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|
// This tests carefully crafted schedules to ensure they are not considered races.
//@compile-flags: -Zmiri-deterministic-concurrency
use std::sync::atomic::*;
use std::thread::{self, spawn};
#[derive(Copy, Clone)]
struct EvilSend<T>(pub T);
unsafe impl<T> Send for EvilSend<T> {}
unsafe impl<T> Sync for EvilSend<T> {}
fn test_fence_sync() {
static SYNC: AtomicUsize = AtomicUsize::new(0);
let mut var = 0u32;
let ptr = &mut var as *mut u32;
let evil_ptr = EvilSend(ptr);
let j1 = spawn(move || {
let evil_ptr = evil_ptr; // avoid field capturing
unsafe { *evil_ptr.0 = 1 };
fence(Ordering::Release);
SYNC.store(1, Ordering::Relaxed)
});
let j2 = spawn(move || {
let evil_ptr = evil_ptr; // avoid field capturing
if SYNC.load(Ordering::Relaxed) == 1 {
fence(Ordering::Acquire);
unsafe { *evil_ptr.0 }
} else {
panic!(); // relies on thread 2 going last
}
});
j1.join().unwrap();
j2.join().unwrap();
}
fn test_multiple_reads() {
let mut var = 42u32;
let ptr = &mut var as *mut u32;
let evil_ptr = EvilSend(ptr);
let j1 = spawn(move || unsafe { *{ evil_ptr }.0 });
let j2 = spawn(move || unsafe { *{ evil_ptr }.0 });
let j3 = spawn(move || unsafe { *{ evil_ptr }.0 });
let j4 = spawn(move || unsafe { *{ evil_ptr }.0 });
assert_eq!(j1.join().unwrap(), 42);
assert_eq!(j2.join().unwrap(), 42);
assert_eq!(j3.join().unwrap(), 42);
assert_eq!(j4.join().unwrap(), 42);
var = 10;
assert_eq!(var, 10);
}
pub fn test_rmw_no_block() {
static SYNC: AtomicUsize = AtomicUsize::new(0);
let mut a = 0u32;
let b = &mut a as *mut u32;
let c = EvilSend(b);
unsafe {
let j1 = spawn(move || {
let c = c; // avoid field capturing
*c.0 = 1;
SYNC.store(1, Ordering::Release);
});
let j2 = spawn(move || {
if SYNC.swap(2, Ordering::Relaxed) == 1 {
//No op, blocking store removed
}
});
let j3 = spawn(move || {
let c = c; // avoid field capturing
if SYNC.load(Ordering::Acquire) == 2 { *c.0 } else { 0 }
});
j1.join().unwrap();
j2.join().unwrap();
let v = j3.join().unwrap();
assert!(v == 1 || v == 2); // relies on thread 3 going last
}
}
pub fn test_simple_release() {
static SYNC: AtomicUsize = AtomicUsize::new(0);
let mut a = 0u32;
let b = &mut a as *mut u32;
let c = EvilSend(b);
unsafe {
let j1 = spawn(move || {
let c = c; // avoid field capturing
*c.0 = 1;
SYNC.store(1, Ordering::Release);
});
let j2 = spawn(move || {
let c = c; // avoid field capturing
if SYNC.load(Ordering::Acquire) == 1 { *c.0 } else { 0 }
});
j1.join().unwrap();
assert_eq!(j2.join().unwrap(), 1); // relies on thread 2 going last
}
}
fn test_local_variable_lazy_write() {
static P: AtomicPtr<u8> = AtomicPtr::new(core::ptr::null_mut());
// Create the local variable, and initialize it.
// This write happens before the thread is spanwed, so there is no data race.
let mut val: u8 = 0;
let t1 = std::thread::spawn(|| {
while P.load(Ordering::Relaxed).is_null() {
std::hint::spin_loop();
}
unsafe {
// Initialize `*P`.
let ptr = P.load(Ordering::Relaxed);
*ptr = 127;
}
});
// Actually generate memory for the local variable.
// This is the time its value is actually written to memory:
// that's *after* the thread above was spawned!
// This may hence look like a data race wrt the access in the thread above.
P.store(std::ptr::addr_of_mut!(val), Ordering::Relaxed);
// Wait for the thread to be done.
t1.join().unwrap();
// Read initialized value.
assert_eq!(val, 127);
}
// This test coverse the case where the non-atomic access come first.
fn test_read_read_race1() {
let a = AtomicU16::new(0);
thread::scope(|s| {
s.spawn(|| {
let ptr = &a as *const AtomicU16 as *mut u16;
unsafe { ptr.read() };
});
s.spawn(|| {
thread::yield_now();
a.load(Ordering::SeqCst);
});
});
}
// This test coverse the case where the atomic access come first.
fn test_read_read_race2() {
let a = AtomicU16::new(0);
thread::scope(|s| {
s.spawn(|| {
a.load(Ordering::SeqCst);
});
s.spawn(|| {
thread::yield_now();
let ptr = &a as *const AtomicU16 as *mut u16;
unsafe { ptr.read() };
});
});
}
fn mixed_size_read_read() {
fn convert(a: &AtomicU16) -> &[AtomicU8; 2] {
unsafe { std::mem::transmute(a) }
}
let a = AtomicU16::new(0);
let a16 = &a;
let a8 = convert(a16);
// Just two different-sized atomic reads without any writes are fine.
thread::scope(|s| {
s.spawn(|| {
a16.load(Ordering::SeqCst);
});
s.spawn(|| {
a8[0].load(Ordering::SeqCst);
});
});
}
fn failing_rmw_is_read() {
let a = AtomicUsize::new(0);
thread::scope(|s| {
s.spawn(|| unsafe {
// Non-atomic read.
let _val = *(&a as *const AtomicUsize).cast::<usize>();
});
s.spawn(|| {
// RMW that will fail.
// This is not considered a write, so there is no data race here.
a.compare_exchange(1, 2, Ordering::SeqCst, Ordering::SeqCst).unwrap_err();
});
});
}
pub fn main() {
test_fence_sync();
test_multiple_reads();
test_rmw_no_block();
test_simple_release();
test_local_variable_lazy_write();
test_read_read_race1();
test_read_read_race2();
mixed_size_read_read();
failing_rmw_is_read();
}
|
