Only join when ecx.release_clock is SOme

Author: tiif

src/shims/unix/linux/eventfd.rs

@@ -10,8 +10,6 @@ use crate::{concurrency::VClock, *};
 
 use self::shims::unix::fd::FileDescriptor;
 
-// TODO: add comment on this
-// Size of u8 array to hold u64 value.
 const U64_ARRAY_SIZE: usize = mem::size_of::<u64>();
 
 /// Maximum value that the eventfd counter can hold.
@@ -113,7 +111,9 @@ impl FileDescription for Event {
         match self.counter.checked_add(num) {
             Some(new_count @ 0..=MAX_COUNTER) => {
                 // Synchronize with all prior `write` calls to this FD.
-                self.clock.join(&ecx.release_clock().unwrap());
+                if let Some(clock) = &ecx.release_clock() {
+                    self.clock.join(clock);
+                }
                 self.counter = new_count;
             }
             None | Some(u64::MAX) => {