Merge pull request #2810 from kumpera/fix_hazard_free

[mono.git] / mcs / class / corlib / System.Runtime.InteropServices / GCHandle.cs

diff --git a/mcs/class/corlib/System.Runtime.InteropServices/GCHandle.cs b/mcs/class/corlib/System.Runtime.InteropServices/GCHandle.cs
index 2256ebde0eab496d2dbbb03aaa04d723d1a1bdf7..ec83a3e0756b6f79737d2acb38b87f4ea11ba02b 100644 (file)
--- a/mcs/class/corlib/System.Runtime.InteropServices/GCHandle.cs
+++ b/mcs/class/corlib/System.Runtime.InteropServices/GCHandle.cs
@@ -30,6 +30,7 @@
 //
 
 using System;
+using System.Threading;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -108,8 +109,17 @@ namespace System.Runtime.InteropServices
 
                public void Free()
                {
-                       FreeHandle(handle);
-                       handle = 0;
+                       // Copy the handle instance member to a local variable. This is required to prevent
+                       // race conditions releasing the handle.
+                       int local_handle = handle;
+
+                       // Free the handle if it hasn't already been freed.
+                       if (local_handle != 0 && Interlocked.CompareExchange (ref handle, 0, local_handle) == local_handle) {
+                               FreeHandle (local_handle);
+                       }
+                       else {
+                               throw new InvalidOperationException ("Handle is not initialized.");
+                       }
                }
                
                public static explicit operator IntPtr (GCHandle value)
@@ -120,7 +130,7 @@ namespace System.Runtime.InteropServices
                public static explicit operator GCHandle(IntPtr value)
                {
                        if (value == IntPtr.Zero)
-                               throw new ArgumentException ("GCHandle value cannot be zero");
+                               throw new InvalidOperationException ("GCHandle value cannot be zero");
                        if (!CheckCurrentDomain ((int)value))
                                throw new ArgumentException ("GCHandle value belongs to a different domain");
                        return new GCHandle (value);