commit d1f4c5733cea31f9c3bd803f2d4c6c074a336744
Author: ddidderr <ddidderr@paul.network>
Date:   Wed Aug 9 21:23:00 2023 +0200

    init

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..a56854b
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,69 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "autocfg"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
+
+[[package]]
+name = "bitflags"
+version = "1.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bef38d45163c2f1dde094a7dfd33ccf595c92905c8f8f4fdc18d06fb1037718a"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "libc"
+version = "0.2.147"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4668fb0ea861c1df094127ac5f1da3409a82116a4ba74fca2e58ef927159bb3"
+
+[[package]]
+name = "memoffset"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5de893c32cde5f383baa4c04c5d6dbdd735cfd4a794b0debdb2bb1b421da5ff4"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
+name = "nix"
+version = "0.26.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bfdda3d196821d6af13126e40375cdf7da646a96114af134d5f417a9a1dc8e1a"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "libc",
+ "memoffset",
+ "pin-utils",
+ "static_assertions",
+]
+
+[[package]]
+name = "parallel-copy"
+version = "0.1.0"
+dependencies = [
+ "nix",
+]
+
+[[package]]
+name = "pin-utils"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b870d8c151b6f2fb93e84a13146138f05d02ed11c7e7c54f8826aaaf7c9f184"
+
+[[package]]
+name = "static_assertions"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..672e57a
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,15 @@
+[package]
+name = "parallel-copy"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+nix = "0.26"
+
+
+[profile.release]
+lto = true
+debug = false
+strip = true
+panic = "unwind"
+codegen-units = 1
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..ce1e9e2
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,103 @@
+use nix::unistd::ftruncate;
+use std::fs::OpenOptions;
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::thread;
+use std::time::Instant;
+use std::{cmp, fs};
+use std::{env, fs::File, os::fd::IntoRawFd};
+
+const NUM_THREADS: i64 = 8;
+
+fn truncate_dst(f: File, len: i64) -> nix::Result<()> {
+    ftruncate(f.into_raw_fd(), len)
+}
+
+fn copy_range(src: &mut File, dst: &mut File, offset: u64, len: u64, chunk_bytes: u64) {
+    src.seek(SeekFrom::Start(offset)).unwrap();
+    dst.seek(SeekFrom::Start(offset)).unwrap();
+
+    let end = cmp::min(offset + chunk_bytes, len);
+
+    // replace chunk_bytes with the actual nr of chunk_bytes
+    // which can be less if we are at the last chunk of src
+    let chunk_bytes = (end - offset) as usize;
+
+    let bufsz = cmp::min(1024 * 1024, chunk_bytes);
+    let mut buf = vec![0u8; bufsz];
+
+    let nr_of_full_reads = chunk_bytes / bufsz;
+    let bytes_for_last_read = chunk_bytes % bufsz;
+
+    // full reads
+    for _ in 0..nr_of_full_reads {
+        src.read_exact(&mut buf).unwrap();
+        dst.write_all(&buf).unwrap();
+    }
+
+    // last (partial) read
+    if bytes_for_last_read > 0 {
+        buf.resize(bytes_for_last_read, 0);
+        src.read_exact(&mut buf).unwrap();
+        dst.write_all(&buf).unwrap();
+    }
+}
+
+fn thread_copy_chunks(thread_nr: i64, src: &str, dst: &str, len: i64) {
+    let mut src = File::open(src).unwrap();
+    let mut dst = OpenOptions::new().write(true).open(dst).unwrap();
+
+    let chunk_bytes = len / (NUM_THREADS * 2);
+
+    let jump = NUM_THREADS * chunk_bytes;
+
+    let mut offset = thread_nr * chunk_bytes;
+    let mut loop_count = 0;
+    loop {
+        println!("t{thread_nr} l{loop_count} {offset} chunk={chunk_bytes}");
+
+        copy_range(
+            &mut src,
+            &mut dst,
+            offset as u64,
+            len as u64,
+            chunk_bytes as u64,
+        );
+
+        offset += jump;
+        if offset >= len {
+            break;
+        }
+
+        loop_count += 1;
+    }
+}
+
+fn main() {
+    let src = env::args().nth(1).unwrap();
+    let dst = env::args().nth(2).unwrap();
+
+    let len = fs::metadata(&src).unwrap().len();
+    if len > i64::MAX as u64 {
+        panic!("src len > i64::MAX");
+    }
+
+    {
+        let dst = File::create(&dst).unwrap();
+        truncate_dst(dst, len as i64).unwrap();
+    }
+
+    println!("Spawning {NUM_THREADS} threads to copy {src} to {dst} ({len} bytes)");
+
+    let now = Instant::now();
+    // create threads in scope so borrows from the main thread
+    // outlive all threads
+    thread::scope(|s| {
+        for thread_nr in 0..NUM_THREADS {
+            let src_ref = &src;
+            let dst_ref = &dst;
+            s.spawn(move || thread_copy_chunks(thread_nr, src_ref, dst_ref, len as i64));
+        }
+    });
+
+    println!("took {:.3}s", now.elapsed().as_secs_f64());
+}