loading_shared_values/loading_cache'es iterators interface is dangerous/fragile because
iterator doesn't "lock" the entry it points to and if there is a
preemption point between aquiring non-end() iterator and its
dereferencing the corresponding cache entry may had already got evicted (for
whatever reason, e.g. cache size constraints or expiration) and then
dereferencing may end up in a use-after-free and we don't have any
protection against it in the value_extractor_fn today.
And this is in addition to #8920.
So, instead of trying to fix the iterator interface this patch kills two
birds in a single shot: we are ditching the iterators interface
completely and return value_ptr from find(...) instead - the same one we
are returning from loading_cache::get_ptr(...) asyncronous APIs.
A similar rework is done to a loading_shared_values loading_cache is
based on: we drop iterators interface and return
loading_shared_values::entry_ptr from find(...) instead.
loading_cache::value_ptr already takes care of "lock"ing the returned value so that it
would relain readable even if it's evicted from the cache by the time
one tries to read it. And of course it also takes care of updating the
last read time stamp and moving the corresponding item to the top of the
MRU list.
Fixes#8920
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
Message-Id: <20210817222404.3097708-1-vladz@scylladb.com>
Seastar recently lost support for the experimental Concepts Technical
Specification (TS) and gained support for C++20 concepts. Re-enable
concepts in Scylla by updating our use of concepts to the C++20
standard.
This change:
- peels off uses of the GCC6_CONCEPT macro
- removes inclusions of <seastar/gcc6-concepts.hh>
- replaces function-style concepts (no longer supported) with
equation-style concepts
- semicolons added and removed as needed
- deprecated std::is_pod replaced by recommended replacement
- updates return type constraints to use concepts instead of
type names (either std::same_as or std::convertible_to, with
std::same_as chosen when possible)
No attempt is made to improve the concepts; this is a specification
update only.
Message-Id: <20200531110254.2555854-1-avi@scylladb.com>
* seastar e708d1df3a...92365e7b87 (11):
> tests: distributed_test: convert to SEASTAR_TEST_CASE
> Merge "Avoid undefined behavior on future self move assignments" from Rafael
> Merge "C++20 support" from Avi
> optimized_optional: don't use experimental C++ features
> tests: scheduling_group_test: verify that later() doesn't modify the current group
> tests: demos: coroutine_demo: add missing include for open_file_dma()
> rpc: minor documentation improvements
> rpc: Assert that sinks are closed
> Merge "Fix most tests under valgrind" from Rafael
> distributed_test: Fix it on slow machines
> rpc_test: Make sure we always flush and close the sink
loading_shard_values.hh: added missing include for gcc6-concepts.hh,
exposed by the submodule update.
Frozen toolchain updated for the new valgrind dependency.
This patch silences those future discard warnings where it is clear that
discarding the future was actually the intent of the original author,
*and* they did the necessary precautions (handling errors). The patch
also adds some trivial error handling (logging the error) in some
places, which were lacking this, but otherwise look ok. No functional
changes.
Replace stdx::optional and stdx::string_view with the C++ std
counterparts.
Some instances of boost::variant were also replaced with std::variant,
namely those that called seastar::visit.
Scylla now requires GCC 8 to compile.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
Message-Id: <20190108111141.5369-1-duarte@scylladb.com>
This overload alows searching the elements by an arbitrary key as long as it is "hashable"
to the same values as the default key and if there is a comparator for
this new key.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
This class implements an key-value container that is populated
using the provided asynchronous callback.
The value is loaded when there are active references to the value for the given key.
Container ensures that only one entry is loaded per key at any given time.
The returned value is a lw_shared_ptr to the actual value.
The value for a specific key is immediately evicted when there are no
more references to it.
The container is based on the boost::intrusive::unordered_set and is rehashed (grown) if needed
every time a new value is added (asynchronously loaded).
The container has a rehash() method that would grow or shrink the container as needed
in order to get the load factor into the [0.25, 0.75] range.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
