Address feedback

src/mscorlib/shared/System/Threading/ReaderWriterLockSlim.cs

@@ -374,11 +374,15 @@ private bool TryEnterReadLockCore(TimeoutTracker timeout)
                     break;
                 }
 
+                if (timeout.IsExpired)
+                {
+                    ExitMyLock();
+                    return false;
+                }
+
                 if (spinCount < MaxSpinCount && ShouldSpinForEnterAnyRead())
                 {
                     ExitMyLock();
-                    if (timeout.IsExpired)
-                        return false;
                     spinCount++;
                     SpinWait(spinCount);
                     EnterMyLockForEnterAnyRead();
@@ -550,11 +554,15 @@ private bool TryEnterWriteLockCore(TimeoutTracker timeout)
                     }
                 }
 
+                if (timeout.IsExpired)
+                {
+                    ExitMyLock();
+                    return false;
+                }
+
                 if (spinCount < MaxSpinCount && ShouldSpinForEnterAnyWrite(upgradingToWrite))
                 {
                     ExitMyLock();
-                    if (timeout.IsExpired)
-                        return false;
                     spinCount++;
                     SpinWait(spinCount);
                     if (upgradingToWrite)
@@ -714,11 +722,15 @@ private bool TryEnterUpgradeableReadLockCore(TimeoutTracker timeout)
                     break;
                 }
 
+                if (timeout.IsExpired)
+                {
+                    ExitMyLock();
+                    return false;
+                }
+
                 if (spinCount < MaxSpinCount && ShouldSpinForEnterAnyRead())
                 {
                     ExitMyLock();
-                    if (timeout.IsExpired)
-                        return false;
                     spinCount++;
                     SpinWait(spinCount);
                     EnterMyLockForEnterAnyRead();
@@ -1125,13 +1137,18 @@ private bool ShouldSpinForEnterAnyRead()
         {
             // If there is a write waiter or write upgrade waiter, the waiter would block a reader from acquiring the RW lock
             // because the waiter takes precedence. In that case, the reader is not likely to make progress by spinning.
-            return _fNoWaiters || _numWriteWaiters == 0 && _numWriteUpgradeWaiters == 0;
+            // Although another thread holding a write lock would prevent this thread from acquiring a read lock, it is by
+            // itself not a good enough reason to skip spinning.
+            return _fNoWaiters || (_numWriteWaiters == 0 && _numWriteUpgradeWaiters == 0);
         }
 
         private bool ShouldSpinForEnterAnyWrite(bool isUpgradeToWrite)
         {
             // If there is a write upgrade waiter, the waiter would block a writer from acquiring the RW lock because the waiter
-            // holds a read lock. In that case, the writer is not likely to make progress by spinning.
+            // holds a read lock. In that case, the writer is not likely to make progress by spinning. Regarding upgrading to a
+            // write lock, there is no type of waiter that would block the upgrade from happening. Although another thread
+            // holding a read or write lock would prevent this thread from acquiring the write lock, it is by itself not a good
+            // enough reason to skip spinning.
             return isUpgradeToWrite || _numWriteUpgradeWaiters == 0;
         }
 
@@ -1215,6 +1232,7 @@ private void EnterMyLockSpinForExitAnyRead()
         {
             // A read lock is held until this thread is able to exit it, so deprioritize enter-write threads as they will not be
             // able to make progress
+            Debug.Assert(DeprioritizeEnterWriteIncrement == 1);
             Interlocked.Increment(ref _enterMyLockDeprioritizationState);
 
             int pc = ProcessorCount;