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Initialize memory for BufferedReader buffer #21076

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Merged
merged 1 commit into from
Jan 14, 2015
Merged

Initialize memory for BufferedReader buffer #21076

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21 changes: 10 additions & 11 deletions src/libstd/io/buffered.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
use cmp;
use fmt;
use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE, IoResult};
use iter::{IteratorExt, ExactSizeIterator};
use iter::{IteratorExt, ExactSizeIterator, repeat};
use ops::Drop;
use option::Option;
use option::Option::{Some, None};
Expand Down Expand Up @@ -62,17 +62,11 @@ impl<R> fmt::Show for BufferedReader<R> where R: fmt::Show {
impl<R: Reader> BufferedReader<R> {
/// Creates a new `BufferedReader` with the specified buffer capacity
pub fn with_capacity(cap: uint, inner: R) -> BufferedReader<R> {
// It's *much* faster to create an uninitialized buffer than it is to
// fill everything in with 0. This buffer is entirely an implementation
// detail and is never exposed, so we're safe to not initialize
// everything up-front. This allows creation of BufferedReader instances
// to be very cheap (large mallocs are not nearly as expensive as large
// callocs).
let mut buf = Vec::with_capacity(cap);
unsafe { buf.set_len(cap); }
BufferedReader {
inner: inner,
buf: buf,
// We can't use the same trick here as we do for BufferedWriter,
// since this memory is visible to the inner Reader.
buf: repeat(0).take(cap).collect(),
pos: 0,
cap: 0,
}
Expand Down Expand Up @@ -166,7 +160,12 @@ impl<W> fmt::Show for BufferedWriter<W> where W: fmt::Show {
impl<W: Writer> BufferedWriter<W> {
/// Creates a new `BufferedWriter` with the specified buffer capacity
pub fn with_capacity(cap: uint, inner: W) -> BufferedWriter<W> {
// See comments in BufferedReader for why this uses unsafe code.
// It's *much* faster to create an uninitialized buffer than it is to
// fill everything in with 0. This buffer is entirely an implementation
// detail and is never exposed, so we're safe to not initialize
// everything up-front. This allows creation of BufferedWriter instances
// to be very cheap (large mallocs are not nearly as expensive as large
// callocs).
let mut buf = Vec::with_capacity(cap);
unsafe { buf.set_len(cap); }
BufferedWriter {
Expand Down