[ruby-core:61452] [ruby-trunk - Feature #9632] [Open] [PATCH 0/2] speedup IO#close with linked-list from ccan

Issue #9632 has been reported by Eric Wong.

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Feature #9632: [PATCH 0/2] speedup IO#close with linked-list from ccan
https://bugs.ruby-lang.org/issues/9632

* Author: Eric Wong
* Status: Open
* Priority: Normal
* Assignee: Koichi Sasada
* Category: core
* Target version: current: 2.2.0
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This imports the ccan linked-list (BSD-MIT licensed version of the Linux kernel
linked list).  I cut out some of the unused str* code (only for debugging),
but it's still a big import of new code.  Modifications to existing code is
minimal, and it makes the living_threads iteration functions simpler.

The improvement is great, and there may be future places where we could
use a doubly linked list.

= vm->living_threads:

* before: st hash table had extra malloc overhead, and slow iteration due
to bad cache locality

* after: guaranteed O(1) insert/remove performance (branchless!)
iteration is still O(n), but performance is improved in IO#close
due to less pointer chasing


= IO#close: further improvement with second linked list

* before: IO#close is linear based on number of living threads
* after: IO#close is linear based on number of waiting threads

No extra malloc is needed (only 2 new pointers in existing structs)
for a secondary linked-list for waiting FDs.


I chose the ccan linked list over BSD <sys/queue.h> for two reasons:
1) insertion and removal are both branchless
2) locality is improved if a struct may be a member of multiple lists

git://80x24.org/ruby.git threads-list


---Files--------------------------------
0001-doubly-linked-list-from-ccan-to-manage-vm-living_thr.patch (68.1 KB)
0002-speedup-IO-close-with-many-living-threads.patch (2.86 KB)


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