refactor(tvix/store/blobsvc): make BlobStore async r/6606

We previously kept the trait of a BlobService sync.

This however had some annoying consequences:

 - It became more and more complicated to track when we're in a context
   with an async runtime in the context or not, producing bugs like
   https://b.tvl.fyi/issues/304
 - The sync trait shielded away async clients from async worloads,
   requiring manual block_on code inside the gRPC client code, and
   spawn_blocking calls in consumers of the trait, even if they were
   async (like the gRPC server)
 - We had to write our own custom glue code (SyncReadIntoAsyncRead)
   to convert a sync io::Read into a tokio::io::AsyncRead, which already
   existed in tokio internally, but upstream ia hesitant to expose.

This now makes the BlobService trait async (via the async_trait macro,
like we already do in various gRPC parts), and replaces the sync readers
and writers with their async counterparts.

Tests interacting with a BlobService now need to have an async runtime
available, the easiest way for this is to mark the test functions
with the tokio::test macro, allowing us to directly .await in the test
function.

In places where we don't have an async runtime available from context
(like tvix-cli), we can pass one down explicitly.

Now that we don't provide a sync interface anymore, the (sync) FUSE
library now holds a pointer to a tokio runtime handle, and needs to at
least have 2 threads available when talking to a blob service (which is
why some of the tests now use the multi_thread flavor).

The FUSE tests got a bit more verbose, as we couldn't use the
setup_and_mount function accepting a callback anymore. We can hopefully
move some of the test fixture setup to rstest in the future to make this
less repetitive.

Co-Authored-By: Connor Brewster <cbrewster@hey.com>
Change-Id: Ia0501b606e32c852d0108de9c9016b21c94a3c05
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9329
Reviewed-by: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

1 files changed, 0 insertions, 158 deletions

diff --git a/tvix/store/src/proto/sync_read_into_async_read.rs b/tvix/store/src/proto/sync_read_into_async_read.rs
deleted file mode 100644
index 0a0ef019781c..000000000000
--- a/tvix/store/src/proto/sync_read_into_async_read.rs
+++ /dev/null
@@ -1,158 +0,0 @@
-use bytes::Buf;
-use core::task::Poll::Ready;
-use futures::ready;
-use futures::Future;
-use std::io;
-use std::io::Read;
-use std::pin::Pin;
-use std::sync::Arc;
-use std::task::Context;
-use std::task::Poll;
-use tokio::io::AsyncRead;
-use tokio::runtime::Handle;
-use tokio::sync::Mutex;
-use tokio::task::JoinHandle;
-
-#[derive(Debug)]
-enum State<Buf: bytes::Buf + bytes::BufMut> {
-    Idle(Option<Buf>),
-    Busy(JoinHandle<(io::Result<usize>, Buf)>),
-}
-
-use State::{Busy, Idle};
-
-/// Use a [`SyncReadIntoAsyncRead`] to asynchronously read from a
-/// synchronous API.
-#[derive(Debug)]
-pub struct SyncReadIntoAsyncRead<R: Read + Send, Buf: bytes::Buf + bytes::BufMut> {
-    state: Mutex<State<Buf>>,
-    reader: Arc<Mutex<R>>,
-    rt: Handle,
-}
-
-impl<R: Read + Send, Buf: bytes::Buf + bytes::BufMut> SyncReadIntoAsyncRead<R, Buf> {
-    /// This must be called from within a Tokio runtime context, or else it will panic.
-    #[track_caller]
-    pub fn new(rt: Handle, reader: R) -> Self {
-        Self {
-            rt,
-            state: State::Idle(None).into(),
-            reader: Arc::new(reader.into()),
-        }
-    }
-
-    /// This must be called from within a Tokio runtime context, or else it will panic.
-    pub fn new_with_reader(readable: R) -> Self {
-        Self::new(Handle::current(), readable)
-    }
-}
-
-/// Repeats operations that are interrupted.
-macro_rules! uninterruptibly {
-    ($e:expr) => {{
-        loop {
-            match $e {
-                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
-                res => break res,
-            }
-        }
-    }};
-}
-
-impl<
-        R: Read + Send + 'static + std::marker::Unpin,
-        Buf: bytes::Buf + bytes::BufMut + Send + Default + std::marker::Unpin + 'static,
-    > AsyncRead for SyncReadIntoAsyncRead<R, Buf>
-{
-    fn poll_read(
-        self: Pin<&mut Self>,
-        cx: &mut Context<'_>,
-        dst: &mut tokio::io::ReadBuf<'_>,
-    ) -> Poll<io::Result<()>> {
-        let me = self.get_mut();
-        // Do we need this mutex?
-        let state = me.state.get_mut();
-
-        loop {
-            match state {
-                Idle(ref mut buf_cell) => {
-                    let mut buf = buf_cell.take().unwrap_or_default();
-
-                    if buf.has_remaining() {
-                        // Here, we will split the `buf` into `[..dst.remaining()... ; rest ]`
-                        // The `rest` is stuffed into the `buf_cell` for further poll_read.
-                        // The other is completely consumed into the unfilled destination.
-                        // `rest` can be empty.
-                        let mut adjusted_src =
-                            buf.copy_to_bytes(std::cmp::min(buf.remaining(), dst.remaining()));
-                        let copied_size = adjusted_src.remaining();
-                        adjusted_src.copy_to_slice(dst.initialize_unfilled_to(copied_size));
-                        dst.set_filled(copied_size);
-                        *buf_cell = Some(buf);
-                        return Ready(Ok(()));
-                    }
-
-                    let reader = me.reader.clone();
-                    *state = Busy(me.rt.spawn_blocking(move || {
-                        let result = uninterruptibly!(reader.blocking_lock().read(
-                            // SAFETY: `reader.read` will *ONLY* write initialized bytes
-                            // and never *READ* uninitialized bytes
-                            // inside this buffer.
-                            //
-                            // Furthermore, casting the slice as `*mut [u8]`
-                            // is safe because it has the same layout.
-                            //
-                            // Finally, the pointer obtained is valid and owned
-                            // by `buf` only as we have a valid mutable reference
-                            // to it, it is valid for write.
-                            //
-                            // Here, we copy an nightly API: https://doc.rust-lang.org/stable/src/core/mem/maybe_uninit.rs.html#994-998
-                            unsafe {
-                                &mut *(buf.chunk_mut().as_uninit_slice_mut()
-                                    as *mut [std::mem::MaybeUninit<u8>]
-                                    as *mut [u8])
-                            }
-                        ));
-
-                        if let Ok(n) = result {
-                            // SAFETY: given we initialize `n` bytes, we can move `n` bytes
-                            // forward.
-                            unsafe {
-                                buf.advance_mut(n);
-                            }
-                        }
-
-                        (result, buf)
-                    }));
-                }
-                Busy(ref mut rx) => {
-                    let (result, mut buf) = ready!(Pin::new(rx).poll(cx))?;
-
-                    match result {
-                        Ok(n) => {
-                            if n > 0 {
-                                let remaining = std::cmp::min(n, dst.remaining());
-                                let mut adjusted_src = buf.copy_to_bytes(remaining);
-                                adjusted_src.copy_to_slice(dst.initialize_unfilled_to(remaining));
-                                dst.advance(remaining);
-                            }
-                            *state = Idle(Some(buf));
-                            return Ready(Ok(()));
-                        }
-                        Err(e) => {
-                            *state = Idle(None);
-                            return Ready(Err(e));
-                        }
-                    }
-                }
-            }
-        }
-    }
-}
-
-impl<R: Read + Send, Buf: bytes::Buf + bytes::BufMut> From<R> for SyncReadIntoAsyncRead<R, Buf> {
-    /// This must be called from within a Tokio runtime context, or else it will panic.
-    fn from(value: R) -> Self {
-        Self::new_with_reader(value)
-    }
-}