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Commit 42b9823

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tbu-tbu-
committed
Optimize Seek::stream_len impl for File
It uses the file metadata on Unix with a fallback for files incorrectly reported as zero-sized. It uses `GetFileSizeEx` on Windows. This reduces the number of syscalls needed for determining the file size of an open file from 3 to 1.
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10 files changed

+84
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‎library/std/src/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/fs.rs
+32Lines changed: 32 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -823,9 +823,38 @@ impl Write for &File {
823823
}
824824
#[stable(feature = "rust1", since = "1.0.0")]
825825
impl Seek for &File {
826+
/// Seek to an offset, in bytes in a file.
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///
828+
/// See [`Seek::seek`] docs for more info.
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///
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/// # Platform-specific behavior
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///
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/// This function currently corresponds to the `lseek64` function on Unix
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/// and the `SetFilePointerEx` function on Windows. Note that this [may
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/// change in the future][changes].
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///
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/// [changes]: io#platform-specific-behavior
826837
fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
827838
self.inner.seek(pos)
828839
}
840+
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/// Returns the length of this file (in bytes).
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///
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/// See [`Seek::stream_len`] docs for more info.
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///
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/// # Platform-specific behavior
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///
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/// This function currently corresponds to the `statx` function on Linux
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/// (with fallbacks) and the `GetFileSizeEx` function on Windows. Note that
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/// this [may change in the future][changes].
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///
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/// [changes]: io#platform-specific-behavior
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fn stream_len(&mut self) -> io::Result<u64> {
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if let Some(result) = self.inner.size() {
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return result;
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}
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io::stream_len_default(self)
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}
829858
}
830859

831860
#[stable(feature = "rust1", since = "1.0.0")]
@@ -872,6 +901,9 @@ impl Seek for File {
872901
fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
873902
(&*self).seek(pos)
874903
}
904+
fn stream_len(&mut self) -> io::Result<u64> {
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(&*self).stream_len()
906+
}
875907
}
876908

877909
#[stable(feature = "io_traits_arc", since = "1.73.0")]

‎library/std/src/io/mod.rs

Copy file name to clipboardExpand all lines: library/std/src/io/mod.rs
+16-10Lines changed: 16 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1995,16 +1995,7 @@ pub trait Seek {
19951995
/// ```
19961996
#[unstable(feature = "seek_stream_len", issue = "59359")]
19971997
fn stream_len(&mut self) -> Result<u64> {
1998-
let old_pos = self.stream_position()?;
1999-
let len = self.seek(SeekFrom::End(0))?;
2000-
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// Avoid seeking a third time when we were already at the end of the
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// stream. The branch is usually way cheaper than a seek operation.
2003-
if old_pos != len {
2004-
self.seek(SeekFrom::Start(old_pos))?;
2005-
}
2006-
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Ok(len)
1998+
stream_len_default(self)
20081999
}
20092000

20102001
/// Returns the current seek position from the start of the stream.
@@ -2066,6 +2057,21 @@ pub trait Seek {
20662057
}
20672058
}
20682059

2060+
#[doc(hidden)]
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#[unstable(feature = "internal_stream_len_default", issue = "none")]
2062+
pub fn stream_len_default<T: Seek + ?Sized>(self_: &mut T) -> Result<u64> {
2063+
let old_pos = self_.stream_position()?;
2064+
let len = self_.seek(SeekFrom::End(0))?;
2065+
2066+
// Avoid seeking a third time when we were already at the end of the
2067+
// stream. The branch is usually way cheaper than a seek operation.
2068+
if old_pos != len {
2069+
self_.seek(SeekFrom::Start(old_pos))?;
2070+
}
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Ok(len)
2073+
}
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20692075
/// Enumeration of possible methods to seek within an I/O object.
20702076
///
20712077
/// It is used by the [`Seek`] trait.

‎library/std/src/sys/pal/hermit/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/hermit/fs.rs
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -426,6 +426,10 @@ impl File {
426426
Err(Error::from_raw_os_error(22))
427427
}
428428

429+
pub fn size(&self) -> Option<io::Result<u64>> {
430+
None
431+
}
432+
429433
pub fn duplicate(&self) -> io::Result<File> {
430434
Err(Error::from_raw_os_error(22))
431435
}

‎library/std/src/sys/pal/solid/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/solid/fs.rs
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -455,6 +455,10 @@ impl File {
455455
}
456456
}
457457

458+
pub fn size(&self) -> Option<io::Result<u64>> {
459+
None
460+
}
461+
458462
pub fn duplicate(&self) -> io::Result<File> {
459463
unsupported()
460464
}

‎library/std/src/sys/pal/unix/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/unix/fs.rs
+9Lines changed: 9 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1307,6 +1307,15 @@ impl File {
13071307
Ok(n as u64)
13081308
}
13091309

1310+
pub fn size(&self) -> Option<io::Result<u64>> {
1311+
match self.file_attr().map(|attr| attr.size()) {
1312+
// Fall back to default implementation if the returned size is 0,
1313+
// we might be in a proc mount.
1314+
Ok(0) => None,
1315+
result => Some(result),
1316+
}
1317+
}
1318+
13101319
pub fn duplicate(&self) -> io::Result<File> {
13111320
self.0.duplicate().map(File)
13121321
}

‎library/std/src/sys/pal/unsupported/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/unsupported/fs.rs
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -238,6 +238,10 @@ impl File {
238238
self.0
239239
}
240240

241+
pub fn size(&self) -> io::Result<u64> {
242+
self.0
243+
}
244+
241245
pub fn duplicate(&self) -> io::Result<File> {
242246
self.0
243247
}

‎library/std/src/sys/pal/wasi/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/wasi/fs.rs
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -465,6 +465,10 @@ impl File {
465465
self.fd.seek(pos)
466466
}
467467

468+
pub fn size(&self) -> Option<io::Result<u64>> {
469+
None
470+
}
471+
468472
pub fn duplicate(&self) -> io::Result<File> {
469473
// https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-rationale.md#why-no-dup
470474
unsupported()

‎library/std/src/sys/pal/windows/c/bindings.txt

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/windows/c/bindings.txt
+1Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2336,6 +2336,7 @@ Windows.Win32.Storage.FileSystem.FlushFileBuffers
23362336
Windows.Win32.Storage.FileSystem.GetFileAttributesW
23372337
Windows.Win32.Storage.FileSystem.GetFileInformationByHandle
23382338
Windows.Win32.Storage.FileSystem.GetFileInformationByHandleEx
2339+
Windows.Win32.Storage.FileSystem.GetFileSizeEx
23392340
Windows.Win32.Storage.FileSystem.GetFileType
23402341
Windows.Win32.Storage.FileSystem.GETFINALPATHNAMEBYHANDLE_FLAGS
23412342
Windows.Win32.Storage.FileSystem.GetFinalPathNameByHandleW

‎library/std/src/sys/pal/windows/c/windows_sys.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/windows/c/windows_sys.rs
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -273,6 +273,10 @@ extern "system" {
273273
) -> BOOL;
274274
}
275275
#[link(name = "kernel32")]
276+
extern "system" {
277+
pub fn GetFileSizeEx(hfile: HANDLE, lpfilesize: *mut i64) -> BOOL;
278+
}
279+
#[link(name = "kernel32")]
276280
extern "system" {
277281
pub fn GetFileType(hfile: HANDLE) -> FILE_TYPE;
278282
}

‎library/std/src/sys/pal/windows/fs.rs

Copy file name to clipboardExpand all lines: library/std/src/sys/pal/windows/fs.rs
+6Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -501,6 +501,12 @@ impl File {
501501
Ok(newpos as u64)
502502
}
503503

504+
pub fn size(&self) -> Option<io::Result<u64>> {
505+
let mut result = 0;
506+
Some(cvt(unsafe { c::GetFileSizeEx(self.handle.as_raw_handle(), &mut result) })
507+
.map(|_| result))
508+
}
509+
504510
pub fn duplicate(&self) -> io::Result<File> {
505511
Ok(Self { handle: self.handle.try_clone()? })
506512
}

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