Rollup merge of #146517 - RalfJung:wait-timeout, r=joboet

fix Condvar::wait_timeout docs [Context](https://rust-lang.zulipchat.com/#narrow/channel/219381-t-libs/topic/Condvar.20wait_timeout.20sleep.20duration.20decremented/with/539279839) r? `@joboet`

Author: jhpratt

library/std/src/sync/nonpoison/condvar.rs

@@ -198,11 +198,10 @@ impl Condvar {
  /// the system time. This function is susceptible to spurious wakeups.
  /// Condition variables normally have a boolean predicate associated with
  /// them, and the predicate must always be checked each time this function
- /// returns to protect against spurious wakeups. Additionally, it is
- /// typically desirable for the timeout to not exceed some duration in
- /// spite of spurious wakes, thus the sleep-duration is decremented by the
- /// amount slept. Alternatively, use the `wait_timeout_while` method
- /// to wait with a timeout while a predicate is true.
+ /// returns to protect against spurious wakeups. Furthermore, since the timeout
+ /// is given relative to the moment this function is called, it needs to be adjusted
+ /// when this function is called in a loop. The [`wait_timeout_while`] method
+ /// lets you wait with a timeout while a predicate is true, taking care of all these concerns.
  ///
  /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
  /// known to have elapsed.

library/std/src/sync/poison/condvar.rs

@@ -269,11 +269,10 @@ impl Condvar {
  /// the system time. This function is susceptible to spurious wakeups.
  /// Condition variables normally have a boolean predicate associated with
  /// them, and the predicate must always be checked each time this function
- /// returns to protect against spurious wakeups. Additionally, it is
- /// typically desirable for the timeout to not exceed some duration in
- /// spite of spurious wakes, thus the sleep-duration is decremented by the
- /// amount slept. Alternatively, use the `wait_timeout_while` method
- /// to wait with a timeout while a predicate is true.
+ /// returns to protect against spurious wakeups. Furthermore, since the timeout
+ /// is given relative to the moment this function is called, it needs to be adjusted
+ /// when this function is called in a loop. The [`wait_timeout_while`] method
+ /// lets you wait with a timeout while a predicate is true, taking care of all these concerns.
  ///
  /// The returned [`WaitTimeoutResult`] value indicates if the timeout is
  /// known to have elapsed.