CP::SystematicsCache< CalibData > Class Template Reference

helper class to cache systematics varied calibration constants inside a ISystematicsTool or IRentrantSystematicsTool More...

#include <SystematicsCache.h>

Inheritance diagram for CP::SystematicsCache< CalibData >:

Collaboration diagram for CP::SystematicsCache< CalibData >:

Public Member Functions
template<typename T2 >
	SystematicsCache (T2 *val_parent)
void	initialize (CP::SystematicSet val_affectingSystematics, std::function< StatusCode(const CP::SystematicSet &sys, CalibData &result)> val_calc) noexcept
	initialize with the list of affecting systematics and a function to calculate the calibration data for each systematic More...
const CP::SystematicSet &	affectingSystematics () const noexcept
	the list of affecting systematics More...
bool	isAffectedBySystematic (const SystematicVariation &systematic) const
	whether we are affected by the given systematic variation More...
StatusCode	get (const CP::SystematicSet &sys, const CalibData *&result) const
	get the pointer to the cached calibration data for the given systematic, calculating it if necessary More...
StatusCode	add (const CP::SystematicSet &sys, CalibData value)
	add an individual systematic variation More...
StatusCode	add (const SystematicVariation &variation, CalibData value)
bool	msgLvl (const MSG::Level lvl) const
	Test the output level of the object. More...
MsgStream &	msg () const
	The standard message stream. More...
MsgStream &	msg (const MSG::Level lvl) const
	The standard message stream. More...

Private Attributes
CP::SystematicSet	m_affectingSystematics
	the list of affecting systematics More...
std::function< StatusCode(const CP::SystematicSet &sys, CalibData &result)>	m_calc
	the function to calculate the calibration data for a given systematics More...
tbb::concurrent_unordered_map< CP::SystematicSet, std::shared_ptr< const CalibData >, SystematicSetHash > m_cache	ATLAS_THREAD_SAFE
	the cache of previously calculated calibration data More...
std::mutex	m_calcMutex
	a mutex to protext against concurrent execution of m_calc More...
std::function< MsgStream &()>	m_msg
	the message stream we use More...

Detailed Description

template<typename CalibData>
class CP::SystematicsCache< CalibData >

helper class to cache systematics varied calibration constants inside a ISystematicsTool or IRentrantSystematicsTool

The general pattern for how systematics are supposed to be implemented inside systematics tools is that the first time a specific systematic variation is requested the tool should calculate the calibration constants for that particular systematic, store it in an (unordered) map and look it up from that map in all subsequent uses. This class tries to implement that particular logic in a thread-safe and (reasonably) fool-proof way.

The basic way to use this class is:

class MyTool : public asg::AsgTool, virtual public IMyTool {
   ...
   struct ConfigData {...};
   CP::SystematicsCache<ConfigData> m_calibCache {this};
   const ConfigData *m_currentConfig {nullptr};
 };
 
 StatusCode MyTool :: initialize () {
   ...
   CP::SystematicSet affectingSystematics = ...;
   ANA_CHECK (m_calibCache.initialize (std::move (affectingSystematics),
                                       [this] (const CP::SystematicSet& sys,
                                               ConfigData& myconfig) {
       myconfig = ...;
       return StatusCode;});
   ANA_CHECK (applySystematicVariation (CP::SystematicSet()));
   return StatusCode::SUCCESS;
 }
 
StatusCode MyTool :: applySystematicVariation (const CP::SystematicSet& sys, ...) {
  return m_calibCache.get (sys, m_currentConfig);
}
 
CP::SystematicSet MyTool :: affectingSystematics () const {
  return m_calibCache.affectingSystematics(); }

There are not too many constraints on the structure and lambda function, just make sure the structure is default constructable and the lambda function is safe to execute while a lock is held (i.e. if you acquire a lock make sure not to create a dead-lock). It is currently not anticipated that this lambda function needs to be thread-safe itself (even if multiple threads use the same tool, they would still just run through the same systematics in the same order). It is guaranteed that the function is called exactly once for each unique set of affecting systematics, and that only a single copy of the calibration data is stored for each unique set of affecting systematics.

Note that while the above example uses a lambda function it is probably a good idea to write this as a separate helper function and have the lambda function wrap that helper. The rationale for that recommendation is that this is usually a rather long function with tedious logic and making it part of initialize can affect the readability of either one.

Definition at line 84 of file SystematicsCache.h.

Constructor & Destructor Documentation

SystematicsCache()

template<typename CalibData >

template<typename T2 >

CP::SystematicsCache< CalibData >::SystematicsCache

(

T2 *

val_parent

)

Function Implementations

Definition at line 150 of file SystematicsCache.h.

    : AsgMessagingForward (val_parent)
  {}

Member Function Documentation

add() [1/2]

template<typename CalibData >

StatusCode CP::SystematicsCache< CalibData >::add	(	const CP::SystematicSet &	sys,
		CalibData	value
	)

add an individual systematic variation

Definition at line 254 of file SystematicsCache.h.

  {
    auto emplace_result = m_cache.emplace (sys, std::make_shared<CalibData> (std::move (value)));
    if (emplace_result.second == false)
    {
      ANA_MSG_ERROR ("failed to add systematic, already present: " << sys.name());
      return StatusCode::FAILURE;
    }
 
    for (const auto& var : sys)
      m_affectingSystematics.insert (var);
 
    return StatusCode::SUCCESS;
  }

add() [2/2]

template<typename CalibData >

StatusCode CP::SystematicsCache< CalibData >::add	(	const SystematicVariation &	variation,
		CalibData	value
	)

Definition at line 273 of file SystematicsCache.h.

  {
    SystematicSet sys;
    sys.insert (variation);
    return add (sys, std::move (value));
  }

affectingSystematics()

template<typename CalibData >

const CP::SystematicSet & CP::SystematicsCache< CalibData >::affectingSystematics

noexcept

the list of affecting systematics

Definition at line 169 of file SystematicsCache.h.

  {
    return m_affectingSystematics;
  }

get()

template<typename CalibData >

StatusCode CP::SystematicsCache< CalibData >::get	(	const CP::SystematicSet &	sys,
		const CalibData *&	result
	)		const

get the pointer to the cached calibration data for the given systematic, calculating it if necessary

Definition at line 188 of file SystematicsCache.h.

  {
    // fast-path, check if we already calculated this
    auto iter = m_cache.find (sys);
    if (ATH_LIKELY (iter != m_cache.end())) //[[likely]], removed until C++20 support
    {
      result = iter->second.get();
      return StatusCode::SUCCESS;
    }
 
    // create a lock to prevent the concurrent (or duplicate)
    // execution of the \ref m_calc function.  if that function is
    // thread-safe this lock is not strictly necessary.  however,
    // given that it is hard to enforce that the function is indeed
    // thread-safe and there are essentially no performance gains to
    // be had, this seems safer (unless \ref m_calc acquires mutexes
    // in a way that causes a dead-lock).
    std::lock_guard<std::mutex> lock (m_calcMutex);
 
    // check if another thread already calculated this value while we
    // acquired the lock
    iter = m_cache.find (sys);
    if (iter != m_cache.end())
    {
      result = iter->second.get();
      return StatusCode::SUCCESS;
    }
 
    // we will only ever calculate the systematics for our set of
    // affecting systematics, any systematics that are not affecting
    // us will be ignored
    CP::SystematicSet mysys;
    ANA_CHECK (SystematicSet::filterForAffectingSystematics (sys, m_affectingSystematics, mysys));
 
    std::shared_ptr<const CalibData> mycalib;
    {
      // check if our affecting systematics are known already
      auto iter = m_cache.find (mysys);
      if (iter != m_cache.end())
        mycalib = iter->second;
      else
      {
        // this will now actually calculate the systematics.  note
        // that if this fails, nothing gets cached, but we should also
        // be aborting
        auto value = std::make_shared<CalibData> ();
        ANA_CHECK (m_calc (mysys, *value));
 
        // store for the affecting systematic
        auto emplace_result = m_cache.emplace (mysys, value);
        mycalib = emplace_result.first->second;
      }
    }
 
    // store for user requested systematics as well, which may or may
    // not be the same as the affecting systematics, but if it is
    // already there, this will do nothing.
    m_cache.emplace (sys, mycalib);
    result = mycalib.get();
    return StatusCode::SUCCESS;
  }

initialize()

template<typename CalibData >

void CP::SystematicsCache< CalibData >::initialize ( CP::SystematicSet  val_affectingSystematics, std::function< StatusCode(const CP::SystematicSet &sys, CalibData &result)>  val_calc  )

noexcept

initialize with the list of affecting systematics and a function to calculate the calibration data for each systematic

Definition at line 157 of file SystematicsCache.h.

  {
    m_calc = std::move (val_calc);
    m_affectingSystematics = std::move (val_affectingSystematics);
    m_cache.clear ();
  }

isAffectedBySystematic()

template<typename CalibData >

bool CP::SystematicsCache< CalibData >::isAffectedBySystematic

(

const SystematicVariation &

systematic

)

const

whether we are affected by the given systematic variation

this is mostly for implementing the ISystematicsTool interface and should probably not be used by anyone.

Definition at line 178 of file SystematicsCache.h.

  {
    // this is not technically correct, but what a lot of people do
    return m_affectingSystematics.find (sys) != m_affectingSystematics.end();
  }

msg() [1/2]

MsgStream & asg::AsgMessagingForward::msg ( ) const

inherited

The standard message stream.

Returns

A reference to the default message stream of this object.

Definition at line 24 of file AsgMessagingForward.cxx.

  {
    return m_msg();
  }

msg() [2/2]

MsgStream & asg::AsgMessagingForward::msg ( const MSG::Level  lvl ) const

inherited

The standard message stream.

Parameters

lvl	The message level to set the stream to

Returns

A reference to the default message stream, set to level "lvl"

Definition at line 29 of file AsgMessagingForward.cxx.

  {
    MsgStream& msg = m_msg ();
    msg << lvl;
    return msg;
  }

msgLvl()

bool asg::AsgMessagingForward::msgLvl ( const MSG::Level  lvl ) const

inherited

Test the output level of the object.

Parameters

lvl	The message level to test against

Returns

boolean Indicting if messages at given level will be printed

true If messages at level "lvl" will be printed

Definition at line 11 of file AsgMessagingForward.cxx.

  {
    MsgStream& msg = m_msg();
    if (msg.level() <= lvl)
    {
      msg << lvl;
      return true;
    } else
    {
      return false;
    }
  }

Member Data Documentation

ATLAS_THREAD_SAFE

template<typename CalibData >

tbb::concurrent_unordered_map<CP::SystematicSet,std::shared_ptr<const CalibData>,SystematicSetHash> m_cache CP::SystematicsCache< CalibData >::ATLAS_THREAD_SAFE

mutableprivate

the cache of previously calculated calibration data

Definition at line 135 of file SystematicsCache.h.

m_affectingSystematics

template<typename CalibData >

CP::SystematicSet CP::SystematicsCache< CalibData >::m_affectingSystematics

private

the list of affecting systematics

Private Members

Definition at line 128 of file SystematicsCache.h.

m_calc

template<typename CalibData >

std::function<StatusCode (const CP::SystematicSet& sys, CalibData& result)> CP::SystematicsCache< CalibData >::m_calc

private

the function to calculate the calibration data for a given systematics

Definition at line 132 of file SystematicsCache.h.

m_calcMutex

template<typename CalibData >

std::mutex CP::SystematicsCache< CalibData >::m_calcMutex

mutableprivate

a mutex to protext against concurrent execution of m_calc

see the comment inside get for a detailed explanation of why this is used/needed.

Definition at line 141 of file SystematicsCache.h.

m_msg

std::function<MsgStream& ()> asg::AsgMessagingForward::m_msg

privateinherited

the message stream we use

This used to be a simple pointer to the MsgStream itself, but in AthenaMT the actual object used is local to the thread. So instead of pointing to it directly we are now using a function to look it up, which will get the thread-local object.

Definition at line 77 of file AsgMessagingForward.h.

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

• SystematicsCache.h