TaskFunctors

Many functions a user might run through apply call into C. But what do you do when the C function you are calling is not threadsafe, or uses a reentrant/context based API?

The answer is to wrap the function in TaskFunctors, which will use an approximation of task local storage to ensure that each task calls its own copy of the function or C object you are invoking.

The primary application of this is Proj reproject, and Proj has a reentrant API based on context objects. So, to make this work, we need to create a new context object per task. We do this and pass the vector of Proj transformation objects to TaskFunctors, which apply and _maptasks dispatch on to behave correctly in this circumstance.

GeometryOpsCore.TaskFunctors Type

TaskFunctors(functors, tasks_per_thread)

A struct to hold the functors and tasks_per_thread, for internal use with _maptasks where functions have state that cannot be shared accross threads, such as Proj.Transformation.

functors must be an array or tuple of functors, one per thread, and tasks_per_thread must be an integer. This also allows you to control the number of tasks per thread that _maptasks launches, useful for tuning performance if you like.

source

"""
    TaskFunctors(functors, tasks_per_thread)

A struct to hold the functors and tasks_per_thread,
for internal use with `_maptasks` where functions have state
that cannot be shared accross threads, such as `Proj.Transformation`.

`functors` must be an array or tuple of functors, one per thread,
and `tasks_per_thread` must be an integer.  This also allows you to control
the number of tasks per thread that `_maptasks` launches, useful for tuning
performance if you like.
"""
struct TaskFunctors{F}
    functors::F
end

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