From: samuel@...
Date: 2020-04-24T10:23:00+00:00
Subject: [ruby-core:98055] [Ruby master Feature#8215] Support accessing Fiber-locals and backtraces for a Fiber

Issue #8215 has been updated by ioquatix (Samuel Williams).


> It's of course unacceptable if a Ruby implementation behaves unsafely (e.g., crashes or loses fiber local variable) for this, so it is a relevant concern for this issue.

We already have situations in JRuby and TruffleRuby where unsynchronized access to shared mutable state can cause a crash or data corruption. So why is this different?

If you believe it's important, then I defer to your judgement. However, from my point of view:

- This method should not be invoked across threads.
- This method should not need to be thread safe.
- The GVL might make it safe but it shouldn't be guaranteed.
- Maybe we need annotations or other documentation to explain this.

> If you think we need the ability to access another Fiber's locals, could you show some examples?

The reason to access other fiber locals is mostly for debugging purposes. In Async, we make a list of tasks:

```
 4874m43s     info: Falcon::Controller::Proxy [oid=0x2b28b0f0d558] [pid=324886] [2020-04-24 09:55:55 +0000]
                  | #<Async::Reactor:0x2b28b10316c8 1 children running>
                  |         #<Async::Task:0x2b28b1031498 (running)>
                  |                 #<Async::Task:0x2b28b10312e0 waiting for signal USR1 (running)>
                  |                 #<Async::Task:0x2b28b1030930 accepting secure connection #<Addrinfo: [::ffff:34.228.115.75]:26564 TCP> (running)>
                  |                         #<Async::Task:0x2b28b1079b1c connected to #<Addrinfo: /srv/http/www.oriontransfer.co.nz/application.ipc SOCK_STREAM> [fd=17] (complete)>
                  |                                 #<Async::Task:0x2b28b109a7b8 h2 reading data for Async::HTTP::Protocol::HTTP2::Client. (running)>
                  |                         #<Async::Task:0x2b28b10869e8 Reading h2 requests for Async::HTTP::Protocol::HTTP2::Server. (complete)>
                  |                                 #<Async::Task:0x2b28b13a2dc0 connected to #<Addrinfo: /srv/http/www.codeotaku.com/application.ipc SOCK_STREAM> [fd=16] (complete)>
                  |                                         #<Async::Task:0x2b28b12fb8f4 h2 reading data for Async::HTTP::Protocol::HTTP2::Client. (running)>
                  |                         #<Async::Task:0x2b28b0fefe30 Reading h2 requests for Async::HTTP::Protocol::HTTP2::Server. (running)>
                  |                                 #<Async::Task:0x2b28b1004b64 h2 reading data for Async::HTTP::Protocol::HTTP2::Server. (running)>
```

When something is going wrong, the ability to dig into the fiber state is very useful. My plan is to make debugging tools to expose this more easily but I can't do it if there are no methods to access the state.


----------------------------------------
Feature #8215: Support accessing Fiber-locals and backtraces for a Fiber
https://bugs.ruby-lang.org/issues/8215#change-85283

* Author: halorgium (Tim Carey-Smith)
* Status: Assigned
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
----------------------------------------
=begin
As part of debugging celluloid, I have been wanting to diagnose where the Fibers are running and their various locals.

I would expect the following to work.

  Thread.current[:key] = "outside"
  fiber = Fiber.new do
    Thread.current[:key] = "inside"
    Fiber.yield
  end
  fiber.resume
  fiber[:key] == "inside" # true
  fiber.backtrace # ...

I also wonder whether (({Fiber#[]})) should be implemented, so (({Fiber.current[:key]})) is possible.

For reference, here is the issue on the rubinius issue tracker: ((<"github/rubinius/rubinius/2200"|URL:https://github.com/rubinius/rubinius/issues/2200>))
=end


---Files--------------------------------
0001-cont.c-fiber-local-accessors.patch (2.94 KB)


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