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Replace ReentrantMutex by a futex-based one on Linux. #95727

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merged 9 commits into from
Apr 13, 2022
Merged

Replace ReentrantMutex by a futex-based one on Linux. #95727

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c62c8cb
Add current_thread_unique_ptr() in std::sys_common.
m-ou-se Apr 6, 2022
bd61bec
Add futex-based ReentrantMutex on Linux.
m-ou-se Apr 6, 2022
ebebe6f
Make current_thread_unique_ptr work during thread destruction.
m-ou-se Apr 6, 2022
319a9b0
Move current_thread_unique_ptr to the only module that uses it.
m-ou-se Apr 6, 2022
43651aa
Initialize thread local with const{}.
m-ou-se Apr 6, 2022
83e8b9e
Add debug asserts to futex ReentrantMutex impl.
m-ou-se Apr 6, 2022
5b25912
Add #[deny(unsafe_op_in_unsafe_fn)] to thread_local!(const).
m-ou-se Apr 6, 2022
8a2c9a9
Allow cvt_nz to be unused on some platforms.
m-ou-se Apr 9, 2022
d4e44a6
Add missing unsafe marker.
m-ou-se Apr 11, 2022
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Initialize thread local with const{}.
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@m-ou-se
m-ou-se committed Apr 12, 2022
commit 43651aa34fd7762058aea6920d2e401561d97076
2 changes: 1 addition & 1 deletion library/std/src/sys/unix/locks/futex.rs
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Expand Up @@ -253,6 +253,6 @@ impl ReentrantMutex {
/// This can be used as a non-null usize-sized ID.
pub fn current_thread_unique_ptr() -> usize {
// Use a non-drop type to make sure it's still available during thread destruction.
thread_local! { static X: u8 = 0 }
thread_local! { static X: u8 = const { 0 } }
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Should we avoid creating new thread_local!? Since pthread keys number available on some platforms is rather small, it would be beneficial for std to use as few pthread keys as possible.

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That'd be nice.

I used the address of the THREAD_INFO thread local in an earlier version, to avoid creating a new one, but that one needs Drop, which makes it inaccessible during thread shutdown. We don't have a good way of getting the address of such a thread local's storage after its destructor ran, since its getter function just returns None after destruction.

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It looks like LOCAL_PANIC_COUNT meets this requirement, but it's a little weird to use it directly. maybe it would be nice to combine the KEYS of map.rs and LOCAL_PANIC_COUNT into one LOCAL_THREAD_STATE .

X.with(|x| <*const _>::addr(x))
}