Make SpinLock.TryEnter(ref bool) fail faster

One uses SpinLock.TryEnter(ref bool) when they want to do a quick test to either acquire the lock or know it's held by someone else.  We can make the latter path much faster so that it fails faster.

Commit migrated from https://github.com/dotnet/coreclr/commit/7ee26ae908da9b1f48c37186b07b3dc860f4f1ba

diff --git a/src/coreclr/src/mscorlib/src/System/Threading/SpinLock.cs b/src/coreclr/src/mscorlib/src/System/Threading/SpinLock.cs
index 1d90890..aad274d 100644 (file)
--- a/src/coreclr/src/mscorlib/src/System/Threading/SpinLock.cs
+++ b/src/coreclr/src/mscorlib/src/System/Threading/SpinLock.cs
@@ -183,7 +183,22 @@ namespace System.Threading
         /// </exception>
         public void TryEnter(ref bool lockTaken)
         {
-            TryEnter(0, ref lockTaken);
+            int observedOwner = m_owner;
+            if (((observedOwner & LOCK_ID_DISABLE_MASK) == 0) | lockTaken)
+            {
+                // Thread tracking enabled or invalid arg. Take slow path.
+                ContinueTryEnter(0, ref lockTaken);
+            }
+            else if ((observedOwner & LOCK_ANONYMOUS_OWNED) != 0)
+            {
+                // Lock already held by someone
+                lockTaken = false;
+            }
+            else
+            {
+                // Lock wasn't held; try to acquire it.
+                Interlocked.CompareExchange(ref m_owner, observedOwner | LOCK_ANONYMOUS_OWNED, observedOwner, ref lockTaken);
+            }
         }
 
         /// <summary>
@@ -522,10 +537,10 @@ namespace System.Threading
         {
             // This is the fast path for the thread tracking is diabled and not to use memory barrier, otherwise go to the slow path
             // The reason not to add else statement if the usememorybarrier is that it will add more barnching in the code and will prevent
-            // method inlining, so this is optimized for useMemoryBarrier=false and Exit() overload optimized for useMemoryBarrier=true
-            if ((m_owner & LOCK_ID_DISABLE_MASK) != 0 && !useMemoryBarrier)
+            // method inlining, so this is optimized for useMemoryBarrier=false and Exit() overload optimized for useMemoryBarrier=true.
+            int tmpOwner = m_owner;
+            if ((tmpOwner & LOCK_ID_DISABLE_MASK) != 0 & !useMemoryBarrier)
             {
-                int tmpOwner = m_owner;
                 m_owner = tmpOwner & (~LOCK_ANONYMOUS_OWNED);
             }
             else