SQLamarr
The stand-alone ultra-fast simulation option for the LHCb experiment
Public Member Functions | Static Public Member Functions | Static Public Attributes | List of all members
SQLamarr::T_GlobalPRNG< PRNG > Class Template Reference

Singleton handler of Pseudo-Random Number Generator(s) More...

#include <GlobalPRNG.h>

Public Member Functions

 T_GlobalPRNG (T_GlobalPRNG const &)=delete
 Copy constructor disabled as per singleton pattern. More...
 
void operator= (T_GlobalPRNG const &)=delete
 Copy operator disabled as per singleton pattern. More...
 

Static Public Member Functions

static T_GlobalPRNG & handle ()
 Return a handle to the hash table, not to the single generator (see below). More...
 
static PRNG * get_or_create (const sqlite3_context *db, uint64_t seed=no_seed)
 Return a pointer to an initialized generator. More...
 
static PRNG * get_or_create (const sqlite3 *db, uint64_t seed=no_seed)
 Return a pointer to an initialized generator. More...
 
static bool release (const sqlite3 *db)
 Releases a generator (delete). May require re-seeding. More...
 

Static Public Attributes

static constexpr uint64_t no_seed = 0xBAD0000000000000L
 Higher part of the int64 is used to identify missing or invalid seed. More...
 

Detailed Description

template<class PRNG>
class SQLamarr::T_GlobalPRNG< PRNG >

Singleton handler of Pseudo-Random Number Generator(s)

The generation of pseudo-random numbers for Monte Carlo applications is a critical aspect in the design of an application.

Pseudo-random numbers should be generated upon a known seed. Reproducibility of the complete simulation process must be guaranteed, provided the same seed.

A further complication arises from multithreaded applications with multiple threads sharing a single Pseudo-Random Number Generator (PRNG). Indeed, the order with which threads may advance the sequence of pseudo-random numbers is defined by the order of execution of threads which is, by nature, stocastic.

In SQLamarr, PRNs are generated with a generator connected to the database instance. Database instances are supposed to live in a thread as concurrent access to the same SQLite database introduces an easily avoidable overhead. If such a good practice is followed, then each thread gets associated to a different random number generator, seeded indepedently (for example based on the number of threads).

From a technical perspective, a Singleton GlobalPRNG class handles a hash table associating a random number generator to each known database instance.

On the attempt to access a generator for a database instance not previously mapped in the hash table, a new instance is allocated, using the seed provided as an argument. If the seed is not provided, an exception is thrown, unless explicitely ignored compiling with flag -DALLOW_RANDOM_DEVICE_FOR_SEEDING.

Generators can be reseeded at any time, by accessing the generator associated to an existing database instance, while passing the seed.

Any pseudo random number generator defined according the STL generator interface can be used to specialize the template class T_GlobalPRNG defining the behaviour described above.

The default GlobalPRNG specialization uses a RANLUX with 48 bit generator as provided by the C++ STL.

Note on multithreading. A std::unordered_map is used to associate a random number generator to a given database. Since the operations of consulting and updating an unordered_map are not thread-safe and since, by design, such a mapping must be shared across multiple threads, the access to the map is protected by a std::mutex.

Definition at line 81 of file GlobalPRNG.h.

Constructor & Destructor Documentation

◆ T_GlobalPRNG()

template<class PRNG >
SQLamarr::T_GlobalPRNG< PRNG >::T_GlobalPRNG ( T_GlobalPRNG< PRNG > const &  )
delete

Copy constructor disabled as per singleton pattern.

Member Function Documentation

◆ get_or_create() [1/2]

template<class PRNG >
static PRNG* SQLamarr::T_GlobalPRNG< PRNG >::get_or_create ( const sqlite3 *  db,
uint64_t  seed = no_seed 
)
inlinestatic

Return a pointer to an initialized generator.

Definition at line 110 of file GlobalPRNG.h.

◆ get_or_create() [2/2]

template<class PRNG >
static PRNG* SQLamarr::T_GlobalPRNG< PRNG >::get_or_create ( const sqlite3_context *  db,
uint64_t  seed = no_seed 
)
inlinestatic

Return a pointer to an initialized generator.

Definition at line 99 of file GlobalPRNG.h.

◆ handle()

template<class PRNG >
static T_GlobalPRNG& SQLamarr::T_GlobalPRNG< PRNG >::handle ( )
inlinestatic

Return a handle to the hash table, not to the single generator (see below).

Definition at line 91 of file GlobalPRNG.h.

◆ operator=()

template<class PRNG >
void SQLamarr::T_GlobalPRNG< PRNG >::operator= ( T_GlobalPRNG< PRNG > const &  )
delete

Copy operator disabled as per singleton pattern.

◆ release()

template<class PRNG >
static bool SQLamarr::T_GlobalPRNG< PRNG >::release ( const sqlite3 *  db)
inlinestatic

Releases a generator (delete). May require re-seeding.

Definition at line 157 of file GlobalPRNG.h.

Member Data Documentation

◆ no_seed

template<class PRNG >
constexpr uint64_t SQLamarr::T_GlobalPRNG< PRNG >::no_seed = 0xBAD0000000000000L
staticconstexpr

Higher part of the int64 is used to identify missing or invalid seed.

Definition at line 86 of file GlobalPRNG.h.

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