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De-stabilize thread::scoped and friends

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Issue #24292 demonstrates that the `scoped` API as currently offered can
be memory-unsafe: the `JoinGuard` can be moved into a context that will
fail to execute destructors prior to the stack frame being popped (for
example, by creating an `Rc` cycle).

This commit reverts the APIs to `unstable` status while a long-term
solution is worked out.

(There are several possible ways to address this issue; it's not a
fundamental problem with the `scoped` idea, but rather an indication
that Rust doesn't currently provide a good way to ensure that
destructors are run within a particular stack frame.)

[breaking-change]
This commit is contained in:
Aaron Turon
2015-04-13 12:08:20 -07:00
parent 588d37c653
commit 6399bb425b
1 changed files with 8 additions and 4 deletions
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12
src/libstd/thread/mod.rs
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@@ -274,7 +274,8 @@ impl Builder {
/// Unlike the `scoped` free function, this method yields an
/// `io::Result` to capture any failure to create the thread at
/// the OS level.
#[stable(feature = "rust1", since = "1.0.0")]
#[unstable(feature = "scoped",
reason = "memory unsafe if destructor is avoided, see #24292")]
pub fn scoped<'a, T, F>(self, f: F) -> io::Result<JoinGuard<'a, T>> where
T: Send + 'a, F: FnOnce() -> T, F: Send + 'a
{
@@ -387,7 +388,8 @@ pub fn spawn<F>(f: F) -> JoinHandle where F: FnOnce(), F: Send + 'static {
///
/// Panics if the OS fails to create a thread; use `Builder::scoped`
/// to recover from such errors.
#[stable(feature = "rust1", since = "1.0.0")]
#[unstable(feature = "scoped",
reason = "memory unsafe if destructor is avoided, see #24292")]
pub fn scoped<'a, T, F>(f: F) -> JoinGuard<'a, T> where
T: Send + 'a, F: FnOnce() -> T, F: Send + 'a
{
@@ -674,7 +676,8 @@ impl Drop for JoinHandle {
/// handle: the ability to join a child thread is a uniquely-owned
/// permission.
#[must_use = "thread will be immediately joined if `JoinGuard` is not used"]
#[stable(feature = "rust1", since = "1.0.0")]
#[unstable(feature = "scoped",
reason = "memory unsafe if destructor is avoided, see #24292")]
pub struct JoinGuard<'a, T: Send + 'a> {
inner: JoinInner<T>,
_marker: PhantomData<&'a T>,
@@ -706,7 +709,8 @@ impl<'a, T: Send + 'a> JoinGuard<'a, T> {
}
#[unsafe_destructor]
#[stable(feature = "rust1", since = "1.0.0")]
#[unstable(feature = "scoped",
reason = "memory unsafe if destructor is avoided, see #24292")]
impl<'a, T: Send + 'a> Drop for JoinGuard<'a, T> {
fn drop(&mut self) {
if !self.inner.joined {