counter).

Get coalesced timer value.

Returns

Coalesced timer value

get_timer() [2/2]

long long mysql::scheduler::Sharded_counter::get_timer

(

std::size_t

thread_id

)

const

Special function to handle timer (helper for add/get when builing a timer over a concurrent counter).

Get timer value for the specified thread id

Parameters

thread_id

Requested thread id

Returns

Timer value for the specified thread

init()

void mysql::scheduler::Sharded_counter::init	(	std::size_t	num_threads,
		bool	enabled = true
	)

Initializes this counter for requested number of threads, starting with thread id equal to 0, up to num_threads-1.

Parameters

num_threads	Requested number of threads
enabled	Specify whether this statistic is enabled

reset()

void mysql::scheduler::Sharded_counter::reset

(

)

Sets the internal value to 0.

start_time()

void mysql::scheduler::Sharded_counter::start_time

(

std::size_t

thread_id = 0

)

Special function to handle timer (helper for add/get when builing a timer over a concurrent counter).

Start timer.

Parameters

thread_id

Requested thread id

stop_time()

void mysql::scheduler::Sharded_counter::stop_time

(

std::size_t

thread_id = 0

)

Special function to handle timer (helper for add/get when builing a timer over a concurrent counter).

Stop timer for the specified thread id

Parameters

thread_id

Requested thread id

store()

void mysql::scheduler::Sharded_counter::store	(	long long	arg,
		std::size_t	thread_id = 0
	)

Stores value for specific thread id.

Parameters

arg	Update op argument
thread_id	Requested thread id

Member Data Documentation

m_enabled

bool mysql::scheduler::Sharded_counter::m_enabled {true}

protected

Flag specifying whether this statistic is enabled, when false, methods are noop and return default values.

m_value

std::unordered_map<long long, Map_value_type> mysql::scheduler::Sharded_counter::m_value

protected

Keeps mapping between thread id and value of the counter for this thread id.

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

• libs/mysql/scheduler/sharded_counter.h
• libs/mysql/scheduler/sharded_counter.cpp