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Marlin
1.17.1
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Marlin
1.17.1
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Processor event seeder - provides independent pseudo-randomly generated seeds for registered processors on an event by event basis. More...
#include <ProcessorEventSeeder.h>
Public Member Functions | |
| ~ProcessorEventSeeder () | |
| Destructor. | |
| void | registerProcessor (Processor *proc) |
| Called by Processors to register themselves for the seeding service. | |
| unsigned int | getSeed (Processor *proc) |
| Called by Processors to obtain seed assigned to it for the current event. | |
Friends | |
| class | ProcessorMgr |
Processor event seeder - provides independent pseudo-randomly generated seeds for registered processors on an event by event basis.
This Class is used to provide individual pseudo-random numbers to Processors on
an event-by-event and run-by-run basis. These may be used by Processors to
seed their random number generator of choice. In order to use this service
a Processor must register itself in the init method using:
Global::EVENTSEEDER->registerProcessor(this);
and should retrieve its allocated event seed during processEvent using:
int eventSeed = Global::EVENTSEEDER->getSeed(this);
and include the header file:
#include "marlin/ProcessorEventSeeder.h"
The global seed is used for a complete job and is set in the Global steering parameters thus:
<parameter name="RandomSeed" value="1234567890"/>
Note that the value must be a positive integer, with max value 2,147,483,647
A pseudo-random event seed is generated using a three step hashing function of unsigned ints,
in the following order: event_number, run_number, RandomSeed. The hashed int from each step
in the above order is used as input to the next hash step. This is used to ensure that in
the likely event of similar values of event_number, run_number and RandomSeed, different
event seeds will be generated.
The event seed is then used to seed rand via srand(seed) and then rand is used to
generate one seed per registered processor.
This mechanism ensures reproducible results for every event, regardless of the sequence
in which the event is processed in a Marlin job, whilst maintaining the full 32bit range
for event and run numbers.
If a call is made to getSeed( Processor* ) preceededing a call to registerProcessor( Processor* )
an exception will be thrown.
1.8.5