use std::time::Duration;
use std::{io, thread};
use actix_rt::{
time::{sleep, Instant},
System,
};
use log::{error, info};
use mio::{Interest, Poll, Token as MioToken};
use slab::Slab;
use crate::server::Server;
use crate::socket::{MioListener, SocketAddr};
use crate::waker_queue::{WakerInterest, WakerQueue, WAKER_TOKEN};
use crate::worker::{Conn, WorkerHandleAccept};
use crate::Token;
struct ServerSocketInfo {
/// Address of socket. Mainly used for logging.
addr: SocketAddr,
/// Beware this is the crate token for identify socket and should not be confused
/// with `mio::Token`.
token: Token,
lst: MioListener,
/// Timeout is used to mark the deadline when this socket's listener should be registered again
/// after an error.
timeout: Option<Instant>,
}
/// Accept loop would live with `ServerBuilder`.
///
/// It's tasked with construct `Poll` instance and `WakerQueue` which would be distributed to
/// `Accept` and `Worker`.
///
/// It would also listen to `ServerCommand` and push interests to `WakerQueue`.
pub(crate) struct AcceptLoop {
srv: Option<Server>,
poll: Option<Poll>,
waker: WakerQueue,
}
impl AcceptLoop {
pub fn new(srv: Server) -> Self {
let poll = Poll::new().unwrap_or_else(|e| panic!("Can not create `mio::Poll`: {}", e));
let waker = WakerQueue::new(poll.registry())
.unwrap_or_else(|e| panic!("Can not create `mio::Waker`: {}", e));
Self {
srv: Some(srv),
poll: Some(poll),
waker,
}
}
pub(crate) fn waker_owned(&self) -> WakerQueue {
self.waker.clone()
}
pub fn wake(&self, i: WakerInterest) {
self.waker.wake(i);
}
pub(crate) fn start(
&mut self,
socks: Vec<(Token, MioListener)>,
handles: Vec<WorkerHandleAccept>,
) {
let srv = self.srv.take().expect("Can not re-use AcceptInfo");
let poll = self.poll.take().unwrap();
let waker = self.waker.clone();
Accept::start(poll, waker, socks, srv, handles);
}
}
/// poll instance of the server.
struct Accept {
poll: Poll,
waker: WakerQueue,
handles: Vec<WorkerHandleAccept>,
srv: Server,
next: usize,
avail: Availability,
backpressure: bool,
}
/// Array of u128 with every bit as marker for a worker handle's availability.
struct Availability([u128; 4]);
impl Default for Availability {
fn default() -> Self {
Self([0; 4])
}
}
impl Availability {
/// Check if any worker handle is available
fn available(&self) -> bool {
self.0.iter().any(|a| *a != 0)
}
/// Set worker handle available state by index.
fn set_available(&mut self, idx: usize, avail: bool) {
let (offset, idx) = if idx < 128 {
(0, idx)
} else if idx < 128 * 2 {
(1, idx - 128)
} else if idx < 128 * 3 {
(2, idx - 128 * 2)
} else if idx < 128 * 4 {
(3, idx - 128 * 3)
} else {
panic!("Max WorkerHandle count is 512")
};
let off = 1 << idx as u128;
if avail {
self.0[offset] |= off;
} else {
self.0[offset] &= !off
}
}
/// Set all worker handle to available state.
/// This would result in a re-check on all workers' availability.
fn set_available_all(&mut self, handles: &[WorkerHandleAccept]) {
handles.iter().for_each(|handle| {
self.set_available(handle.idx(), true);
})
}
}
/// This function defines errors that are per-connection. Which basically
/// means that if we get this error from `accept()` system call it means
/// next connection might be ready to be accepted.
///
/// All other errors will incur a timeout before next `accept()` is performed.
/// The timeout is useful to handle resource exhaustion errors like ENFILE
/// and EMFILE. Otherwise, could enter into tight loop.
fn connection_error(e: &io::Error) -> bool {
e.kind() == io::ErrorKind::ConnectionRefused
|| e.kind() == io::ErrorKind::ConnectionAborted
|| e.kind() == io::ErrorKind::ConnectionReset
}
impl Accept {
pub(crate) fn start(
poll: Poll,
waker: WakerQueue,
socks: Vec<(Token, MioListener)>,
srv: Server,
handles: Vec<WorkerHandleAccept>,
) {
// Accept runs in its own thread and would want to spawn additional futures to current
// actix system.
let sys = System::current();
thread::Builder::new()
.name("actix-server accept loop".to_owned())
.spawn(move || {
System::set_current(sys);
let (mut accept, sockets) =
Accept::new_with_sockets(poll, waker, socks, handles, srv);
accept.poll_with(sockets);
})
.unwrap();
}
fn new_with_sockets(
poll: Poll,
waker: WakerQueue,
socks: Vec<(Token, MioListener)>,
handles: Vec<WorkerHandleAccept>,
srv: Server,
) -> (Accept, Slab<ServerSocketInfo>) {
let mut sockets = Slab::new();
for (hnd_token, mut lst) in socks.into_iter() {
let addr = lst.local_addr();
let entry = sockets.vacant_entry();
let token = entry.key();
// Start listening for incoming connections
poll.registry()
.register(&mut lst, MioToken(token), Interest::READABLE)
.unwrap_or_else(|e| panic!("Can not register io: {}", e));
entry.insert(ServerSocketInfo {
addr,
token: hnd_token,
lst,
timeout: None,
});
}
let mut avail = Availability::default();
// Assume all handles are avail at construct time.
avail.set_available_all(&handles);
let accept = Accept {
poll,
waker,
handles,
srv,
next: 0,
avail,
backpressure: false,
};
(accept, sockets)
}
fn poll_with(&mut self, mut sockets: Slab<ServerSocketInfo>) {
let mut events = mio::Events::with_capacity(128);
loop {
if let Err(e) = self.poll.poll(&mut events, None) {
match e.kind() {
std::io::ErrorKind::Interrupted => continue,
_ => panic!("Poll error: {}", e),
}
}
for event in events.iter() {
let token = event.token();
match token {
// This is a loop because interests for command from previous version was
// a loop that would try to drain the command channel. It's yet unknown
// if it's necessary/good practice to actively drain the waker queue.
WAKER_TOKEN => 'waker: loop {
// take guard with every iteration so no new interest can be added
// until the current task is done.
let mut guard = self.waker.guard();
match guard.pop_front() {
// worker notify it becomes available. we may want to recover
// from backpressure.
Some(WakerInterest::WorkerAvailable(idx)) => {
drop(guard);
self.maybe_backpressure(&mut sockets, false);
self.avail.set_available(idx, true);
}
// a new worker thread is made and it's handle would be added to Accept
Some(WakerInterest::Worker(handle)) => {
drop(guard);
// maybe we want to recover from a backpressure.
self.maybe_backpressure(&mut sockets, false);
self.avail.set_available(handle.idx(), true);
self.handles.push(handle);
}
// got timer interest and it's time to try register socket(s) again
Some(WakerInterest::Timer) => {
drop(guard);
self.process_timer(&mut sockets)
}
Some(WakerInterest::Pause) => {
drop(guard);
self.deregister_all(&mut sockets);
}
Some(WakerInterest::Resume) => {
drop(guard);
sockets.iter_mut().for_each(|(token, info)| {
self.register_logged(token, info);
});
}
Some(WakerInterest::Stop) => {
return self.deregister_all(&mut sockets);
}
// waker queue is drained
None => {
// Reset the WakerQueue before break so it does not grow infinitely
WakerQueue::reset(&mut guard);
break 'waker;
}
}
},
_ => {
let token = usize::from(token);
self.accept(&mut sockets, token);
}
}
}
}
}
fn process_timer(&self, sockets: &mut Slab<ServerSocketInfo>) {
let now = Instant::now();
sockets
.iter_mut()
// Only sockets that had an associated timeout were deregistered.
.filter(|(_, info)| info.timeout.is_some())
.for_each(|(token, info)| {
let inst = info.timeout.take().unwrap();
if now < inst {
info.timeout = Some(inst);
} else if !self.backpressure {
self.register_logged(token, info);
}
// Drop the timeout if server is in backpressure and socket timeout is expired.
// When server recovers from backpressure it will register all sockets without
// a timeout value so this socket register will be delayed till then.
});
}
#[cfg(not(target_os = "windows"))]
fn register(&self, token: usize, info: &mut ServerSocketInfo) -> io::Result<()> {
self.poll
.registry()
.register(&mut info.lst, MioToken(token), Interest::READABLE)
}
#[cfg(target_os = "windows")]
fn register(&self, token: usize, info: &mut ServerSocketInfo) -> io::Result<()> {
// On windows, calling register without deregister cause an error.
// See https://github.com/actix/actix-web/issues/905
// Calling reregister seems to fix the issue.
self.poll
.registry()
.register(&mut info.lst, mio::Token(token), Interest::READABLE)
.or_else(|_| {
self.poll.registry().reregister(
&mut info.lst,
mio::Token(token),
Interest::READABLE,
)
})
}
fn register_logged(&self, token: usize, info: &mut ServerSocketInfo) {
match self.register(token, info) {
Ok(_) => info!("Resume accepting connections on {}", info.addr),
Err(e) => error!("Can not register server socket {}", e),
}
}
fn deregister(&self, info: &mut ServerSocketInfo) -> io::Result<()> {
self.poll.registry().deregister(&mut info.lst)
}
fn deregister_logged(&self, info: &mut ServerSocketInfo) {
match self.deregister(info) {
Ok(_) => info!("Paused accepting connections on {}", info.addr),
Err(e) => {
error!("Can not deregister server socket {}", e)
}
}
}
fn deregister_all(&self, sockets: &mut Slab<ServerSocketInfo>) {
// This is a best effort implementation with following limitation:
//
// Every ServerSocketInfo with associate timeout will be skipped and it's timeout
// is removed in the process.
//
// Therefore WakerInterest::Pause followed by WakerInterest::Resume in a very short
// gap (less than 500ms) would cause all timing out ServerSocketInfos be reregistered
// before expected timing.
sockets
.iter_mut()
// Take all timeout.
// This is to prevent Accept::process_timer method re-register a socket afterwards.
.map(|(_, info)| (info.timeout.take(), info))
// Socket info with a timeout is already deregistered so skip them.
.filter(|(timeout, _)| timeout.is_none())
.for_each(|(_, info)| self.deregister_logged(info));
}
fn maybe_backpressure(&mut self, sockets: &mut Slab<ServerSocketInfo>, on: bool) {
// Only operate when server is in a different backpressure than the given flag.
if self.backpressure != on {
self.backpressure = on;
sockets
.iter_mut()
// Only operate on sockets without associated timeout.
// Sockets with it should be handled by `accept` and `process_timer` methods.
// They are already deregistered or need to be reregister in the future.
.filter(|(_, info)| info.timeout.is_none())
.for_each(|(token, info)| {
if on {
self.deregister_logged(info);
} else {
self.register_logged(token, info);
}
});
}
}
fn accept_one(&mut self, sockets: &mut Slab<ServerSocketInfo>, mut conn: Conn) {
if self.backpressure {
// send_connection would remove fault worker from handles.
// worst case here is conn get dropped after all handles are gone.
while let Err(c) = self.send_connection(sockets, conn) {
conn = c
}
} else {
while self.avail.available() {
let next = self.next();
let idx = next.idx();
if next.available() {
self.avail.set_available(idx, true);
match self.send_connection(sockets, conn) {
Ok(_) => return,
Err(c) => conn = c,
}
} else {
self.avail.set_available(idx, false);
self.set_next();
}
}
// Sending Conn failed due to either all workers are in error or not available.
// Enter backpressure state and try again.
self.maybe_backpressure(sockets, true);
self.accept_one(sockets, conn);
}
}
// Send connection to worker and handle error.
fn send_connection(
&mut self,
sockets: &mut Slab<ServerSocketInfo>,
conn: Conn,
) -> Result<(), Conn> {
match self.next().send(conn) {
Ok(_) => {
self.set_next();
Ok(())
}
Err(conn) => {
// Worker thread is error and could be gone.
// Remove worker handle and notify `ServerBuilder`.
self.remove_next();
if self.handles.is_empty() {
error!("No workers");
self.maybe_backpressure(sockets, true);
// All workers are gone and Conn is nowhere to be sent.
// Treat this situation as Ok and drop Conn.
return Ok(());
} else if self.handles.len() <= self.next {
self.next = 0;
}
Err(conn)
}
}
}
fn accept(&mut self, sockets: &mut Slab<ServerSocketInfo>, token: usize) {
loop {
let info = sockets
.get_mut(token)
.expect("ServerSocketInfo is removed from Slab");
match info.lst.accept() {
Ok(io) => {
let msg = Conn {
io,
token: info.token,
};
self.accept_one(sockets, msg);
}
Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => return,
Err(ref e) if connection_error(e) => continue,
Err(e) => {
error!("Error accepting connection: {}", e);
// deregister listener temporary
self.deregister_logged(info);
// sleep after error. write the timeout to socket info as later
// the poll would need it mark which socket and when it's
// listener should be registered
info.timeout = Some(Instant::now() + Duration::from_millis(500));
// after the sleep a Timer interest is sent to Accept Poll
let waker = self.waker.clone();
System::current().arbiter().spawn(async move {
sleep(Duration::from_millis(510)).await;
waker.wake(WakerInterest::Timer);
});
return;
}
};
}
}
fn next(&self) -> &WorkerHandleAccept {
&self.handles[self.next]
}
/// Set next worker handle that would accept connection.
fn set_next(&mut self) {
self.next = (self.next + 1) % self.handles.len();
}
/// Remove next worker handle that fail to accept connection.
fn remove_next(&mut self) {
let handle = self.handles.swap_remove(self.next);
let idx = handle.idx();
// A message is sent to `ServerBuilder` future to notify it a new worker
// should be made.
self.srv.worker_faulted(idx);
self.avail.set_available(idx, false);
}
}
#[cfg(test)]
mod test {
use super::Availability;
fn single(aval: &mut Availability, idx: usize) {
aval.set_available(idx, true);
assert!(aval.available());
aval.set_available(idx, true);
aval.set_available(idx, false);
assert!(!aval.available());
aval.set_available(idx, false);
assert!(!aval.available());
}
fn multi(aval: &mut Availability, mut idx: Vec<usize>) {
idx.iter().for_each(|idx| aval.set_available(*idx, true));
assert!(aval.available());
while let Some(idx) = idx.pop() {
assert!(aval.available());
aval.set_available(idx, false);
}
assert!(!aval.available());
}
#[test]
fn availability() {
let mut aval = Availability::default();
single(&mut aval, 1);
single(&mut aval, 128);
single(&mut aval, 256);
single(&mut aval, 511);
let idx = (0..511).filter(|i| i % 3 == 0 && i % 5 == 0).collect();
multi(&mut aval, idx);
multi(&mut aval, (0..511).collect())
}
#[test]
#[should_panic]
fn overflow() {
let mut aval = Availability::default();
single(&mut aval, 512);
}
#[test]
fn pin_point() {
let mut aval = Availability::default();
aval.set_available(438, true);
aval.set_available(479, true);
assert_eq!(aval.0[3], 1 << (438 - 384) | 1 << (479 - 384));
}
}