Skip to content

Navigation Menu

Sign in
Appearance settings

Search code, repositories, users, issues, pull requests...

Provide feedback

We read every piece of feedback, and take your input very seriously.

Saved searches

Use saved searches to filter your results more quickly
Sign up
Appearance settings

Commit 3321ce6

Browse files
Ensure non-empty buffers for large vectored I/O
`readv` and `writev` are constrained by a platform-specific upper bound on the number of buffers which can be passed. Currently, `read_vectored` and `write_vectored` implementations simply truncate to this limit when larger. However, when the only non-empty buffers are at indices above this limit, they will erroneously return `Ok(0)`. Instead, slice the buffers starting at the first non-empty buffer. This trades a conditional move for a branch, so it's barely a penalty in the common case. The new method `limit_slices` on `IoSlice` and `IoSliceMut` may be generally useful to users like `advance_slices` is, but I have left it as `pub(crate)` for now.
1 parent ae8ab87 commit 3321ce6

File tree

6 files changed

+125
-53
lines changed

6 files changed

+125
-53
lines changed

‎library/std/src/io/mod.rs

Lines changed: 37 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -297,6 +297,7 @@
297297
#[cfg(test)]
298298
mod tests;
299299

300+
use core::intrinsics;
300301
#[unstable(feature = "read_buf", issue = "78485")]
301302
pub use core::io::{BorrowedBuf, BorrowedCursor};
302303
use core::slice::memchr;
@@ -1388,6 +1389,24 @@ impl<'a> IoSliceMut<'a> {
13881389
}
13891390
}
13901391

1392+
/// Limits a slice of buffers to at most `n` buffers.
1393+
///
1394+
/// When the slice contains over `n` buffers, ensure that at least one
1395+
/// non-empty buffer is in the truncated slice, if there is one.
1396+
#[inline]
1397+
pub(crate) fn limit_slices(bufs: &mut &mut [IoSliceMut<'a>], n: usize) {
1398+
if intrinsics::unlikely(bufs.len() > n) {
1399+
for (i, buf) in bufs.iter().enumerate() {
1400+
if !buf.is_empty() {
1401+
let len = cmp::min(bufs.len() - i, n);
1402+
*bufs = &mut take(bufs)[i..i + len];
1403+
return;
1404+
}
1405+
}
1406+
*bufs = &mut take(bufs)[..0];
1407+
}
1408+
}
1409+
13911410
/// Get the underlying bytes as a mutable slice with the original lifetime.
13921411
///
13931412
/// # Examples
@@ -1549,6 +1568,24 @@ impl<'a> IoSlice<'a> {
15491568
}
15501569
}
15511570

1571+
/// Limits a slice of buffers to at most `n` buffers.
1572+
///
1573+
/// When the slice contains over `n` buffers, ensure that at least one
1574+
/// non-empty buffer is in the truncated slice, if there is one.
1575+
#[inline]
1576+
pub(crate) fn limit_slices(bufs: &mut &[IoSlice<'a>], n: usize) {
1577+
if intrinsics::unlikely(bufs.len() > n) {
1578+
for (i, buf) in bufs.iter().enumerate() {
1579+
if !buf.is_empty() {
1580+
let len = cmp::min(bufs.len() - i, n);
1581+
*bufs = &bufs[i..i + len];
1582+
return;
1583+
}
1584+
}
1585+
*bufs = &bufs[..0];
1586+
}
1587+
}
1588+
15521589
/// Get the underlying bytes as a slice with the original lifetime.
15531590
///
15541591
/// This doesn't borrow from `self`, so is less restrictive than calling

‎library/std/src/sys/net/connection/socket/solid.rs

Lines changed: 7 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@ use crate::os::solid::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, Owne
99
use crate::sys::abi;
1010
use crate::sys_common::{FromInner, IntoInner};
1111
use crate::time::Duration;
12-
use crate::{cmp,mem, ptr, str};
12+
use crate::{mem, ptr, str};
1313

1414
pub(super) mod netc {
1515
pub use crate::sys::abi::sockets::*;
@@ -222,13 +222,10 @@ impl Socket {
222222
self.recv_with_flags(buf, 0)
223223
}
224224

225-
pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
225+
pub fn read_vectored(&self, mut bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
226+
IoSliceMut::limit_slices(&mut bufs, max_iov());
226227
let ret = cvt(unsafe {
227-
netc::readv(
228-
self.as_raw_fd(),
229-
bufs.as_ptr() as *const netc::iovec,
230-
cmp::min(bufs.len(), max_iov()) as c_int,
231-
)
228+
netc::readv(self.as_raw_fd(), bufs.as_ptr() as *const netc::iovec, bufs.len() as c_int)
232229
})?;
233230
Ok(ret as usize)
234231
}
@@ -267,13 +264,10 @@ impl Socket {
267264
self.recv_from_with_flags(buf, MSG_PEEK)
268265
}
269266

270-
pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
267+
pub fn write_vectored(&self, mut bufs: &[IoSlice<'_>]) -> io::Result<usize> {
268+
IoSlice::limit_slices(&mut bufs, max_iov());
271269
let ret = cvt(unsafe {
272-
netc::writev(
273-
self.as_raw_fd(),
274-
bufs.as_ptr() as *const netc::iovec,
275-
cmp::min(bufs.len(), max_iov()) as c_int,
276-
)
270+
netc::writev(self.as_raw_fd(), bufs.as_ptr() as *const netc::iovec, bufs.len() as c_int)
277271
})?;
278272
Ok(ret as usize)
279273
}

‎library/std/src/sys/net/connection/socket/windows.rs

Lines changed: 15 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -299,8 +299,6 @@ impl Socket {
299299
}
300300

301301
fn recv_with_flags(&self, mut buf: BorrowedCursor<'_>, flags: c_int) -> io::Result<()> {
302-
// On unix when a socket is shut down all further reads return 0, so we
303-
// do the same on windows to map a shut down socket to returning EOF.
304302
let length = cmp::min(buf.capacity(), i32::MAX as usize) as i32;
305303
let result =
306304
unsafe { c::recv(self.as_raw(), buf.as_mut().as_mut_ptr() as *mut _, length, flags) };
@@ -309,6 +307,9 @@ impl Socket {
309307
c::SOCKET_ERROR => {
310308
let error = unsafe { c::WSAGetLastError() };
311309

310+
// On Unix when a socket is shut down, all further reads return
311+
// 0, so we do the same on Windows to map a shut down socket to
312+
// returning EOF.
312313
if error == c::WSAESHUTDOWN {
313314
Ok(())
314315
} else {
@@ -332,17 +333,15 @@ impl Socket {
332333
self.recv_with_flags(buf, 0)
333334
}
334335

335-
pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
336-
// On unix when a socket is shut down all further reads return 0, so we
337-
// do the same on windows to map a shut down socket to returning EOF.
338-
let length = cmp::min(bufs.len(), u32::MAX as usize) as u32;
336+
pub fn read_vectored(&self, mut bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
337+
IoSliceMut::limit_slices(&mut bufs, u32::MAX as usize);
339338
let mut nread = 0;
340339
let mut flags = 0;
341340
let result = unsafe {
342341
c::WSARecv(
343342
self.as_raw(),
344343
bufs.as_mut_ptr() as *mut c::WSABUF,
345-
length,
344+
bufs.len()asu32,
346345
&mut nread,
347346
&mut flags,
348347
ptr::null_mut(),
@@ -355,6 +354,9 @@ impl Socket {
355354
_ => {
356355
let error = unsafe { c::WSAGetLastError() };
357356

357+
// On Unix when a socket is shut down, all further reads return
358+
// 0, so we do the same on Windows to map a shut down socket to
359+
// returning EOF.
358360
if error == c::WSAESHUTDOWN {
359361
Ok(0)
360362
} else {
@@ -384,8 +386,6 @@ impl Socket {
384386
let mut addrlen = size_of_val(&storage) as netc::socklen_t;
385387
let length = cmp::min(buf.len(), <wrlen_t>::MAX as usize) as wrlen_t;
386388

387-
// On unix when a socket is shut down all further reads return 0, so we
388-
// do the same on windows to map a shut down socket to returning EOF.
389389
let result = unsafe {
390390
c::recvfrom(
391391
self.as_raw(),
@@ -401,6 +401,9 @@ impl Socket {
401401
c::SOCKET_ERROR => {
402402
let error = unsafe { c::WSAGetLastError() };
403403

404+
// On Unix when a socket is shut down, all further reads return
405+
// 0, so we do the same on Windows to map a shut down socket to
406+
// returning EOF.
404407
if error == c::WSAESHUTDOWN {
405408
Ok((0, unsafe { socket_addr_from_c(&storage, addrlen as usize)? }))
406409
} else {
@@ -419,14 +422,14 @@ impl Socket {
419422
self.recv_from_with_flags(buf, c::MSG_PEEK)
420423
}
421424

422-
pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
423-
let length = cmp::min(bufs.len(), u32::MAX as usize)asu32;
425+
pub fn write_vectored(&self, mutbufs: &[IoSlice<'_>]) -> io::Result<usize> {
426+
IoSlice::limit_slices(&mutbufs, u32::MAX as usize);
424427
let mut nwritten = 0;
425428
let result = unsafe {
426429
c::WSASend(
427430
self.as_raw(),
428431
bufs.as_ptr() as *const c::WSABUF as *mut _,
429-
length,
432+
bufs.len()asu32,
430433
&mut nwritten,
431434
0,
432435
ptr::null_mut(),

‎library/std/src/sys/pal/hermit/fd.rs

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1,7 +1,6 @@
11
#![unstable(reason = "not public", issue = "none", feature = "fd")]
22

33
use super::hermit_abi;
4-
use crate::cmp;
54
use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read, SeekFrom};
65
use crate::os::hermit::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
76
use crate::sys::{cvt, unsupported};
@@ -38,12 +37,13 @@ impl FileDesc {
3837
Ok(())
3938
}
4039

41-
pub fn read_vectored(&self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
40+
pub fn read_vectored(&self, mut bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
41+
IoSliceMut::limit_slices(&mut bufs, max_iov());
4242
let ret = cvt(unsafe {
4343
hermit_abi::readv(
4444
self.as_raw_fd(),
4545
bufs.as_mut_ptr() as *mut hermit_abi::iovec as *const hermit_abi::iovec,
46-
cmp::min(bufs.len(),max_iov()),
46+
bufs.len(),
4747
)
4848
})?;
4949
Ok(ret as usize)
@@ -65,12 +65,13 @@ impl FileDesc {
6565
Ok(result as usize)
6666
}
6767

68-
pub fn write_vectored(&self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
68+
pub fn write_vectored(&self, mut bufs: &[IoSlice<'_>]) -> io::Result<usize> {
69+
IoSlice::limit_slices(&mut bufs, max_iov());
6970
let ret = cvt(unsafe {
7071
hermit_abi::writev(
7172
self.as_raw_fd(),
7273
bufs.as_ptr() as *const hermit_abi::iovec,
73-
cmp::min(bufs.len(),max_iov()),
74+
bufs.len(),
7475
)
7576
})?;
7677
Ok(ret as usize)

0 commit comments

Comments
(0)

AltStyle によって変換されたページ (->オリジナル) /