Auto merge of #56490 - faern:add-checked-add-to-instant, r=alexcrichton

Add checked_add method to Instant time type

Appending functionality to the already opened topic of `checked_add` on time types over at #55940.

Doing checked addition between an `Instant` and a `Duration` is important to reliably determine a future instant. We could use this in the `parking_lot` crate to compute an instant when in the future to wake a thread up without risking a panic.

3 files changed, 26 insertions, 38 deletions

diff --git a/src/libstd/sys/cloudabi/condvar.rs b/src/libstd/sys/cloudabi/condvar.rs
index ccf848a9be4..3229d98624e 100644
--- a/src/libstd/sys/cloudabi/condvar.rs
+++ b/src/libstd/sys/cloudabi/condvar.rs
@@ -13,7 +13,7 @@ use mem;
 use sync::atomic::{AtomicU32, Ordering};
 use sys::cloudabi::abi;
 use sys::mutex::{self, Mutex};
-use sys::time::dur2intervals;
+use sys::time::checked_dur2intervals;
 use time::Duration;
 
 extern "C" {
@@ -114,6 +114,8 @@ impl Condvar {
 
         // Call into the kernel to wait on the condition variable.
         let condvar = self.condvar.get();
+        let timeout = checked_dur2intervals(&dur)
+            .expect("overflow converting duration to nanoseconds");
         let subscriptions = [
             abi::subscription {
                 type_: abi::eventtype::CONDVAR,
@@ -132,7 +134,7 @@ impl Condvar {
                 union: abi::subscription_union {
                     clock: abi::subscription_clock {
                         clock_id: abi::clockid::MONOTONIC,
-                        timeout: dur2intervals(&dur),
+                        timeout,
                         ..mem::zeroed()
                     },
                 },
diff --git a/src/libstd/sys/cloudabi/thread.rs b/src/libstd/sys/cloudabi/thread.rs
index a76e1fa3345..177321439d8 100644
--- a/src/libstd/sys/cloudabi/thread.rs
+++ b/src/libstd/sys/cloudabi/thread.rs
@@ -16,7 +16,7 @@ use libc;
 use mem;
 use ptr;
 use sys::cloudabi::abi;
-use sys::time::dur2intervals;
+use sys::time::checked_dur2intervals;
 use sys_common::thread::*;
 use time::Duration;
 
@@ -70,13 +70,15 @@ impl Thread {
     }
 
     pub fn sleep(dur: Duration) {
+        let timeout = checked_dur2intervals(&dur)
+            .expect("overflow converting duration to nanoseconds");
         unsafe {
             let subscription = abi::subscription {
                 type_: abi::eventtype::CLOCK,
                 union: abi::subscription_union {
                     clock: abi::subscription_clock {
                         clock_id: abi::clockid::MONOTONIC,
-                        timeout: dur2intervals(&dur),
+                        timeout,
                         ..mem::zeroed()
                     },
                 },
diff --git a/src/libstd/sys/cloudabi/time.rs b/src/libstd/sys/cloudabi/time.rs
index a442d1e4ad7..c9fea18fda6 100644
--- a/src/libstd/sys/cloudabi/time.rs
+++ b/src/libstd/sys/cloudabi/time.rs
@@ -19,15 +19,10 @@ pub struct Instant {
     t: abi::timestamp,
 }
 
-fn checked_dur2intervals(dur: &Duration) -> Option<abi::timestamp> {
+pub fn checked_dur2intervals(dur: &Duration) -> Option<abi::timestamp> {
     dur.as_secs()
-        .checked_mul(NSEC_PER_SEC)
-        .and_then(|nanos| nanos.checked_add(dur.subsec_nanos() as abi::timestamp))
-}
-
-pub fn dur2intervals(dur: &Duration) -> abi::timestamp {
-    checked_dur2intervals(dur)
-        .expect("overflow converting duration to nanoseconds")
+        .checked_mul(NSEC_PER_SEC)?
+        .checked_add(dur.subsec_nanos() as abi::timestamp)
 }
 
 impl Instant {
@@ -47,20 +42,16 @@ impl Instant {
         Duration::new(diff / NSEC_PER_SEC, (diff % NSEC_PER_SEC) as u32)
     }
 
-    pub fn add_duration(&self, other: &Duration) -> Instant {
-        Instant {
-            t: self.t
-                .checked_add(dur2intervals(other))
-                .expect("overflow when adding duration to instant"),
-        }
+    pub fn checked_add_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant {
+            t: self.t.checked_add(checked_dur2intervals(other)?)?,
+        })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> Instant {
-        Instant {
-            t: self.t
-                .checked_sub(dur2intervals(other))
-                .expect("overflow when subtracting duration from instant"),
-        }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<Instant> {
+        Some(Instant {
+            t: self.t.checked_sub(checked_dur2intervals(other)?)?,
+        })
     }
 }
 
@@ -95,23 +86,16 @@ impl SystemTime {
         }
     }
 
-    pub fn add_duration(&self, other: &Duration) -> SystemTime {
-        self.checked_add_duration(other)
-            .expect("overflow when adding duration to instant")
-    }
-
     pub fn checked_add_duration(&self, other: &Duration) -> Option<SystemTime> {
-        checked_dur2intervals(other)
-            .and_then(|d| self.t.checked_add(d))
-            .map(|t| SystemTime {t})
+        Some(SystemTime {
+            t: self.t.checked_add(checked_dur2intervals(other)?)?,
+        })
     }
 
-    pub fn sub_duration(&self, other: &Duration) -> SystemTime {
-        SystemTime {
-            t: self.t
-                .checked_sub(dur2intervals(other))
-                .expect("overflow when subtracting duration from instant"),
-        }
+    pub fn checked_sub_duration(&self, other: &Duration) -> Option<SystemTime> {
+        Some(SystemTime {
+            t: self.t.checked_sub(checked_dur2intervals(other)?)?,
+        })
     }
 }