3 files changed, 39 insertions, 47 deletions

diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 4def601f1c0..2a1294f23b2 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -120,7 +120,7 @@ impl<R> fmt::Debug for BufReader<R> where R: fmt::Debug {
 ///
 /// The buffer will be written out when the writer is dropped.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct BufWriter<W> {
+pub struct BufWriter<W: Write> {
     inner: Option<W>,
     buf: Vec<u8>,
 }
@@ -220,7 +220,7 @@ impl<W: Write> Write for BufWriter<W> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W> fmt::Debug for BufWriter<W> where W: fmt::Debug {
+impl<W: Write> fmt::Debug for BufWriter<W> where W: fmt::Debug {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         write!(fmt, "BufWriter {{ writer: {:?}, buffer: {}/{} }}",
                self.inner.as_ref().unwrap(), self.buf.len(), self.buf.capacity())
@@ -276,7 +276,7 @@ impl<W> fmt::Display for IntoInnerError<W> {
 ///
 /// The buffer will be written out when the writer is dropped.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct LineWriter<W> {
+pub struct LineWriter<W: Write> {
     inner: BufWriter<W>,
 }
 
@@ -335,7 +335,7 @@ impl<W: Write> Write for LineWriter<W> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<W> fmt::Debug for LineWriter<W> where W: fmt::Debug {
+impl<W: Write> fmt::Debug for LineWriter<W> where W: fmt::Debug {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         write!(fmt, "LineWriter {{ writer: {:?}, buffer: {}/{} }}",
                self.inner.inner, self.inner.buf.len(),
@@ -343,16 +343,16 @@ impl<W> fmt::Debug for LineWriter<W> where W: fmt::Debug {
     }
 }
 
-struct InternalBufWriter<W>(BufWriter<W>);
+struct InternalBufWriter<W: Write>(BufWriter<W>);
 
-impl<W> InternalBufWriter<W> {
+impl<W: Read + Write> InternalBufWriter<W> {
     fn get_mut(&mut self) -> &mut BufWriter<W> {
         let InternalBufWriter(ref mut w) = *self;
         return w;
     }
 }
 
-impl<W: Read> Read for InternalBufWriter<W> {
+impl<W: Read + Write> Read for InternalBufWriter<W> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         self.get_mut().inner.as_mut().unwrap().read(buf)
     }
@@ -367,7 +367,7 @@ impl<W: Read> Read for InternalBufWriter<W> {
 ///
 /// The output buffer will be written out when this stream is dropped.
 #[stable(feature = "rust1", since = "1.0.0")]
-pub struct BufStream<S> {
+pub struct BufStream<S: Write> {
     inner: BufReader<InternalBufWriter<S>>
 }
 
@@ -448,7 +448,7 @@ impl<S: Read + Write> Write for BufStream<S> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<S> fmt::Debug for BufStream<S> where S: fmt::Debug {
+impl<S: Write> fmt::Debug for BufStream<S> where S: fmt::Debug {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
         let reader = &self.inner;
         let writer = &self.inner.inner.0;
diff --git a/src/libstd/io/lazy.rs b/src/libstd/io/lazy.rs
index c9b105f72a5..df280dab37d 100644
--- a/src/libstd/io/lazy.rs
+++ b/src/libstd/io/lazy.rs
@@ -35,25 +35,33 @@ impl<T: Send + Sync + 'static> Lazy<T> {
     pub fn get(&'static self) -> Option<Arc<T>> {
         let _g = self.lock.lock();
         unsafe {
-            let mut ptr = *self.ptr.get();
+            let ptr = *self.ptr.get();
             if ptr.is_null() {
-                ptr = boxed::into_raw(self.init());
-                *self.ptr.get() = ptr;
+                Some(self.init())
             } else if ptr as usize == 1 {
-                return None
+                None
+            } else {
+                Some((*ptr).clone())
             }
-            Some((*ptr).clone())
         }
     }
 
-    fn init(&'static self) -> Box<Arc<T>> {
-        rt::at_exit(move || unsafe {
+    unsafe fn init(&'static self) -> Arc<T> {
+        // If we successfully register an at exit handler, then we cache the
+        // `Arc` allocation in our own internal box (it will get deallocated by
+        // the at exit handler). Otherwise we just return the freshly allocated
+        // `Arc`.
+        let registered = rt::at_exit(move || {
             let g = self.lock.lock();
             let ptr = *self.ptr.get();
             *self.ptr.get() = 1 as *mut _;
             drop(g);
             drop(Box::from_raw(ptr))
         });
-        Box::new((self.init)())
+        let ret = (self.init)();
+        if registered.is_ok() {
+            *self.ptr.get() = boxed::into_raw(Box::new(ret.clone()));
+        }
+        return ret
     }
 }
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 39c718c96b3..c6ae4d0dbec 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -16,13 +16,12 @@ use cmp;
 use unicode::str as core_str;
 use error as std_error;
 use fmt;
-use iter::Iterator;
+use iter::{self, Iterator, IteratorExt, Extend};
 use marker::Sized;
 use ops::{Drop, FnOnce};
 use option::Option::{self, Some, None};
 use result::Result::{Ok, Err};
 use result;
-use slice;
 use string::String;
 use str;
 use vec::Vec;
@@ -50,41 +49,26 @@ mod stdio;
 const DEFAULT_BUF_SIZE: usize = 64 * 1024;
 
 // Acquires a slice of the vector `v` from its length to its capacity
-// (uninitialized data), reads into it, and then updates the length.
+// (after initializing the data), reads into it, and then updates the length.
 //
 // This function is leveraged to efficiently read some bytes into a destination
 // vector without extra copying and taking advantage of the space that's already
 // in `v`.
-//
-// The buffer we're passing down, however, is pointing at uninitialized data
-// (the end of a `Vec`), and many operations will be *much* faster if we don't
-// have to zero it out. In order to prevent LLVM from generating an `undef`
-// value when reads happen from this uninitialized memory, we force LLVM to
-// think it's initialized by sending it through a black box. This should prevent
-// actual undefined behavior after optimizations.
 fn with_end_to_cap<F>(v: &mut Vec<u8>, f: F) -> Result<usize>
     where F: FnOnce(&mut [u8]) -> Result<usize>
 {
-    unsafe {
-        let n = try!(f({
-            let base = v.as_mut_ptr().offset(v.len() as isize);
-            black_box(slice::from_raw_parts_mut(base,
-                                                v.capacity() - v.len()))
-        }));
-
-        // If the closure (typically a `read` implementation) reported that it
-        // read a larger number of bytes than the vector actually has, we need
-        // to be sure to clamp the vector to at most its capacity.
-        let new_len = cmp::min(v.capacity(), v.len() + n);
-        v.set_len(new_len);
-        return Ok(n);
-    }
-
-    // Semi-hack used to prevent LLVM from retaining any assumptions about
-    // `dummy` over this function call
-    unsafe fn black_box<T>(mut dummy: T) -> T {
-        asm!("" :: "r"(&mut dummy) : "memory");
-        dummy
+    let len = v.len();
+    let new_area = v.capacity() - len;
+    v.extend(iter::repeat(0).take(new_area));
+    match f(&mut v[len..]) {
+        Ok(n) => {
+            v.truncate(len + n);
+            Ok(n)
+        }
+        Err(e) => {
+            v.truncate(len);
+            Err(e)
+        }
     }
 }