Auto merge of rust-lang#2631 - RalfJung:futex-wait-no-isolate, r=RalfJung

Support timeouts with monotonic clocks even when isolation is enabled

With the deterministic monotonic clock support we now have, we can allow some synchronization primitives with timeouts even under isolation:
- Linux futex waiting (when set to the monotonic clock)
- pthread_cond_timedwait (when set to the monotonic clock)
- Windows WaitOnAddress

Unfortunately none of these exist on macOS -- the standard library always uses the system clock for timeouts on macOS, so that will still require `-Zmiri-disable-isolation`.

Author: bors

src/shims/unix/linux/sync.rs

@@ -90,9 +90,11 @@ pub fn futex<'tcx>(
             let timeout_time = if this.ptr_is_null(timeout.ptr)? {
                 None
             } else {
-                this.check_no_isolation(
-                    "`futex` syscall with `op=FUTEX_WAIT` and non-null timeout",
-                )?;
+                if op & futex_realtime != 0 {
+                    this.check_no_isolation(
+                        "`futex` syscall with `op=FUTEX_WAIT` and non-null timeout with `FUTEX_CLOCK_REALTIME`",
+                    )?;
+                }
                 let duration = match this.read_timespec(&timeout)? {
                     Some(duration) => duration,
                     None => {

src/shims/unix/sync.rs

@@ -743,8 +743,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     ) -> InterpResult<'tcx> {
         let this = self.eval_context_mut();
 
-        this.check_no_isolation("`pthread_cond_timedwait`")?;
-
         let id = this.condvar_get_or_create_id(cond_op, CONDVAR_ID_OFFSET)?;
         let mutex_id = this.mutex_get_or_create_id(mutex_op, MUTEX_ID_OFFSET)?;
         let active_thread = this.get_active_thread();
@@ -761,6 +759,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         };
 
         let timeout_time = if clock_id == this.eval_libc_i32("CLOCK_REALTIME")? {
+            this.check_no_isolation("`pthread_cond_timedwait` with `CLOCK_REALTIME`")?;
             Time::RealTime(SystemTime::UNIX_EPOCH.checked_add(duration).unwrap())
         } else if clock_id == this.eval_libc_i32("CLOCK_MONOTONIC")? {
             Time::Monotonic(this.machine.clock.anchor().checked_add(duration).unwrap())

src/shims/windows/sync.rs

@@ -254,8 +254,6 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
         let timeout_time = if timeout_ms == this.eval_windows("c", "INFINITE")?.to_u32()? {
             None
         } else {
-            this.check_no_isolation("`WaitOnAddress` with non-infinite timeout")?;
-
             let duration = Duration::from_millis(timeout_ms.into());
             Some(Time::Monotonic(this.machine.clock.now().checked_add(duration).unwrap()))
         };

tests/pass-dep/concurrency/libc_pthread_cond_isolated.rs

@@ -0,0 +1,82 @@
+//@ignore-target-windows: No libc on Windows
+//@ignore-target-apple: pthread_condattr_setclock is not supported on MacOS.
+
+/// Test that conditional variable timeouts are working properly
+/// with monotonic clocks even under isolation.
+use std::mem::MaybeUninit;
+use std::time::Instant;
+
+fn test_timed_wait_timeout(clock_id: i32) {
+    unsafe {
+        let mut attr: MaybeUninit<libc::pthread_condattr_t> = MaybeUninit::uninit();
+        assert_eq!(libc::pthread_condattr_init(attr.as_mut_ptr()), 0);
+        assert_eq!(libc::pthread_condattr_setclock(attr.as_mut_ptr(), clock_id), 0);
+
+        let mut cond: MaybeUninit<libc::pthread_cond_t> = MaybeUninit::uninit();
+        assert_eq!(libc::pthread_cond_init(cond.as_mut_ptr(), attr.as_ptr()), 0);
+        assert_eq!(libc::pthread_condattr_destroy(attr.as_mut_ptr()), 0);
+
+        let mut mutex: libc::pthread_mutex_t = libc::PTHREAD_MUTEX_INITIALIZER;
+
+        let mut now_mu: MaybeUninit<libc::timespec> = MaybeUninit::uninit();
+        assert_eq!(libc::clock_gettime(clock_id, now_mu.as_mut_ptr()), 0);
+        let now = now_mu.assume_init();
+        // Waiting for a second... mostly because waiting less requires mich more tricky arithmetic.
+        // FIXME: wait less.
+        let timeout = libc::timespec { tv_sec: now.tv_sec + 1, tv_nsec: now.tv_nsec };
+
+        assert_eq!(libc::pthread_mutex_lock(&mut mutex as *mut _), 0);
+        let current_time = Instant::now();
+        assert_eq!(
+            libc::pthread_cond_timedwait(cond.as_mut_ptr(), &mut mutex as *mut _, &timeout),
+            libc::ETIMEDOUT
+        );
+        let elapsed_time = current_time.elapsed().as_millis();
+        assert!(900 <= elapsed_time && elapsed_time <= 1300);
+
+        // Test calling `pthread_cond_timedwait` again with an already elapsed timeout.
+        assert_eq!(
+            libc::pthread_cond_timedwait(cond.as_mut_ptr(), &mut mutex as *mut _, &timeout),
+            libc::ETIMEDOUT
+        );
+
+        // Test that invalid nanosecond values (above 10^9 or negative) are rejected with the
+        // correct error code.
+        let invalid_timeout_1 = libc::timespec { tv_sec: now.tv_sec + 1, tv_nsec: 1_000_000_000 };
+        assert_eq!(
+            libc::pthread_cond_timedwait(
+                cond.as_mut_ptr(),
+                &mut mutex as *mut _,
+                &invalid_timeout_1
+            ),
+            libc::EINVAL
+        );
+        let invalid_timeout_2 = libc::timespec { tv_sec: now.tv_sec + 1, tv_nsec: -1 };
+        assert_eq!(
+            libc::pthread_cond_timedwait(
+                cond.as_mut_ptr(),
+                &mut mutex as *mut _,
+                &invalid_timeout_2
+            ),
+            libc::EINVAL
+        );
+        // Test that invalid second values (negative) are rejected with the correct error code.
+        let invalid_timeout_3 = libc::timespec { tv_sec: -1, tv_nsec: 0 };
+        assert_eq!(
+            libc::pthread_cond_timedwait(
+                cond.as_mut_ptr(),
+                &mut mutex as *mut _,
+                &invalid_timeout_3
+            ),
+            libc::EINVAL
+        );
+
+        assert_eq!(libc::pthread_mutex_unlock(&mut mutex as *mut _), 0);
+        assert_eq!(libc::pthread_mutex_destroy(&mut mutex as *mut _), 0);
+        assert_eq!(libc::pthread_cond_destroy(cond.as_mut_ptr()), 0);
+    }
+}
+
+fn main() {
+    test_timed_wait_timeout(libc::CLOCK_MONOTONIC);
+}

tests/pass/concurrency/thread_park_isolated.rs

@@ -0,0 +1,12 @@
+//@ignore-target-apple: park_timeout on macOS uses the system clock
+use std::thread;
+use std::time::{Duration, Instant};
+
+fn main() {
+    let start = Instant::now();
+
+    thread::park_timeout(Duration::from_millis(200));
+
+    // Thanks to deterministic execution, this will wiat *exactly* 200ms (rounded to 1ms).
+    assert!((200..201).contains(&start.elapsed().as_millis()));
+}