Auto merge of #57655 - mtak-:fix-tls-dtors-macos, r=alexcrichton
OSX: fix #57534 registering thread dtors while running thread dtors
r? @alexcrichton
- "fast" `thread_local` destructors get run even on the main thread
- "fast" `thread_local` dtors, can initialize other `thread_local`'s
One corner case where this fix doesn't work, is when a C++ `thread_local` triggers the initialization of a rust `thread_local`.
I did not add any std::thread specific flag to indicate that the thread is currently exiting, which would be checked before registering a new dtor (I didn't really know where to stick that). I think this does the trick tho!
Let me know if anything needs tweaking/fixing/etc.
resolves this for macos: https://github.com/rust-lang/rust/issues/28129
fixes: https://github.com/rust-lang/rust/issues/57534
diff --git a/src/libstd/sys/unix/fast_thread_local.rs b/src/libstd/sys/unix/fast_thread_local.rs
index d48d701d..742ffd1 100644
--- a/src/libstd/sys/unix/fast_thread_local.rs
+++ b/src/libstd/sys/unix/fast_thread_local.rs
@@ -33,30 +33,57 @@
register_dtor_fallback(t, dtor);
}
-// macOS's analog of the above linux function is this _tlv_atexit function.
-// The disassembly of thread_local globals in C++ (at least produced by
-// clang) will have this show up in the output.
+// This implementation is very similar to register_dtor_fallback in
+// sys_common/thread_local.rs. The main difference is that we want to hook into
+// macOS's analog of the above linux function, _tlv_atexit. OSX will run the
+// registered dtors before any TLS slots get freed, and when the main thread
+// exits.
+//
+// Unfortunately, calling _tlv_atexit while tls dtors are running is UB. The
+// workaround below is to register, via _tlv_atexit, a custom DTOR list once per
+// thread. thread_local dtors are pushed to the DTOR list without calling
+// _tlv_atexit.
#[cfg(target_os = "macos")]
pub unsafe fn register_dtor(t: *mut u8, dtor: unsafe extern fn(*mut u8)) {
+ use cell::Cell;
+ use ptr;
+
+ #[thread_local]
+ static REGISTERED: Cell<bool> = Cell::new(false);
+ if !REGISTERED.get() {
+ _tlv_atexit(run_dtors, ptr::null_mut());
+ REGISTERED.set(true);
+ }
+
+ type List = Vec<(*mut u8, unsafe extern fn(*mut u8))>;
+
+ #[thread_local]
+ static DTORS: Cell<*mut List> = Cell::new(ptr::null_mut());
+ if DTORS.get().is_null() {
+ let v: Box<List> = box Vec::new();
+ DTORS.set(Box::into_raw(v));
+ }
+
extern {
fn _tlv_atexit(dtor: unsafe extern fn(*mut u8),
arg: *mut u8);
}
- _tlv_atexit(dtor, t);
+
+ let list: &mut List = &mut *DTORS.get();
+ list.push((t, dtor));
+
+ unsafe extern fn run_dtors(_: *mut u8) {
+ let mut ptr = DTORS.replace(ptr::null_mut());
+ while !ptr.is_null() {
+ let list = Box::from_raw(ptr);
+ for (ptr, dtor) in list.into_iter() {
+ dtor(ptr);
+ }
+ ptr = DTORS.replace(ptr::null_mut());
+ }
+ }
}
pub fn requires_move_before_drop() -> bool {
- // The macOS implementation of TLS apparently had an odd aspect to it
- // where the pointer we have may be overwritten while this destructor
- // is running. Specifically if a TLS destructor re-accesses TLS it may
- // trigger a re-initialization of all TLS variables, paving over at
- // least some destroyed ones with initial values.
- //
- // This means that if we drop a TLS value in place on macOS that we could
- // revert the value to its original state halfway through the
- // destructor, which would be bad!
- //
- // Hence, we use `ptr::read` on macOS (to move to a "safe" location)
- // instead of drop_in_place.
- cfg!(target_os = "macos")
+ false
}
diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
index efd231e..5d2eb5f 100644
--- a/src/libstd/thread/local.rs
+++ b/src/libstd/thread/local.rs
@@ -69,9 +69,6 @@
/// destroyed, but not all platforms have this guard. Those platforms that do
/// not guard typically have a synthetic limit after which point no more
/// destructors are run.
-/// 3. On macOS, initializing TLS during destruction of other TLS slots can
-/// sometimes cancel *all* destructors for the current thread, whether or not
-/// the slots have already had their destructors run or not.
///
/// [`with`]: ../../std/thread/struct.LocalKey.html#method.with
/// [`thread_local!`]: ../../std/macro.thread_local.html
@@ -604,11 +601,8 @@
}
// Note that this test will deadlock if TLS destructors aren't run (this
- // requires the destructor to be run to pass the test). macOS has a known bug
- // where dtors-in-dtors may cancel other destructors, so we just ignore this
- // test on macOS.
+ // requires the destructor to be run to pass the test).
#[test]
- #[cfg_attr(target_os = "macos", ignore)]
fn dtors_in_dtors_in_dtors() {
struct S1(Sender<()>);
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
