Protect initialization of TraceEventSession.ProviderNameToGuid and

TraceEventSession.ProviderGuidToName with a lock to allow for multiple concurrent callers. This does not change the concurrency guarantees for TraceEvent, but does allow for multiple concurrent callers of TraceEventSession.EnableProvider on different instances of TraceEventSession, where prior to this change it was possible for this to produce a crash on insertion into the Dictionary or SortedDictionary.
microsoft · Oct 19, 2023 · e76170f · e76170f
1 parent d52d78f
commit e76170f
Showing 1 changed file with 37 additions and 20 deletions.
diff --git a/src/TraceEvent/TraceEventSession.cs b/src/TraceEvent/TraceEventSession.cs
@@ -1631,27 +1631,35 @@ internal static SortedDictionary<string, Guid> ProviderNameToGuid
             {
                 if (s_providersByName == null)
                 {
-                    s_providersByName = new SortedDictionary<string, Guid>(StringComparer.OrdinalIgnoreCase);
-                    int buffSize = 0;
-                    var hr = TraceEventNativeMethods.TdhEnumerateProviders(null, ref buffSize);
-                    Debug.Assert(hr == 122);     // ERROR_INSUFFICIENT_BUFFER
-                    var buffer = stackalloc byte[buffSize];
-                    var providersDesc = (TraceEventNativeMethods.PROVIDER_ENUMERATION_INFO*)buffer;
-
-                    hr = TraceEventNativeMethods.TdhEnumerateProviders(providersDesc, ref buffSize);
-                    if ((hr == 0) && (providersDesc != null))
+                    lock (s_lock)
                     {
-                        var providers = (TraceEventNativeMethods.TRACE_PROVIDER_INFO*)&providersDesc[1];
-                        for (int i = 0; i < providersDesc->NumberOfProviders; i++)
+                        if (s_providersByName == null)
                         {
-                            var name = new string((char*)&buffer[providers[i].ProviderNameOffset]);
-                            s_providersByName[name] = providers[i].ProviderGuid;
+                            SortedDictionary<string, Guid> providersByName = new SortedDictionary<string, Guid>(StringComparer.OrdinalIgnoreCase);
+                            int buffSize = 0;
+                            var hr = TraceEventNativeMethods.TdhEnumerateProviders(null, ref buffSize);
+                            Debug.Assert(hr == 122);     // ERROR_INSUFFICIENT_BUFFER
+                            var buffer = stackalloc byte[buffSize];
+                            var providersDesc = (TraceEventNativeMethods.PROVIDER_ENUMERATION_INFO*)buffer;
+
+                            hr = TraceEventNativeMethods.TdhEnumerateProviders(providersDesc, ref buffSize);
+                            if ((hr == 0) && (providersDesc != null))
+                            {
+                                var providers = (TraceEventNativeMethods.TRACE_PROVIDER_INFO*)&providersDesc[1];
+                                for (int i = 0; i < providersDesc->NumberOfProviders; i++)
+                                {
+                                    var name = new string((char*)&buffer[providers[i].ProviderNameOffset]);
+                                    providersByName[name] = providers[i].ProviderGuid;
+                                }
+
+                                s_providersByName = providersByName;
+                            }
+                            else
+                            {
+                                Trace.WriteLine("TdhEnumerateProviders failed HR = " + hr);
+                            }
                         }
                     }
-                    else
-                    {
-                        Trace.WriteLine("TdhEnumerateProviders failed HR = " + hr);
-                    }
                 }
                 return s_providersByName;
             }
@@ -1663,10 +1671,18 @@ internal static Dictionary<Guid, string> ProviderGuidToName
             {
                 if (s_providerNames == null)
                 {
-                    s_providerNames = new Dictionary<Guid, string>(ProviderNameToGuid.Count);
-                    foreach (var keyValue in ProviderNameToGuid)
+                    lock (s_lock)
                     {
-                        s_providerNames[keyValue.Value] = keyValue.Key;
+                        if (s_providerNames == null)
+                        {
+                            Dictionary<Guid, string> providerNames = new Dictionary<Guid, string>(ProviderNameToGuid.Count);
+                            foreach (var keyValue in ProviderNameToGuid)
+                            {
+                                providerNames[keyValue.Value] = keyValue.Key;
+                            }
+
+                            s_providerNames = providerNames;
+                        }
                     }
                 }
                 return s_providerNames;
@@ -1721,6 +1737,7 @@ private int ComputeEventIdsBufferSize(IList<int> eventIds)
             return (eventIds.Count - 1) * 2 + sizeof(TraceEventNativeMethods.EVENT_FILTER_EVENT_ID);
         }
 
+        private static object s_lock = new object();
         private static SortedDictionary<string, Guid> s_providersByName;
         private static Dictionary<Guid, string> s_providerNames;