fix(gpu): use shared locks to check for an exclusive lock (filecoin-p…

…roject#213)

Trying to use an exclusive lock, means that the file is actually getting locked
exclusively, even if we just want to check if there is an exclusive lock.
Additionally we now check for the correct error when checking the lock

src/gpu/locks.rs

@@ -53,22 +53,37 @@ impl PriorityLock {
         debug!("Priority lock acquired!");
         PriorityLock(f)
     }
+
     pub fn wait(priority: bool) {
         if !priority {
-            File::create(tmp_path(PRIORITY_LOCK_NAME))
+            if let Err(err) = File::create(tmp_path(PRIORITY_LOCK_NAME))
                 .unwrap()
                 .lock_exclusive()
-                .unwrap();
+            {
+                warn!("failed to create priority log: {:?}", err);
+            }
         }
     }
+
     pub fn should_break(priority: bool) -> bool {
-        !priority
-            && File::create(tmp_path(PRIORITY_LOCK_NAME))
-                .unwrap()
-                .try_lock_exclusive()
-                .is_err()
+        if priority {
+            return false;
+        }
+        if let Err(err) = File::create(tmp_path(PRIORITY_LOCK_NAME))
+            .unwrap()
+            .try_lock_shared()
+        {
+            // Check that the error is actually a locking one
+            if err.raw_os_error() == fs2::lock_contended_error().raw_os_error() {
+                return true;
+            } else {
+                warn!("failed to check lock: {:?}", err);
+            }
+        }
+        false
     }
 }
+
 impl Drop for PriorityLock {
     fn drop(&mut self) {
         self.0.unlock().unwrap();