Jeremy Soller
147 lines
4.8 KiB
Rust
147 lines
4.8 KiB
Rust
//! # Futex
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//! Futex or Fast Userspace Mutex is "a method for waiting until a certain condition becomes true."
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//!
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//! For more information about futexes, please read [this](https://eli.thegreenplace.net/2018/basics-of-futexes/) blog post, and the [futex(2)](http://man7.org/linux/man-pages/man2/futex.2.html) man page
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use alloc::sync::Arc;
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use alloc::collections::VecDeque;
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use core::intrinsics;
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use spin::{Once, RwLock, RwLockReadGuard, RwLockWriteGuard};
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use crate::context::{self, Context};
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use crate::time;
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use crate::syscall::data::TimeSpec;
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use crate::syscall::error::{Error, Result, ESRCH, EAGAIN, EINVAL};
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use crate::syscall::flag::{FUTEX_WAIT, FUTEX_WAKE, FUTEX_REQUEUE};
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use crate::syscall::validate::{validate_slice, validate_slice_mut};
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type FutexList = VecDeque<(usize, Arc<RwLock<Context>>)>;
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/// Fast userspace mutex list
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static FUTEXES: Once<RwLock<FutexList>> = Once::new();
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/// Initialize futexes, called if needed
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fn init_futexes() -> RwLock<FutexList> {
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RwLock::new(VecDeque::new())
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}
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/// Get the global futexes list, const
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pub fn futexes() -> RwLockReadGuard<'static, FutexList> {
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FUTEXES.call_once(init_futexes).read()
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}
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/// Get the global futexes list, mutable
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pub fn futexes_mut() -> RwLockWriteGuard<'static, FutexList> {
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FUTEXES.call_once(init_futexes).write()
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}
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pub fn futex(addr: &mut i32, op: usize, val: i32, val2: usize, addr2: *mut i32) -> Result<usize> {
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match op {
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FUTEX_WAIT => {
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let timeout_opt = if val2 != 0 {
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Some(validate_slice(val2 as *const TimeSpec, 1).map(|req| &req[0])?)
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} else {
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None
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};
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{
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let mut futexes = futexes_mut();
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let context_lock = {
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let contexts = context::contexts();
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let context_lock = contexts.current().ok_or(Error::new(ESRCH))?;
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Arc::clone(&context_lock)
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};
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if unsafe { intrinsics::atomic_load(addr) != val } {
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return Err(Error::new(EAGAIN));
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}
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{
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let mut context = context_lock.write();
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if let Some(timeout) = timeout_opt {
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let start = time::monotonic();
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let sum = start.1 + timeout.tv_nsec as u64;
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let end = (start.0 + timeout.tv_sec as u64 + sum / 1_000_000_000, sum % 1_000_000_000);
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context.wake = Some(end);
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}
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context.block("futex");
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}
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futexes.push_back((addr as *mut i32 as usize, context_lock));
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}
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unsafe { context::switch(); }
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if timeout_opt.is_some() {
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let context_lock = {
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let contexts = context::contexts();
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let context_lock = contexts.current().ok_or(Error::new(ESRCH))?;
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Arc::clone(&context_lock)
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};
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{
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let mut context = context_lock.write();
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context.wake = None;
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}
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}
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Ok(0)
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},
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FUTEX_WAKE => {
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let mut woken = 0;
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{
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let mut futexes = futexes_mut();
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let mut i = 0;
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while i < futexes.len() && (woken as i32) < val {
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if futexes[i].0 == addr as *mut i32 as usize {
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if let Some(futex) = futexes.swap_remove_back(i) {
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futex.1.write().unblock();
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woken += 1;
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}
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} else {
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i += 1;
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}
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}
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}
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Ok(woken)
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},
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FUTEX_REQUEUE => {
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let addr2_safe = validate_slice_mut(addr2, 1).map(|addr2_safe| &mut addr2_safe[0])?;
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let mut woken = 0;
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let mut requeued = 0;
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{
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let mut futexes = futexes_mut();
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let mut i = 0;
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while i < futexes.len() && (woken as i32) < val {
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if futexes[i].0 == addr as *mut i32 as usize {
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if let Some(futex) = futexes.swap_remove_back(i) {
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futex.1.write().unblock();
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woken += 1;
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}
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} else {
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i += 1;
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}
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}
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while i < futexes.len() && requeued < val2 {
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if futexes[i].0 == addr as *mut i32 as usize {
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futexes[i].0 = addr2_safe as *mut i32 as usize;
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requeued += 1;
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}
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i += 1;
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}
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}
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Ok(woken)
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},
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_ => Err(Error::new(EINVAL))
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}
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}
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