backoff::future::retry doesn't work on wasm32-unknown-unknown with tokio because of reliance on TokioSleeper and time

[leighmcculloch]

The backoff::future::retry works well on wasm32-unknown-unknown with tokio as long as there is never an error that triggers the backoff. Once a backoff is triggered the TokioSleeper is used and tokio::time is used.

backoff/src/future.rs

Lines 218 to 224 in 587e2da

	struct TokioSleeper;
	#[cfg(feature = "tokio")]
	#[cfg_attr(docsrs, doc(cfg(feature = "tokio")))]
	impl Sleeper for TokioSleeper {
	type Sleep = ::tokio_1::time::Sleep;
	fn sleep(&self, dur: Duration) -> Self::Sleep {
	::tokio_1::time::sleep(dur)

The problem with this is that on wasm32-unknown-unknown with no time source, a panic is caused by this attempt to sleep with tokio. This is because tokio only uses the std time which isn't implemented. The following panic will be seen:

panicked at 'time not implemented on this platform', library/std/src/sys/wasm/../unsupported/time.rs:13:9

Stack:

<?>.wasm-function[console_error_panic_hook::Error::new::hf6b67bbb1aa769d8]@[wasm code]
<?>.wasm-function[console_error_panic_hook::hook_impl::h1826ea7fdfe0e730]@[wasm code]
<?>.wasm-function[console_error_panic_hook::hook::ha2b94ff4b371fbc5]@[wasm code]
<?>.wasm-function[core::ops::function::Fn::call::h80ff1f496bb96ef1]@[wasm code]
<?>.wasm-function[std::panicking::rust_panic_with_hook::h70a0e195f4db2a29]@[wasm code]
<?>.wasm-function[std::panicking::begin_panic_handler::{{closure}}::hdcfc819ce836829e]@[wasm code]
<?>.wasm-function[std::sys_common::backtrace::__rust_end_short_backtrace::h53cabafab5b09ada]@[wasm code]
<?>.wasm-function[rust_begin_unwind]@[wasm code]
<?>.wasm-function[core::panicking::panic_fmt::h751be80779d42b53]@[wasm code]
<?>.wasm-function[std::time::Instant::now::h191947beee8509bf]@[wasm code]
<?>.wasm-function[tokio::time::instant::variant::now::h3c864f6578f780bc]@[wasm code]
<?>.wasm-function[tokio::time::instant::Instant::now::haaab15ba5b70db5b]@[wasm code]
<?>.wasm-function[tokio::time::driver::sleep::sleep::ha840de8dc1dc85fb]@[wasm code]
<?>.wasm-function[<backoff::future::TokioSleeper as backoff::future::Sleeper>::sleep::hd6eb274f5257e1c5]@[wasm code]
<?>.wasm-function[<backoff::future::Retry<S,B,N,Fn,Fut> as core::future::future::Future>::poll::h5307a8e7cbba1773]@[wasm code]

When the backoff crate has the wasm-bindgen feature enabled, it would be ideal if it leaned on another form of sleeping, such as using gloo-timer, or if there was a way to choose the time that is used. I note that this crate already uses instant instead of std Instant, so something like this would be aligned with that.

[leighmcculloch]

I got backoff working with the following change, and using it in place of the TokioSleeper when using wasm-bindgen.

#[cfg(feature = "gloo-timers")]
#[cfg_attr(docsrs, doc(cfg(feature = "gloo-timers")))]
struct GlooTimersSleeper;

#[cfg(feature = "gloo-timers")]
#[cfg_attr(docsrs, doc(cfg(feature = "gloo-timers")))]
impl Sleeper for GlooTimersSleeper {
    type Sleep = ::gloo_timers::future::TimeoutFuture;
    fn sleep(&self, dur: Duration) -> Self::Sleep {
        ::gloo_timers::future::sleep(dur)
    }
}

[wackazong]

I got backoff working with the following change, and using it in place of the TokioSleeper when using wasm-bindgen.

#[cfg(feature = "gloo-timers")]
#[cfg_attr(docsrs, doc(cfg(feature = "gloo-timers")))]
struct GlooTimersSleeper;

#[cfg(feature = "gloo-timers")]
#[cfg_attr(docsrs, doc(cfg(feature = "gloo-timers")))]
impl Sleeper for GlooTimersSleeper {
    type Sleep = ::gloo_timers::future::TimeoutFuture;
    fn sleep(&self, dur: Duration) -> Self::Sleep {
        ::gloo_timers::future::sleep(dur)
    }
}

Does not work for me, I get the following error:

264 |     type Sleep = ::gloo_timers::future::TimeoutFuture;
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `(dyn FnMut() + 'static)` cannot be sent between threads safely

@leighmcculloch would you be able to share a working example? I am currently stuck here.