493 lines
12 KiB
Rust
493 lines
12 KiB
Rust
use std::alloc::{alloc, dealloc, handle_alloc_error, realloc, Layout};
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use std::fmt;
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use std::mem::{align_of, ManuallyDrop};
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use std::ops::{Add, AddAssign};
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use std::ptr;
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/// Buffer for rendered contents
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///
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/// This struct is quite simular to `String`, but some methods are
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/// re-implemented for faster buffering.
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pub struct Buffer {
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data: *mut u8,
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len: usize,
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capacity: usize,
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}
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impl Buffer {
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/// Create an empty buffer
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#[inline]
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pub const fn new() -> Buffer {
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Self {
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data: align_of::<u8>() as *mut u8, // dangling pointer
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len: 0,
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capacity: 0,
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}
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}
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/// Create a empty buffer with a particular capacity
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#[inline]
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pub fn with_capacity(n: usize) -> Buffer {
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if unlikely!(n == 0) {
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Self::new()
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} else {
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Self {
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data: safe_alloc(n),
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len: 0,
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capacity: n,
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}
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}
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}
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/// Extracts a string slice containing the entire buffer
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#[inline]
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pub fn as_str(&self) -> &str {
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unsafe {
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let bytes = std::slice::from_raw_parts(self.data, self.len);
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std::str::from_utf8_unchecked(bytes)
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}
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}
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/// Returns an unsafe mutable pointer to the inner data
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#[inline]
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pub fn as_mut_ptr(&self) -> *mut u8 {
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self.data
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}
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/// Returns the length of this buffer in bytes
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#[inline]
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pub fn len(&self) -> usize {
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self.len
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}
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/// Returns this buffer's capacity in bytes
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#[inline]
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pub fn capacity(&self) -> usize {
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self.capacity
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}
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#[inline]
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#[doc(hidden)]
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pub unsafe fn _set_len(&mut self, new_len: usize) {
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debug_assert!(new_len <= self.capacity);
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self.len = new_len;
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}
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/// Increase the length of buffer by `additional` bytes
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///
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/// # Safety
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///
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/// - `additional` must be less than or equal to `capacity() - len()`
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/// - The elements at `old_len..old_len + additional` must be initialized
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#[inline]
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pub unsafe fn advance(&mut self, additional: usize) {
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self.len += additional;
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}
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/// Returns `true` if this buffer has a length of zero, and `false` otherwise
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#[inline]
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pub fn is_empty(&self) -> bool {
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self.len == 0
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}
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/// Same as String::reserve
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///
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/// # Panics
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///
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/// This method panics if `size` overflows `isize::MAX`.
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#[inline]
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pub fn reserve(&mut self, size: usize) {
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if likely!(size <= self.capacity - self.len) {
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return;
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}
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self.reserve_internal(size);
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}
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/// Same as String::reserve except that undefined behaviour can result if `size`
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/// overflows `isize::MAX`.
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#[inline]
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pub(crate) unsafe fn reserve_small(&mut self, size: usize) {
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debug_assert!(size <= std::isize::MAX as usize);
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if likely!(self.len + size <= self.capacity) {
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return;
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}
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self.reserve_internal(size);
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}
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#[inline]
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#[doc(hidden)]
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pub fn clear(&mut self) {
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self.len = 0;
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}
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/// Converts a `Buffer` into a `String` without copy/realloc operation.
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#[inline]
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pub fn into_string(self) -> String {
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debug_assert!(self.len <= self.capacity);
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let buf = ManuallyDrop::new(self);
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// SAFETY: This operations satisfy all requirements specified in
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// https://doc.rust-lang.org/std/string/struct.String.html#safety
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unsafe { String::from_raw_parts(buf.data, buf.len, buf.capacity) }
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}
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/// Appends a given string slice onto the end of this buffer
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#[inline]
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pub fn push_str(&mut self, data: &str) {
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let size = data.len();
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unsafe {
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// SAFETY: this operation won't overflow because slice cannot exceeds
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// isize::MAX bytes.
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// https://doc.rust-lang.org/reference/behavior-considered-undefined.html
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self.reserve_small(size);
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let p = self.data.add(self.len);
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std::ptr::copy_nonoverlapping(data.as_ptr(), p, size);
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self.len += size;
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}
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debug_assert!(self.len <= self.capacity);
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}
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/// Appends the given `char` to the end of this buffer
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#[inline]
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pub fn push(&mut self, data: char) {
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// Question: Is it safe to pass uninitialized memory to `encode_utf8` function?
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unsafe {
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self.reserve_small(4);
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let bp = self.data.add(self.len) as *mut [u8; 4];
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let result = data.encode_utf8(&mut *bp);
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self.len += result.len();
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}
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}
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#[cfg_attr(feature = "perf-inline", inline)]
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fn reserve_internal(&mut self, size: usize) {
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debug_assert!(size <= std::isize::MAX as usize);
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let new_capacity = std::cmp::max(self.capacity * 2, self.capacity + size);
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debug_assert!(new_capacity > self.capacity);
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self.data = unsafe { safe_realloc(self.data, self.capacity, new_capacity) };
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self.capacity = new_capacity;
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debug_assert!(!self.data.is_null());
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debug_assert!(self.len <= self.capacity);
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}
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}
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#[inline(never)]
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fn safe_alloc(capacity: usize) -> *mut u8 {
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assert!(capacity > 0);
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assert!(
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capacity <= std::isize::MAX as usize,
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"capacity is too large"
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);
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// SAFETY: capacity is non-zero, and always multiple of alignment (1).
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unsafe {
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let layout = Layout::from_size_align_unchecked(capacity, 1);
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let data = alloc(layout);
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if data.is_null() {
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handle_alloc_error(layout);
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}
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data
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}
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}
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/// # Safety
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///
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/// - if `capacity > 0`, `capacity` is the same value that was used to allocate the block
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/// of memory pointed by `ptr`.
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#[cold]
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#[inline(never)]
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unsafe fn safe_realloc(ptr: *mut u8, capacity: usize, new_capacity: usize) -> *mut u8 {
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assert!(new_capacity > 0);
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assert!(
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new_capacity <= std::isize::MAX as usize,
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"capacity is too large"
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);
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let data = if unlikely!(capacity == 0) {
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let new_layout = Layout::from_size_align_unchecked(new_capacity, 1);
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alloc(new_layout)
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} else {
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let old_layout = Layout::from_size_align_unchecked(capacity, 1);
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realloc(ptr, old_layout, new_capacity)
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};
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if data.is_null() {
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handle_alloc_error(Layout::from_size_align_unchecked(new_capacity, 1));
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}
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data
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}
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impl Clone for Buffer {
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fn clone(&self) -> Self {
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unsafe {
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if self.is_empty() {
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Self::new()
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} else {
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let buf = Self {
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data: safe_alloc(self.len),
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len: self.len,
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capacity: self.len,
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};
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ptr::copy_nonoverlapping(self.data, buf.data, self.len);
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buf
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}
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}
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}
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}
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impl fmt::Debug for Buffer {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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self.as_str().fmt(f)
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}
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}
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impl Drop for Buffer {
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fn drop(&mut self) {
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if self.capacity != 0 {
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// SAFETY: when `self.capacity > 0`, `self.capacity` is the same value
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// used for allocate the block of memory pointed by `self.data`.
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unsafe {
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let layout = Layout::from_size_align_unchecked(self.capacity, 1);
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dealloc(self.data, layout);
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}
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}
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}
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}
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impl fmt::Write for Buffer {
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#[inline]
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fn write_str(&mut self, s: &str) -> fmt::Result {
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Buffer::push_str(self, s);
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Ok(())
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}
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}
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impl From<String> for Buffer {
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/// Shrink the data and pass raw pointer directory to buffer
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///
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/// This operation is `O(1)`
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#[inline]
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fn from(other: String) -> Buffer {
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let bs = other.into_boxed_str();
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let data = Box::leak(bs);
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Buffer {
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data: data.as_mut_ptr(),
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len: data.len(),
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capacity: data.len(),
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}
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}
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}
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impl From<&str> for Buffer {
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#[inline]
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fn from(other: &str) -> Buffer {
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let mut buf = Buffer::with_capacity(other.len());
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if !other.is_empty() {
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// SAFETY: `Buffer.capacity()` should be same as `other.len()`, so if `other`
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// is not empty, `buf.as_mut_ptr()` is supporsed to point to valid memory.
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unsafe {
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ptr::copy_nonoverlapping(other.as_ptr(), buf.as_mut_ptr(), other.len());
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buf.advance(other.len());
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}
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}
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buf
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}
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}
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impl Add<&str> for Buffer {
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type Output = Buffer;
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#[inline]
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fn add(mut self, other: &str) -> Buffer {
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self.push_str(other);
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self
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}
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}
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impl AddAssign<&str> for Buffer {
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#[inline]
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fn add_assign(&mut self, other: &str) {
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self.push_str(other)
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}
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}
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impl Default for Buffer {
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#[inline]
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fn default() -> Buffer {
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Buffer::new()
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}
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}
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unsafe impl Send for Buffer {}
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unsafe impl Sync for Buffer {}
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#[cfg(test)]
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mod tests {
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use super::*;
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use std::sync::{Arc, Barrier, Mutex};
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use std::thread;
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#[test]
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fn push_str() {
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let mut buffer = Buffer::new();
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assert_eq!(buffer.len(), 0);
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assert_eq!(buffer.capacity(), 0);
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buffer.push_str("apple");
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assert_eq!(buffer.len(), 5);
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assert_eq!(buffer.capacity(), 5);
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buffer.push_str("pie");
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assert_eq!(buffer.len(), 8);
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assert_eq!(buffer.capacity(), 10);
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for _ in 0..16 {
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buffer.push_str("zomg");
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}
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assert_eq!(buffer.len(), 72);
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assert_eq!(buffer.capacity(), 80);
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}
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#[test]
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fn with_capacity() {
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let buffer = Buffer::with_capacity(1);
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assert!(buffer.is_empty());
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assert_eq!(buffer.len(), 0);
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assert!(buffer.capacity() >= 1);
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}
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#[test]
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fn string_conversion() {
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// from empty string
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let s = String::with_capacity(2);
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assert!(s.capacity() >= 2);
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let mut buf = Buffer::from(s);
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assert_eq!(buf.as_str(), "");
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// capacity should be shrinked for safety
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assert_eq!(buf.capacity(), 0);
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buf.push_str("abc");
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assert_eq!(buf.as_str(), "abc");
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// into non-empty string
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let mut s = buf.into_string();
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assert_eq!(s, "abc");
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s += "defghijklmn";
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assert_eq!(s, "abcdefghijklmn");
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// from non-empty string
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let mut buf = Buffer::from(s);
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assert_eq!(buf.as_str(), "abcdefghijklmn");
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buf.clear();
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assert_eq!(buf.as_str(), "");
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// into empty string
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let buf = Buffer::default();
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let mut s = buf.into_string();
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assert_eq!(s, "");
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s.push_str("apple");
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assert_eq!(s, "apple");
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}
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#[test]
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fn from_str() {
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let buf = Buffer::from("abcdefgh");
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assert_eq!(buf.as_str(), "abcdefgh");
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}
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#[test]
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fn clone() {
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use std::fmt::Write;
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let mut s1 = Buffer::with_capacity(0);
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let mut s2 = s1.clone();
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s1.push('a');
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s2.push_str("b");
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assert_eq!(s1.as_str(), "a");
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assert_eq!(s2.as_str(), "b");
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let mut s1 = Buffer::from("foo");
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let mut s2 = s1.clone();
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s1 = s1 + "bar";
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write!(s2, "baz").unwrap();
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assert_eq!(s1.as_str(), "foobar");
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assert_eq!(s2.as_str(), "foobaz");
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s2.clear();
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let _ = s2.clone();
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}
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#[test]
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fn push() {
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for initial_capacity in &[0, 4, 16] {
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let mut s = Buffer::with_capacity(*initial_capacity);
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s.push('a');
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s.push('é');
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s.push('A');
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s.push('🄫');
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assert_eq!(s.as_str(), "aéA🄫");
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}
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}
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#[test]
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fn multi_thread() {
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const THREADS: usize = 8;
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const ITERS: usize = 100;
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let barrier = Arc::new(Barrier::new(THREADS));
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let buffer = Arc::new(Mutex::new(Buffer::new()));
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let mut handles = Vec::with_capacity(THREADS);
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for _ in 0..THREADS {
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let barrier = barrier.clone();
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let buffer = buffer.clone();
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handles.push(thread::spawn(move || {
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barrier.wait();
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for _ in 0..ITERS {
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buffer.lock().unwrap().push_str("a");
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}
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}));
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}
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for handle in handles {
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handle.join().unwrap();
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}
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assert_eq!(buffer.lock().unwrap().as_str(), "a".repeat(ITERS * THREADS));
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}
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#[test]
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#[should_panic]
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fn reserve_overflow() {
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let mut buf = Buffer::new();
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buf.reserve(std::isize::MAX as usize + 1);
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}
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#[test]
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#[should_panic]
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fn empty_alloc() {
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safe_alloc(0);
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}
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}
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