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 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
22 use crate::sys_common::thread_local_dtor::register_dtor_fallback;
25 #[linkage = "extern_weak"]
26 static __dso_handle: *mut u8;
27 #[linkage = "extern_weak"]
28 static __cxa_thread_atexit_impl: *const libc::c_void;
30 if !__cxa_thread_atexit_impl.is_null() {
31 type F = unsafe extern "C" fn(
32 dtor: unsafe extern "C" fn(*mut u8),
36 mem::transmute::<*const libc::c_void, F>(__cxa_thread_atexit_impl)(
39 &__dso_handle as *const _ as *mut _,
43 register_dtor_fallback(t, dtor);
46 // This implementation is very similar to register_dtor_fallback in
47 // sys_common/thread_local.rs. The main difference is that we want to hook into
48 // macOS's analog of the above linux function, _tlv_atexit. OSX will run the
49 // registered dtors before any TLS slots get freed, and when the main thread
52 // Unfortunately, calling _tlv_atexit while tls dtors are running is UB. The
53 // workaround below is to register, via _tlv_atexit, a custom DTOR list once per
54 // thread. thread_local dtors are pushed to the DTOR list without calling
56 #[cfg(target_os = "macos")]
57 pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
58 use crate::cell::Cell;
62 static REGISTERED: Cell<bool> = Cell::new(false);
63 if !REGISTERED.get() {
64 _tlv_atexit(run_dtors, ptr::null_mut());
68 type List = Vec<(*mut u8, unsafe extern "C" fn(*mut u8))>;
71 static DTORS: Cell<*mut List> = Cell::new(ptr::null_mut());
72 if DTORS.get().is_null() {
73 let v: Box<List> = box Vec::new();
74 DTORS.set(Box::into_raw(v));
78 fn _tlv_atexit(dtor: unsafe extern "C" fn(*mut u8), arg: *mut u8);
81 let list: &mut List = &mut *DTORS.get();
84 unsafe extern "C" fn run_dtors(_: *mut u8) {
85 let mut ptr = DTORS.replace(ptr::null_mut());
86 while !ptr.is_null() {
87 let list = Box::from_raw(ptr);
88 for (ptr, dtor) in list.into_iter() {
91 ptr = DTORS.replace(ptr::null_mut());