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Restore some type-erasure to transform_mpi to avoid debug bloat #1390

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Restore some type-erasure to transform_mpi to avoid debug bloat #1390

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aae6046
Restore some type-erasure in transform_mpi to avoid debug bloat
msimberg Jan 17, 2025
243c360
Add a bit more type-erasure to transform_mpi
msimberg Jan 20, 2025
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43 changes: 13 additions & 30 deletions libs/pika/async_mpi/include/pika/async_mpi/transform_mpi.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,7 @@ namespace pika::mpi::experimental {
using pika::execution::experimental::continues_on;
using pika::execution::experimental::just;
using pika::execution::experimental::let_value;
using pika::execution::experimental::unique_any_sender;
using pika::execution::experimental::unpack;

// get mpi completion mode settings
Expand All @@ -63,40 +64,22 @@ namespace pika::mpi::experimental {
execution::thread_priority::boost :
execution::thread_priority::normal;

if (completions_inline)
{
auto f_completion = [mode, f = std::forward<F>(f)](auto&... args) mutable {
return just(std::forward_as_tuple(args...)) | unpack() |
dispatch_mpi(std::move(f)) | trigger_mpi(mode);
};
auto f_completion = [f = std::forward<F>(f), mode, completions_inline, p](
auto&... args) mutable -> unique_any_sender<> {
unique_any_sender<> s = just(std::forward_as_tuple(args...)) | unpack() |
dispatch_mpi(std::move(f)) | trigger_mpi(mode);
if (completions_inline) { return s; }
else { return std::move(s) | continues_on(default_pool_scheduler(p)); }
};
Comment on lines +67 to +73
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The inline branch returns s as an any sender - the non inline returns an any sender of an any sender - do they get collapsed into one create, or can/should we just expand the other branch to just return one?

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In if (completions_inline) { return s; }, s is not going to get wrapped again and even a move construction should be avoided because of NRVO.

In the second branch there will indeed be two unique_any_senders. It's a tradeoff between debug bloat and wrapping. The first commit on this PR (aae6046) doesn't type-erase s; it only type-erases whatever is returned. That on its own already significantly reduces bloat, and then type-erasing s reduces bloat a bit more.


if (requests_inline)
{
return std::forward<Sender>(sender) | let_value(std::move(f_completion));
}
else
{
return std::forward<Sender>(sender) | continues_on(mpi_pool_scheduler(p)) |
let_value(std::move(f_completion));
}
if (requests_inline)
{
return std::forward<Sender>(sender) | let_value(std::move(f_completion));
}
else
{
auto f_completion = [mode, p, f = std::forward<F>(f)](auto&... args) mutable {
return just(std::forward_as_tuple(args...)) | unpack() |
dispatch_mpi(std::move(f)) | trigger_mpi(mode) |
continues_on(default_pool_scheduler(p));
};

if (requests_inline)
{
return std::forward<Sender>(sender) | let_value(std::move(f_completion));
}
else
{
return std::forward<Sender>(sender) | continues_on(mpi_pool_scheduler(p)) |
let_value(std::move(f_completion));
}
return std::forward<Sender>(sender) | continues_on(mpi_pool_scheduler(p)) |
let_value(std::move(f_completion));
}
}

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