From d868fdce6b9ddef6abcc8de86b3ba8459def36a2 Mon Sep 17 00:00:00 2001 From: joboet Date: Thu, 18 Jul 2024 13:59:48 +0200 Subject: [PATCH] std: make `thread::current` available in all `thread_local!` destructors --- library/std/src/rt.rs | 34 ++- library/std/src/sys/pal/hermit/mod.rs | 6 +- library/std/src/sys/pal/hermit/thread.rs | 1 + library/std/src/sys/sync/rwlock/queue.rs | 6 +- .../std/src/sys/thread_local/guard/apple.rs | 1 + library/std/src/sys/thread_local/guard/key.rs | 39 ++- .../std/src/sys/thread_local/guard/solid.rs | 5 +- .../std/src/sys/thread_local/guard/windows.rs | 8 +- library/std/src/sys/thread_local/key/xous.rs | 2 + library/std/src/sys/thread_local/mod.rs | 48 ++-- .../std/src/sys/thread_local/native/mod.rs | 31 +++ library/std/src/sys/thread_local/os.rs | 34 ++- library/std/src/sys/thread_local/statik.rs | 33 ++- library/std/src/thread/current.rs | 252 ++++++++++++++++++ library/std/src/thread/local/tests.rs | 33 ++- library/std/src/thread/mod.rs | 128 +++------ 16 files changed, 529 insertions(+), 132 deletions(-) create mode 100644 library/std/src/thread/current.rs diff --git a/library/std/src/rt.rs b/library/std/src/rt.rs index b6f36931ec2..0a841f07e3b 100644 --- a/library/std/src/rt.rs +++ b/library/std/src/rt.rs @@ -21,9 +21,10 @@ pub use core::panicking::{panic_display, panic_fmt}; #[rustfmt::skip] +use crate::any::Any; use crate::sync::Once; -use crate::sys; use crate::thread::{self, Thread}; +use crate::{mem, panic, sys}; // Prints to the "panic output", depending on the platform this may be: // - the standard error output @@ -66,6 +67,11 @@ macro_rules! rtunwrap { }; } +fn handle_rt_panic(e: Box) { + mem::forget(e); + rtabort!("initialization or cleanup bug"); +} + // One-time runtime initialization. // Runs before `main`. // SAFETY: must be called only once during runtime initialization. @@ -101,6 +107,20 @@ unsafe fn init(argc: isize, argv: *const *const u8, sigpipe: u8) { thread::set_current(thread); } +/// Clean up the thread-local runtime state. This *should* be run after all other +/// code managed by the Rust runtime, but will not cause UB if that condition is +/// not fulfilled. Also note that this function is not guaranteed to be run, but +/// skipping it will cause leaks and therefore is to be avoided. +pub(crate) fn thread_cleanup() { + // This function is run in situations where unwinding leads to an abort + // (think `extern "C"` functions). Abort here instead so that we can + // print a nice message. + panic::catch_unwind(|| { + crate::thread::drop_current(); + }) + .unwrap_or_else(handle_rt_panic); +} + // One-time runtime cleanup. // Runs after `main` or at program exit. // NOTE: this is not guaranteed to run, for example when the program aborts. @@ -123,11 +143,6 @@ fn lang_start_internal( argv: *const *const u8, sigpipe: u8, ) -> Result { - use crate::{mem, panic}; - let rt_abort = move |e| { - mem::forget(e); - rtabort!("initialization or cleanup bug"); - }; // Guard against the code called by this function from unwinding outside of the Rust-controlled // code, which is UB. This is a requirement imposed by a combination of how the // `#[lang="start"]` attribute is implemented as well as by the implementation of the panicking @@ -139,16 +154,17 @@ fn lang_start_internal( // prevent std from accidentally introducing a panic to these functions. Another is from // user code from `main` or, more nefariously, as described in e.g. issue #86030. // SAFETY: Only called once during runtime initialization. - panic::catch_unwind(move || unsafe { init(argc, argv, sigpipe) }).map_err(rt_abort)?; + panic::catch_unwind(move || unsafe { init(argc, argv, sigpipe) }) + .unwrap_or_else(handle_rt_panic); let ret_code = panic::catch_unwind(move || panic::catch_unwind(main).unwrap_or(101) as isize) .map_err(move |e| { mem::forget(e); rtabort!("drop of the panic payload panicked"); }); - panic::catch_unwind(cleanup).map_err(rt_abort)?; + panic::catch_unwind(cleanup).unwrap_or_else(handle_rt_panic); // Guard against multiple threads calling `libc::exit` concurrently. // See the documentation for `unique_thread_exit` for more information. - panic::catch_unwind(|| crate::sys::exit_guard::unique_thread_exit()).map_err(rt_abort)?; + panic::catch_unwind(crate::sys::exit_guard::unique_thread_exit).unwrap_or_else(handle_rt_panic); ret_code } diff --git a/library/std/src/sys/pal/hermit/mod.rs b/library/std/src/sys/pal/hermit/mod.rs index f49ef947174..b62afb40a61 100644 --- a/library/std/src/sys/pal/hermit/mod.rs +++ b/library/std/src/sys/pal/hermit/mod.rs @@ -92,7 +92,11 @@ pub unsafe fn cleanup() {} unsafe { crate::sys::thread_local::destructors::run(); } - unsafe { hermit_abi::exit(result) } + crate::rt::thread_cleanup(); + + unsafe { + hermit_abi::exit(result); + } } #[inline] diff --git a/library/std/src/sys/pal/hermit/thread.rs b/library/std/src/sys/pal/hermit/thread.rs index 4c0c0919f47..41f2c3e2123 100644 --- a/library/std/src/sys/pal/hermit/thread.rs +++ b/library/std/src/sys/pal/hermit/thread.rs @@ -53,6 +53,7 @@ extern "C" fn thread_start(main: usize) { // run all destructors crate::sys::thread_local::destructors::run(); + crate::rt::thread_cleanup(); } } } diff --git a/library/std/src/sys/sync/rwlock/queue.rs b/library/std/src/sys/sync/rwlock/queue.rs index 0e658328c2e..733f51cae8c 100644 --- a/library/std/src/sys/sync/rwlock/queue.rs +++ b/library/std/src/sys/sync/rwlock/queue.rs @@ -113,7 +113,7 @@ use crate::ptr::{self, NonNull, null_mut, without_provenance_mut}; use crate::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release}; use crate::sync::atomic::{AtomicBool, AtomicPtr}; -use crate::thread::{self, Thread}; +use crate::thread::{self, Thread, ThreadId}; // Locking uses exponential backoff. `SPIN_COUNT` indicates how many times the // locking operation will be retried. @@ -200,7 +200,9 @@ fn new(write: bool) -> 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::try_current().unwrap_or_else(Thread::new_unnamed)); + self.thread.get_or_init(|| { + thread::try_current().unwrap_or_else(|| Thread::new_unnamed(ThreadId::new())) + }); self.completed = AtomicBool::new(false); } diff --git a/library/std/src/sys/thread_local/guard/apple.rs b/library/std/src/sys/thread_local/guard/apple.rs index 6c27f7ae35c..fa25b116622 100644 --- a/library/std/src/sys/thread_local/guard/apple.rs +++ b/library/std/src/sys/thread_local/guard/apple.rs @@ -26,6 +26,7 @@ pub fn enable() { unsafe extern "C" fn run_dtors(_: *mut u8) { unsafe { destructors::run(); + crate::rt::thread_cleanup(); } } } diff --git a/library/std/src/sys/thread_local/guard/key.rs b/library/std/src/sys/thread_local/guard/key.rs index 77575547c14..59581e6f281 100644 --- a/library/std/src/sys/thread_local/guard/key.rs +++ b/library/std/src/sys/thread_local/guard/key.rs @@ -3,10 +3,12 @@ //! that will run all native TLS destructors in the destructor list. use crate::ptr; -use crate::sys::thread_local::destructors; use crate::sys::thread_local::key::{LazyKey, set}; +#[cfg(target_thread_local)] pub fn enable() { + use crate::sys::thread_local::destructors; + static DTORS: LazyKey = LazyKey::new(Some(run)); // Setting the key value to something other than NULL will result in the @@ -18,6 +20,41 @@ pub fn enable() { unsafe extern "C" fn run(_: *mut u8) { unsafe { destructors::run(); + // On platforms with `__cxa_thread_atexit_impl`, `destructors::run` + // does nothing on newer systems as the TLS destructors are + // registered with the system. But because all of those platforms + // call the destructors of TLS keys after the registered ones, this + // function will still be run last (at the time of writing). + crate::rt::thread_cleanup(); + } + } +} + +/// On platforms with key-based TLS, the system runs the destructors for us. +/// We still have to make sure that [`crate::rt::thread_cleanup`] is called, +/// however. This is done by defering the execution of a TLS destructor to +/// the next round of destruction inside the TLS destructors. +#[cfg(not(target_thread_local))] +pub fn enable() { + const DEFER: *mut u8 = ptr::without_provenance_mut(1); + const RUN: *mut u8 = ptr::without_provenance_mut(2); + + static CLEANUP: LazyKey = LazyKey::new(Some(run)); + + unsafe { set(CLEANUP.force(), DEFER) } + + unsafe extern "C" fn run(state: *mut u8) { + if state == DEFER { + // Make sure that this function is run again in the next round of + // TLS destruction. If there is no futher round, there will be leaks, + // but that's okay, `thread_cleanup` is not guaranteed to be called. + unsafe { set(CLEANUP.force(), RUN) } + } else { + debug_assert_eq!(state, RUN); + // If the state is still RUN in the next round of TLS destruction, + // it means that no other TLS destructors defined by this runtime + // have been run, as they would have set the state to DEFER. + crate::rt::thread_cleanup(); } } } diff --git a/library/std/src/sys/thread_local/guard/solid.rs b/library/std/src/sys/thread_local/guard/solid.rs index 054b2d561c8..3bcd46c481d 100644 --- a/library/std/src/sys/thread_local/guard/solid.rs +++ b/library/std/src/sys/thread_local/guard/solid.rs @@ -19,6 +19,9 @@ pub fn enable() { } unsafe extern "C" fn tls_dtor(_unused: *mut u8) { - unsafe { destructors::run() }; + unsafe { + destructors::run(); + crate::rt::thread_cleanup(); + } } } diff --git a/library/std/src/sys/thread_local/guard/windows.rs b/library/std/src/sys/thread_local/guard/windows.rs index bf94f7d6e3d..7ee8e695c75 100644 --- a/library/std/src/sys/thread_local/guard/windows.rs +++ b/library/std/src/sys/thread_local/guard/windows.rs @@ -80,13 +80,13 @@ pub fn enable() { unsafe extern "system" fn tls_callback(_h: *mut c_void, dw_reason: u32, _pv: *mut c_void) { if dw_reason == c::DLL_THREAD_DETACH || dw_reason == c::DLL_PROCESS_DETACH { - #[cfg(target_thread_local)] unsafe { + #[cfg(target_thread_local)] super::super::destructors::run(); - } - #[cfg(not(target_thread_local))] - unsafe { + #[cfg(not(target_thread_local))] super::super::key::run_dtors(); + + crate::rt::thread_cleanup(); } } } diff --git a/library/std/src/sys/thread_local/key/xous.rs b/library/std/src/sys/thread_local/key/xous.rs index 295fb848b30..2ab4bba7d8e 100644 --- a/library/std/src/sys/thread_local/key/xous.rs +++ b/library/std/src/sys/thread_local/key/xous.rs @@ -212,4 +212,6 @@ unsafe fn run_dtors() { unsafe { cur = (*cur).next }; } } + + crate::rt::thread_cleanup(); } diff --git a/library/std/src/sys/thread_local/mod.rs b/library/std/src/sys/thread_local/mod.rs index 3d1b91a7ea0..31d3b439060 100644 --- a/library/std/src/sys/thread_local/mod.rs +++ b/library/std/src/sys/thread_local/mod.rs @@ -31,12 +31,15 @@ ))] { mod statik; pub use statik::{EagerStorage, LazyStorage, thread_local_inner}; + pub(crate) use statik::{LocalPointer, local_pointer}; } else if #[cfg(target_thread_local)] { mod native; pub use native::{EagerStorage, LazyStorage, thread_local_inner}; + pub(crate) use native::{LocalPointer, local_pointer}; } else { mod os; pub use os::{Storage, thread_local_inner}; + pub(crate) use os::{LocalPointer, local_pointer}; } } @@ -72,36 +75,47 @@ pub(crate) mod destructors { } /// This module provides a way to schedule the execution of the destructor list -/// on systems without a per-variable destructor system. -mod guard { +/// and the [runtime cleanup](crate::rt::thread_cleanup) function. Calling `enable` +/// should ensure that these functions are called at the right times. +pub(crate) mod guard { cfg_if::cfg_if! { if #[cfg(all(target_thread_local, target_vendor = "apple"))] { mod apple; - pub(super) use apple::enable; + pub(crate) use apple::enable; } else if #[cfg(target_os = "windows")] { mod windows; - pub(super) use windows::enable; + pub(crate) use windows::enable; } else if #[cfg(any( - all(target_family = "wasm", target_feature = "atomics"), + target_family = "wasm", + target_os = "uefi", + target_os = "zkvm", ))] { - pub(super) fn enable() { - // FIXME: Right now there is no concept of "thread exit", but - // this is likely going to show up at some point in the form of - // an exported symbol that the wasm runtime is going to be - // expected to call. For now we just leak everything, but if - // such a function starts to exist it will probably need to - // iterate the destructor list with this function: + pub(crate) fn enable() { + // FIXME: Right now there is no concept of "thread exit" on + // wasm, but this is likely going to show up at some point in + // the form of an exported symbol that the wasm runtime is going + // to be expected to call. For now we just leak everything, but + // if such a function starts to exist it will probably need to + // iterate the destructor list with these functions: + #[cfg(all(target_family = "wasm", target_feature = "atomics"))] #[allow(unused)] use super::destructors::run; + #[allow(unused)] + use crate::rt::thread_cleanup; } - } else if #[cfg(target_os = "hermit")] { - pub(super) fn enable() {} + } else if #[cfg(any( + target_os = "hermit", + target_os = "xous", + ))] { + // `std` is the only runtime, so it just calls the destructor functions + // itself when the time comes. + pub(crate) fn enable() {} } else if #[cfg(target_os = "solid_asp3")] { mod solid; - pub(super) use solid::enable; - } else if #[cfg(all(target_thread_local, not(target_family = "wasm")))] { + pub(crate) use solid::enable; + } else { mod key; - pub(super) use key::enable; + pub(crate) use key::enable; } } } diff --git a/library/std/src/sys/thread_local/native/mod.rs b/library/std/src/sys/thread_local/native/mod.rs index 1cc45fe892d..f498dee0899 100644 --- a/library/std/src/sys/thread_local/native/mod.rs +++ b/library/std/src/sys/thread_local/native/mod.rs @@ -29,6 +29,9 @@ //! eliminates the `Destroyed` state for these values, which can allow more niche //! optimizations to occur for the `State` enum. For `Drop` types, `()` is used. +use crate::cell::Cell; +use crate::ptr; + mod eager; mod lazy; @@ -107,3 +110,31 @@ fn __init() -> $t { $crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*); }, } + +#[rustc_macro_transparency = "semitransparent"] +pub(crate) macro local_pointer { + () => {}, + ($vis:vis static $name:ident; $($rest:tt)*) => { + #[thread_local] + $vis static $name: $crate::sys::thread_local::LocalPointer = $crate::sys::thread_local::LocalPointer::__new(); + $crate::sys::thread_local::local_pointer! { $($rest)* } + }, +} + +pub(crate) struct LocalPointer { + p: Cell<*mut ()>, +} + +impl LocalPointer { + pub const fn __new() -> LocalPointer { + LocalPointer { p: Cell::new(ptr::null_mut()) } + } + + pub fn get(&self) -> *mut () { + self.p.get() + } + + pub fn set(&self, p: *mut ()) { + self.p.set(p) + } +} diff --git a/library/std/src/sys/thread_local/os.rs b/library/std/src/sys/thread_local/os.rs index f09c396ef0f..26ce3322a16 100644 --- a/library/std/src/sys/thread_local/os.rs +++ b/library/std/src/sys/thread_local/os.rs @@ -1,8 +1,8 @@ -use super::abort_on_dtor_unwind; +use super::key::{Key, LazyKey, get, set}; +use super::{abort_on_dtor_unwind, guard}; use crate::cell::Cell; use crate::marker::PhantomData; use crate::ptr; -use crate::sys::thread_local::key::{Key, LazyKey, get, set}; #[doc(hidden)] #[allow_internal_unstable(thread_local_internals)] @@ -138,5 +138,35 @@ unsafe fn try_initialize( drop(ptr); // SAFETY: `key` is the TLS key `ptr` was stored under. unsafe { set(key, ptr::null_mut()) }; + // Make sure that the runtime cleanup will be performed + // after the next round of TLS destruction. + guard::enable(); }); } + +#[rustc_macro_transparency = "semitransparent"] +pub(crate) macro local_pointer { + () => {}, + ($vis:vis static $name:ident; $($rest:tt)*) => { + $vis static $name: $crate::sys::thread_local::LocalPointer = $crate::sys::thread_local::LocalPointer::__new(); + $crate::sys::thread_local::local_pointer! { $($rest)* } + }, +} + +pub(crate) struct LocalPointer { + key: LazyKey, +} + +impl LocalPointer { + pub const fn __new() -> LocalPointer { + LocalPointer { key: LazyKey::new(None) } + } + + pub fn get(&'static self) -> *mut () { + unsafe { get(self.key.force()) as *mut () } + } + + pub fn set(&'static self, p: *mut ()) { + unsafe { set(self.key.force(), p as *mut u8) } + } +} diff --git a/library/std/src/sys/thread_local/statik.rs b/library/std/src/sys/thread_local/statik.rs index a3451ab74e0..ba94caa6690 100644 --- a/library/std/src/sys/thread_local/statik.rs +++ b/library/std/src/sys/thread_local/statik.rs @@ -1,7 +1,8 @@ //! On some targets like wasm there's no threads, so no need to generate //! thread locals and we can instead just use plain statics! -use crate::cell::UnsafeCell; +use crate::cell::{Cell, UnsafeCell}; +use crate::ptr; #[doc(hidden)] #[allow_internal_unstable(thread_local_internals)] @@ -93,3 +94,33 @@ fn initialize(&'static self, i: Option<&mut Option>, f: impl FnOnce() -> T) - // SAFETY: the target doesn't have threads. unsafe impl Sync for LazyStorage {} + +#[rustc_macro_transparency = "semitransparent"] +pub(crate) macro local_pointer { + () => {}, + ($vis:vis static $name:ident; $($rest:tt)*) => { + $vis static $name: $crate::sys::thread_local::LocalPointer = $crate::sys::thread_local::LocalPointer::__new(); + $crate::sys::thread_local::local_pointer! { $($rest)* } + }, +} + +pub(crate) struct LocalPointer { + p: Cell<*mut ()>, +} + +impl LocalPointer { + pub const fn __new() -> LocalPointer { + LocalPointer { p: Cell::new(ptr::null_mut()) } + } + + pub fn get(&self) -> *mut () { + self.p.get() + } + + pub fn set(&self, p: *mut ()) { + self.p.set(p) + } +} + +// SAFETY: the target doesn't have threads. +unsafe impl Sync for LocalPointer {} diff --git a/library/std/src/thread/current.rs b/library/std/src/thread/current.rs new file mode 100644 index 00000000000..b38149a0da7 --- /dev/null +++ b/library/std/src/thread/current.rs @@ -0,0 +1,252 @@ +use super::{Thread, ThreadId}; +use crate::mem::ManuallyDrop; +use crate::ptr; +use crate::sys::thread_local::local_pointer; + +const NONE: *mut () = ptr::null_mut(); +const BUSY: *mut () = ptr::without_provenance_mut(1); +const DESTROYED: *mut () = ptr::without_provenance_mut(2); + +local_pointer! { + static CURRENT; +} + +/// Persistent storage for the thread ID. +/// +/// We store the thread ID so that it never gets destroyed during the lifetime +/// of a thread, either using `#[thread_local]` or multiple `local_pointer!`s. +mod id { + use super::*; + + cfg_if::cfg_if! { + if #[cfg(target_thread_local)] { + use crate::cell::Cell; + + #[thread_local] + static ID: Cell> = Cell::new(None); + + pub(super) const CHEAP: bool = true; + + pub(super) fn get() -> Option { + ID.get() + } + + pub(super) fn set(id: ThreadId) { + ID.set(Some(id)) + } + } else if #[cfg(target_pointer_width = "16")] { + local_pointer! { + static ID0; + static ID16; + static ID32; + static ID48; + } + + pub(super) const CHEAP: bool = false; + + pub(super) fn get() -> Option { + let id0 = ID0.get().addr() as u64; + let id16 = ID16.get().addr() as u64; + let id32 = ID32.get().addr() as u64; + let id48 = ID48.get().addr() as u64; + ThreadId::from_u64((id48 << 48) + (id32 << 32) + (id16 << 16) + id0) + } + + pub(super) fn set(id: ThreadId) { + let val = id.as_u64().get(); + ID0.set(ptr::without_provenance_mut(val as usize)); + ID16.set(ptr::without_provenance_mut((val >> 16) as usize)); + ID32.set(ptr::without_provenance_mut((val >> 32) as usize)); + ID48.set(ptr::without_provenance_mut((val >> 48) as usize)); + } + } else if #[cfg(target_pointer_width = "32")] { + local_pointer! { + static ID0; + static ID32; + } + + pub(super) const CHEAP: bool = false; + + pub(super) fn get() -> Option { + let id0 = ID0.get().addr() as u64; + let id32 = ID32.get().addr() as u64; + ThreadId::from_u64((id32 << 32) + id0) + } + + pub(super) fn set(id: ThreadId) { + let val = id.as_u64().get(); + ID0.set(ptr::without_provenance_mut(val as usize)); + ID32.set(ptr::without_provenance_mut((val >> 32) as usize)); + } + } else { + local_pointer! { + static ID; + } + + pub(super) const CHEAP: bool = true; + + pub(super) fn get() -> Option { + let id = ID.get().addr() as u64; + ThreadId::from_u64(id) + } + + pub(super) fn set(id: ThreadId) { + let val = id.as_u64().get(); + ID.set(ptr::without_provenance_mut(val as usize)); + } + } + } + + #[inline] + pub(super) fn get_or_init() -> ThreadId { + get().unwrap_or_else( + #[cold] + || { + let id = ThreadId::new(); + id::set(id); + id + }, + ) + } +} + +/// Sets the thread handle for the current thread. +/// +/// Aborts if the handle or the ID has been set already. +pub(crate) fn set_current(thread: Thread) { + if CURRENT.get() != NONE || id::get().is_some() { + // Using `panic` here can add ~3kB to the binary size. We have complete + // control over where this is called, so just abort if there is a bug. + rtabort!("thread::set_current should only be called once per thread"); + } + + id::set(thread.id()); + + // Make sure that `crate::rt::thread_cleanup` will be run, which will + // call `drop_current`. + crate::sys::thread_local::guard::enable(); + CURRENT.set(thread.into_raw().cast_mut()); +} + +/// Gets the id of the thread that invokes it. +/// +/// This function will always succeed, will always return the same value for +/// one thread and is guaranteed not to call the global allocator. +#[inline] +pub(crate) fn current_id() -> ThreadId { + // If accessing the persistant thread ID takes multiple TLS accesses, try + // to retrieve it from the current thread handle, which will only take one + // TLS access. + if !id::CHEAP { + let current = CURRENT.get(); + if current > DESTROYED { + unsafe { + let current = ManuallyDrop::new(Thread::from_raw(current)); + return current.id(); + } + } + } + + id::get_or_init() +} + +/// Gets a handle to the thread that invokes it, if the handle has been initialized. +pub(crate) fn try_current() -> Option { + let current = CURRENT.get(); + if current > DESTROYED { + unsafe { + let current = ManuallyDrop::new(Thread::from_raw(current)); + Some((*current).clone()) + } + } else { + None + } +} + +/// Gets a handle to the thread that invokes it. +/// +/// # Examples +/// +/// Getting a handle to the current thread with `thread::current()`: +/// +/// ``` +/// use std::thread; +/// +/// let handler = thread::Builder::new() +/// .name("named thread".into()) +/// .spawn(|| { +/// let handle = thread::current(); +/// assert_eq!(handle.name(), Some("named thread")); +/// }) +/// .unwrap(); +/// +/// handler.join().unwrap(); +/// ``` +#[must_use] +#[stable(feature = "rust1", since = "1.0.0")] +pub fn current() -> Thread { + let current = CURRENT.get(); + if current > DESTROYED { + unsafe { + let current = ManuallyDrop::new(Thread::from_raw(current)); + (*current).clone() + } + } else { + init_current(current) + } +} + +#[cold] +fn init_current(current: *mut ()) -> Thread { + if current == NONE { + CURRENT.set(BUSY); + // If the thread ID was initialized already, use it. + let id = id::get_or_init(); + let thread = Thread::new_unnamed(id); + + // Make sure that `crate::rt::thread_cleanup` will be run, which will + // call `drop_current`. + crate::sys::thread_local::guard::enable(); + CURRENT.set(thread.clone().into_raw().cast_mut()); + thread + } else if current == BUSY { + // BUSY exists solely for this check, but as it is in the slow path, the + // extra TLS write above shouldn't matter. The alternative is nearly always + // a stack overflow. + + // If you came across this message, contact the author of your allocator. + // If you are said author: A surprising amount of functions inside the + // standard library (e.g. `Mutex`, `thread_local!`, `File` when using long + // paths, even `panic!` when using unwinding), need memory allocation, so + // you'll get circular dependencies all over the place when using them. + // I (joboet) highly recommend using only APIs from core in your allocator + // and implementing your own system abstractions. Still, if you feel that + // a particular API should be entirely allocation-free, feel free to open + // an issue on the Rust repository, we'll see what we can do. + rtabort!( + "\n + Attempted to access thread-local data while allocating said data.\n + Do not access functions that allocate in the global allocator!\n + This is a bug in the global allocator.\n + " + ) + } else { + debug_assert_eq!(current, DESTROYED); + panic!( + "use of std::thread::current() is not possible after the thread's + local data has been destroyed" + ) + } +} + +/// This should be run in [`crate::rt::thread_cleanup`] to reset the thread +/// handle. +pub(crate) fn drop_current() { + let current = CURRENT.get(); + if current > DESTROYED { + unsafe { + CURRENT.set(DESTROYED); + drop(Thread::from_raw(current)); + } + } +} diff --git a/library/std/src/thread/local/tests.rs b/library/std/src/thread/local/tests.rs index 6abb9b85a2e..9d4f52a0921 100644 --- a/library/std/src/thread/local/tests.rs +++ b/library/std/src/thread/local/tests.rs @@ -1,7 +1,7 @@ use crate::cell::{Cell, UnsafeCell}; use crate::sync::atomic::{AtomicU8, Ordering}; use crate::sync::{Arc, Condvar, Mutex}; -use crate::thread::{self, LocalKey}; +use crate::thread::{self, Builder, LocalKey}; use crate::thread_local; #[derive(Clone, Default)] @@ -343,3 +343,34 @@ fn drop(&mut self) { jh2.join().unwrap(); } } + +// Test that thread::current is still available in TLS destructors. +#[test] +fn thread_current_in_dtor() { + // Go through one round of TLS destruction first. + struct Defer; + impl Drop for Defer { + fn drop(&mut self) { + RETRIEVE.with(|_| {}); + } + } + + struct RetrieveName; + impl Drop for RetrieveName { + fn drop(&mut self) { + *NAME.lock().unwrap() = Some(thread::current().name().unwrap().to_owned()); + } + } + + static NAME: Mutex> = Mutex::new(None); + + thread_local! { + static DEFER: Defer = const { Defer }; + static RETRIEVE: RetrieveName = const { RetrieveName }; + } + + Builder::new().name("test".to_owned()).spawn(|| DEFER.with(|_| {})).unwrap().join().unwrap(); + let name = NAME.lock().unwrap(); + let name = name.as_ref().unwrap(); + assert_eq!(name, "test"); +} diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs index 22d65583365..d1d4eabb9bd 100644 --- a/library/std/src/thread/mod.rs +++ b/library/std/src/thread/mod.rs @@ -141,7 +141,7 @@ //! [`Result`]: crate::result::Result //! [`Ok`]: crate::result::Result::Ok //! [`Err`]: crate::result::Result::Err -//! [`thread::current`]: current +//! [`thread::current`]: current::current //! [`thread::Result`]: Result //! [`unpark`]: Thread::unpark //! [`thread::park_timeout`]: park_timeout @@ -159,7 +159,7 @@ mod tests; use crate::any::Any; -use crate::cell::{Cell, OnceCell, UnsafeCell}; +use crate::cell::UnsafeCell; use crate::ffi::CStr; use crate::marker::PhantomData; use crate::mem::{self, ManuallyDrop, forget}; @@ -179,6 +179,12 @@ #[stable(feature = "scoped_threads", since = "1.63.0")] pub use scoped::{Scope, ScopedJoinHandle, scope}; +mod current; + +#[stable(feature = "rust1", since = "1.0.0")] +pub use current::current; +pub(crate) use current::{current_id, drop_current, set_current, try_current}; + //////////////////////////////////////////////////////////////////////////////// // Thread-local storage //////////////////////////////////////////////////////////////////////////////// @@ -471,7 +477,11 @@ unsafe fn spawn_unchecked_<'scope, F, T>( amt }); - let my_thread = name.map_or_else(Thread::new_unnamed, Thread::new); + let id = ThreadId::new(); + let my_thread = match name { + Some(name) => Thread::new(id, name.into()), + None => Thread::new_unnamed(id), + }; let their_thread = my_thread.clone(); let my_packet: Arc> = Arc::new(Packet { @@ -509,6 +519,9 @@ fn drop(&mut self) { let f = MaybeDangling::new(f); let main = move || { + // Immediately store the thread handle to avoid setting it or its ID + // twice, which would cause an abort. + set_current(their_thread.clone()); if let Some(name) = their_thread.cname() { imp::Thread::set_name(name); } @@ -516,7 +529,6 @@ fn drop(&mut self) { crate::io::set_output_capture(output_capture); let f = f.into_inner(); - set_current(their_thread); let try_result = panic::catch_unwind(panic::AssertUnwindSafe(|| { crate::sys::backtrace::__rust_begin_short_backtrace(f) })); @@ -690,84 +702,6 @@ pub fn spawn(f: F) -> JoinHandle Builder::new().spawn(f).expect("failed to spawn thread") } -thread_local! { - // Invariant: `CURRENT` and `CURRENT_ID` will always be initialized together. - // If `CURRENT` is initialized, then `CURRENT_ID` will hold the same value - // as `CURRENT.id()`. - static CURRENT: OnceCell = const { OnceCell::new() }; - static CURRENT_ID: Cell> = const { Cell::new(None) }; -} - -/// Sets the thread handle for the current thread. -/// -/// Aborts if the handle has been set already to reduce code size. -pub(crate) fn set_current(thread: Thread) { - let tid = thread.id(); - // Using `unwrap` here can add ~3kB to the binary size. We have complete - // control over where this is called, so just abort if there is a bug. - CURRENT.with(|current| match current.set(thread) { - Ok(()) => CURRENT_ID.set(Some(tid)), - Err(_) => rtabort!("thread::set_current should only be called once per thread"), - }); -} - -/// 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 { - CURRENT - .try_with(|current| { - current - .get_or_init(|| { - let thread = Thread::new_unnamed(); - CURRENT_ID.set(Some(thread.id())); - thread - }) - .clone() - }) - .ok() -} - -/// Gets the id of the thread that invokes it. -#[inline] -pub(crate) fn current_id() -> ThreadId { - CURRENT_ID.get().unwrap_or_else(|| { - // If `CURRENT_ID` isn't initialized yet, then `CURRENT` must also not be initialized. - // `current()` will initialize both `CURRENT` and `CURRENT_ID` so subsequent calls to - // `current_id()` will succeed immediately. - current().id() - }) -} - -/// Gets a handle to the thread that invokes it. -/// -/// # Examples -/// -/// Getting a handle to the current thread with `thread::current()`: -/// -/// ``` -/// use std::thread; -/// -/// let handler = thread::Builder::new() -/// .name("named thread".into()) -/// .spawn(|| { -/// let handle = thread::current(); -/// assert_eq!(handle.name(), Some("named thread")); -/// }) -/// .unwrap(); -/// -/// handler.join().unwrap(); -/// ``` -#[must_use] -#[stable(feature = "rust1", since = "1.0.0")] -pub fn current() -> Thread { - try_current().expect( - "use of std::thread::current() is not possible \ - after the thread's local data has been destroyed", - ) -} - /// Cooperatively gives up a timeslice to the OS scheduler. /// /// This calls the underlying OS scheduler's yield primitive, signaling @@ -1225,8 +1159,11 @@ pub fn park_timeout(dur: Duration) { pub struct ThreadId(NonZero); impl ThreadId { + // DO NOT rely on this value. + const MAIN_THREAD: ThreadId = ThreadId(unsafe { NonZero::new_unchecked(1) }); + // Generate a new unique thread ID. - fn new() -> ThreadId { + pub(crate) fn new() -> ThreadId { #[cold] fn exhausted() -> ! { panic!("failed to generate unique thread ID: bitspace exhausted") @@ -1236,7 +1173,7 @@ fn exhausted() -> ! { if #[cfg(target_has_atomic = "64")] { use crate::sync::atomic::AtomicU64; - static COUNTER: AtomicU64 = AtomicU64::new(0); + static COUNTER: AtomicU64 = AtomicU64::new(1); let mut last = COUNTER.load(Ordering::Relaxed); loop { @@ -1252,7 +1189,7 @@ fn exhausted() -> ! { } else { use crate::sync::{Mutex, PoisonError}; - static COUNTER: Mutex = Mutex::new(0); + static COUNTER: Mutex = Mutex::new(1); let mut counter = COUNTER.lock().unwrap_or_else(PoisonError::into_inner); let Some(id) = counter.checked_add(1) else { @@ -1269,6 +1206,11 @@ fn exhausted() -> ! { } } + #[cfg(not(target_thread_local))] + fn from_u64(v: u64) -> Option { + NonZero::new(v).map(ThreadId) + } + /// This returns a numeric identifier for the thread identified by this /// `ThreadId`. /// @@ -1369,27 +1311,27 @@ fn parker(self: Pin<&Self>) -> Pin<&Parker> { /// should instead use a function like `spawn` to create new threads, see the /// docs of [`Builder`] and [`spawn`] for more details. /// -/// [`thread::current`]: current +/// [`thread::current`]: current::current pub struct Thread { inner: Pin>, } impl Thread { /// Used only internally to construct a thread object without spawning. - pub(crate) fn new(name: String) -> Thread { - Self::new_inner(ThreadName::Other(name.into())) + pub(crate) fn new(id: ThreadId, name: String) -> Thread { + Self::new_inner(id, ThreadName::Other(name.into())) } - pub(crate) fn new_unnamed() -> Thread { - Self::new_inner(ThreadName::Unnamed) + pub(crate) fn new_unnamed(id: ThreadId) -> Thread { + Self::new_inner(id, ThreadName::Unnamed) } // Used in runtime to construct main thread pub(crate) fn new_main() -> Thread { - Self::new_inner(ThreadName::Main) + Self::new_inner(ThreadId::MAIN_THREAD, ThreadName::Main) } - fn new_inner(name: ThreadName) -> Thread { + fn new_inner(id: ThreadId, name: ThreadName) -> Thread { // We have to use `unsafe` here to construct the `Parker` in-place, // which is required for the UNIX implementation. // @@ -1399,7 +1341,7 @@ fn new_inner(name: ThreadName) -> Thread { let mut arc = Arc::::new_uninit(); let ptr = Arc::get_mut_unchecked(&mut arc).as_mut_ptr(); (&raw mut (*ptr).name).write(name); - (&raw mut (*ptr).id).write(ThreadId::new()); + (&raw mut (*ptr).id).write(id); Parker::new_in_place(&raw mut (*ptr).parker); Pin::new_unchecked(arc.assume_init()) };