use crate::{HostOutputStream, StreamError, Subscribe};
use anyhow::anyhow;
use bytes::Bytes;
use std::sync::{Arc, Mutex};
#[derive(Debug)]
struct WorkerState {
alive: bool,
items: std::collections::VecDeque<Bytes>,
write_budget: usize,
flush_pending: bool,
error: Option<anyhow::Error>,
}
impl WorkerState {
fn check_error(&mut self) -> Result<(), StreamError> {
if let Some(e) = self.error.take() {
return Err(StreamError::LastOperationFailed(e));
}
if !self.alive {
return Err(StreamError::Closed);
}
Ok(())
}
}
struct Worker {
state: Mutex<WorkerState>,
new_work: tokio::sync::Notify,
write_ready_changed: tokio::sync::Notify,
}
enum Job {
Flush,
Write(Bytes),
}
impl Worker {
fn new(write_budget: usize) -> Self {
Self {
state: Mutex::new(WorkerState {
alive: true,
items: std::collections::VecDeque::new(),
write_budget,
flush_pending: false,
error: None,
}),
new_work: tokio::sync::Notify::new(),
write_ready_changed: tokio::sync::Notify::new(),
}
}
async fn ready(&self) {
loop {
{
let state = self.state();
if state.error.is_some()
|| !state.alive
|| (!state.flush_pending && state.write_budget > 0)
{
return;
}
}
self.write_ready_changed.notified().await;
}
}
fn check_write(&self) -> Result<usize, StreamError> {
let mut state = self.state();
if let Err(e) = state.check_error() {
return Err(e);
}
if state.flush_pending || state.write_budget == 0 {
return Ok(0);
}
Ok(state.write_budget)
}
fn state(&self) -> std::sync::MutexGuard<WorkerState> {
self.state.lock().unwrap()
}
fn pop(&self) -> Option<Job> {
let mut state = self.state();
if state.items.is_empty() {
if state.flush_pending {
return Some(Job::Flush);
}
} else if let Some(bytes) = state.items.pop_front() {
return Some(Job::Write(bytes));
}
None
}
fn report_error(&self, e: std::io::Error) {
{
let mut state = self.state();
state.alive = false;
state.error = Some(e.into());
state.flush_pending = false;
}
self.write_ready_changed.notify_one();
}
async fn work<T: tokio::io::AsyncWrite + Send + Unpin + 'static>(&self, mut writer: T) {
use tokio::io::AsyncWriteExt;
loop {
while let Some(job) = self.pop() {
match job {
Job::Flush => {
if let Err(e) = writer.flush().await {
self.report_error(e);
return;
}
tracing::debug!("worker marking flush complete");
self.state().flush_pending = false;
}
Job::Write(mut bytes) => {
tracing::debug!("worker writing: {bytes:?}");
let len = bytes.len();
match writer.write_all_buf(&mut bytes).await {
Err(e) => {
self.report_error(e);
return;
}
Ok(_) => {
self.state().write_budget += len;
}
}
}
}
self.write_ready_changed.notify_one();
}
self.new_work.notified().await;
}
}
}
pub struct AsyncWriteStream {
worker: Arc<Worker>,
join_handle: Option<crate::runtime::AbortOnDropJoinHandle<()>>,
}
impl AsyncWriteStream {
pub fn new<T: tokio::io::AsyncWrite + Send + Unpin + 'static>(
write_budget: usize,
writer: T,
) -> Self {
let worker = Arc::new(Worker::new(write_budget));
let w = Arc::clone(&worker);
let join_handle = crate::runtime::spawn(async move { w.work(writer).await });
AsyncWriteStream {
worker,
join_handle: Some(join_handle),
}
}
}
#[async_trait::async_trait]
impl HostOutputStream for AsyncWriteStream {
fn write(&mut self, bytes: Bytes) -> Result<(), StreamError> {
let mut state = self.worker.state();
state.check_error()?;
if state.flush_pending {
return Err(StreamError::Trap(anyhow!(
"write not permitted while flush pending"
)));
}
match state.write_budget.checked_sub(bytes.len()) {
Some(remaining_budget) => {
state.write_budget = remaining_budget;
state.items.push_back(bytes);
}
None => return Err(StreamError::Trap(anyhow!("write exceeded budget"))),
}
drop(state);
self.worker.new_work.notify_one();
Ok(())
}
fn flush(&mut self) -> Result<(), StreamError> {
let mut state = self.worker.state();
state.check_error()?;
state.flush_pending = true;
self.worker.new_work.notify_one();
Ok(())
}
fn check_write(&mut self) -> Result<usize, StreamError> {
self.worker.check_write()
}
async fn cancel(&mut self) {
match self.join_handle.take() {
Some(task) => _ = task.cancel().await,
None => {}
}
}
}
#[async_trait::async_trait]
impl Subscribe for AsyncWriteStream {
async fn ready(&mut self) {
self.worker.ready().await;
}
}