Remove writers preference test for RWLock

Summary:
Writers preference is not guaranteed by the standard and as such
 there are variations between implementations in different versions
of libphthread.

Reviewers: dgleich

Reviewed By: dgleich

Differential Revision: https://phabricator.memgraph.io/D1305

src/threading/sync/rwlock.hpp

@@ -13,8 +13,7 @@ namespace threading {
 /// though there is a thread waiting for an exclusive (write) lock, which can
 /// lead to writer starvation. If the priority is set to `WRITE`, readers will
 /// be blocked from obtaining new shared locks while there are writers waiting,
-/// which can lead to reader starvation. However, if there is an exclusive lock
+/// which can lead to reader starvation.
-/// held, writers will always be preferred upon it's release.
 enum RWLockPriority { READ, WRITE };
 
 /// A wrapper around `pthread_rwlock_t`, useful because it is not possible to

tests/unit/rwlock.cpp

@@ -52,53 +52,6 @@ TEST(RWLock, SingleWriter) {
   EXPECT_GE(timer.Elapsed(), 290ms);
 }
 
-/* Next two tests demonstrate that writers are always preferred when an unique
- * lock is released. */
-
-TEST(RWLock, WritersPreferred_1) {
-  RWLock rwlock(RWLockPriority::READ);
-  rwlock.lock();
-  bool first = true;
-
-  std::thread t1([&rwlock, &first] {
-    std::shared_lock<RWLock> lock(rwlock);
-    EXPECT_FALSE(first);
-  });
-
-  std::thread t2([&rwlock, &first] {
-    std::unique_lock<RWLock> lock(rwlock);
-    EXPECT_TRUE(first);
-    first = false;
-  });
-
-  std::this_thread::sleep_for(100ms);
-  rwlock.unlock();
-  t1.join();
-  t2.join();
-}
-
-TEST(RWLock, WritersPreferred_2) {
-  RWLock rwlock(RWLockPriority::WRITE);
-  rwlock.lock();
-  bool first = true;
-
-  std::thread t1([&rwlock, &first] {
-    std::shared_lock<RWLock> lock(rwlock);
-    EXPECT_FALSE(first);
-  });
-
-  std::thread t2([&rwlock, &first] {
-    std::unique_lock<RWLock> lock(rwlock);
-    EXPECT_TRUE(first);
-    first = false;
-  });
-
-  std::this_thread::sleep_for(100ms);
-  rwlock.unlock();
-  t1.join();
-  t2.join();
-}
-
 TEST(RWLock, ReadPriority) {
   /*
    * - Main thread is holding a shared lock until T = 100ms.