From 75c5c04bee5928b4e9c86ca9d0d9536178083f18 Mon Sep 17 00:00:00 2001
From: jD91mZM2 <me@krake.one>
Date: Sun, 14 Oct 2018 15:56:34 +0200
Subject: [PATCH] Implement a proper mutex type for future usage
---
src/header/stdio/default.rs | 3 +-
src/header/stdio/helpers.rs | 3 +-
src/header/stdio/mod.rs | 39 +++++-----
src/lib.rs | 1 +
src/mutex.rs | 119 ++++++++++++++++++++++++++++++
src/platform/linux/mod.rs | 4 +
src/platform/pal/mod.rs | 2 +
src/platform/redox/mod.rs | 7 ++
tests/Makefile | 1 +
tests/expected/stdio/mutex.stderr | 0
tests/expected/stdio/mutex.stdout | 0
tests/stdio/mutex.c | 26 +++++++
12 files changed, 185 insertions(+), 20 deletions(-)
create mode 100644 src/mutex.rs
create mode 100644 tests/expected/stdio/mutex.stderr
create mode 100644 tests/expected/stdio/mutex.stdout
create mode 100644 tests/stdio/mutex.c
diff --git a/src/header/stdio/default.rs b/src/header/stdio/default.rs
index 315d5f75..5d3fe1e0 100644
--- a/src/header/stdio/default.rs
+++ b/src/header/stdio/default.rs
@@ -5,6 +5,7 @@ use core::sync::atomic::AtomicBool;
use fs::File;
use io::LineWriter;
+use mutex::Mutex;
use platform::types::*;
pub struct GlobalFile(UnsafeCell<FILE>);
@@ -13,7 +14,7 @@ impl GlobalFile {
let file = File::new(file);
let writer = LineWriter::new(unsafe { file.get_ref() });
GlobalFile(UnsafeCell::new(FILE {
- lock: AtomicBool::new(false),
+ lock: Mutex::new(()),
file,
flags: constants::F_PERM | flags,
diff --git a/src/header/stdio/helpers.rs b/src/header/stdio/helpers.rs
index 1544462f..3fff7993 100644
--- a/src/header/stdio/helpers.rs
+++ b/src/header/stdio/helpers.rs
@@ -7,6 +7,7 @@ use header::errno;
use header::fcntl::*;
use header::string::strchr;
use io::LineWriter;
+use mutex::Mutex;
use platform::types::*;
use platform;
@@ -68,7 +69,7 @@ pub unsafe fn _fdopen(fd: c_int, mode: *const c_char) -> Option<*mut FILE> {
let writer = LineWriter::new(file.get_ref());
Some(Box::into_raw(Box::new(FILE {
- lock: AtomicBool::new(false),
+ lock: Mutex::new(()),
file,
flags,
diff --git a/src/header/stdio/mod.rs b/src/header/stdio/mod.rs
index 3b3de751..0653c1d6 100644
--- a/src/header/stdio/mod.rs
+++ b/src/header/stdio/mod.rs
@@ -17,6 +17,7 @@ use header::fcntl;
use header::stdlib::mkstemp;
use header::string::strlen;
use io::{self, BufRead, LineWriter, SeekFrom, Read, Write};
+use mutex::Mutex;
use platform::types::*;
use platform::{Pal, Sys};
use platform::{errno, WriteByte};
@@ -59,7 +60,7 @@ impl<'a> DerefMut for Buffer<'a> {
/// This struct gets exposed to the C API.
pub struct FILE {
// Can't use spin crate because *_unlocked functions are things in C :(
- lock: AtomicBool,
+ lock: Mutex<()>,
file: File,
flags: c_int,
@@ -148,7 +149,9 @@ impl WriteByte for FILE {
}
impl FILE {
pub fn lock(&mut self) -> LockGuard {
- flockfile(self);
+ unsafe {
+ flockfile(self);
+ }
LockGuard(self)
}
}
@@ -168,7 +171,9 @@ impl<'a> DerefMut for LockGuard<'a> {
}
impl<'a> Drop for LockGuard<'a> {
fn drop(&mut self) {
- funlockfile(self.0);
+ unsafe {
+ funlockfile(self.0);
+ }
}
}
@@ -196,7 +201,7 @@ pub extern "C" fn cuserid(_s: *mut c_char) -> *mut c_char {
#[no_mangle]
pub extern "C" fn fclose(stream: *mut FILE) -> c_int {
let stream = unsafe { &mut *stream };
- flockfile(stream);
+ unsafe { flockfile(stream); }
let mut r = stream.flush().is_err();
let close = Sys::close(*stream.file) < 0;
@@ -208,7 +213,7 @@ pub extern "C" fn fclose(stream: *mut FILE) -> c_int {
// Reference files aren't closed on drop, so pretend to be a reference
stream.file.reference = true;
} else {
- funlockfile(stream);
+ unsafe { funlockfile(stream); }
}
r as c_int
@@ -347,10 +352,8 @@ pub extern "C" fn fileno(stream: *mut FILE) -> c_int {
/// Do not call any functions other than those with the `_unlocked` postfix while the file is
/// locked
#[no_mangle]
-pub extern "C" fn flockfile(file: *mut FILE) {
- while ftrylockfile(file) != 0 {
- atomic::spin_loop_hint();
- }
+pub unsafe extern "C" fn flockfile(file: *mut FILE) {
+ (*file).lock.manual_lock();
}
/// Open the file in mode `mode`
@@ -427,7 +430,7 @@ pub extern "C" fn freopen(
stream: &mut FILE,
) -> *mut FILE {
let mut flags = unsafe { helpers::parse_mode_flags(mode) };
- flockfile(stream);
+ unsafe { flockfile(stream); }
let _ = stream.flush();
if filename.is_null() {
@@ -437,14 +440,14 @@ pub extern "C" fn freopen(
}
flags &= !(fcntl::O_CREAT | fcntl::O_EXCL | fcntl::O_CLOEXEC);
if fcntl::sys_fcntl(*stream.file, fcntl::F_SETFL, flags) < 0 {
- funlockfile(stream);
+ unsafe { funlockfile(stream); }
fclose(stream);
return ptr::null_mut();
}
} else {
let new = fopen(filename, mode);
if new.is_null() {
- funlockfile(stream);
+ unsafe { funlockfile(stream); }
fclose(stream);
return ptr::null_mut();
}
@@ -454,7 +457,7 @@ pub extern "C" fn freopen(
} else if Sys::dup2(*new.file, *stream.file) < 0
|| fcntl::sys_fcntl(*stream.file, fcntl::F_SETFL, flags & fcntl::O_CLOEXEC) < 0
{
- funlockfile(stream);
+ unsafe { funlockfile(stream); }
fclose(new);
fclose(stream);
return ptr::null_mut();
@@ -462,7 +465,7 @@ pub extern "C" fn freopen(
stream.flags = (stream.flags & constants::F_PERM) | new.flags;
fclose(new);
}
- funlockfile(stream);
+ unsafe { funlockfile(stream); }
stream
}
@@ -521,14 +524,14 @@ pub extern "C" fn ftello(stream: *mut FILE) -> off_t {
/// Try to lock the file. Returns 0 for success, 1 for failure
#[no_mangle]
-pub extern "C" fn ftrylockfile(file: *mut FILE) -> c_int {
- unsafe { &mut *file }.lock.compare_and_swap(false, true, Ordering::Acquire) as c_int
+pub unsafe extern "C" fn ftrylockfile(file: *mut FILE) -> c_int {
+ if (*file).lock.manual_try_lock().is_ok() { 0 } else { 1 }
}
/// Unlock the file
#[no_mangle]
-pub extern "C" fn funlockfile(file: *mut FILE) {
- unsafe { &mut *file }.lock.store(false, Ordering::Release);
+pub unsafe extern "C" fn funlockfile(file: *mut FILE) {
+ (*file).lock.manual_unlock();
}
/// Write `nitems` of size `size` from `ptr` to `stream`
diff --git a/src/lib.rs b/src/lib.rs
index 4319f6d7..465e1da9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -41,6 +41,7 @@ pub mod c_str;
pub mod fs;
pub mod header;
pub mod io;
+pub mod mutex;
pub mod platform;
pub mod start;
diff --git a/src/mutex.rs b/src/mutex.rs
new file mode 100644
index 00000000..87efc246
--- /dev/null
+++ b/src/mutex.rs
@@ -0,0 +1,119 @@
+use core::cell::UnsafeCell;
+use core::intrinsics;
+use core::ops::{Deref, DerefMut};
+use core::sync::atomic;
+use platform::{Pal, Sys};
+use platform::types::*;
+
+pub const FUTEX_WAIT: c_int = 0;
+pub const FUTEX_WAKE: c_int = 1;
+
+pub struct Mutex<T> {
+ lock: UnsafeCell<c_int>,
+ content: UnsafeCell<T>
+}
+unsafe impl<T: Send> Send for Mutex<T> {}
+unsafe impl<T: Send> Sync for Mutex<T> {}
+impl<T> Mutex<T> {
+ /// Create a new mutex
+ pub fn new(content: T) -> Self {
+ Self {
+ lock: UnsafeCell::new(0),
+ content: UnsafeCell::new(content)
+ }
+ }
+
+ /// Tries to lock the mutex, fails if it's already locked. Manual means
+ /// it's up to you to unlock it after mutex. Returns the last atomic value
+ /// on failure. You should probably not worry about this, it's used for
+ /// internal optimizations.
+ pub unsafe fn manual_try_lock(&self) -> Result<&mut T, c_int> {
+ let value = intrinsics::atomic_cxchg(self.lock.get(), 0, 1).0;
+ if value == 0 {
+ return Ok(&mut *self.content.get());
+ }
+ Err(value)
+ }
+ /// Lock the mutex, returning the inner content. After doing this, it's
+ /// your responsibility to unlock it after usage. Mostly useful for FFI:
+ /// Prefer normal .lock() where possible.
+ pub unsafe fn manual_lock(&self) -> &mut T {
+ let mut last = 0;
+
+ // First, try spinning for really short durations:
+ for _ in 0..100 {
+ atomic::spin_loop_hint();
+ last = match self.manual_try_lock() {
+ Ok(content) => return content,
+ Err(value) => value
+ };
+ }
+
+ // We're waiting for a longer duration, so let's employ a futex.
+ loop {
+ // If the value is 1, set it to 2 to signify that we're waiting for
+ // it to to send a FUTEX_WAKE on unlock.
+ //
+ // - Skip the atomic operation if the last value was 2, since it most likely hasn't changed.
+ // - Skip the futex wait if the atomic operation says the mutex is unlocked.
+ if last == 2 || intrinsics::atomic_cxchg(self.lock.get(), 1, 2).0 != 0 {
+ Sys::futex(self.lock.get(), FUTEX_WAIT, 2);
+ }
+
+ last = match self.manual_try_lock() {
+ Ok(content) => return content,
+ Err(value) => value
+ };
+ }
+ }
+ /// Unlock the mutex, if it's locked.
+ pub unsafe fn manual_unlock(&self) {
+ if intrinsics::atomic_xchg(self.lock.get(), 0) == 2 {
+ // At least one futex is up, so let's notify it
+ Sys::futex(self.lock.get(), FUTEX_WAKE, 1);
+ }
+ }
+
+ /// Tries to lock the mutex and returns a guard that automatically unlocks
+ /// the mutex when it falls out of scope.
+ pub fn try_lock(&self) -> Option<MutexGuard<T>> {
+ unsafe {
+ self.manual_try_lock().ok().map(|content| MutexGuard {
+ mutex: self,
+ content
+ })
+ }
+ }
+ /// Locks the mutex and returns a guard that automatically unlocks the
+ /// mutex when it falls out of scope.
+ pub fn lock(&self) -> MutexGuard<T> {
+ MutexGuard {
+ mutex: self,
+ content: unsafe { self.manual_lock() }
+ }
+ }
+}
+
+pub struct MutexGuard<'a, T: 'a> {
+ mutex: &'a Mutex<T>,
+ content: &'a mut T
+}
+impl<'a, T> Deref for MutexGuard<'a, T> {
+ type Target = T;
+
+ fn deref(&self) -> &Self::Target {
+ &self.content
+ }
+}
+impl<'a, T> DerefMut for MutexGuard<'a, T> {
+ fn deref_mut(&mut self) -> &mut Self::Target {
+ self.content
+ }
+}
+impl<'a, T> Drop for MutexGuard<'a, T> {
+ fn drop(&mut self) {
+ unsafe {
+ self.mutex.manual_unlock();
+ }
+ }
+}
diff --git a/src/platform/linux/mod.rs b/src/platform/linux/mod.rs
index 7d2df45b..a2df0e66 100644
--- a/src/platform/linux/mod.rs
+++ b/src/platform/linux/mod.rs
@@ -166,6 +166,10 @@ impl Pal for Sys {
e(unsafe { syscall!(FTRUNCATE, fildes, length) }) as c_int
}
+ fn futex(addr: *mut c_int, op: c_int, val: c_int) -> c_int {
+ unsafe { syscall!(FUTEX, addr, op, val, 0, 0, 0) as c_int }
+ }
+
fn futimens(fd: c_int, times: *const timespec) -> c_int {
e(unsafe { syscall!(UTIMENSAT, fd, ptr::null::<c_char>(), times, 0) }) as c_int
}
diff --git a/src/platform/pal/mod.rs b/src/platform/pal/mod.rs
index f4fdd25f..caea5473 100644
--- a/src/platform/pal/mod.rs
+++ b/src/platform/pal/mod.rs
@@ -57,6 +57,8 @@ pub trait Pal {
fn ftruncate(fildes: c_int, length: off_t) -> c_int;
+ fn futex(addr: *mut c_int, op: c_int, val: c_int) -> c_int;
+
fn futimens(fd: c_int, times: *const timespec) -> c_int;
fn utimens(path: &CStr, times: *const timespec) -> c_int;
diff --git a/src/platform/redox/mod.rs b/src/platform/redox/mod.rs
index fef69bff..c372a62c 100644
--- a/src/platform/redox/mod.rs
+++ b/src/platform/redox/mod.rs
@@ -340,6 +340,13 @@ impl Pal for Sys {
e(syscall::ftruncate(fd as usize, len as usize)) as c_int
}
+ fn futex(addr: *mut c_int, op: c_int, val: c_int) -> c_int {
+ match unsafe { syscall::futex(addr as *mut i32, op as usize, val as i32, 0, ptr::null_mut()) } {
+ Ok(success) => success as c_int,
+ Err(err) => -(err.errno as c_int)
+ }
+ }
+
fn futimens(fd: c_int, times: *const timespec) -> c_int {
let times = [unsafe { redox_timespec::from(&*times) }, unsafe {
redox_timespec::from(&*times.offset(1))
diff --git a/tests/Makefile b/tests/Makefile
index f234a8ae..bdc7168f 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -26,6 +26,7 @@ EXPECT_BINS=\
stdio/fseek \
stdio/fwrite \
stdio/getc_unget \
+ stdio/mutex \
stdio/printf \
stdio/rename \
stdio/scanf \
diff --git a/tests/expected/stdio/mutex.stderr b/tests/expected/stdio/mutex.stderr
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/expected/stdio/mutex.stdout b/tests/expected/stdio/mutex.stdout
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/stdio/mutex.c b/tests/stdio/mutex.c
new file mode 100644
index 00000000..032ced27
--- /dev/null
+++ b/tests/stdio/mutex.c
@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+int main() {
+ FILE* f = fopen("stdio/stdio.in", "r");
+
+ flockfile(f);
+
+ // Commenting this out should cause a deadlock:
+ // flockfile(f);
+
+ if (!ftrylockfile(f)) {
+ puts("Mutex unlocked but it shouldn't be");
+ return -1;
+ }
+ funlockfile(f);
+
+ if (ftrylockfile(f)) {
+ puts("Mutex locked but it shouldn't be");
+ return -1;
+ }
+ if (!ftrylockfile(f)) {
+ puts("Mutex unlocked but it shouldn't be");
+ return -1;
+ }
+ funlockfile(f);
+}
--
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