add NANOSECONDS_PER_BASIC_BLOCK and comments

Author: pvdrz

src/shims/time.rs

@@ -6,6 +6,8 @@ use rustc_data_structures::sync::Ordering;
 use crate::concurrency::thread::Time;
 use crate::*;
 
+const NANOSECOND_PER_BASIC_BLOCK: u64 = 10;
+
 #[derive(Debug)]
 pub enum Clock {
     Host {
@@ -37,9 +39,11 @@ impl Clock {
 
     pub fn tick(&self) {
         match self {
-            Self::Host { .. } => (),
+            Self::Host { .. } => {
+                // Time will pass without us doing anything.
+            }
             Self::Virtual { nanoseconds } => {
-                nanoseconds.fetch_add(1, Ordering::Relaxed);
+                nanoseconds.fetch_add(NANOSECOND_PER_BASIC_BLOCK, Ordering::Relaxed);
             }
         }
     }
@@ -48,11 +52,13 @@ impl Clock {
         match self {
             Self::Host { .. } => std::thread::sleep(duration),
             Self::Virtual { nanoseconds } => {
+                // Just pretend that we have slept for some time.
                 nanoseconds.fetch_add(duration.as_nanos().try_into().unwrap(), Ordering::Relaxed);
             }
         }
     }
 
+
     pub fn checked_add_since_now(&self, duration: Duration) -> Option<Time> {
         match self {
             Self::Host { .. } => Instant::now().checked_add(duration).map(Time::Monotonic),
@@ -291,10 +297,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         // If adding the duration overflows, let's just sleep for an hour. Waking up early is always acceptable.
         let timeout_time =
             this.machine.clock.checked_add_since_now(duration).unwrap_or_else(|| {
-                this.machine
-                    .clock
-                    .checked_add_since_now(Duration::from_secs(3600))
-                    .unwrap()
+                this.machine.clock.checked_add_since_now(Duration::from_secs(3600)).unwrap()
             });
 
         let active_thread = this.get_active_thread();
@@ -321,8 +324,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
         let timeout_ms = this.read_scalar(timeout)?.to_u32()?;
 
         let duration = Duration::from_millis(timeout_ms.into());
-        let timeout_time =
-            this.machine.clock.checked_add_since_now(duration).unwrap();
+        let timeout_time = this.machine.clock.checked_add_since_now(duration).unwrap();
 
         let active_thread = this.get_active_thread();
         this.block_thread(active_thread);