hmmm

src/collection.rs

@@ -171,6 +171,8 @@ pub struct DataCollector {
     prev_idle: f64,
     #[cfg(target_os = "linux")]
     prev_non_idle: f64,
+    #[cfg(target_os = "linux")]
+    process_buffer: String,
 
     #[cfg(feature = "battery")]
     battery_manager: Option<Manager>,
@@ -224,6 +226,9 @@ impl DataCollector {
             gpus_total_mem: None,
             last_list_collection_time: last_collection_time,
             should_run_less_routine_tasks: true,
+            #[cfg(target_os = "linux")]
+            // SAFETY: This is an empty string.
+            process_buffer: unsafe { String::from_utf8_unchecked(Vec::with_capacity(16_384)) }
         }
     }
 

src/collection/processes/linux/mod.rs

@@ -404,14 +404,16 @@ pub(crate) fn linux_process_data(
     };
 
     // TODO: Maybe pre-allocate these buffers in the future w/ routine cleanup.
-    let mut buffer = String::new();
+    // SAFETY: This is safe, we're converting an empty string.
     let mut process_threads_to_check = HashMap::new();
 
     let mut process_vector: Vec<ProcessHarvest> = pids
         .filter_map(|pid_path| {
-            if let Ok((process, threads)) =
-                Process::from_path(pid_path, &mut buffer, args.get_process_threads)
-            {
+            if let Ok((process, threads)) = Process::from_path(
+                pid_path,
+                &mut collector.process_buffer,
+                args.get_process_threads,
+            ) {
                 let pid = process.pid;
                 let prev_proc_details = prev_process_details.entry(pid).or_default();
 
@@ -455,7 +457,9 @@ pub(crate) fn linux_process_data(
     // Get thread data.
     for (pid, tid_paths) in process_threads_to_check {
         for tid_path in tid_paths {
-            if let Ok((process, _)) = Process::from_path(tid_path, &mut buffer, false) {
+            if let Ok((process, _)) =
+                Process::from_path(tid_path, &mut collector.process_buffer, false)
+            {
                 let tid = process.pid;
                 let prev_proc_details = prev_process_details.entry(tid).or_default();
 

src/collection/processes/linux/process.rs

@@ -3,7 +3,7 @@
 
 use std::{
     fs::File,
-    io::{self, BufRead, BufReader, Read},
+    io::{self, BufRead, BufReader},
     path::PathBuf,
     sync::OnceLock,
 };
@@ -65,10 +65,13 @@ impl Stat {
     /// Get process stats from a file; this assumes the file is located at
     /// `/proc/<PID>/stat`. For documentation, see
     /// [here](https://manpages.ubuntu.com/manpages/noble/man5/proc_pid_stat.5.html) as a reference.
-    fn from_file(mut f: File, buffer: &mut String) -> anyhow::Result<Stat> {
+    fn from_file(fd: OwnedFd, buffer: &mut String) -> anyhow::Result<Stat> {
         // Since this is just one line, we can read it all at once. However, since it
         // (technically) might have non-utf8 characters, we can't just use read_to_string.
-        f.read_to_end(unsafe { buffer.as_mut_vec() })?;
+        //
+        // TODO: Can we read per delim. token to avoid memory?
+        // SAFETY: We are only going to be reading strings.
+        rustix::io::read(&fd, unsafe { buffer.as_mut_vec() })?;
 
         // TODO: Is this needed?
         let line = buffer.trim();
@@ -136,13 +139,15 @@ pub(crate) struct Io {
 
 impl Io {
     #[inline]
-    fn from_file(f: File, buffer: &mut String) -> anyhow::Result<Io> {
+    fn from_file(fd: OwnedFd, buffer: &mut String) -> anyhow::Result<Io> {
         const NUM_FIELDS: u16 = 0; // Make sure to update this if you want more fields!
         enum Fields {
             ReadBytes,
             WriteBytes,
         }
 
+        let f = File::from(fd);
+
         let mut read_fields = 0;
         let mut reader = BufReader::new(f);
 
@@ -272,7 +277,7 @@ impl Process {
 
         // Stat is pretty long, do this first to pre-allocate up-front.
         let stat =
-            open_at(&mut root, "stat", &pid_dir).and_then(|file| Stat::from_file(file, buffer))?;
+            open_at(&mut root, "stat", &pid_dir).and_then(|fd| Stat::from_file(fd, buffer))?;
         reset(&mut root, buffer);
 
         let cmdline = if cmdline(&mut root, &pid_dir, buffer).is_ok() {
@@ -306,20 +311,22 @@ impl Process {
 
 #[inline]
 fn cmdline(root: &mut PathBuf, fd: &OwnedFd, buffer: &mut String) -> anyhow::Result<()> {
-    let _ = open_at(root, "cmdline", fd).map(|mut file| file.read_to_string(buffer))?;
+    // SAFETY: This is safe, we are only writing strings.
+    let _ = open_at(root, "cmdline", fd)
+        .map(|cmdline_fd| rustix::io::read(cmdline_fd, unsafe { buffer.as_mut_vec() }))?;
 
     Ok(())
 }
 
-/// Opens a path. Note that this function takes in a mutable root - this will
+/// Opens a path and return the file. Note that this function takes in a mutable root - this will
 /// mutate it to avoid allocations. You probably will want to pop the most
 /// recent child after if you need to use the buffer again.
 #[inline]
-fn open_at(root: &mut PathBuf, child: &str, fd: &OwnedFd) -> anyhow::Result<File> {
+fn open_at(root: &mut PathBuf, child: &str, fd: &OwnedFd) -> anyhow::Result<OwnedFd> {
     root.push(child);
     let new_fd = rustix::fs::openat(fd, &*root, OFlags::RDONLY | OFlags::CLOEXEC, Mode::empty())?;
 
-    Ok(File::from(new_fd))
+    Ok(new_fd)
 }
 
 #[inline]