Updated docs

src/kernel/synch.rs

@@ -4,8 +4,6 @@ use crate::simulator::interrupt::InterruptStatus::InterruptOff;
 use crate::simulator::machine::Machine;
 use std::cell::RefCell;
 use std::rc::Rc;
-
-use super::system::System;
 use super::thread_manager::ThreadManager;
 
 ///     Structure of a Semaphore used for synchronisation
@@ -169,6 +167,8 @@ impl Lock {
         machine.interrupt.set_status(old_status);
     }
 
+    ///    True if the current thread holds this lock.
+    /// Useful for checking in Release, and in Condition operations below.
     pub fn held_by_current_thread(&mut self, thread_manager: &mut ThreadManager) -> bool {
         match &self.owner {
             Some(x) =>