# Parallelization control¶

This module defines the singleton class Parallelism to govern the parallelization of computations in some specific topics. It allows the user to set the number of processes to be used for parallelization.

Some examples of use are provided in the documentation of sage.tensor.modules.comp.Components.contract().

AUTHORS:

• Marco Mancini, Eric Gourgoulhon, Michal Bejger (2015): initial version
class sage.parallel.parallelism.Parallelism

Singleton class for managing the number of processes used in parallel computations involved in various fields.

EXAMPLES:

The number of processes is initialized to 1 (no parallelization) for each field:

sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 1


Using 4 processes to parallelize tensor computations:

sage: Parallelism().set('tensor', nproc=4)
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 4
sage: Parallelism().get('tensor')
4


Using 6 processes to parallelize all types of computations:

sage: Parallelism().set(nproc=6)
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 6
- tensor computations: 6


Using all the cores available on the computer to parallelize tensor computations:

sage: Parallelism().set('tensor')
sage: Parallelism()  # random (depends on the computer)
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 8


Using all the cores available on the computer to parallelize all types of computations:

sage: Parallelism().set()
sage: Parallelism()  # random (depends on the computer)
Number of processes for parallelization:
- linbox computations: 8
- tensor computations: 8


Switching off all parallelizations:

sage: Parallelism().set(nproc=1)

get(field)

Return the number of processes which will be used in parallel computations regarding some specific field.

INPUT:

• field – string specifying the part of Sage involved in parallel computations

OUTPUT:

• number of processes used in parallelization of computations pertaining to field

EXAMPLES:

The default is a single process (no parallelization):

sage: Parallelism().reset()
sage: Parallelism().get('tensor')
1


Asking for parallelization on 4 cores:

sage: Parallelism().set('tensor', nproc=4)
sage: Parallelism().get('tensor')
4

get_all()

Return the number of processes which will be used in parallel computations in all fields

OUTPUT:

• dictionary of the number of processes, with the computational fields as keys

EXAMPLES:

sage: Parallelism().reset()
sage: Parallelism().get_all()
{'linbox': 1, 'tensor': 1}


Asking for parallelization on 4 cores:

sage: Parallelism().set(nproc=4)
sage: Parallelism().get_all()
{'linbox': 4, 'tensor': 4}

get_default()

Return the default number of processes to be launched in parallel computations.

EXAMPLES:

A priori, the default number of process for parallelization is the total number of cores found on the computer:

sage: Parallelism().reset()
sage: Parallelism().get_default()  # random (depends on the computer)
8


It can be changed via set_default():

sage: Parallelism().set_default(nproc=4)
sage: Parallelism().get_default()
4

reset()

Put the singleton object Parallelism() in the same state as immediately after its creation.

EXAMPLES:

State of Parallelism() just after its creation:

sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 1
sage: Parallelism().get_default()  # random (depends on the computer)
8


Changing some values:

sage: Parallelism().set_default(6)
sage: Parallelism().set()
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 6
- tensor computations: 6
sage: Parallelism().get_default()
6


Back to the initial state:

sage: Parallelism().reset()
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 1
sage: Parallelism().get_default()  # random (depends on the computer)
8

set(field=None, nproc=None)

Set the number of processes to be launched for parallel computations regarding some specific field.

INPUT:

• field – (default: None) string specifying the computational field for which the number of parallel processes is to be set; if None, all fields are considered
• nproc – (default: None) number of processes to be used for parallelization; if None, the number of processes will be set to the default value, which, unless redefined by set_default(), is the total number of cores found on the computer.

EXAMPLES:

The default is a single processor (no parallelization):

sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 1


Asking for parallelization on 4 cores in tensor algebra:

sage: Parallelism().set('tensor', nproc=4)
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 4


Using all the cores available on the computer:

sage: Parallelism().set('tensor')
sage: Parallelism()  # random (depends on the computer)
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 8


Using 6 cores in all parallelizations:

sage: Parallelism().set(nproc=6)
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 6
- tensor computations: 6


Using all the cores available on the computer in all parallelizations:

sage: Parallelism().set()
sage: Parallelism()  # random (depends on the computer)
Number of processes for parallelization:
- linbox computations: 8
- tensor computations: 8


Switching off the parallelization:

sage: Parallelism().set(nproc=1)
sage: Parallelism()
Number of processes for parallelization:
- linbox computations: 1
- tensor computations: 1

set_default(nproc=None)

Set the default number of processes to be launched in parallel computations.

INPUT:

• nproc – (default: None) default number of processes; if None, the number of processes will be set to the total number of cores found on the computer.

EXAMPLES:

A priori the default number of process for parallelization is the total number of cores found on the computer:

sage: Parallelism().get_default()  # random (depends on the computer)
8


Changing it thanks to set_default:

sage: Parallelism().set_default(nproc=4)
sage: Parallelism().get_default()
4


Setting it back to the total number of cores available on the computer:

sage: Parallelism().set_default()
sage: Parallelism().get_default()  # random (depends on the computer)
8