nordic-dev.net/rust
nordic-dev.net/rust
2
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-06-05 11:48:30 +00:00
Code Issues Packages Projects Releases Wiki Activity

Improve comments from https://github.com/rust-lang/rust/pull/72617, as suggested by RalfJung.

Browse Source
This commit is contained in:
Eduardo Sánchez Muñoz 2020-07-01 16:59:50 +02:00
parent d462551a86
commit aac2f734de
1 changed files with 9 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
src/libstd/panicking.rs
View File

@ -229,10 +229,10 @@ pub mod panic_count {
thread_local! { static LOCAL_PANIC_COUNT: Cell<usize> = Cell::new(0) }
// Sum of panic counts from all threads. The purpose of this is to have
// a fast path in `is_zero` (which is used by `panicking`). Access to
// this variable can be always be done with relaxed ordering because
// it is always guaranteed that, if `GLOBAL_PANIC_COUNT` is zero,
// `LOCAL_PANIC_COUNT` will be zero.
// a fast path in `is_zero` (which is used by `panicking`). In any particular
// thread, if that thread currently views `GLOBAL_PANIC_COUNT` as being zero,
// then `LOCAL_PANIC_COUNT` in that thread is zero. This invariant holds before
// and after increase and decrease, but not necessarily during their execution.
static GLOBAL_PANIC_COUNT: AtomicUsize = AtomicUsize::new(0);
pub fn increase() -> usize {
@ -263,6 +263,11 @@ pub mod panic_count {
// Fast path: if `GLOBAL_PANIC_COUNT` is zero, all threads
// (including the current one) will have `LOCAL_PANIC_COUNT`
// equal to zero, so TLS access can be avoided.
//
// A relaxed atomic load is equivalent to a normal aligned memory read
// (e.g., a `mov` instruction in x86), while a TLS access might require
// calling a non-inlinable function (such as `__tls_get_addr` when using
// the GD TLS model).
true
} else {
is_zero_slow_path()