attempt to optimise vectored write

1 files changed, 48 insertions, 0 deletions

diff --git a/library/std/src/io/cursor/tests.rs b/library/std/src/io/cursor/tests.rs
index f1ee177b7f3..d7c203c297f 100644
--- a/library/std/src/io/cursor/tests.rs
+++ b/library/std/src/io/cursor/tests.rs
@@ -20,6 +20,7 @@ fn test_vec_writer() {
 #[test]
 fn test_mem_writer() {
     let mut writer = Cursor::new(Vec::new());
+    writer.set_position(10);
     assert_eq!(writer.write(&[0]).unwrap(), 1);
     assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
     assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
@@ -30,6 +31,17 @@ fn test_mem_writer() {
         3
     );
     let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+    assert_eq!(&writer.get_ref()[..10], &[0; 10]);
+    assert_eq!(&writer.get_ref()[10..], b);
+}
+
+#[test]
+fn test_mem_writer_preallocated() {
+    let mut writer = Cursor::new(vec![0, 0, 0, 0, 0, 0, 0, 0, 8, 9, 10]);
+    assert_eq!(writer.write(&[0]).unwrap(), 1);
+    assert_eq!(writer.write(&[1, 2, 3]).unwrap(), 3);
+    assert_eq!(writer.write(&[4, 5, 6, 7]).unwrap(), 4);
+    let b: &[_] = &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
     assert_eq!(&writer.get_ref()[..], b);
 }
 
@@ -517,3 +529,39 @@ fn const_cursor() {
     const _: &&[u8] = CURSOR.get_ref();
     const _: u64 = CURSOR.position();
 }
+
+#[bench]
+fn bench_write_vec(b: &mut test::Bencher) {
+    let slice = &[1; 128];
+
+    b.iter(|| {
+        let mut buf = b"some random data to overwrite".to_vec();
+        let mut cursor = Cursor::new(&mut buf);
+
+        let _ = cursor.write_all(slice);
+        test::black_box(&cursor);
+    })
+}
+
+#[bench]
+fn bench_write_vec_vectored(b: &mut test::Bencher) {
+    let slices = [
+        IoSlice::new(&[1; 128]),
+        IoSlice::new(&[2; 256]),
+        IoSlice::new(&[3; 512]),
+        IoSlice::new(&[4; 1024]),
+        IoSlice::new(&[5; 2048]),
+        IoSlice::new(&[6; 4096]),
+        IoSlice::new(&[7; 8192]),
+        IoSlice::new(&[8; 8192 * 2]),
+    ];
+
+    b.iter(|| {
+        let mut buf = b"some random data to overwrite".to_vec();
+        let mut cursor = Cursor::new(&mut buf);
+
+        let mut slices = slices;
+        let _ = cursor.write_all_vectored(&mut slices);
+        test::black_box(&cursor);
+    })
+}