314 lines
12 KiB
Rust
314 lines
12 KiB
Rust
use crate::handle::{Filetype, Handle};
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use crate::sched::{
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ClockEventData, Errno, Event, EventFdReadwrite, Eventrwflags, Eventtype, FdEventData,
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};
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use crate::sys::osdir::OsDir;
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use crate::sys::osfile::OsFile;
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use crate::sys::osother::OsOther;
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use crate::sys::stdio::{Stderr, Stdin, Stdout};
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use crate::sys::AsFile;
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use crate::{Error, Result};
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use lazy_static::lazy_static;
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use std::convert::TryInto;
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use std::sync::mpsc::{self, Receiver, RecvTimeoutError, Sender, TryRecvError};
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use std::sync::Mutex;
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use std::thread;
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use std::time::Duration;
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use tracing::{debug, error, trace, warn};
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struct StdinPoll {
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request_tx: Sender<()>,
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notify_rx: Receiver<PollState>,
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}
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enum PollState {
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Ready,
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NotReady, // it's not ready, but we didn't wait
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TimedOut, // it's not ready and a timeout has occurred
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Error(Errno),
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}
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enum WaitMode {
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Timeout(Duration),
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Infinite,
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Immediate,
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}
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impl StdinPoll {
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// This function should not be used directly
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// Correctness of this function crucially depends on the fact that
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// mpsc::Receiver is !Sync.
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fn poll(&self, wait_mode: WaitMode) -> PollState {
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// Clean up possible unread result from the previous poll
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match self.notify_rx.try_recv() {
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Ok(_) | Err(TryRecvError::Empty) => {}
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Err(TryRecvError::Disconnected) => panic!("notify_rx channel closed"),
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}
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// Notify the worker thread that we want to poll stdin
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self.request_tx.send(()).expect("request_tx channel closed");
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// Wait for the worker thread to send a readiness notification
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let pollret = match wait_mode {
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WaitMode::Timeout(timeout) => {
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self.notify_rx
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.recv_timeout(timeout)
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.unwrap_or_else(|e| match e {
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RecvTimeoutError::Disconnected => panic!("notify_rx channel closed"),
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RecvTimeoutError::Timeout => PollState::TimedOut,
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})
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}
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WaitMode::Infinite => self.notify_rx.recv().expect("notify_rx channel closed"),
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WaitMode::Immediate => self.notify_rx.try_recv().unwrap_or_else(|e| match e {
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TryRecvError::Disconnected => panic!("notify_rx channel closed"),
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TryRecvError::Empty => PollState::NotReady,
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}),
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};
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pollret
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}
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fn event_loop(request_rx: Receiver<()>, notify_tx: Sender<PollState>) -> ! {
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use std::io::BufRead;
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loop {
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// Wait for the request to poll stdin
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request_rx.recv().expect("request_rx channel closed");
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// Wait for data to appear in stdin.
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// If `fill_buf` returns any slice, then it means that either
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// (a) there some data in stdin, if it's non-empty
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// (b) EOF was received, if it's empty
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// Linux returns `POLLIN` in both cases, and we imitate this behavior.
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let resp = match std::io::stdin().lock().fill_buf() {
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Ok(_) => PollState::Ready,
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Err(e) => PollState::Error(Errno::from(Error::from(e))),
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};
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// Notify the requestor about data in stdin. They may have already timed out,
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// then the next requestor will have to clean the channel.
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notify_tx.send(resp).expect("notify_tx channel closed");
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}
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}
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}
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lazy_static! {
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static ref STDIN_POLL: Mutex<StdinPoll> = {
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let (request_tx, request_rx) = mpsc::channel();
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let (notify_tx, notify_rx) = mpsc::channel();
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thread::spawn(move || StdinPoll::event_loop(request_rx, notify_tx));
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Mutex::new(StdinPoll {
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request_tx,
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notify_rx,
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})
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};
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}
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fn make_rw_event(event: &FdEventData, nbytes: std::result::Result<u64, Errno>) -> Event {
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let (nbytes, error) = match nbytes {
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Ok(nbytes) => (nbytes, Errno::Success),
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Err(e) => (u64::default(), e),
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};
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Event {
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userdata: event.userdata,
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type_: event.r#type,
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error,
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fd_readwrite: EventFdReadwrite {
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nbytes,
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flags: Eventrwflags::empty(),
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},
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}
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}
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fn make_timeout_event(timeout: &ClockEventData) -> Event {
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Event {
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userdata: timeout.userdata,
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type_: Eventtype::Clock,
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error: Errno::Success,
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fd_readwrite: EventFdReadwrite {
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nbytes: 0,
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flags: Eventrwflags::empty(),
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},
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}
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}
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fn handle_timeout(timeout_event: ClockEventData, timeout: Duration, events: &mut Vec<Event>) {
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thread::sleep(timeout);
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handle_timeout_event(timeout_event, events);
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}
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fn handle_timeout_event(timeout_event: ClockEventData, events: &mut Vec<Event>) {
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let new_event = make_timeout_event(&timeout_event);
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events.push(new_event);
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}
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fn handle_rw_event(event: FdEventData, out_events: &mut Vec<Event>) {
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let handle = &event.handle;
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let size = if let Some(_) = handle.as_any().downcast_ref::<Stdin>() {
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// We return the only universally correct lower bound, see the comment later in the function.
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Ok(1)
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} else if let Some(_) = handle.as_any().downcast_ref::<Stdout>() {
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// On Unix, ioctl(FIONREAD) will return 0 for stdout. Emulate the same behavior on Windows.
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Ok(0)
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} else if let Some(_) = handle.as_any().downcast_ref::<Stderr>() {
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// On Unix, ioctl(FIONREAD) will return 0 for stdout/stderr. Emulate the same behavior on Windows.
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Ok(0)
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} else {
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if event.r#type == Eventtype::FdRead {
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handle
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.as_file()
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.and_then(|f| f.metadata())
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.map(|m| m.len())
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.map_err(|ioerror| Errno::from(Error::from(ioerror)))
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} else {
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// The spec is unclear what nbytes should actually be for __WASI_EVENTTYPE_FD_WRITE and
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// the implementation on Unix just returns 0 here, so it's probably fine
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// to do the same on Windows for now.
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// cf. https://github.com/WebAssembly/WASI/issues/148
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Ok(0)
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}
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};
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let new_event = make_rw_event(&event, size);
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out_events.push(new_event);
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}
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fn handle_error_event(event: FdEventData, error: Errno, out_events: &mut Vec<Event>) {
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let new_event = make_rw_event(&event, Err(error));
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out_events.push(new_event);
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}
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pub(crate) fn oneoff(
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timeout: Option<ClockEventData>,
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fd_events: Vec<FdEventData>,
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events: &mut Vec<Event>,
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) -> Result<()> {
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let timeout = timeout
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.map(|event| {
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event
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.delay
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.try_into()
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.map(Duration::from_nanos)
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.map(|dur| (event, dur))
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})
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.transpose()?;
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// With no events to listen, poll_oneoff just becomes a sleep.
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if fd_events.is_empty() {
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match timeout {
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Some((event, dur)) => return Ok(handle_timeout(event, dur, events)),
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// The implementation has to return Ok(()) in this case,
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// cf. the comment in src/hostcalls_impl/misc.rs
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None => return Ok(()),
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}
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}
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let mut stdin_events = vec![];
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let mut immediate_events = vec![];
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let mut pipe_events = vec![];
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for event in fd_events {
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let handle = &event.handle;
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if let Some(_) = handle.as_any().downcast_ref::<OsFile>() {
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immediate_events.push(event);
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} else if let Some(_) = handle.as_any().downcast_ref::<OsDir>() {
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immediate_events.push(event);
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} else if let Some(_) = handle.as_any().downcast_ref::<Stdin>() {
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stdin_events.push(event);
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} else if let Some(_) = handle.as_any().downcast_ref::<Stdout>() {
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// stdout are always considered ready to write because there seems to
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// be no way of checking if a write to stdout would block.
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//
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// If stdin is polled for anything else then reading, then it is also
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// considered immediately ready, following the behavior on Linux.
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immediate_events.push(event);
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} else if let Some(_) = handle.as_any().downcast_ref::<Stderr>() {
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// stderr are always considered ready to write because there seems to
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// be no way of checking if a write to stdout would block.
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//
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// If stdin is polled for anything else then reading, then it is also
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// considered immediately ready, following the behavior on Linux.
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immediate_events.push(event);
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} else if let Some(other) = handle.as_any().downcast_ref::<OsOther>() {
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if other.get_file_type() == Filetype::SocketStream {
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// We map pipe to SocketStream
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pipe_events.push(event);
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} else {
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debug!(
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"poll_oneoff: unsupported file type: {}",
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other.get_file_type()
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);
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handle_error_event(event, Errno::Notsup, events);
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}
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} else {
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tracing::error!("can poll FdEvent for OS resources only");
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return Err(Error::Badf);
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}
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}
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let immediate = !immediate_events.is_empty();
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// Process all the events that do not require waiting.
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if immediate {
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trace!(" | have immediate events, will return immediately");
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for event in immediate_events {
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handle_rw_event(event, events);
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}
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}
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if !stdin_events.is_empty() {
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// waiting for data to arrive on stdin. This thread will not terminate.
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//
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// We'd like to do the following:
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// (1) wait in a non-blocking way for data to be available in stdin, with timeout
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// (2) find out, how many bytes are there available to be read.
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//
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// One issue is that we are currently relying on the Rust libstd for interaction
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// with stdin. More precisely, `io::stdin` is used via the `BufRead` trait,
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// in the `fd_read` function, which always does buffering on the libstd side. [1]
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// This means that even if there's still some unread data in stdin,
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// the lower-level Windows system calls may return false negatives,
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// claiming that stdin is empty.
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//
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// Theoretically, one could use `WaitForSingleObject` on the stdin handle
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// to achieve (1). Unfortunately, this function doesn't seem to honor the
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// requested timeout and to misbehaves after the stdin is closed.
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//
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// There appears to be no way of achieving (2) on Windows.
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// [1]: https://github.com/rust-lang/rust/pull/12422
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let waitmode = if immediate {
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trace!(" | tentatively checking stdin");
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WaitMode::Immediate
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} else {
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trace!(" | passively waiting on stdin");
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match timeout {
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Some((_event, dur)) => WaitMode::Timeout(dur),
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None => WaitMode::Infinite,
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}
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};
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let state = STDIN_POLL.lock().unwrap().poll(waitmode);
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for event in stdin_events {
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match state {
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PollState::Ready => handle_rw_event(event, events),
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PollState::NotReady => {} // not immediately available, so just ignore
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PollState::TimedOut => handle_timeout_event(timeout.unwrap().0, events),
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PollState::Error(e) => handle_error_event(event, e, events),
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}
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}
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}
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if !immediate && !pipe_events.is_empty() {
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trace!(" | actively polling pipes");
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match timeout {
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Some((event, dur)) => {
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// In the tests stdin is replaced with a dummy pipe, so for now
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// we just time out. Support for pipes will be decided later on.
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warn!("Polling pipes not supported on Windows, will just time out.");
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handle_timeout(event, dur, events);
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}
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None => {
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error!("Polling only pipes with no timeout not supported on Windows.");
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return Err(Error::Notsup);
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}
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}
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}
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Ok(())
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}
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