"there is no reactor running" panic when system is quickly dropped

[prk3]

Here is code that reproduces the issue: main.rs

struct A {}

impl actix::Actor for A {
    type Context = actix::Context<Self>;

    fn started(&mut self, ctx: &mut Self::Context) {
        use actix::AsyncContext;
        ctx.run_interval(std::time::Duration::from_millis(100), |_a, _c| {
            println!("Hi!");
        });
    }
}

fn main() {
    actix_rt::System::new().block_on(async {
        actix::Actor::start(A {});
        // tokio::time::sleep(std::time::Duration::from_millis(1)).await;
    });
}

Cargo.toml

[dependencies]
actix = "0.13.0"
actix-rt = "2.7.0"
tokio = { version = "1.17.0", features = ["time"]}

Expected Behavior

The program does not panic. Nothing should be sent to stdout, as system is dropped before 100 milliseconds pass (interval).

Current Behavior

The program panics and produces the following backtrace on crash:

thread 'main' panicked at 'there is no reactor running, must be called from the context of a Tokio 1.x runtime', /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/context.rs:54:26
stack backtrace:
   0: rust_begin_unwind
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/panicking.rs:517:5
   1: core::panicking::panic_fmt
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/panicking.rs:101:14
   2: core::option::expect_failed
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/option.rs:1615:5
   3: core::option::Option<T>::expect
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/option.rs:698:21
   4: tokio::runtime::context::time_handle::{{closure}}
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/context.rs:54:13
   5: std::thread::local::LocalKey<T>::try_with
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/thread/local.rs:399:16
   6: tokio::runtime::context::time_handle
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/context.rs:52:15
   7: tokio::time::driver::handle::Handle::current
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/time/driver/handle.rs:57:13
   8: tokio::time::driver::sleep::Sleep::new_timeout
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/time/driver/sleep.rs:257:22
   9: tokio::time::driver::sleep::sleep
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/time/driver/sleep.rs:129:27
  10: actix::utils::IntervalFunc<A>::new
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.13.0/src/utils.rs:186:20
  11: actix::actor::AsyncContext::run_interval
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.13.0/src/actor.rs:459:20
  12: <playround::A as actix::actor::Actor>::started
             at ./src/main.rs:8:9
  13: <actix::contextimpl::ContextFut<A,C> as core::future::future::Future>::poll
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.13.0/src/contextimpl.rs:360:13
  14: <actix::contextimpl::ContextFut<A,C> as core::ops::drop::Drop>::drop
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.13.0/src/contextimpl.rs:226:21
  15: core::ptr::drop_in_place<actix::contextimpl::ContextFut<playround::A,actix::context::Context<playround::A>>>
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ptr/mod.rs:188:1
  16: core::ptr::drop_in_place<tokio::runtime::task::core::Stage<actix::contextimpl::ContextFut<playround::A,actix::context::Context<playround::A>>>>
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ptr/mod.rs:188:1
  17: tokio::runtime::task::core::CoreStage<T>::set_stage::{{closure}}
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/core.rs:214:35
  18: tokio::loom::std::unsafe_cell::UnsafeCell<T>::with_mut
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/loom/std/unsafe_cell.rs:14:9
  19: tokio::runtime::task::core::CoreStage<T>::set_stage
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/core.rs:214:9
  20: tokio::runtime::task::core::CoreStage<T>::drop_future_or_output
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/core.rs:180:13
  21: tokio::runtime::task::harness::cancel_task::{{closure}}
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/harness.rs:438:9
  22: core::ops::function::FnOnce::call_once
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ops/function.rs:227:5
  23: <core::panic::unwind_safe::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/panic/unwind_safe.rs:271:9
  24: std::panicking::try::do_call
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/panicking.rs:403:40
  25: __rust_try
  26: std::panicking::try
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/panicking.rs:367:19
  27: std::panic::catch_unwind
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/panic.rs:129:14
  28: tokio::runtime::task::harness::cancel_task
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/harness.rs:437:15
  29: tokio::runtime::task::harness::Harness<T,S>::shutdown
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/harness.rs:147:9
  30: tokio::runtime::task::raw::shutdown
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/raw.rs:164:5
  31: tokio::runtime::task::raw::RawTask::shutdown
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/raw.rs:109:18
  32: tokio::runtime::task::Task<S>::shutdown
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/mod.rs:338:9
  33: tokio::runtime::task::list::LocalOwnedTasks<S>::close_and_shutdown_all
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/runtime/task/list.rs:225:13
  34: <tokio::task::local::LocalSet as core::ops::drop::Drop>::drop::{{closure}}
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/task/local.rs:606:13
  35: tokio::macros::scoped_tls::ScopedKey<T>::set
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/macros/scoped_tls.rs:61:9
  36: tokio::task::local::LocalSet::with
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/task/local.rs:561:9
  37: <tokio::task::local::LocalSet as core::ops::drop::Drop>::drop
             at /home/prk3/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.17.0/src/task/local.rs:603:9
  38: core::ptr::drop_in_place<tokio::task::local::LocalSet>
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ptr/mod.rs:188:1
  39: core::ptr::drop_in_place<actix_rt::runtime::Runtime>
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ptr/mod.rs:188:1
  40: core::ptr::drop_in_place<actix_rt::system::SystemRunner>
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ptr/mod.rs:188:1
  41: playround::main
             at ./src/main.rs:18:7
  42: core::ops::function::FnOnce::call_once
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ops/function.rs:227:5

Possible Solution

I suspect run_interval creates some task that isn't dropped in time or it always assumes tokio runtime exists. I noticed that a short sleep just after staring the actor fixes the issue (commented in the example). Explicit ctx.cancel_future in stopping or stopped method does not fix the problem.

Steps to Reproduce (for bugs)

1. Call run_interval in actor's started method.
2. Start actor in actix-rt system.
3. Quickly drop the system.

Context

We came across this error twice. Once when running a test function with should_panic attribute. It looks like the expected panic triggers drops and the drop of the system causes this panic. Another case was starting and dropping a system in a loop in a fuzz test.

Your Environment

Linux work 5.16.13-200.fc35.x86_64 #1 SMP PREEMPT Tue Mar 8 22:50:58 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

• Rust Version (I.e, output of rustc -V): rustc 1.58.1 (db9d1b20b 2022-01-20)
• Actix Version: 0.13.0, 0.12.0

[mstyura]

Hi there! I'm encountering the same problem. As an additional detail I could add that the same crash happen when ctx.notify_later is used. It seems like both ctx.notify_later and ctx.run_internval crashed due to access to tokio::runtime::Handle::current(). Crash is also happen when directly accessing current tokio handle:

use actix::prelude::*;

struct MyActor;

impl Actor for MyActor {
    type Context = Context<Self>;
    
    fn started(&mut self, ctx: &mut Self::Context) {
        tokio::runtime::Handle::current(); // will be paniced
    }
}

fn main() {
    let system = actix::System::new();
    system.block_on(async {
        MyActor.start();
        // Next line fixes panic when uncommented: 
        // tokio::task::yield_now().await;
    });
}

[thalesfragoso]

I believe this is caused by the Drop implementation of ContextFut: https://github.com/actix/actix/blob/d7aab0a0f439679a570d08aaa6972ad8b60003de/actix/src/contextimpl.rs#L219-L232

The poll will call your started function if ContextFut didn't get the change to be polled before. The thing is, tokio drops its spawned futures after shutting down the runtime, run_interval will try to create a Sleep instance from tokio and then panic.

The Drop implementation is arguably wrong, the poll can run arbitrary code provided by the user (through started, stopping and stopped), and it's understandable that the user will assume that a tokio runtime exists in at least some of these methods.