From 52fa9daa645772603dc170a3f3bed5cab73d646d Mon Sep 17 00:00:00 2001 From: Christiaan Dirkx Date: Wed, 28 Apr 2021 15:51:14 +0200 Subject: Rework `wasm::thread` to `thread_atomics` --- library/std/src/sys/wasm/mod.rs | 5 +- library/std/src/sys/wasm/thread.rs | 98 ------------------------------ library/std/src/sys/wasm/thread_atomics.rs | 84 +++++++++++++++++++++++++ 3 files changed, 88 insertions(+), 99 deletions(-) delete mode 100644 library/std/src/sys/wasm/thread.rs create mode 100644 library/std/src/sys/wasm/thread_atomics.rs (limited to 'library/std/src/sys') diff --git a/library/std/src/sys/wasm/mod.rs b/library/std/src/sys/wasm/mod.rs index 8705910c73a..71877fce993 100644 --- a/library/std/src/sys/wasm/mod.rs +++ b/library/std/src/sys/wasm/mod.rs @@ -37,7 +37,6 @@ pub mod pipe; pub mod process; #[path = "../unsupported/stdio.rs"] pub mod stdio; -pub mod thread; #[path = "../unsupported/thread_local_dtor.rs"] pub mod thread_local_dtor; #[path = "../unsupported/thread_local_key.rs"] @@ -57,6 +56,8 @@ cfg_if::cfg_if! { pub mod rwlock; #[path = "futex_atomics.rs"] pub mod futex; + #[path = "thread_atomics.rs"] + pub mod thread; } else { #[path = "../unsupported/condvar.rs"] pub mod condvar; @@ -64,6 +65,8 @@ cfg_if::cfg_if! { pub mod mutex; #[path = "../unsupported/rwlock.rs"] pub mod rwlock; + #[path = "../unsupported/thread.rs"] + pub mod thread; } } diff --git a/library/std/src/sys/wasm/thread.rs b/library/std/src/sys/wasm/thread.rs deleted file mode 100644 index b7bf95c89b4..00000000000 --- a/library/std/src/sys/wasm/thread.rs +++ /dev/null @@ -1,98 +0,0 @@ -use crate::ffi::CStr; -use crate::io; -use crate::sys::unsupported; -use crate::time::Duration; - -pub struct Thread(!); - -pub const DEFAULT_MIN_STACK_SIZE: usize = 4096; - -impl Thread { - // unsafe: see thread::Builder::spawn_unchecked for safety requirements - pub unsafe fn new(_stack: usize, _p: Box) -> io::Result { - unsupported() - } - - pub fn yield_now() { - // do nothing - } - - pub fn set_name(_name: &CStr) { - // nope - } - - #[cfg(not(target_feature = "atomics"))] - pub fn sleep(_dur: Duration) { - panic!("can't sleep"); - } - - #[cfg(target_feature = "atomics")] - pub fn sleep(dur: Duration) { - use crate::arch::wasm32; - use crate::cmp; - - // Use an atomic wait to block the current thread artificially with a - // timeout listed. Note that we should never be notified (return value - // of 0) or our comparison should never fail (return value of 1) so we - // should always only resume execution through a timeout (return value - // 2). - let mut nanos = dur.as_nanos(); - while nanos > 0 { - let amt = cmp::min(i64::MAX as u128, nanos); - let mut x = 0; - let val = unsafe { wasm32::memory_atomic_wait32(&mut x, 0, amt as i64) }; - debug_assert_eq!(val, 2); - nanos -= amt; - } - } - - pub fn join(self) { - self.0 - } -} - -pub mod guard { - pub type Guard = !; - pub unsafe fn current() -> Option { - None - } - pub unsafe fn init() -> Option { - None - } -} - -// This is only used by atomics primitives when the `atomics` feature is -// enabled. In that mode we currently just use our own thread-local to store our -// current thread's ID, and then we lazily initialize it to something allocated -// from a global counter. -#[cfg(target_feature = "atomics")] -pub fn my_id() -> u32 { - use crate::sync::atomic::{AtomicU32, Ordering::SeqCst}; - - static NEXT_ID: AtomicU32 = AtomicU32::new(0); - - #[thread_local] - static mut MY_ID: u32 = 0; - - unsafe { - // If our thread ID isn't set yet then we need to allocate one. Do so - // with with a simple "atomically add to a global counter" strategy. - // This strategy doesn't handled what happens when the counter - // overflows, however, so just abort everything once the counter - // overflows and eventually we could have some sort of recycling scheme - // (or maybe this is all totally irrelevant by that point!). In any case - // though we're using a CAS loop instead of a `fetch_add` to ensure that - // the global counter never overflows. - if MY_ID == 0 { - let mut cur = NEXT_ID.load(SeqCst); - MY_ID = loop { - let next = cur.checked_add(1).unwrap_or_else(|| crate::process::abort()); - match NEXT_ID.compare_exchange(cur, next, SeqCst, SeqCst) { - Ok(_) => break next, - Err(i) => cur = i, - } - }; - } - MY_ID - } -} diff --git a/library/std/src/sys/wasm/thread_atomics.rs b/library/std/src/sys/wasm/thread_atomics.rs new file mode 100644 index 00000000000..54bc877aa7d --- /dev/null +++ b/library/std/src/sys/wasm/thread_atomics.rs @@ -0,0 +1,84 @@ +use crate::ffi::CStr; +use crate::io; +use crate::sys::unsupported; +use crate::time::Duration; + +pub struct Thread(!); + +pub const DEFAULT_MIN_STACK_SIZE: usize = 4096; + +impl Thread { + // unsafe: see thread::Builder::spawn_unchecked for safety requirements + pub unsafe fn new(_stack: usize, _p: Box) -> io::Result { + unsupported() + } + + pub fn yield_now() {} + + pub fn set_name(_name: &CStr) {} + + pub fn sleep(dur: Duration) { + use crate::arch::wasm32; + use crate::cmp; + + // Use an atomic wait to block the current thread artificially with a + // timeout listed. Note that we should never be notified (return value + // of 0) or our comparison should never fail (return value of 1) so we + // should always only resume execution through a timeout (return value + // 2). + let mut nanos = dur.as_nanos(); + while nanos > 0 { + let amt = cmp::min(i64::MAX as u128, nanos); + let mut x = 0; + let val = unsafe { wasm32::memory_atomic_wait32(&mut x, 0, amt as i64) }; + debug_assert_eq!(val, 2); + nanos -= amt; + } + } + + pub fn join(self) {} +} + +pub mod guard { + pub type Guard = !; + pub unsafe fn current() -> Option { + None + } + pub unsafe fn init() -> Option { + None + } +} + +// We currently just use our own thread-local to store our +// current thread's ID, and then we lazily initialize it to something allocated +// from a global counter. +pub fn my_id() -> u32 { + use crate::sync::atomic::{AtomicU32, Ordering::SeqCst}; + + static NEXT_ID: AtomicU32 = AtomicU32::new(0); + + #[thread_local] + static mut MY_ID: u32 = 0; + + unsafe { + // If our thread ID isn't set yet then we need to allocate one. Do so + // with with a simple "atomically add to a global counter" strategy. + // This strategy doesn't handled what happens when the counter + // overflows, however, so just abort everything once the counter + // overflows and eventually we could have some sort of recycling scheme + // (or maybe this is all totally irrelevant by that point!). In any case + // though we're using a CAS loop instead of a `fetch_add` to ensure that + // the global counter never overflows. + if MY_ID == 0 { + let mut cur = NEXT_ID.load(SeqCst); + MY_ID = loop { + let next = cur.checked_add(1).unwrap_or_else(|| crate::process::abort()); + match NEXT_ID.compare_exchange(cur, next, SeqCst, SeqCst) { + Ok(_) => break next, + Err(i) => cur = i, + } + }; + } + MY_ID + } +} -- cgit 1.4.1-3-g733a5