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
We will need them to replace bytes with managed_bytes in some places in an
upcoming patch.
The change to configure.py is necessary because opearator<< links to to_hex
in bytes.cc.
Remove the following bits of `managed_bytes` since they are unused:
* `with_linearized_managed_bytes` function template
* `linearization_context_guard` RAII wrapper class for managing
`linearization_context` instances.
* `do_linearize` function
* `linearization_context` class
Since there is no more public or private methods in `managed_class`
to linearize the value except for explicit `with_linearized()`,
which doesn't use any of aforementioned parts, we can safely remove
these.
Signed-off-by: Pavel Solodovnikov <pa.solodovnikov@scylladb.com>
do_linearize() is an impure function as it changes state
in linearization_context. Extract the pure parts into a new
do_linearize_pure(). This will be used to linearize managed_bytes
without a linearization_context, during the transition period where
fragmented and non-fragmented values coexist.
Since linearization_context is thread_local every time it is accessed
the compiler needs to emit code that checks if it was already
constructed and does so if it wasn't. Moreover, upon leaving the context
from the outermost scope the map needs to be cleared.
All these operations impose some performance overhead and aren't really
necessary if no buffers were linearised (the expected case). This patch
rearranges the code so that lineatization_context is trivially
constructible and the map is cleared only if it was modified.
It is needed for noexcept destruction, which we need for exception
safety in higher layers.
According to [1], erase() only throws if key comparison throws, and in
our case it doesn't.
[1] http://en.cppreference.com/w/cpp/container/unordered_map/erase
A large managed_bytes blob can be scattered in lsa memory. Usually this is
fine, but someone we want to examine it in place without copying it out, but
using contiguous iterators for efficiency.
For this use case, introduce with_linearized_managed_bytes(Func),
which runs a function in a "linearization context". Within the linearization
context, reads of managed_bytes object will see temporarily linearized copies
instead of scattered data.
