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use std::{debug_assert, io::Write, sync::Arc, thread::JoinHandle, time::Duration};
use crossbeam_channel::{Receiver, RecvTimeoutError, Sender, TryRecvError, bounded, unbounded};
use crossbeam_utils::CachePadded;
use parking_lot::{Mutex, MutexGuard};
use thread_local::ThreadLocal;
type ThreadLocalState = CachePadded<Mutex<Option<TraceInfoBuffer>>>;
/// The amount of data that is accumulated in the thread local buffer before it is sent to the
/// writer. The buffer might grow if a single write is larger than this size.
const THREAD_LOCAL_INITIAL_BUFFER_SIZE: usize = 1024 * 1024;
/// Data buffered by the write thread before issuing a filesystem write
const WRITE_BUFFER_SIZE: usize = 100 * 1024 * 1024;
struct TraceInfoBuffer {
buffer: Vec<u8>,
}
impl TraceInfoBuffer {
fn new(capacity: usize) -> Self {
Self {
buffer: Vec::with_capacity(capacity),
}
}
fn push(&mut self, data: u8) {
self.buffer.push(data);
}
fn extend(&mut self, data: &[u8]) {
self.buffer.extend_from_slice(data);
}
fn clear(&mut self) {
self.buffer.clear();
}
}
#[derive(Clone)]
pub struct TraceWriter {
data_tx: Sender<Option<TraceInfoBuffer>>,
return_rx: Receiver<TraceInfoBuffer>,
thread_locals: Arc<ThreadLocal<ThreadLocalState>>,
}
impl TraceWriter {
/// This is a non-blocking writer that writes a file in a background thread.
/// This is inspired by tracing-appender non_blocking, but has some
/// differences:
/// * It allows writing an owned Vec<u8> instead of a reference, so avoiding additional
/// allocation.
/// * It uses an unbounded channel to avoid slowing down the application at all (memory) cost.
/// * It issues less writes by buffering the data into chunks of WRITE_BUFFER_SIZE, when
/// possible.
pub fn new<W: Write + Send + 'static>(mut writer: W) -> (Self, TraceWriterGuard) {
let (data_tx, data_rx) = unbounded::<Option<TraceInfoBuffer>>();
let (return_tx, return_rx) = bounded::<TraceInfoBuffer>(1024);
let thread_locals: Arc<ThreadLocal<ThreadLocalState>> = Default::default();
let trace_writer = Self {
data_tx: data_tx.clone(),
return_rx: return_rx.clone(),
thread_locals: thread_locals.clone(),
};
fn steal_from_thread_locals(
thread_locals: &Arc<ThreadLocal<ThreadLocalState>>,
stolen_buffers: &mut Vec<TraceInfoBuffer>,
) {
for state in thread_locals.iter() {
let mut buffer = state.lock();
if let Some(buffer) = buffer.take() {
stolen_buffers.push(buffer);
}
}
}
let handle: std::thread::JoinHandle<()> = std::thread::spawn(move || {
let _ = writer.write(b"TRACEv0");
let mut buf = Vec::with_capacity(WRITE_BUFFER_SIZE);
let mut stolen_buffers = Vec::new();
let mut should_exit = false;
'outer: loop {
if !buf.is_empty() {
let _ = writer.write_all(&buf);
let _ = writer.flush();
buf.clear();
}
let recv = if should_exit {
Ok(None)
} else {
data_rx.recv_timeout(Duration::from_secs(1))
};
let mut data = match recv {
Ok(Some(data)) => data,
result => {
if result.is_ok() {
// On exit signal
should_exit = true;
}
// When we receive no data for a second or we want to exit we poll the
// thread local buffers to steal some data. This
// prevents unsend data if a thread is hanging or the
// system just go into idle.
steal_from_thread_locals(&thread_locals, &mut stolen_buffers);
if let Some(data) = stolen_buffers.pop() {
data
} else {
match result {
Ok(Some(_)) => unreachable!(),
Ok(None) | Err(RecvTimeoutError::Disconnected) => {
// We should exit.
break 'outer;
}
Err(RecvTimeoutError::Timeout) => {
// No data stolen, wait again
continue;
}
}
}
}
};
if data.buffer.len() > buf.capacity() {
let _ = writer.write_all(&data.buffer);
} else {
buf.extend_from_slice(&data.buffer);
}
data.clear();
let _ = return_tx.try_send(data);
loop {
let recv = stolen_buffers.pop().map(Some).ok_or(()).or_else(|_| {
if should_exit {
Ok(None)
} else {
data_rx.try_recv()
}
});
match recv {
Ok(Some(mut data)) => {
let data_buffer = &data.buffer;
if data_buffer.is_empty() {
break 'outer;
}
if buf.len() + data_buffer.len() > buf.capacity() {
let _ = writer.write_all(&buf);
buf.clear();
if data_buffer.len() > buf.capacity() {
let _ = writer.write_all(data_buffer);
} else {
buf.extend_from_slice(data_buffer);
}
} else {
buf.extend_from_slice(data_buffer);
}
data.clear();
let _ = return_tx.try_send(data);
}
Ok(None) | Err(TryRecvError::Disconnected) => {
should_exit = true;
break;
}
Err(TryRecvError::Empty) => {
break;
}
}
}
}
drop(writer);
});
let guard = TraceWriterGuard {
data_tx: Some(data_tx),
return_rx: Some(return_rx),
handle: Some(handle),
};
(trace_writer, guard)
}
fn send(&self, data: TraceInfoBuffer) {
debug_assert!(!data.buffer.is_empty());
let _ = self.data_tx.send(Some(data));
}
fn get_empty_buffer(&self, capacity: usize) -> TraceInfoBuffer {
self.return_rx
.try_recv()
.ok()
.unwrap_or_else(|| TraceInfoBuffer::new(capacity))
}
pub fn start_write(&self) -> WriteGuard<'_> {
let thread_local_buffer = self.thread_locals.get_or_default();
let buffer = thread_local_buffer.lock();
WriteGuard::new(buffer, self)
}
}
pub struct TraceWriterGuard {
data_tx: Option<Sender<Option<TraceInfoBuffer>>>,
return_rx: Option<Receiver<TraceInfoBuffer>>,
handle: Option<JoinHandle<()>>,
}
impl Drop for TraceWriterGuard {
fn drop(&mut self) {
// Send exit signal, we can't use disconnect since there is another instance in TraceWriter
let _ = self.data_tx.take().unwrap().send(None);
// Receive all return buffers and drop them here. The thread is already busy writing.
let return_rx = self.return_rx.take().unwrap();
while return_rx.recv().is_ok() {}
// Wait for the thread to finish completely
let _ = self.handle.take().unwrap().join();
}
}
pub struct WriteGuard<'l> {
// Safety: The buffer must not be None
buffer: MutexGuard<'l, Option<TraceInfoBuffer>>,
trace_writer: &'l TraceWriter,
}
impl<'l> WriteGuard<'l> {
fn new(
mut buffer: MutexGuard<'l, Option<TraceInfoBuffer>>,
trace_writer: &'l TraceWriter,
) -> Self {
// Safety: The buffer must not be None, so we initialize it here
if buffer.is_none() {
*buffer = Some(trace_writer.get_empty_buffer(THREAD_LOCAL_INITIAL_BUFFER_SIZE));
};
Self {
buffer,
trace_writer,
}
}
fn buffer(&mut self) -> &mut TraceInfoBuffer {
// Safety: The struct invariant ensures that the buffer is not None
unsafe { self.buffer.as_mut().unwrap_unchecked() }
}
pub fn push(&mut self, data: u8) {
self.buffer().push(data);
}
pub fn extend(&mut self, data: &[u8]) {
self.buffer().extend(data);
}
}
impl Drop for WriteGuard<'_> {
fn drop(&mut self) {
if self.buffer().buffer.capacity() * 2 < self.buffer().buffer.len() * 3 {
let capacity = self.buffer().buffer.capacity();
let new_buffer = self.trace_writer.get_empty_buffer(capacity);
let buffer = std::mem::replace(self.buffer(), new_buffer);
self.trace_writer.send(buffer);
}
}
}
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