std: Re-enable at_exit()

The new semantics of this function are that the callbacks are run when the *main
thread* exits, not when all threads have exited. This implies that other threads
may still be running when the `at_exit` callbacks are invoked and users need to
be prepared for this situation.

Users in the standard library have been audited in accordance to these new rules
as well.

Closes #20012

1 files changed, 5 insertions, 1 deletions

diff --git a/src/libstd/sys/common/net.rs b/src/libstd/sys/common/net.rs
index 7a09137a225..24d22eb58c5 100644
--- a/src/libstd/sys/common/net.rs
+++ b/src/libstd/sys/common/net.rs
@@ -22,7 +22,9 @@ use io::{IoResult, IoError};
 use sys::{mod, retry, c, sock_t, last_error, last_net_error, last_gai_error, close_sock,
           wrlen, msglen_t, os, wouldblock, set_nonblocking, timer, ms_to_timeval,
           decode_error_detailed};
-use sync::{Mutex, MutexGuard};
+use sync::Mutex;
+#[cfg(not(target_os = "linux"))]
+use sync::MutexGuard;
 use sys_common::{mod, keep_going, short_write, timeout};
 use prelude::*;
 use cmp;
@@ -573,11 +575,13 @@ impl Drop for Inner {
     fn drop(&mut self) { unsafe { close_sock(self.fd); } }
 }
 
+#[cfg(not(target_os = "linux"))]
 pub struct Guard<'a> {
     pub fd: sock_t,
     pub guard: MutexGuard<'a, ()>,
 }
 
+#[cfg(not(target_os = "linux"))]
 #[unsafe_destructor]
 impl<'a> Drop for Guard<'a> {
     fn drop(&mut self) {