std/sys/
exit_guard.rs

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1cfg_if::cfg_if! {
2    if #[cfg(target_os = "linux")] {
3        /// pthread_t is a pointer on some platforms,
4        /// so we wrap it in this to impl Send + Sync.
5        #[derive(Clone, Copy)]
6        #[repr(transparent)]
7        struct PThread(libc::pthread_t);
8        // Safety: pthread_t is safe to send between threads
9        unsafe impl Send for PThread {}
10        // Safety: pthread_t is safe to share between threads
11        unsafe impl Sync for PThread {}
12        /// Mitigation for <https://github.com/rust-lang/rust/issues/126600>
13        ///
14        /// On glibc, `libc::exit` has been observed to not always be thread-safe.
15        /// It is currently unclear whether that is a glibc bug or allowed by the standard.
16        /// To mitigate this problem, we ensure that only one
17        /// Rust thread calls `libc::exit` (or returns from `main`) by calling this function before
18        /// calling `libc::exit` (or returning from `main`).
19        ///
20        /// Technically, this is not enough to ensure soundness, since other code directly calling
21        /// `libc::exit` will still race with this.
22        ///
23        /// *This function does not itself call `libc::exit`.* This is so it can also be used
24        /// to guard returning from `main`.
25        ///
26        /// This function will return only the first time it is called in a process.
27        ///
28        /// * If it is called again on the same thread as the first call, it will abort.
29        /// * If it is called again on a different thread, it will wait in a loop
30        ///   (waiting for the process to exit).
31        #[cfg_attr(any(test, doctest), allow(dead_code))]
32        pub(crate) fn unique_thread_exit() {
33            let this_thread_id = unsafe { libc::pthread_self() };
34            use crate::sync::{Mutex, PoisonError};
35            static EXITING_THREAD_ID: Mutex<Option<PThread>> = Mutex::new(None);
36            let mut exiting_thread_id =
37                EXITING_THREAD_ID.lock().unwrap_or_else(PoisonError::into_inner);
38            match *exiting_thread_id {
39                None => {
40                    // This is the first thread to call `unique_thread_exit`,
41                    // and this is the first time it is called.
42                    // Set EXITING_THREAD_ID to this thread's ID and return.
43                    *exiting_thread_id = Some(PThread(this_thread_id));
44                },
45                Some(exiting_thread_id) if exiting_thread_id.0 == this_thread_id => {
46                    // This is the first thread to call `unique_thread_exit`,
47                    // but this is the second time it is called.
48                    // Abort the process.
49                    core::panicking::panic_nounwind("std::process::exit called re-entrantly")
50                }
51                Some(_) => {
52                    // This is not the first thread to call `unique_thread_exit`.
53                    // Pause until the process exits.
54                    drop(exiting_thread_id);
55                    loop {
56                        // Safety: libc::pause is safe to call.
57                        unsafe { libc::pause(); }
58                    }
59                }
60            }
61        }
62    } else {
63        /// Mitigation for <https://github.com/rust-lang/rust/issues/126600>
64        ///
65        /// Mitigation is ***NOT*** implemented on this platform, either because this platform
66        /// is not affected, or because mitigation is not yet implemented for this platform.
67        #[cfg_attr(any(test, doctest), allow(dead_code))]
68        pub(crate) fn unique_thread_exit() {
69            // Mitigation not required on platforms where `exit` is thread-safe.
70        }
71    }
72}
std/sys/exit_guard.rs

std/sys/
exit_guard.rs
