tee: improve throughput by raw syscall

src/uu/tee/Cargo.toml

@@ -22,7 +22,7 @@ doctest = false
 [dependencies]
 clap = { workspace = true }
 rustix = { workspace = true, features = ["stdio", "fs"] }
-uucore = { workspace = true, features = ["parser", "signals"] }
+uucore = { workspace = true, features = ["fs", "parser", "signals"] }
 fluent = { workspace = true }
 
 [dev-dependencies]

src/uu/tee/src/tee.rs

@@ -7,7 +7,7 @@
 
 use std::ffi::OsString;
 use std::fs::OpenOptions;
-use std::io::{Error, ErrorKind, Read, Result, Write, stderr, stdin, stdout};
+use std::io::{Error, ErrorKind, Read, Result, Write, stderr, stdin};
 use std::path::PathBuf;
 use uucore::display::Quotable;
 use uucore::error::{UResult, strip_errno};
@@ -80,7 +80,10 @@ fn tee(options: &Options) -> Result<()> {
         0,
         NamedWriter {
             name: translate!("tee-standard-output").into(),
-            inner: Writer::Stdout(stdout()),
+            #[cfg(any(unix, target_os = "wasi"))]
+            inner: Writer::Stdout(uucore::io::RawWriter(rustix::stdio::stdout())),
+            #[cfg(not(any(unix, target_os = "wasi")))]
+            inner: Writer::Stdout(std::io::stdout()),
         },
     );
 
@@ -197,21 +200,16 @@ impl MultiWriter {
 
     fn write_flush(&mut self, buf: &[u8]) -> Result<()> {
         let mode = self.output_error_mode;
-        self.writers.retain_mut(|writer| {
-            let res = (|| {
-                writer.inner.write_all(buf)?;
-                writer.inner.flush()
-            })();
-            match res {
+        self.writers
+            .retain_mut(|writer| match writer.inner.write_all(buf) {
                 Ok(()) => true,
                 Err(e) => {
                     if let Err(e) = process_error(mode, e, writer, &mut self.ignored_errors) {
                         self.aborted.get_or_insert(e);
                     }
                     false
                 }
-            }
-        });
+            });
         self.aborted.take().map_or(
             if self.writers.is_empty() {
                 // This error kind will never be raised by the standard
@@ -251,21 +249,26 @@ fn process_error(
 
 enum Writer {
     File(std::fs::File),
+    // remove buffering for posix requirement and improve throughput
+    #[cfg(any(unix, target_os = "wasi"))]
+    Stdout(uucore::io::RawWriter<rustix::fd::BorrowedFd<'static>>),
+    #[cfg(not(any(unix, target_os = "wasi")))]
     Stdout(std::io::Stdout),
 }
 
-impl Write for Writer {
-    fn write(&mut self, buf: &[u8]) -> Result<usize> {
-        match self {
-            Self::File(f) => f.write(buf),
-            Self::Stdout(s) => s.write(buf),
-        }
-    }
-
-    fn flush(&mut self) -> Result<()> {
+impl Writer {
+    pub fn write_all(&mut self, buf: &[u8]) -> Result<()> {
         match self {
-            Self::File(f) => f.flush(),
-            Self::Stdout(s) => s.flush(),
+            // File does not have line buffering
+            Self::File(f) => f.write_all(buf),
+            #[cfg(any(unix, target_os = "wasi"))]
+            Self::Stdout(s) => s.write_all(buf),
+            #[cfg(not(any(unix, target_os = "wasi")))]
+            Self::Stdout(s) => {
+                s.write_all(buf)?;
+                // needs unsafe to remove buffering... flush after write_all to keep overhead minimal
+                s.flush()
+            }
         }
     }
 }