Crash when receive_signal is called concurrently

[zeenix]

In GitLab by @siegfriedweber on Aug 4, 2021, 14:22

When azync::Proxy::receive_signal is called concurrently on different threads, threads can panic as follows:

thread 'tokio-runtime-worker' panicked at 'Attempted to set dest_unique_name twice: OwnedUniqueName(UniqueName(Str(":1.0")))', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/zbus-2.0.0-beta.6/src/azync/proxy.rs:797:14

We encountered the problem in the following code:

/// Calls a systemd method and waits until the dependent job is
/// finished.
///
/// The given method enqueues a job in systemd and returns the job
/// object. Systemd sends out a `JobRemoved` signal when the job is
/// dequeued. The signal contains the reason for the dequeuing like
/// `"done"`, `"failed"`, or `"canceled"`.
///
/// This function subscribes to `JobRemoved` signals, calls the
/// given method, awaits the signal for the corresponding job, and
/// returns `Ok(())` if the result is [`JobRemovedResult::Done`].
/// If the signal contains another result or no signal is returned
/// (which should never happen) then an error with a corresponding
/// message is returned.
async fn call_method<'a, F, Fut>(&'a self, method: F) -> anyhow::Result<()>
where
    F: Fn(&'a AsyncManagerProxy) -> Fut,
    Fut: Future<Output = zbus::Result<AsyncJobProxy<'a>>>,
{
    let signals = self
        .proxy
        .receive_signal(ManagerSignals::JobRemoved)
        .await?
        .map(|message| message.body::<JobRemovedSignal>().unwrap());

    let job = method(&self.proxy).await?;

    let mut signals = signals
        .filter(|signal| future::ready(&signal.job.to_owned().into_inner() == job.path()));

    let signal = signals.next().await;

    match signal {
        Some(message) if message.result == JobRemovedResult::Done => Ok(()),
        Some(message) => Err(anyhow!("The systemd job failed: {:?}", message)),
        None => Err(anyhow!(
            "No signal was returned for the systemd job: {:?}",
            job
        )),
    }
}

This code worked with zbus-2.0.0-beta.5 but fails with zbus-2.0.0-beta.6.

[zeenix]

@siegfriedweber Thanks for filling this report. Could you kindly test !354 and let us know if that actually fixes the issue for you?

[zeenix]

In GitLab by @siegfriedweber on Aug 5, 2021, 12:46

@zeenix The problem did not occur anymore in our tests with your fix. Thank you very much!

[zeenix]

@siegfriedweber Thanks so much for testing.

[zeenix]

mentioned in commit 0a8a4268be0f844ab4bca429f27766347dc3af58