Fixes deadlock in BTree split..

koculu · Aug 30, 2022 · 8416d2d · 8416d2d
1 parent a6fb79f
commit 8416d2d
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Showing 8 changed files with 74 additions and 7 deletions.
diff --git a/src/Playground/Program.cs b/src/Playground/Program.cs
@@ -53,7 +53,7 @@
         CompressionMethod.Zstd,
         CompressionMethod.Gzip
     };
-    test2.Count = test1.Count = 100_000_000;
+    test2.Count = test1.Count = 5_000_000;
     test2.WALMode = test1.WALMode = WriteAheadLogMode.None;
 
     b.NewSection("int-int insert");
@@ -72,7 +72,7 @@
         test2.AddDatabaseFileUsage(stats);
     }
 
-    /*b.NewSection("int-int iterate");
+    b.NewSection("int-int iterate");
     foreach (var method in methods)
     {
         test1.CompressionMethod = method;
@@ -84,7 +84,7 @@
     {
         test2.CompressionMethod = method;
         b.Run(test2.Iterate);
-    }*/
+    }
 
     File.WriteAllText(@"..\..\data\benchmark.json", b.ToJSON());
 }
diff --git a/src/ZoneTree/Collections/BTree/BTree.Node.cs b/src/ZoneTree/Collections/BTree/BTree.Node.cs
@@ -106,6 +106,11 @@ public void WriteLock()
             Locker.WriteLock();
         }
 
+        public bool TryEnterWriteLock(int millisecondsTimeout)
+        {
+            return Locker.TryEnterWriteLock(millisecondsTimeout);
+        }
+
         public void WriteUnlock()
         {
             Locker.WriteUnlock();

diff --git a/src/ZoneTree/Collections/BTree/BTree.Write.cs b/src/ZoneTree/Collections/BTree/BTree.Write.cs
@@ -162,14 +162,59 @@ void SplitChild(Node parent, int parentInsertPosition, Node child)
                 pre.WriteLock();
             }
 
+            // HANDLE DEADLOCK
+            // childLeaf => LOCKED BY US
+            // PRE => LOCKED BY US
+            // NEXT => LOCKED BY ANOTHER SPLIT!!!
+            // DEADLOCK !!!...
+            // SOLUTION:
+            // TRY TO LOCK NEXT WITH TIMEOUT
+            // IF CAN NOT LOCK IN TIME UNLOCK PRE
+            // THEN SLEEP SOME
+            // THEN RELOCK PRE
+            // AND TRY TO LOCK NEXT ONCE AGAIN IN A LOOP.
+            var lockTimeout = 500;
             var next = childLeaf.Next;
-            next?.WriteLock();
+            var isNextLocked = true;
+            while(true)
+            {
+                if (next != null)
+                    isNextLocked = next.TryEnterWriteLock(lockTimeout);
+                if (isNextLocked)
+                    break;
+                pre?.WriteUnlock();
+                Thread.Sleep(100);
+                pre?.WriteLock();
+                while (childLeaf.Previous != pre)
+                {
+                    pre.WriteUnlock();
+                    pre = childLeaf.Previous;
+                    pre.WriteLock();
+                }
+            }
+
             // prevent neighbour split at the same time.
             while (childLeaf.Next != next)
             {
                 next.WriteUnlock();
                 next = childLeaf.Next;
-                next.WriteLock();
+                isNextLocked = true;
+                while (true)
+                {
+                    if (next != null)
+                        isNextLocked = next.TryEnterWriteLock(lockTimeout);
+                    if (isNextLocked)
+                        break;
+                    pre?.WriteUnlock();
+                    Thread.Sleep(100);
+                    pre?.WriteLock();
+                    while (childLeaf.Previous != pre)
+                    {
+                        pre.WriteUnlock();
+                        pre = childLeaf.Previous;
+                        pre.WriteLock();
+                    }
+                }
             }
 
             left.Previous = pre;

diff --git a/src/ZoneTree/Collections/BTree/ILocker.cs b/src/ZoneTree/Collections/BTree/ILocker.cs
@@ -4,6 +4,8 @@ namespace Tenray.ZoneTree.Collections.BTree;
 
 public interface ILocker
 {
+    bool TryEnterWriteLock(int millisecondsTimeout);
+
     void WriteLock();
 
     void WriteUnlock();

diff --git a/src/ZoneTree/Collections/BTree/Lock/MonitorLock.cs b/src/ZoneTree/Collections/BTree/Lock/MonitorLock.cs
@@ -21,4 +21,9 @@ public void ReadUnlock()
     {
         Monitor.Exit(this);
     }
+
+    public bool TryEnterWriteLock(int millisecondsTimeout)
+    {
+        return Monitor.TryEnter(this, millisecondsTimeout);
+    }
 }
diff --git a/src/ZoneTree/Collections/BTree/Lock/NoLock.cs b/src/ZoneTree/Collections/BTree/Lock/NoLock.cs
@@ -23,4 +23,9 @@ public void ReadLock()
     public void ReadUnlock()
     {
     }
+
+    public bool TryEnterWriteLock(int millisecondsTimeout)
+    {
+        return true;
+    }
 }
diff --git a/src/ZoneTree/Collections/BTree/Lock/ReaderWriter.cs b/src/ZoneTree/Collections/BTree/Lock/ReaderWriter.cs
@@ -23,4 +23,9 @@ public void ReadUnlock()
     {
         Locker.ExitReadLock();
     }
+
+    public bool TryEnterWriteLock(int millisecondsTimeout)
+    {
+        return Locker.TryEnterWriteLock(millisecondsTimeout);
+    }
 }
diff --git a/src/ZoneTree/Directory.Build.props b/src/ZoneTree/Directory.Build.props
@@ -5,8 +5,8 @@
     <Authors>Ahmed Yasin Koculu</Authors>
     <PackageId>ZoneTree</PackageId>
     <Title>ZoneTree</Title>
-    <ProductVersion>1.4.6.0</ProductVersion>
-    <Version>1.4.6.0</Version>
+    <ProductVersion>1.4.7.0</ProductVersion>
+    <Version>1.4.7.0</Version>
     <Authors>Ahmed Yasin Koculu</Authors>
     <AssemblyTitle>ZoneTree</AssemblyTitle>
     <Description>ZoneTree is a persistent, high-performance, transactional, ACID-compliant ordered key-value database for NET. It can operate in memory or on local/cloud storage.</Description>