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
Fixes#865
(Some) gcc 5 (5.3.0 for me) on ubuntu will generate errors on
compilation of this code (compiling logalloc_test). The memcpy
to inline storage seems to confuse the compiler.
Simply change to std::copy, which shuts the compiler up.
Any decent stl should convert primitive std::copy to memcpy
anyway, but since it is also the inline (small storage),
it should not matter which way.
Message-Id: <1456931988-5876-4-git-send-email-calle@scylladb.com>
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.
blob_storage defined with attribute packed which makes its alignment
requirement equal 1. This means that its members may be unaligned.
GCC is obviously aware of that and will generate appropriate code
(and not generate ubsan checks). However, there are few places where
members of blob_storage are accessed via pointers, these have to be
wrapped by unaligned_cast<> to let the compiler know that the location
pointed to may be not aligned properly.
Signed-off-by: Paweł Dziepak <pdziepak@scylladb.com>
Instead of allocating a single blob_storage, chain multiple blob_storage
objects in a list, each limited not to exceed the allocation_strategy's
max_preferred_allocation_size. This allows lsa to allocate each blob_storage
object as an lsa managed object that can be migrated in memory.
Also provide linearize()/scatter() methods that can be used to temporarily
consolidate the storage into a single blob_storage. This makes the data
contiguous, so we can use a regular bytes_view to examine it.
The migrator tells lsa how to move an object when it is compacted.
Currently it is a function pointer, which means we must know how to move
the object at compile time. Making it an object allows us to build the
migration function at runtime, making it suitable for runtime-defined types
(such as tuples and user-defined types).
In the future, we may also store the size there for fixed-size types,
reducing lsa overhead.
C++ variable templates would have made this patch smaller, but unfortunately
they are only supported on gcc 5+.
