Skip to content

Attempt at fixing mpmc_bounded_queue on 32bit where integer overflow is a concern. #10258

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Closed
wants to merge 1 commit into from
Closed

Attempt at fixing mpmc_bounded_queue on 32bit where integer overflow is a concern. #10258

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 15 additions & 7 deletions src/libstd/rt/mpmc_bounded_queue.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,7 @@ use option::*;
use vec;
use clone::Clone;
use kinds::Send;
use num::{Exponential,Algebraic,Round};
use uint;

struct Node<T> {
sequence: AtomicUint,
Expand Down Expand Up @@ -62,8 +62,7 @@ impl<T: Send> State<T> {
if capacity < 2 {
2u
} else {
// use next power of 2 as capacity
2f64.pow(&((capacity as f64).log2().ceil())) as uint
uint::next_power_of_two(capacity)
}
} else {
capacity
Expand All @@ -84,12 +83,13 @@ impl<T: Send> State<T> {
}

fn push(&mut self, value: T) -> bool {
let buffer_len = self.buffer.len();
let mask = self.mask;
let mut pos = self.enqueue_pos.load(Relaxed);
loop {
let node = &mut self.buffer[pos & mask];
let seq = node.sequence.load(Acquire);
let diff: int = seq as int - pos as int;
let diff = seq - pos;

if diff == 0 {
let enqueue_pos = self.enqueue_pos.compare_and_swap(pos, pos+1, Relaxed);
Expand All @@ -100,7 +100,11 @@ impl<T: Send> State<T> {
} else {
pos = enqueue_pos;
}
} else if (diff < 0) {
} else if diff < 0 {
return false
} else if pos == 0 && (seq-1) as uint % buffer_len == 0 {
// handle the case where enqueue_pos has overflowed
// back to 0 but the queue is full
return false
} else {
pos = self.enqueue_pos.load(Relaxed);
Expand All @@ -115,8 +119,12 @@ impl<T: Send> State<T> {
loop {
let node = &mut self.buffer[pos & mask];
let seq = node.sequence.load(Acquire);
let diff: int = seq as int - (pos + 1) as int;
if diff == 0 {
let diff: i64 = seq as i64 - (pos as i64 + 1i64);
if diff == 0 || (seq == 0 && pos == uint::max_value) {
// the part after || handles the case where
// pos+1 would overflow back to 0 causing
// diff to be negative and thus dequeue to fail
// when there is infact data in the queue
let dequeue_pos = self.dequeue_pos.compare_and_swap(pos, pos+1, Relaxed);
if dequeue_pos == pos {
let value = node.value.take();
Expand Down