the log.hh under the root of the tree was created keep the backward
compatibility when seastar was extracted into a separate library.
so log.hh should belong to `utils` directory, as it is based solely
on seastar, and can be used all subsystems.
in this change, we move log.hh into utils/log.hh to that it is more
modularized. and this also improves the readability, when one see
`#include "utils/log.hh"`, it is obvious that this source file
needs the logging system, instead of its own log facility -- please
note, we do have two other `log.hh` in the tree.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
as alien::run_on() requires the function to be noexcept, let's
make this explicit. also, this paves the road to the type constraint
added to `alien::run_on()`. the type contraint will enforce this
requirement to the function passed to `alien::run_on()`.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13375
The Wasm compilation is a slow, low priority task, so it should
not compete with reactor threads or the networking core.
To achieve that, we increase the niceness of the thread by 10.
An alternative solution would be to set the priority using
pthread_setschedparam, but it's not currently feasible,
because as long as we're using the SCHED_OTHER policy for our
threads, we cannot select any other priority than 0.
Closes#13307
as in main(), we use `stop_signal` to handle SIGINT and SIGTERM,
so when scylla receives a SIGTERM, the corresponding signal handler
could get called on any threads created by this program. so there
is chance that the alien_runner thread could be choosen to run the
signal handler setup by `main()`, but that signal handler assumes
the availability of Seastar reactor. unfortunately, we don't have
a Seastar reactor in alien thread. the same applies to Seastar's
`thread_pool` which handles the slow and blocking POSIX calls typically
used for interacting with files.
so, in this change, we use the same approach as Seastar's
`thread_pool::work()` -- just block all signals, so the alien threads
used by wasm for compiling UDF won't handle the signals using the
handlers planted by `main()`.
Fixes#13228
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13233
The compilation of wasm UDFs is performed by a call to a foreign
function, which cannot be divided with yielding points and, as a
result, causes long reactor stalls for big UDFs.
We avoid them by submitting the compilation task to a non-seastar
std::thread, and retrieving the result using seastar::alien.
The thread is created at the start of the program. It executes
tasks from a queue in an infinite loop.
All seastar shards reference the thread through a std::shared_ptr
to a `alien_thread_runner`.
Considering that the compilation takes a long time anyway, the
alien_thread_runner is implemented with focus on simplicity more
than on performance. The tasks are stored in an std::queue, reading
and writing to it is synchronized using an std::mutex for reading/
writing to the queue, and an std::condition_variable waiting until
the queue has elements.
When the destructor of the alien runner is called, an std::nullopt
sentinel is pushed to the queue, and after all remaining tasks are
finished and the sentinel is read, the thread finishes.
