net_instaweb::UpDownCounter Class Reference

#include "statistics.h"

Inheritance diagram for net_instaweb::UpDownCounter:

Public Member Functions
virtual int64	Get () const =0
virtual StringPiece	GetName () const =0
virtual int64	SetReturningPreviousValue (int64 value)
virtual void	Set (int64 value)=0
void	Clear ()
int64	Add (int64 delta)

Protected Member Functions
virtual int64	AddHelper (int64 delta)=0
	This is virtual so that subclasses can add platform-specific atomicity.

Detailed Description

UpDownCounters are variables that can also be decreased (e.g. Add of a negative number) or Set to an arbitrary value.

Todo:

TODO(jmarantz): Make this not inherit from Variable, which will simplify the 'CheckNotNegative' and its ifndefs, but will require us to do more accurate type bookkeeping in tests, etc.

Todo:

TODO(jmarantz): consider renaming Variable->Counter, UpDownCounter->Variable.

Member Function Documentation

virtual StringPiece net_instaweb::UpDownCounter::GetName ( ) const

pure virtual

Return some name representing the variable, provided that the specific implementation has some sensible way of doing so.

Implemented in net_instaweb::UpDownTemplate< Impl >, net_instaweb::UpDownTemplate< SharedMemVariable >, net_instaweb::UpDownTemplate< NullStatisticsVariable >, net_instaweb::UpDownTemplate< SimpleStatsVariable >, and net_instaweb::SplitUpDownCounter.

virtual int64 net_instaweb::UpDownCounter::SetReturningPreviousValue ( int64  value )

virtual

Sets the specified value, returning the previous value. This can be used to by two competing threads/processes to determine which thread modified the value first. The default implementation is non-atomic, but implementations can override to provide an atomic version.

Non-atomic implementations may result in multiple concurrent updates each returning the old value. In an atomic implementation, only one concurrent update will return the old value.

Reimplemented in net_instaweb::SplitUpDownCounter.

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

• pagespeed/kernel/base/statistics.h