os_once Class Reference

Execute a given function exactly once in a multi-threaded environment or wait for the function to be executed by another thread. More...

#include <os0once.h>

Public Types
typedef uint32_t	state_t
	Control variables' state type. More...

Static Public Member Functions
static void	do_or_wait_for_done (std::atomic< state_t > *state, void(*do_func)(void *), void *do_func_arg)
	Call a given function or wait its execution to complete if it is already called by another thread. More...

Static Public Attributes
static const state_t	NEVER_DONE = 0
	Not yet executed. More...
static const state_t	IN_PROGRESS = 1
	Currently being executed by this or another thread. More...
static const state_t	DONE = 2
	Finished execution. More...

Detailed Description

Execute a given function exactly once in a multi-threaded environment or wait for the function to be executed by another thread.

Example usage: First the user must create a control variable of type os_once::state_t and assign it os_once::NEVER_DONE. Then the user must pass this variable, together with a function to be executed to os_once::do_or_wait_for_done().

Multiple threads can call os_once::do_or_wait_for_done() simultaneously with the same (os_once::state_t) control variable. The provided function will be called exactly once and when os_once::do_or_wait_for_done() returns then this function has completed execution, by this or another thread. In other words os_once::do_or_wait_for_done() will either execute the provided function or will wait for its execution to complete if it is already called by another thread or will do nothing if the function has already completed its execution earlier.

This mimics pthread_once(3), but unfortunately pthread_once(3) does not support passing arguments to the init_routine() function. We should use std::call_once() when we start compiling with C++11 enabled.

Member Typedef Documentation

state_t

typedef uint32_t os_once::state_t

Control variables' state type.

Member Function Documentation

do_or_wait_for_done()

static void os_once::do_or_wait_for_done ( std::atomic< state_t > *  state, void(*)(void *)  do_func, void *  do_func_arg  )

inlinestatic

Call a given function or wait its execution to complete if it is already called by another thread.

Parameters

[in,out]	state	control variable
[in]	do_func	function to call
[in,out]	do_func_arg	an argument to pass to do_func().

Member Data Documentation

DONE

const state_t os_once::DONE = 2

static

Finished execution.

IN_PROGRESS

const state_t os_once::IN_PROGRESS = 1

static

Currently being executed by this or another thread.

NEVER_DONE

const state_t os_once::NEVER_DONE = 0

static

Not yet executed.

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

• storage/innobase/include/os0once.h