these unused includes were identifier by clang-include-cleaner. after
auditing these source files, all of the reports have been confirmed.
please note, because quite a few source files relied on
`utils/to_string.hh` to pull in the specialization of
`fmt::formatter<std::optional<T>>`, after removing
`#include <fmt/std.h>` from `utils/to_string.hh`, we have to
include `fmt/std.h` directly.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
get0() dates back from the days where Seastar futures carried tuples, and
get0() was a way to get the first (and usually only) element. Now
it's a distraction, and Seastar is likely to deprecate and remove it.
Replace with seastar::future::get(), which does the same thing.
this change prepares for replacing `seastar::future::get0()` with
`seastar::future::get()`. the former's return type is a plain `T`,
while the latter is `T&&`. in this case `T` is
`boost::outcome::result<..>`. in order to extract its `error_type`,
we need to get its decayed type. since `std::remove_reference_t<T>`
also returns `T`, let's use it so it works with both `get0()` and `get()`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Checking a concept in a requires-expression requires an additional
requires keyword. Moreover, the constraint is incorrect (at least
all callers pass a T, not a result<T>), so remove it.
Found by gcc 12.
Adds a result-aware counterpart to seastar::repeat. The new function
does not base on seastar::repeat, but rather is a rewrite of the
original (using a coroutine instead of an open-coded task). The main
consequence of using a coroutine is that exceptions from AsyncAction
need to be thrown once more.
Adds a result-aware counterpart to seastar::do_until. The new function
does not base on seastar::do_until, but rather is a rewrite of the
original (using a coroutine instead of an open-coded task). The main
consequence of using a coroutine is that exceptions from StopCondition
or AsyncAction need to be thrown once more.
Adds result-aware counterparts to all seastar::map_reduce overloads.
Fortunately, it was possible to implement the functions by basing them
on seastar::map_reduce and get the same number of allocation. The only
exception happens when reducer::get() returns a non-ready future, which
doesn't seem to happen on the read coordinator path.
It now resembles the original parallel_for_each more, but uses a
coroutine instead of a custom `task` to collect not-ready futures.
Although the usage of a coroutine saves on allocations, the drawback is
that there is currently no way to co_await on a future and handle its
exception without throwing or without unconditionally allocating a
then_wrapped or handle_exception continuation - so it introduces a
rethrow.
Furthermore, now failed results and exceptions are treated as equals.
Previously, in case one parallel invocation returned failed result and
another returned an exception, the exception would always be returned.
Now, the failed result/exception of the invocation with the lowest index
is always preferred, regardless of the failure type.
The reimplementation manages to save about 350-400 instructions, one
task and one allocation in the perf_simple_query benchmark in write
mode.
Results from `perf_simple_query --smp 1 --operations-per-shard 1000000
--write` (before vs. after):
```
126872.54 tps ( 67.2 allocs/op, 14.2 tasks/op, 52404 insns/op)
126532.13 tps ( 67.2 allocs/op, 14.2 tasks/op, 52408 insns/op)
126864.99 tps ( 67.2 allocs/op, 14.2 tasks/op, 52428 insns/op)
127073.10 tps ( 67.2 allocs/op, 14.2 tasks/op, 52404 insns/op)
126895.85 tps ( 67.2 allocs/op, 14.2 tasks/op, 52411 insns/op)
127894.02 tps ( 66.2 allocs/op, 13.2 tasks/op, 52036 insns/op)
127671.51 tps ( 66.2 allocs/op, 13.2 tasks/op, 52042 insns/op)
127541.42 tps ( 66.2 allocs/op, 13.2 tasks/op, 52044 insns/op)
127409.10 tps ( 66.2 allocs/op, 13.2 tasks/op, 52052 insns/op)
127831.30 tps ( 66.2 allocs/op, 13.2 tasks/op, 52043 insns/op)
```
Test: unit(dev), unit(result_utils_test, debug)
Segregates result utilities into:
- result.hh - basic definitions related to results with exception
containers,
- result_combinators.hh - combinators for working with results in
conjunction with futures,
- result_loop.hh - loop-like combinators, currently has only
result_parallel_for_each.
The motivation for the split is:
1. In headers, usually only result.hh will be needed, so no need to
force most .cc files to compile definitions from other files,
2. Less files need to be recompiled when a combinator is added to
result_combinators or result_loop.
As a bonus, `result_with_exception` was moved from `utils::internal` to
just `utils`.
