Dear list,
in our current HPX driven project, we encountered the need
for a functionality, of which we are unsure if it
currently exists in HPX:
We picture in an abstract way the HPX runtime to behave
like the following:
Whenever a task is scheduled on a locality (with e.g.
async) this task is pushed into a FIFO-Queue and whenever
resources for computation become available the queue is
polled.
However we would need a functionality to modify the order
of execution of already scheduled tasks, e.g. replace this
(imaginary, behind-the-scenes) FIFO-Queue with a
Priority-Queue.
In other words:
Our program schedules a lot of tasks locally and continues
to schedule more and more batches of tasks locally over
time. However we would like tasks that are scheduled at a
later point in time to possible be run before
not-yet-started tasks that were scheduled earlier on. For
this, in our application each task can be assigned a
unique priority which is calculatable from the arguments
passed to the asynchronously called function.
Consider the following explanatory code:
for (int i = 0; (i < n); i++)
hpx::async<some_action>(float priority, T
other_parameters);
This code snippet would be called multiple times on the
same locality scheduling multiple batches of tasks of type
some_action. We now want all tasks of type some_action on
a certain locality to be executed in an order where the
priority is considered.
Note that it is no problem to run tasks with a lower
priority before other tasks with a higher priority, if
these higher priority tasks just was not scheduled for now
(think Priority-Queue functionality).
Is there a way to intervene with the hpx runtime on such a
low level?
Thanks in advance,
Kilian Werner
P.S.: The problem could also be solved by scheduling the
tasks of type some_action with an executor, which
internally forwards the tasks through a priority-queue
based semaphore, but it would be hard to allow just enough
tasks through the semaphore to fill all computational
resources.
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