This patch adds an example using the asynchronous Rust bindings. --- rust/Cargo.toml | 1 + rust/examples/concurrent-read-write.rs | 135 +++++++++++++++++++++++++ rust/run-tests.sh.in | 2 + 3 files changed, 138 insertions(+) create mode 100644 rust/examples/concurrent-read-write.rs
diff --git a/rust/Cargo.toml b/rust/Cargo.toml index d001248..4332783 100644 --- a/rust/Cargo.toml +++ b/rust/Cargo.toml @@ -54,5 +54,6 @@ default = ["log", "tokio"] anyhow = "1.0.72" once_cell = "1.18.0" pretty-hex = "0.3.0" +rand = { version = "0.8.5", default-features = false, features = ["small_rng", "min_const_gen"] } tempfile = "3.6.0" tokio = { version = "1.29.1", default-features = false, features = ["rt-multi-thread", "macros"] } diff --git a/rust/examples/concurrent-read-write.rs b/rust/examples/concurrent-read-write.rs new file mode 100644 index 0000000..a1c3e8a --- /dev/null +++ b/rust/examples/concurrent-read-write.rs @@ -0,0 +1,135 @@ +//! Example usage with nbdkit: +//! +//! nbdkit -U - memory 100M \ +//! --run 'cargo run --example concurrent-read-write -- $unixsocket' +//! +//! This will read and write randomly over the first megabyte of the +//! plugin using multi-conn, multiple threads and multiple requests in +//! flight on each thread. + +#![deny(warnings)] +use rand::prelude::*; +use std::env; +use std::path::PathBuf; +use std::sync::Arc; +use tokio::task::JoinSet; + +/// Number of simultaneous connections to the NBD server. +/// +/// Note that some servers only support a limited number of +/// simultaneous connections, and/or have a configurable thread pool +/// internally, and if you exceed those limits then something will break. +const NR_MULTI_CONN: usize = 8; + +/// Number of commands that can be "in flight" at the same time on each +/// connection. (Therefore the total number of requests in flight may +/// be up to NR_MULTI_CONN * MAX_IN_FLIGHT). +const MAX_IN_FLIGHT: usize = 16; + +/// The size of large reads and writes, must be > 512. +const BUFFER_SIZE: usize = 1024; + +/// Number of commands we issue (per [task][tokio::task]). +const NR_CYCLES: usize = 32; + +/// Statistics gathered during the run. +#[derive(Debug, Default)] +struct Stats { + /// The total number of requests made. + requests: usize, +} + +#[tokio::main] +async fn main() -> anyhow::Result<()> { + let args = env::args_os().collect::<Vec<_>>(); + if args.len() != 2 { + anyhow::bail!("Usage: {:?} socket", args[0]); + } + let socket = &args[1]; + + // We begin by making a connection to the server to get the export size + // and ensure that it supports multiple connections and is writable. + let nbd = libnbd::Handle::new()?; + nbd.connect_unix(&socket)?; + let export_size = nbd.get_size()?; + anyhow::ensure!( + (BUFFER_SIZE as u64) < export_size, + "export is {export_size}B, must be larger than {BUFFER_SIZE}B" + ); + anyhow::ensure!( + !nbd.is_read_only()?, + "error: this NBD export is read-only" + ); + anyhow::ensure!( + nbd.can_multi_conn()?, + "error: this NBD export does not support multi-conn" + ); + drop(nbd); // Close the connection. + + // Start the worker tasks, one per connection. + let mut tasks = JoinSet::new(); + for i in 0..NR_MULTI_CONN { + tasks.spawn(run_thread(i, socket.clone().into(), export_size)); + } + + // Wait for the tasks to complete. + let mut stats = Stats::default(); + while !tasks.is_empty() { + let this_stats = tasks.join_next().await.unwrap().unwrap()?; + stats.requests += this_stats.requests; + } + + // Make sure the number of requests that were required matches what + // we expect. + assert_eq!(stats.requests, NR_MULTI_CONN * NR_CYCLES); + + Ok(()) +} + +async fn run_thread( + task_idx: usize, + socket: PathBuf, + export_size: u64, +) -> anyhow::Result<Stats> { + // Start a new connection to the server. + // We shall spawn many commands concurrently on different tasks and those + // futures must be `'static`, hence we wrap the handle in an [Arc]. + let nbd = Arc::new(libnbd::AsyncHandle::new()?); + nbd.connect_unix(socket).await?; + + let mut rng = SmallRng::seed_from_u64(44 as u64); + + // Issue commands. + let mut stats = Stats::default(); + let mut join_set = JoinSet::new(); + //tokio::time::sleep(std::time::Duration::from_secs(1)).await; + while stats.requests < NR_CYCLES || !join_set.is_empty() { + while stats.requests < NR_CYCLES && join_set.len() < MAX_IN_FLIGHT { + // If we want to issue another request, do so. Note that we reuse + // the same buffer for multiple in-flight requests. It doesn't + // matter here because we're just trying to write random stuff, + // but that would be Very Bad in a real application. + // Simulate a mix of large and small requests. + let size = if rng.gen() { BUFFER_SIZE } else { 512 }; + let offset = rng.gen_range(0..export_size - size as u64); + + let mut buf = [0u8; BUFFER_SIZE]; + let nbd = nbd.clone(); + if rng.gen() { + join_set.spawn(async move { + nbd.pread(&mut buf, offset, None).await + }); + } else { + // Fill the buf with random data. + rng.fill(&mut buf); + join_set + .spawn(async move { nbd.pwrite(&buf, offset, None).await }); + } + stats.requests += 1; + } + join_set.join_next().await.unwrap().unwrap()?; + } + + if task_idx == 0 {} + Ok(stats) +} diff --git a/rust/run-tests.sh.in b/rust/run-tests.sh.in index 138a1fa..24858dd 100755 --- a/rust/run-tests.sh.in +++ b/rust/run-tests.sh.in @@ -32,6 +32,8 @@ if [ -z "$VG" ]; then --run '@CARGO@ run --example get-size -- $unixsocket' nbdkit -U - floppy . \ --run '@CARGO@ run --example fetch-first-sector -- $unixsocket' + nbdkit -U - memory 10M \ + --run '@CARGO@ run --example concurrent-read-write -- $unixsocket' else @CARGO@ test --config "target.'cfg(all())'.runner = \"$VG\"" -- --nocapture fi -- 2.41.0 _______________________________________________ Libguestfs mailing list Libguestfs@redhat.com https://listman.redhat.com/mailman/listinfo/libguestfs