Server panic on player disconnect

[jivvy]

Can be reproduced with the combat example:

1. Connect two clients to the combat example
2. Disconnect one of them

Backtrace

thread '<unnamed>' panicked at 'there is no reactor running, must be called from the context of a Tokio 1.x runtime', /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/context.rs:56:13
stack backtrace:
   0: rust_begin_unwind
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/panicking.rs:65:14
   2: core::panicking::panic_display
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/panicking.rs:139:5
   3: core::panicking::panic_str
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/panicking.rs:123:5
   4: core::option::expect_failed
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/option.rs:1876:5
   5: core::option::Option<T>::expect
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/context.rs:56:13
   6: tokio::runtime::context::time_handle::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/context.rs:56:13
   7: std::thread::local::LocalKey<T>::try_with
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/thread/local.rs:446:16
   8: tokio::runtime::context::time_handle
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/runtime/context.rs:54:15
   9: tokio::time::driver::handle::Handle::current
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/time/driver/handle.rs:58:13
  10: tokio::time::driver::sleep::Sleep::new_timeout
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/time/driver/sleep.rs:260:22
  11: tokio::time::timeout::timeout
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.21.2/src/time/timeout.rs:79:27
  12: <valence::server::packet_controller::PlayPacketController as core::ops::drop::Drop>::drop
             at /home/jivvy/.cargo/git/checkouts/valence-a175964027d82956/43435b8/src/server/packet_controller.rs:218:30
  13: core::ptr::drop_in_place<valence::server::packet_controller::PlayPacketController>
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/ptr/mod.rs:491:1
  14: valence::client::Client<C>::handle_serverbound_packets
             at /home/jivvy/.cargo/git/checkouts/valence-a175964027d82956/43435b8/src/client.rs:911:9
  15: valence::server::do_update_loop::{{closure}}
             at /home/jivvy/.cargo/git/checkouts/valence-a175964027d82956/43435b8/src/server.rs:407:13
  16: <rayon::iter::for_each::ForEachConsumer<F> as rayon::iter::plumbing::Folder<T>>::consume
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/for_each.rs:47:9
  17: <rayon::iter::map::MapFolder<C,F> as rayon::iter::plumbing::Folder<T>>::consume
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/map.rs:239:19
  18: <rayon::iter::map::MapFolder<C,F> as rayon::iter::plumbing::Folder<T>>::consume
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/map.rs:239:19
  19: <rayon::iter::filter_map::FilterMapFolder<C,P> as rayon::iter::plumbing::Folder<T>>::consume
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/filter_map.rs:124:24
  20: rayon::iter::plumbing::Folder::consume_iter
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/plumbing/mod.rs:179:20
  21: rayon::iter::plumbing::Producer::fold_with
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/plumbing/mod.rs:110:9
  22: rayon::iter::plumbing::bridge_producer_consumer::helper
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/plumbing/mod.rs:438:13
  23: rayon::iter::plumbing::bridge_producer_consumer::helper::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-1.5.3/src/iter/plumbing/mod.rs:418:21
  24: rayon_core::join::join_context::call_a::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/join/mod.rs:124:17
  25: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/panic/unwind_safe.rs:271:9
  26: std::panicking::try::do_call
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panicking.rs:483:40
  27: std::panicking::try
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panicking.rs:447:19
  28: std::panic::catch_unwind
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panic.rs:137:14
  29: rayon_core::unwind::halt_unwinding
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/unwind.rs:17:5
  30: rayon_core::join::join_context::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/join/mod.rs:141:24
  31: rayon_core::registry::Registry::in_worker_cold::{{closure}}::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:468:21
  32: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute::call::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/job.rs:113:21
  33: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/core/src/panic/unwind_safe.rs:271:9
  34: std::panicking::try::do_call
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panicking.rs:483:40
  35: std::panicking::try
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panicking.rs:447:19
  36: std::panic::catch_unwind
             at /rustc/bf15a9e5263fcea065a7ae9c179b2d24c2deb670/library/std/src/panic.rs:137:14
  37: rayon_core::unwind::halt_unwinding
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/unwind.rs:17:5
  38: <rayon_core::job::StackJob<L,F,R> as rayon_core::job::Job>::execute
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/job.rs:119:38
  39: rayon_core::job::JobRef::execute
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:729:17
  40: rayon_core::registry::WorkerThread::execute
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:752:9
  41: rayon_core::registry::WorkerThread::wait_until_cold
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:729:17
  42: rayon_core::registry::WorkerThread::wait_until
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:703:13
  43: rayon_core::registry::main_loop
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:836:5
  44: rayon_core::registry::ThreadBuilder::run
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:55:18
  45: <rayon_core::registry::DefaultSpawn as rayon_core::registry::ThreadSpawn>::spawn::{{closure}}
             at /home/jivvy/.cargo/registry/src/github.com-1ecc6299db9ec823/rayon-core-1.9.3/src/registry.rs:100:20
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[rj00a]

The Drop impl on PlayPacketController spawns a tokio task (requiring a tokio context). The PlayPacketController is dropped whenever a client is deleted. Looks like it's not in a tokio context when that happens for some reason.

[jivvy]

So I started trying to investigate this

It looks like there is a tokio context up until this point:

valence/src/server.rs

Lines 405 to 408 in bb43856

	// Get serverbound packets first so they are not dealt with a tick late.
	server.clients.par_iter_mut().for_each(|(_, client)| {
	client.handle_serverbound_packets(&server.entities);
	});

If iter_mut() is used instead of par_iter_mut(), the server doesn't panic

[rj00a]

Nice find. This is happening because the tokio context is thread-local, but rayon tasks run in their own thread pool. Fixed in 923fabe.

[jivvy]

Thanks for explaining this!