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Make Eio_linux.wakeup signal-safe #381
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I can fix the leak with barriers in the future, it's a pretty simple solution, I just have to write it. |
That sounds interesting. How does it work? |
Reinstating the current problem so we're on the same pageThe current problem is How barriers could helpLet there be two domains, At Issuing a barrier call makes sure any remote Domain switched fibers at least once, meaning they can't be in the middle of a In EIO, a window or epoch could be
BackgroundThis is mostly what RCU does, OpenBSD calls it SMR (Safe Memory Reclamation), DPDK calls it something else, but it's quite popular in C in order to properly know when you can How the barrier is implemented varies, it just needs to guarantee "wait till next epoch". The classic implementation on non preemptive kernels was pinning your thread to every different cpu and just continuing. Barriers need not to be synchronous as well, it's common to be able to "schedule a callback for the next window" so you could say "call Unix.close () in the next epoch". https://pdos.csail.mit.edu/6.828/2008/readings/rcu.pdf |
That would be useful, but I don't see how it could be implemented. It's not just |
We would have to make concessions like "you're only supposed to have Eio Domains", or X is only safe within an Eio context and unsafe if accessed outside. It would work out for this eventfd case though (I think). |
We want to use wakeup to e.g. let a Domainslib domain send a message to an Eio one. |
that's a bummer |
end = struct | ||
external eio_eventfd : int -> Unix.file_descr = "caml_eio_eventfd" | ||
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let free = Lf_queue.create () |
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Can we change this to something else, free
for me is the opposite of alloc
.
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What name do you suggest? It's the list of free FDs.
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free_list
, fd_list
, fd_pool
, free_pool
, but don't let this block you, there's no point in me bikeshedding it over this, if free
is of your preference please go ahead.
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OK, I'm going to keep it as it is. free_list
can be misread as a command just like free
can; fd_list
doesn't say why the FDs are there, which seems the most important thing; and the module already has pool
in the name. Also, it's only in scope for 6 lines.
So regarding this PR, I don't like the name |
This will eventually allow Waiters to be used from signal handlers and GC finalizers (once that's lock-free too). Previously, `wakeup` couldn't be used from a signal handler because it took a lock (to ensure that the eventfd wasn't closed while it wrote to it). Now, we avoid ever closing eventfds and simply keep free ones in a pool.
CHANGES: New features: - Add `Eio.Net.run_server` (@bikallem @talex5 ocaml-multicore/eio#408). Runs an accept loop in one or more domains, with cancellation and graceful shutdown, and an optional maximum number of concurrent connections. - Add `Buf_read.BE` and `LE` parsers (@Cjen1 ocaml-multicore/eio#399). Parse numbers in various binary formats. - Add `Eio.Buf_read.uint8` (@talex5 ocaml-multicore/eio#418). Performance: - Make `Eio.Condition` lock-free (@talex5 ocaml-multicore/eio#397 ocaml-multicore/eio#381). In addition to being faster, this allows using conditions in signal handlers. - Make `Eio.Semaphore` lock-free (@talex5 @polytypic ocaml-multicore/eio#398). - Make `Eio.Stream` lock-free when the capacity is zero (@talex5 ocaml-multicore/eio#413 ocaml-multicore/eio#411). - Make `Eio.Promise` lock-free (@talex5 ocaml-multicore/eio#401). Bug fixes: - eio_linux: call `Uring.submit` as needed (@talex5 @bikallem ocaml-multicore/eio#428). Previously, we could fail to submit a job promptly because the SQE queue was full. - Fix luv signals (@haesbaert ocaml-multicore/eio#412). `libuv` automatically retries polling if it gets `EINTR`, without giving OCaml signal handlers a chance to run. - eio_luv: fix some resource leaks (@talex5 @patricoferris ocaml-multicore/eio#421). - eio_luv: fix "unavailable signal" error on Windows (@talex5 ocaml-multicore/eio#420, reported by @nojb). - Fix `Buf_write.BE.uint48` and `LE.uint48` (@adatario ocaml-multicore/eio#418). Documentation: - Add example programs (@talex5 ocaml-multicore/eio#389). - Update network examples to use `run_server` (@talex5 ocaml-multicore/eio#417). - Add a warning to the tutorial about `Fiber.first` (@talex5 ocaml-multicore/eio#394). - Clarify the epoch used for `Eio.Time.now` (@bikallem ocaml-multicore/eio#395). - Describe `secure_random` as an infinite source (@patricoferris ocaml-multicore/eio#426). - Update README for OCaml 5 release (@talex5 ocaml-multicore/eio#384 ocaml-multicore/eio#391 ocaml-multicore/eio#393). Other changes: - Delay setting `SIGPIPE` handler until the `run` function is called (@talex5 ocaml-multicore/eio#420). - Remove debug-level logging (@talex5 ocaml-multicore/eio#403). - eio-luv: improve `process.md` test (@smondet ocaml-multicore/eio#414). - Update to Dune 3 (@talex5 ocaml-multicore/eio#410). - Remove test dependency on Astring (@talex5 ocaml-multicore/eio#402 ocaml-multicore/eio#404). - Simplify cancellation logic (@talex5 ocaml-multicore/eio#396). - time: `Mtime.Spand.to_s` has been deprecated in mtime 2.0.0 (@bikallem ocaml-multicore/eio#385).
CHANGES: New features: - Add `Eio.Net.run_server` (@bikallem @talex5 ocaml-multicore/eio#408). Runs an accept loop in one or more domains, with cancellation and graceful shutdown, and an optional maximum number of concurrent connections. - Add `Buf_read.BE` and `LE` parsers (@Cjen1 ocaml-multicore/eio#399). Parse numbers in various binary formats. - Add `Eio.Buf_read.uint8` (@talex5 ocaml-multicore/eio#418). Performance: - Make `Eio.Condition` lock-free (@talex5 ocaml-multicore/eio#397 ocaml-multicore/eio#381). In addition to being faster, this allows using conditions in signal handlers. - Make `Eio.Semaphore` lock-free (@talex5 @polytypic ocaml-multicore/eio#398). - Make `Eio.Stream` lock-free when the capacity is zero (@talex5 ocaml-multicore/eio#413 ocaml-multicore/eio#411). - Make `Eio.Promise` lock-free (@talex5 ocaml-multicore/eio#401). Bug fixes: - eio_linux: call `Uring.submit` as needed (@talex5 @bikallem ocaml-multicore/eio#428). Previously, we could fail to submit a job promptly because the SQE queue was full. - Fix luv signals (@haesbaert ocaml-multicore/eio#412). `libuv` automatically retries polling if it gets `EINTR`, without giving OCaml signal handlers a chance to run. - eio_luv: fix some resource leaks (@talex5 @patricoferris ocaml-multicore/eio#421). - eio_luv: fix "unavailable signal" error on Windows (@talex5 ocaml-multicore/eio#420, reported by @nojb). - Fix `Buf_write.BE.uint48` and `LE.uint48` (@adatario ocaml-multicore/eio#418). Documentation: - Add example programs (@talex5 ocaml-multicore/eio#389). - Update network examples to use `run_server` (@talex5 ocaml-multicore/eio#417). - Add a warning to the tutorial about `Fiber.first` (@talex5 ocaml-multicore/eio#394). - Clarify the epoch used for `Eio.Time.now` (@bikallem ocaml-multicore/eio#395). - Describe `secure_random` as an infinite source (@patricoferris ocaml-multicore/eio#426). - Update README for OCaml 5 release (@talex5 ocaml-multicore/eio#384 ocaml-multicore/eio#391 ocaml-multicore/eio#393). Other changes: - Delay setting `SIGPIPE` handler until the `run` function is called (@talex5 ocaml-multicore/eio#420). - Remove debug-level logging (@talex5 ocaml-multicore/eio#403). - eio-luv: improve `process.md` test (@smondet ocaml-multicore/eio#414). - Update to Dune 3 (@talex5 ocaml-multicore/eio#410). - Remove test dependency on Astring (@talex5 ocaml-multicore/eio#402 ocaml-multicore/eio#404). - Simplify cancellation logic (@talex5 ocaml-multicore/eio#396). - time: `Mtime.Spand.to_s` has been deprecated in mtime 2.0.0 (@bikallem ocaml-multicore/eio#385).
CHANGES: New features: - Add `Eio.Net.run_server` (@bikallem @talex5 ocaml-multicore/eio#408). Runs an accept loop in one or more domains, with cancellation and graceful shutdown, and an optional maximum number of concurrent connections. - Add `Buf_read.BE` and `LE` parsers (@Cjen1 ocaml-multicore/eio#399). Parse numbers in various binary formats. - Add `Eio.Buf_read.uint8` (@talex5 ocaml-multicore/eio#418). Performance: - Make `Eio.Condition` lock-free (@talex5 ocaml-multicore/eio#397 ocaml-multicore/eio#381). In addition to being faster, this allows using conditions in signal handlers. - Make `Eio.Semaphore` lock-free (@talex5 @polytypic ocaml-multicore/eio#398). - Make `Eio.Stream` lock-free when the capacity is zero (@talex5 ocaml-multicore/eio#413 ocaml-multicore/eio#411). - Make `Eio.Promise` lock-free (@talex5 ocaml-multicore/eio#401). Bug fixes: - eio_linux: call `Uring.submit` as needed (@talex5 @bikallem ocaml-multicore/eio#428). Previously, we could fail to submit a job promptly because the SQE queue was full. - Fix luv signals (@haesbaert ocaml-multicore/eio#412). `libuv` automatically retries polling if it gets `EINTR`, without giving OCaml signal handlers a chance to run. - eio_luv: fix some resource leaks (@talex5 @patricoferris ocaml-multicore/eio#421). - eio_luv: fix "unavailable signal" error on Windows (@talex5 ocaml-multicore/eio#420, reported by @nojb). - Fix `Buf_write.BE.uint48` and `LE.uint48` (@adatario ocaml-multicore/eio#418). Documentation: - Add example programs (@talex5 ocaml-multicore/eio#389). - Update network examples to use `run_server` (@talex5 ocaml-multicore/eio#417). - Add a warning to the tutorial about `Fiber.first` (@talex5 ocaml-multicore/eio#394). - Clarify the epoch used for `Eio.Time.now` (@bikallem ocaml-multicore/eio#395). - Describe `secure_random` as an infinite source (@patricoferris ocaml-multicore/eio#426). - Update README for OCaml 5 release (@talex5 ocaml-multicore/eio#384 ocaml-multicore/eio#391 ocaml-multicore/eio#393). Other changes: - Delay setting `SIGPIPE` handler until the `run` function is called (@talex5 ocaml-multicore/eio#420). - Remove debug-level logging (@talex5 ocaml-multicore/eio#403). - eio-luv: improve `process.md` test (@smondet ocaml-multicore/eio#414). - Update to Dune 3 (@talex5 ocaml-multicore/eio#410). - Remove test dependency on Astring (@talex5 ocaml-multicore/eio#402 ocaml-multicore/eio#404). - Simplify cancellation logic (@talex5 ocaml-multicore/eio#396). - time: `Mtime.Spand.to_s` has been deprecated in mtime 2.0.0 (@bikallem ocaml-multicore/eio#385).
CHANGES: New features: - Add `Eio.Net.run_server` (@bikallem @talex5 ocaml-multicore/eio#408). Runs an accept loop in one or more domains, with cancellation and graceful shutdown, and an optional maximum number of concurrent connections. - Add `Buf_read.BE` and `LE` parsers (@Cjen1 ocaml-multicore/eio#399). Parse numbers in various binary formats. - Add `Eio.Buf_read.uint8` (@talex5 ocaml-multicore/eio#418). Performance: - Make `Eio.Condition` lock-free (@talex5 ocaml-multicore/eio#397 ocaml-multicore/eio#381). In addition to being faster, this allows using conditions in signal handlers. - Make `Eio.Semaphore` lock-free (@talex5 @polytypic ocaml-multicore/eio#398). - Make `Eio.Stream` lock-free when the capacity is zero (@talex5 ocaml-multicore/eio#413 ocaml-multicore/eio#411). - Make `Eio.Promise` lock-free (@talex5 ocaml-multicore/eio#401). Bug fixes: - eio_linux: call `Uring.submit` as needed (@talex5 @bikallem ocaml-multicore/eio#428). Previously, we could fail to submit a job promptly because the SQE queue was full. - Fix luv signals (@haesbaert ocaml-multicore/eio#412). `libuv` automatically retries polling if it gets `EINTR`, without giving OCaml signal handlers a chance to run. - eio_luv: fix some resource leaks (@talex5 @patricoferris ocaml-multicore/eio#421). - eio_luv: fix "unavailable signal" error on Windows (@talex5 ocaml-multicore/eio#420, reported by @nojb). - Fix `Buf_write.BE.uint48` and `LE.uint48` (@adatario ocaml-multicore/eio#418). Documentation: - Add example programs (@talex5 ocaml-multicore/eio#389). - Update network examples to use `run_server` (@talex5 ocaml-multicore/eio#417). - Add a warning to the tutorial about `Fiber.first` (@talex5 ocaml-multicore/eio#394). - Clarify the epoch used for `Eio.Time.now` (@bikallem ocaml-multicore/eio#395). - Describe `secure_random` as an infinite source (@patricoferris ocaml-multicore/eio#426). - Update README for OCaml 5 release (@talex5 ocaml-multicore/eio#384 ocaml-multicore/eio#391 ocaml-multicore/eio#393). Other changes: - Delay setting `SIGPIPE` handler until the `run` function is called (@talex5 ocaml-multicore/eio#420). - Remove debug-level logging (@talex5 ocaml-multicore/eio#403). - eio-luv: improve `process.md` test (@smondet ocaml-multicore/eio#414). - Update to Dune 3 (@talex5 ocaml-multicore/eio#410). - Remove test dependency on Astring (@talex5 ocaml-multicore/eio#402 ocaml-multicore/eio#404). - Simplify cancellation logic (@talex5 ocaml-multicore/eio#396). - time: `Mtime.Spand.to_s` has been deprecated in mtime 2.0.0 (@bikallem ocaml-multicore/eio#385).
This will eventually allow Waiters to be used from signal handlers and GC finalizers (once that's lock-free too).
Previously,
wakeup
couldn't be used from a signal handler because it took a lock (to ensure that the eventfd wasn't closed while it wrote to it). Now, we avoid ever closing eventfds and simply keep free ones in a pool./cc @haesbaert