0.1: deadlock when poll mpsc::Receiver and mpsc::Sender in one thread

[hicqu]

When using grpcio we found that if poll mpsc::Receiver and mpsc::Sender in one thread, it could be blocked. We guess it's a bug of futures channel.

Here is a little demo to show it: https://github.com/hicqu/futures-mpsc-deadlock.

build: cargo build --release
run: ./target/release/futures-mpsc-deadlock

In my environment I can see the program is blocked forever.

With gdb to debug it, the stack is

(gdb) bt
#0  0x00007f6f8617c41f in __lll_lock_wait () from /usr/lib/libpthread.so.0
#1  0x00007f6f86174ea3 in pthread_mutex_lock () from /usr/lib/libpthread.so.0
#2  0x000055a9a858364c in futures::sync::mpsc::Sender<T>::poll_unparked ()
#3  0x000055a9a8584eb2 in <futures::sink::send_all::SendAll<T,U> as futures::future::Future>::poll ()
#4  0x000055a9a8584c28 in <futures::future::map::Map<A,F> as futures::future::Future>::poll ()
#5  0x000055a9a8585abd in futures::task_impl::std::set ()
#6  0x000055a9a8586ba0 in <futures_mpsc_deadlock::Notifier<F> as futures::task_impl::Notify>::notify ()
#7  0x000055a9a85888f1 in futures::sync::mpsc::SenderTask::notify ()
#8  0x000055a9a8583fd0 in futures::sync::mpsc::Receiver<T>::next_message ()
#9  0x000055a9a85846a9 in <futures::sync::mpsc::Receiver<T> as futures::stream::Stream>::poll ()
#10 0x000055a9a858597c in futures::task_impl::std::set ()
#11 0x000055a9a8585f36 in futures::task_impl::Spawn<T>::poll_stream_notify ()
#12 0x000055a9a85870dd in futures_mpsc_deadlock::main ()
#13 0x000055a9a8584943 in std::rt::lang_start::{{closure}} ()
#14 0x000055a9a8591343 in std::rt::lang_start_internal::{{closure}} () at src/libstd/rt.rs:49
#15 std::panicking::try::do_call () at src/libstd/panicking.rs:296
#16 0x000055a9a8592b8a in __rust_maybe_catch_panic () at src/libpanic_unwind/lib.rs:80
#17 0x000055a9a8591e0d in std::panicking::try () at src/libstd/panicking.rs:275
#18 std::panic::catch_unwind () at src/libstd/panic.rs:394
#19 std::rt::lang_start_internal () at src/libstd/rt.rs:48
#20 0x000055a9a8587312 in main ()

Please take look if you are free, thanks!

[Nemo157]

(for others that get confused when looking at the code, this is with futures 0.1)

[LucioFranco]

@Nemo157 might be useful to have a label for that

[hicqu]

I'm trying to reproduce it in futures 0.3. But seems struct Spawn and poll_future_notify are not in futures 0.3? Any other things to replace them?

[hicqu]

PTAL @Nemo157 thanks!

[Nemo157]

I think Spawn and poll_future_notify are basically replaced with the abstraction available in std::task, there are some concrete implementations of these available in futures-test that you may be able to test with. But I'm not really familiar with these internal 0.1 APIs.