std: move thread::current TLS variable out of thread_info

Author: joboet

library/std/src/panicking.rs

@@ -21,7 +21,6 @@ use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::{PoisonError, RwLock};
 use crate::sys::stdio::panic_output;
 use crate::sys_common::backtrace;
-use crate::sys_common::thread_info;
 use crate::thread;
 
 #[cfg(not(test))]
@@ -256,7 +255,7 @@ fn default_hook(info: &PanicInfo<'_>) {
             None => "Box<dyn Any>",
         },
     };
-    let thread = thread_info::current_thread();
+    let thread = thread::try_current();
     let name = thread.as_ref().and_then(|t| t.name()).unwrap_or("<unnamed>");
 
     let write = |err: &mut dyn crate::io::Write| {

library/std/src/rt.rs

@@ -24,8 +24,7 @@ pub use core::panicking::{panic_display, panic_fmt};
 
 use crate::sync::Once;
 use crate::sys;
-use crate::sys_common::thread_info;
-use crate::thread::Thread;
+use crate::thread::{self, Thread};
 
 // Prints to the "panic output", depending on the platform this may be:
 // - the standard error output
@@ -96,13 +95,12 @@ unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) {
     unsafe {
         sys::init(argc, argv, sigpipe);
 
-        let main_guard = sys::thread::guard::init();
         // Next, set up the current Thread with the guard information we just
         // created. Note that this isn't necessary in general for new threads,
         // but we just do this to name the main thread and to give it correct
         // info about the stack bounds.
         let thread = Thread::new(Some(rtunwrap!(Ok, CString::new("main"))));
-        thread_info::set(main_guard, thread);
+        thread::set_current(thread);
     }
 }
 

library/std/src/sys/pal/hermit/thread.rs

@@ -104,13 +104,3 @@ impl Thread {
 pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     unsafe { Ok(NonZero::new_unchecked(abi::get_processor_count())) }
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/itron/thread.rs

@@ -312,16 +312,6 @@ impl Drop for Thread {
     }
 }
 
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}
-
 /// Terminate and delete the specified task.
 ///
 /// This function will abort if `deleted_task` refers to the calling task.

library/std/src/sys/pal/sgx/thread.rs

@@ -149,13 +149,3 @@ impl Thread {
 pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     unsupported()
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/teeos/thread.rs

@@ -151,18 +151,6 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     ))
 }
 
-// stub
-pub mod guard {
-    use crate::ops::Range;
-    pub type Guard = Range<usize>;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}
-
 fn min_stack_size(_: *const libc::pthread_attr_t) -> usize {
     libc::PTHREAD_STACK_MIN.try_into().expect("Infallible")
 }

library/std/src/sys/pal/uefi/thread.rs

@@ -52,13 +52,3 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     // UEFI is single threaded
     Ok(NonZero::new(1).unwrap())
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/unix/thread.rs

@@ -729,17 +729,6 @@ mod cgroups {
     }
 }
 
-pub mod guard {
-    use crate::ops::Range;
-    pub type Guard = Range<usize>;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}
-
 // glibc >= 2.15 has a __pthread_get_minstack() function that returns
 // PTHREAD_STACK_MIN plus bytes needed for thread-local storage.
 // We need that information to avoid blowing up when a small stack

library/std/src/sys/pal/unsupported/thread.rs

@@ -38,13 +38,3 @@ impl Thread {
 pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     unsupported()
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/wasi/thread.rs

@@ -193,13 +193,3 @@ impl Thread {
 pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     unsupported()
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/windows/thread.rs

@@ -144,14 +144,3 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
         cpus => Ok(unsafe { NonZero::new_unchecked(cpus) }),
     }
 }
-
-#[cfg_attr(test, allow(dead_code))]
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/pal/xous/thread.rs

@@ -140,13 +140,3 @@ pub fn available_parallelism() -> io::Result<NonZero<usize>> {
     // We're unicore right now.
     Ok(unsafe { NonZero::new_unchecked(1) })
 }
-
-pub mod guard {
-    pub type Guard = !;
-    pub unsafe fn current() -> Option<Guard> {
-        None
-    }
-    pub unsafe fn init() -> Option<Guard> {
-        None
-    }
-}

library/std/src/sys/sync/rwlock/queue.rs

@@ -115,8 +115,7 @@ use crate::sync::atomic::{
     AtomicBool, AtomicPtr,
     Ordering::{AcqRel, Acquire, Relaxed, Release},
 };
-use crate::sys_common::thread_info;
-use crate::thread::Thread;
+use crate::thread::{self, Thread};
 
 // Locking uses exponential backoff. `SPIN_COUNT` indicates how many times the
 // locking operation will be retried.
@@ -203,8 +202,7 @@ impl Node {
     fn prepare(&mut self) {
         // Fall back to creating an unnamed `Thread` handle to allow locking in
         // TLS destructors.
-        self.thread
-            .get_or_init(|| thread_info::current_thread().unwrap_or_else(|| Thread::new(None)));
+        self.thread.get_or_init(|| thread::try_current().unwrap_or_else(|| Thread::new(None)));
         self.completed = AtomicBool::new(false);
     }
 

library/std/src/sys_common/mod.rs

@@ -26,7 +26,6 @@ pub mod io;
 pub mod lazy_box;
 pub mod process;
 pub mod thread;
-pub mod thread_info;
 pub mod thread_local_dtor;
 pub mod thread_parking;
 pub mod wstr;

library/std/src/sys_common/thread_info.rs

@@ -159,7 +159,7 @@
 mod tests;
 
 use crate::any::Any;
-use crate::cell::UnsafeCell;
+use crate::cell::{OnceCell, UnsafeCell};
 use crate::ffi::{CStr, CString};
 use crate::fmt;
 use crate::io;
@@ -174,7 +174,6 @@ use crate::str;
 use crate::sync::Arc;
 use crate::sys::thread as imp;
 use crate::sys_common::thread;
-use crate::sys_common::thread_info;
 use crate::sys_common::thread_parking::Parker;
 use crate::sys_common::{AsInner, IntoInner};
 use crate::time::{Duration, Instant};
@@ -518,12 +517,8 @@ impl Builder {
 
             crate::io::set_output_capture(output_capture);
 
-            // SAFETY: we constructed `f` initialized.
             let f = f.into_inner();
-            // SAFETY: the stack guard passed is the one for the current thread.
-            // This means the current thread's stack and the new thread's stack
-            // are properly set and protected from each other.
-            thread_info::set(unsafe { imp::guard::current() }, their_thread);
+            set_current(their_thread);
             let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| {
                 crate::sys_common::backtrace::__rust_begin_short_backtrace(f)
             }));
@@ -683,6 +678,27 @@ where
     Builder::new().spawn(f).expect("failed to spawn thread")
 }
 
+thread_local! {
+    static CURRENT: OnceCell<Thread> = const { OnceCell::new() };
+}
+
+/// Sets the thread handle for the current thread.
+///
+/// Panics if the handle has been set already or when called from a TLS destructor.
+pub(crate) fn set_current(thread: Thread) {
+    CURRENT.with(|current| current.set(thread).unwrap());
+}
+
+/// Gets a handle to the thread that invokes it.
+///
+/// In contrast to the public `current` function, this will not panic if called
+/// from inside a TLS destructor.
+pub(crate) fn try_current() -> Option<Thread> {
+    CURRENT
+        .try_with(|current| current.get_or_init(|| Thread::new(imp::Thread::get_name())).clone())
+        .ok()
+}
+
 /// Gets a handle to the thread that invokes it.
 ///
 /// # Examples
@@ -705,7 +721,7 @@ where
 #[must_use]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn current() -> Thread {
-    thread_info::current_thread().expect(
+    try_current().expect(
         "use of std::thread::current() is not possible \
          after the thread's local data has been destroyed",
     )