bslmt::Once Class Reference

#include <bslmt_once.h>

Public Types
typedef QLockGuard	OnceLock

Public Member Functions
bool	enter (OnceLock *onceLock)
void	leave (OnceLock *onceLock)
void	cancel (OnceLock *onceLock)
template<class FUNC >
void	callOnce (FUNC &function)
template<class FUNC >
void	callOnce (const FUNC &function)
bool	isMaybeUninitialized () const

Public Attributes
QLock	d_mutex
bsls::AtomicOperations::AtomicTypes::Int	d_state

Detailed Description

Gate-keeper class for code that should only execute once per process. This class is a POD-type and can be statically initialized to the value of the BSLMT_ONCE_INITIALIZE macro. For this reason, it does not have any explicitly-declared constructors or destructor.

See bslmt_once

Member Typedef Documentation

OnceLock

typedef QLockGuard bslmt::Once::OnceLock

Special token created by a single thread to pass to the enter, leave, and cancel methods.

Member Function Documentation

callOnce() [1/2]

template<class FUNC >

void bslmt::Once::callOnce ( const FUNC &  function )

inline

callOnce() [2/2]

template<class FUNC >

void bslmt::Once::callOnce ( FUNC &  function )

inline

If no other thread has yet called enter or callOnce, then call the specified function and set this object to the state where pending and future calls to enter or callOnce will return false or do nothing, respectively. Otherwise, wait for the one-time code to complete and return without calling function where function is a function or functor that can be called with no arguments. Note that one-time code is considered not to have run if function terminates with an exception.

cancel()

void bslmt::Once::cancel

(

OnceLock *

onceLock

)

Revert this object to the state it was in before enter or callOnce was called, then unlock the internal mutex using the specified onceLock (possibly unblocking pending calls to enter or callOnce). This method may only be used to cancel execution of one-time code that has not yet completed. The behavior is undefined unless onceLock was locked by a matching call to enter on this object and has not been tampered-with since (especially by calling leave).

enter()

bool bslmt::Once::enter

(

OnceLock *

onceLock

)

Lock the internal mutex using the specified onceLock (possibly blocking if another thread has already locked the mutex). If no other thread has yet called enter or callOnce on this object, return true. Otherwise, unlock the mutex and return false. The mutex lock may be skipped if it can be determined that it will not be needed. The behavior is undefined if onceLock is already in a locked state on entry to this method. Note that if enter returns true, the caller must eventually call leave, or else other threads may block indefinitely.

isMaybeUninitialized()

bool bslmt::Once::isMaybeUninitialized ( ) const

inline

Return true if this object may not be in the "done" state (that is, leave has not been called).

leave()

void bslmt::Once::leave

(

OnceLock *

onceLock

)

Set this object into a state such that pending and future calls to enter or callOnce will return false or do nothing, respectively, then unlock the internal mutex using the specified onceLock (possibly unblocking pending calls to enter or callOnce). The behavior is undefined unless onceLock was locked by a matching call to enter on this object and has not been tampered-with since.

Member Data Documentation

d_mutex

QLock bslmt::Once::d_mutex

d_state

bsls::AtomicOperations::AtomicTypes::Int bslmt::Once::d_state

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

• bslmt_once.h