diff options
Diffstat (limited to 'library/std/src/thread/mod.rs')
| -rw-r--r-- | library/std/src/thread/mod.rs | 276 |
1 files changed, 143 insertions, 133 deletions
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs index 85ee369ca2b..59b395336f2 100644 --- a/library/std/src/thread/mod.rs +++ b/library/std/src/thread/mod.rs @@ -158,12 +158,9 @@ #[cfg(all(test, not(any(target_os = "emscripten", target_os = "wasi"))))] mod tests; -use core::cell::SyncUnsafeCell; -use core::ffi::CStr; -use core::mem::MaybeUninit; - use crate::any::Any; use crate::cell::UnsafeCell; +use crate::ffi::CStr; use crate::marker::PhantomData; use crate::mem::{self, ManuallyDrop, forget}; use crate::num::NonZero; @@ -186,7 +183,8 @@ mod current; #[stable(feature = "rust1", since = "1.0.0")] pub use current::current; -pub(crate) use current::{current_id, current_or_unnamed, drop_current, set_current, try_current}; +pub(crate) use current::{current_id, current_or_unnamed, drop_current}; +use current::{set_current, try_with_current}; mod spawnhook; @@ -501,10 +499,7 @@ impl Builder { }); let id = ThreadId::new(); - let my_thread = match name { - Some(name) => Thread::new(id, name.into()), - None => Thread::new_unnamed(id), - }; + let my_thread = Thread::new(id, name); let hooks = if no_hooks { spawnhook::ChildSpawnHooks::default() @@ -1235,7 +1230,7 @@ impl ThreadId { } } - #[cfg(not(target_thread_local))] + #[cfg(any(not(target_thread_local), target_has_atomic = "64"))] fn from_u64(v: u64) -> Option<ThreadId> { NonZero::new(v).map(ThreadId) } @@ -1261,29 +1256,14 @@ impl ThreadId { // This module ensures private fields are kept private, which is necessary to enforce the safety requirements. mod thread_name_string { - use core::str; - use crate::ffi::{CStr, CString}; + use crate::str; /// Like a `String` it's guaranteed UTF-8 and like a `CString` it's null terminated. pub(crate) struct ThreadNameString { inner: CString, } - impl ThreadNameString { - pub fn as_str(&self) -> &str { - // SAFETY: `self.inner` is only initialised via `String`, which upholds the validity invariant of `str`. - unsafe { str::from_utf8_unchecked(self.inner.to_bytes()) } - } - } - - impl core::ops::Deref for ThreadNameString { - type Target = CStr; - fn deref(&self) -> &CStr { - &self.inner - } - } - impl From<String> for ThreadNameString { fn from(s: String) -> Self { Self { @@ -1291,82 +1271,124 @@ mod thread_name_string { } } } -} -pub(crate) use thread_name_string::ThreadNameString; - -static MAIN_THREAD_INFO: SyncUnsafeCell<(MaybeUninit<ThreadId>, MaybeUninit<Parker>)> = - SyncUnsafeCell::new((MaybeUninit::uninit(), MaybeUninit::uninit())); - -/// The internal representation of a `Thread` that is not the main thread. -struct OtherInner { - name: Option<ThreadNameString>, - id: ThreadId, - parker: Parker, -} - -/// The internal representation of a `Thread` handle. -#[derive(Clone)] -enum Inner { - /// Represents the main thread. May only be constructed by Thread::new_main. - Main(&'static (ThreadId, Parker)), - /// Represents any other thread. - Other(Pin<Arc<OtherInner>>), -} - -impl Inner { - fn id(&self) -> ThreadId { - match self { - Self::Main((thread_id, _)) => *thread_id, - Self::Other(other) => other.id, - } - } - fn cname(&self) -> Option<&CStr> { - match self { - Self::Main(_) => Some(c"main"), - Self::Other(other) => other.name.as_deref(), + impl ThreadNameString { + pub fn as_cstr(&self) -> &CStr { + &self.inner } - } - fn name(&self) -> Option<&str> { - match self { - Self::Main(_) => Some("main"), - Self::Other(other) => other.name.as_ref().map(ThreadNameString::as_str), + pub fn as_str(&self) -> &str { + // SAFETY: `ThreadNameString` is guaranteed to be UTF-8. + unsafe { str::from_utf8_unchecked(self.inner.to_bytes()) } } } +} - fn into_raw(self) -> *const () { - match self { - // Just return the pointer to `MAIN_THREAD_INFO`. - Self::Main(ptr) => crate::ptr::from_ref(ptr).cast(), - Self::Other(arc) => { - // Safety: We only expose an opaque pointer, which maintains the `Pin` invariant. - let inner = unsafe { Pin::into_inner_unchecked(arc) }; - Arc::into_raw(inner) as *const () +use thread_name_string::ThreadNameString; + +/// Store the ID of the main thread. +/// +/// The thread handle for the main thread is created lazily, and this might even +/// happen pre-main. Since not every platform has a way to identify the main +/// thread when that happens – macOS's `pthread_main_np` function being a notable +/// exception – we cannot assign it the right name right then. Instead, in our +/// runtime startup code, we remember the thread ID of the main thread (through +/// this modules `set` function) and use it to identify the main thread from then +/// on. This works reliably and has the additional advantage that we can report +/// the right thread name on main even after the thread handle has been destroyed. +/// Note however that this also means that the name reported in pre-main functions +/// will be incorrect, but that's just something we have to live with. +pub(crate) mod main_thread { + cfg_if::cfg_if! { + if #[cfg(target_has_atomic = "64")] { + use super::ThreadId; + use crate::sync::atomic::AtomicU64; + use crate::sync::atomic::Ordering::Relaxed; + + static MAIN: AtomicU64 = AtomicU64::new(0); + + pub(super) fn get() -> Option<ThreadId> { + ThreadId::from_u64(MAIN.load(Relaxed)) } - } - } - /// # Safety - /// - /// See [`Thread::from_raw`]. - unsafe fn from_raw(ptr: *const ()) -> Self { - // If the pointer is to `MAIN_THREAD_INFO`, we know it is the `Main` variant. - if crate::ptr::eq(ptr.cast(), &MAIN_THREAD_INFO) { - Self::Main(unsafe { &*ptr.cast() }) + /// # Safety + /// May only be called once. + pub(crate) unsafe fn set(id: ThreadId) { + MAIN.store(id.as_u64().get(), Relaxed) + } } else { - // Safety: Upheld by caller - Self::Other(unsafe { Pin::new_unchecked(Arc::from_raw(ptr as *const OtherInner)) }) + use super::ThreadId; + use crate::mem::MaybeUninit; + use crate::sync::atomic::AtomicBool; + use crate::sync::atomic::Ordering::{Acquire, Release}; + + static INIT: AtomicBool = AtomicBool::new(false); + static mut MAIN: MaybeUninit<ThreadId> = MaybeUninit::uninit(); + + pub(super) fn get() -> Option<ThreadId> { + if INIT.load(Acquire) { + Some(unsafe { MAIN.assume_init() }) + } else { + None + } + } + + /// # Safety + /// May only be called once. + pub(crate) unsafe fn set(id: ThreadId) { + unsafe { MAIN = MaybeUninit::new(id) }; + INIT.store(true, Release); + } } } +} - fn parker(&self) -> Pin<&Parker> { - match self { - Self::Main((_, parker_ref)) => Pin::static_ref(parker_ref), - Self::Other(inner) => unsafe { - Pin::map_unchecked(inner.as_ref(), |inner| &inner.parker) - }, +/// Run a function with the current thread's name. +/// +/// Modulo thread local accesses, this function is safe to call from signal +/// handlers and in similar circumstances where allocations are not possible. +pub(crate) fn with_current_name<F, R>(f: F) -> R +where + F: FnOnce(Option<&str>) -> R, +{ + try_with_current(|thread| { + if let Some(thread) = thread { + // If there is a current thread handle, try to use the name stored + // there. + if let Some(name) = &thread.inner.name { + return f(Some(name.as_str())); + } else if Some(thread.inner.id) == main_thread::get() { + // The main thread doesn't store its name in the handle, we must + // identify it through its ID. Since we already have the `Thread`, + // we can retrieve the ID from it instead of going through another + // thread local. + return f(Some("main")); + } + } else if let Some(main) = main_thread::get() + && let Some(id) = current::id::get() + && id == main + { + // The main thread doesn't always have a thread handle, we must + // identify it through its ID instead. The checks are ordered so + // that the current ID is only loaded if it is actually needed, + // since loading it from TLS might need multiple expensive accesses. + return f(Some("main")); } + + f(None) + }) +} + +/// The internal representation of a `Thread` handle +struct Inner { + name: Option<ThreadNameString>, + id: ThreadId, + parker: Parker, +} + +impl Inner { + fn parker(self: Pin<&Self>) -> Pin<&Parker> { + unsafe { Pin::map_unchecked(self, |inner| &inner.parker) } } } @@ -1390,47 +1412,21 @@ impl Inner { /// docs of [`Builder`] and [`spawn`] for more details. /// /// [`thread::current`]: current::current -pub struct Thread(Inner); +pub struct Thread { + inner: Pin<Arc<Inner>>, +} impl Thread { - /// Used only internally to construct a thread object without spawning. - pub(crate) fn new(id: ThreadId, name: String) -> Thread { - Self::new_inner(id, Some(ThreadNameString::from(name))) - } + pub(crate) fn new(id: ThreadId, name: Option<String>) -> Thread { + let name = name.map(ThreadNameString::from); - pub(crate) fn new_unnamed(id: ThreadId) -> Thread { - Self::new_inner(id, None) - } - - /// Used in runtime to construct main thread - /// - /// # Safety - /// - /// This must only ever be called once, and must be called on the main thread. - pub(crate) unsafe fn new_main(thread_id: ThreadId) -> Thread { - // Safety: As this is only called once and on the main thread, nothing else is accessing MAIN_THREAD_INFO - // as the only other read occurs in `main_thread_info` *after* the main thread has been constructed, - // and this function is the only one that constructs the main thread. - // - // Pre-main thread spawning cannot hit this either, as the caller promises that this is only called on the main thread. - let main_thread_info = unsafe { &mut *MAIN_THREAD_INFO.get() }; - - unsafe { Parker::new_in_place((&raw mut main_thread_info.1).cast()) }; - main_thread_info.0.write(thread_id); - - // Store a `'static` ref to the initialised ThreadId and Parker, - // to avoid having to repeatedly prove initialisation. - Self(Inner::Main(unsafe { &*MAIN_THREAD_INFO.get().cast() })) - } - - fn new_inner(id: ThreadId, name: Option<ThreadNameString>) -> Thread { // We have to use `unsafe` here to construct the `Parker` in-place, // which is required for the UNIX implementation. // // SAFETY: We pin the Arc immediately after creation, so its address never // changes. let inner = unsafe { - let mut arc = Arc::<OtherInner>::new_uninit(); + let mut arc = Arc::<Inner>::new_uninit(); let ptr = Arc::get_mut_unchecked(&mut arc).as_mut_ptr(); (&raw mut (*ptr).name).write(name); (&raw mut (*ptr).id).write(id); @@ -1438,7 +1434,7 @@ impl Thread { Pin::new_unchecked(arc.assume_init()) }; - Self(Inner::Other(inner)) + Thread { inner } } /// Like the public [`park`], but callable on any handle. This is used to @@ -1447,7 +1443,7 @@ impl Thread { /// # Safety /// May only be called from the thread to which this handle belongs. pub(crate) unsafe fn park(&self) { - unsafe { self.0.parker().park() } + unsafe { self.inner.as_ref().parker().park() } } /// Like the public [`park_timeout`], but callable on any handle. This is @@ -1456,7 +1452,7 @@ impl Thread { /// # Safety /// May only be called from the thread to which this handle belongs. pub(crate) unsafe fn park_timeout(&self, dur: Duration) { - unsafe { self.0.parker().park_timeout(dur) } + unsafe { self.inner.as_ref().parker().park_timeout(dur) } } /// Atomically makes the handle's token available if it is not already. @@ -1492,7 +1488,7 @@ impl Thread { #[stable(feature = "rust1", since = "1.0.0")] #[inline] pub fn unpark(&self) { - self.0.parker().unpark(); + self.inner.as_ref().parker().unpark(); } /// Gets the thread's unique identifier. @@ -1512,7 +1508,7 @@ impl Thread { #[stable(feature = "thread_id", since = "1.19.0")] #[must_use] pub fn id(&self) -> ThreadId { - self.0.id() + self.inner.id } /// Gets the thread's name. @@ -1555,11 +1551,13 @@ impl Thread { #[stable(feature = "rust1", since = "1.0.0")] #[must_use] pub fn name(&self) -> Option<&str> { - self.0.name() - } - - fn cname(&self) -> Option<&CStr> { - self.0.cname() + if let Some(name) = &self.inner.name { + Some(name.as_str()) + } else if main_thread::get() == Some(self.inner.id) { + Some("main") + } else { + None + } } /// Consumes the `Thread`, returning a raw pointer. @@ -1583,7 +1581,9 @@ impl Thread { /// ``` #[unstable(feature = "thread_raw", issue = "97523")] pub fn into_raw(self) -> *const () { - self.0.into_raw() + // Safety: We only expose an opaque pointer, which maintains the `Pin` invariant. + let inner = unsafe { Pin::into_inner_unchecked(self.inner) }; + Arc::into_raw(inner) as *const () } /// Constructs a `Thread` from a raw pointer. @@ -1605,7 +1605,17 @@ impl Thread { #[unstable(feature = "thread_raw", issue = "97523")] pub unsafe fn from_raw(ptr: *const ()) -> Thread { // Safety: Upheld by caller. - unsafe { Thread(Inner::from_raw(ptr)) } + unsafe { Thread { inner: Pin::new_unchecked(Arc::from_raw(ptr as *const Inner)) } } + } + + fn cname(&self) -> Option<&CStr> { + if let Some(name) = &self.inner.name { + Some(name.as_cstr()) + } else if main_thread::get() == Some(self.inner.id) { + Some(c"main") + } else { + None + } } } |