Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
When a template is instantiated in a header file which is included by many
source files, the compiler needs to compile it again and again.
ClangBuildAnalyzer helps find the worst cases of this happening, and one
of the worst happens to be
seastar::throw_with_backtrace<marshal_exception, sstring>
This specific template function takes (according to ClangBuildAnalyzer)
362 milliseconds to instantiate, and this is done 312 (!) times, because
it reaches virtually every Scylla source file via either types.hh or
compound.hh which use this idiom.
Unfortunately, C++ as it exists today does not have a mechanism to
avoid compiling a specific template instantiation if this was already
done in some other source file. But we can do this manually using
the C++11 feature of "extern template":
1. For a specific template instance, in this case
seastar::throw_with_backtrace<marhsal_exception, sstring>,
all source files except one specify it as "extern template".
This means that the code for it will NOT be built in this source
file, and the compiler assumes the linker will eventually supply it.
2. At the same time, one source file instantiates this template
instance once regularly, without "extern".
The numbers from ClangBuildAnalyzer suggest that this patch should
reduce total build time by 1% (in dev build mode), but this is hard to
measure in practice because the very long build time (210 CPU minutes on
my laptop) usually fluctuates by more than 1% in consecutive runs.
However, we've seen in the past that a good estimate of build time is
the total produced object size (du -bc build/dev/**/*.o). This patch
indeed reduces this total object size (in dev build mode) by exactly 1%.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20220105171453.308821-1-nyh@scylladb.com>
For better or worse, marshal_exception is used from utils/, and it's not good
to have utils/ depend on types.hh. Extract marshal_exception to make it possible
to remove the dependency.
