1 #![cfg(target_thread_local)]
2 #![unstable(feature = "thread_local_internals", issue = "none")]
4 //! Provides thread-local destructors without an associated "key", which
5 //! can be more efficient.
7 // Since what appears to be glibc 2.18 this symbol has been shipped which
8 // GCC and clang both use to invoke destructors in thread_local globals, so
11 // Note, however, that we run on lots older linuxes, as well as cross
12 // compiling from a newer linux to an older linux, so we also have a
13 // fallback implementation to use as well.
16 target_os = "fuchsia",
18 target_os = "emscripten"
20 #[cfg_attr(target_family = "wasm", allow(unused))] // might remain unused depending on target details (e.g. wasm32-unknown-emscripten)
21 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
23 use crate::sys_common::thread_local_dtor::register_dtor_fallback;
26 #[linkage = "extern_weak"]
27 static __dso_handle: *mut u8;
28 #[linkage = "extern_weak"]
29 static __cxa_thread_atexit_impl: *const libc::c_void;
31 if !__cxa_thread_atexit_impl.is_null() {
32 type F = unsafe extern "C" fn(
33 dtor: unsafe extern "C" fn(*mut u8),
37 mem::transmute::<*const libc::c_void, F>(__cxa_thread_atexit_impl)(
40 &__dso_handle as *const _ as *mut _,
44 register_dtor_fallback(t, dtor);
47 // This implementation is very similar to register_dtor_fallback in
48 // sys_common/thread_local.rs. The main difference is that we want to hook into
49 // macOS's analog of the above linux function, _tlv_atexit. OSX will run the
50 // registered dtors before any TLS slots get freed, and when the main thread
53 // Unfortunately, calling _tlv_atexit while tls dtors are running is UB. The
54 // workaround below is to register, via _tlv_atexit, a custom DTOR list once per
55 // thread. thread_local dtors are pushed to the DTOR list without calling
57 #[cfg(target_os = "macos")]
58 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
59 use crate::cell::Cell;
63 static REGISTERED: Cell<bool> = Cell::new(false);
64 if !REGISTERED.get() {
65 _tlv_atexit(run_dtors, ptr::null_mut());
69 type List = Vec<(*mut u8, unsafe extern "C" fn(*mut u8))>;
72 static DTORS: Cell<*mut List> = Cell::new(ptr::null_mut());
73 if DTORS.get().is_null() {
74 let v: Box<List> = box Vec::new();
75 DTORS.set(Box::into_raw(v));
79 fn _tlv_atexit(dtor: unsafe extern "C" fn(*mut u8), arg: *mut u8);
82 let list: &mut List = &mut *DTORS.get();
85 unsafe extern "C" fn run_dtors(_: *mut u8) {
86 let mut ptr = DTORS.replace(ptr::null_mut());
87 while !ptr.is_null() {
88 let list = Box::from_raw(ptr);
89 for (ptr, dtor) in list.into_iter() {
92 ptr = DTORS.replace(ptr::null_mut());
97 #[cfg(any(target_os = "vxworks", target_os = "horizon"))]
98 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
99 use crate::sys_common::thread_local_dtor::register_dtor_fallback;
100 register_dtor_fallback(t, dtor);