Task Constraints

It is possible to define constraints for each task. To this end, the @constraint (or @Constraint) decorator followed by the desired constraints needs to be placed ON TOP of the @task decorator (Code 72).

Important

Please note the the order of @constraint and @task decorators is important.

Code 72 Constrained task example

from pycompss.api.task import task
from pycompss.api.constraint import constraint
from pycompss.api.parameter import INOUT

@constraint(computing_units="4")
@task(c=INOUT)
def func(a, b, c):
     c += a * b
     ...

This decorator enables the user to set the particular constraints for each task, such as the amount of Cores required explicitly. Alternatively, it is also possible to indicate that the value of a constraint is specified in a environment variable (Code 73). A full description of the supported constraints can be found in Table 14.

For example:

Code 73 Constrained task with environment variable example

from pycompss.api.task import task
from pycompss.api.constraint import constraint
from pycompss.api.parameter import INOUT

@constraint(computing_units="4",
            app_software="numpy,scipy,gnuplot",
            memory_size="$MIN_MEM_REQ")
@task(c=INOUT)
def func(a, b, c):
     c += a * b
     ...

Or another example requesting a CPU core and a GPU (Code 74).

Code 74 CPU and GPU constrained task example

from pycompss.api.task import task
from pycompss.api.constraint import constraint

@constraint(processors=[{'processorType':'CPU', 'computingUnits':'1'},
                        {'processorType':'GPU', 'computingUnits':'1'}])
@task(returns=1)
def func(a, b, c):
     ...
     return result

When the task requests a GPU, COMPSs provides the information about the assigned GPU through the COMPSS_BINDED_GPUS, CUDA_VISIBLE_DEVICES and GPU_DEVICE_ORDINAL environment variables. This information can be gathered from the task code in order to use the GPU.

Please, take into account that in order to respect the constraints, the peculiarities of the infrastructure must be defined in the resources.xml file.