Move a few stackallocs out of loops (dotnet#34149)

JimBobSquarePants · Mar 27, 2020 · 1d9067b · 1d9067b
1 parent 0c9094e
commit 1d9067b
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Showing 2 changed files with 48 additions and 30 deletions.
diff --git a/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs b/src/libraries/System.Private.CoreLib/src/System/Diagnostics/Tracing/EventProvider.cs
@@ -467,42 +467,59 @@ private unsafe void GetSessionInfo(SessionInfoCallback action, ref List<SessionI
             // does not have this issue.
 #if (TARGET_WINDOWS && (ES_SESSION_INFO || !ES_BUILD_STANDALONE))
             int buffSize = 256;     // An initial guess that probably works most of the time.
-            byte* buffer;
-            while (true)
+            byte* stackSpace = stackalloc byte[buffSize];
+            byte* buffer = stackSpace;
+            try
             {
-                byte* space = stackalloc byte[buffSize];
-                buffer = space;
-                int hr = 0;
+                while (true)
+                {
+                    int hr = 0;
 
-                fixed (Guid* provider = &m_providerId)
+                    fixed (Guid* provider = &m_providerId)
+                    {
+                        hr = Interop.Advapi32.EnumerateTraceGuidsEx(Interop.Advapi32.TRACE_QUERY_INFO_CLASS.TraceGuidQueryInfo,
+                            provider, sizeof(Guid), buffer, buffSize, out buffSize);
+                    }
+                    if (hr == 0)
+                        break;
+                    if (hr != Interop.Errors.ERROR_INSUFFICIENT_BUFFER)
+                        return;
+
+                    if (buffer != stackSpace)
+                    {
+                        byte* toFree = buffer;
+                        buffer = null;
+                        Marshal.FreeHGlobal((IntPtr)toFree);
+                    }
+                    buffer = (byte*)Marshal.AllocHGlobal(buffSize);
+                }
+
+                var providerInfos = (Interop.Advapi32.TRACE_GUID_INFO*)buffer;
+                var providerInstance = (Interop.Advapi32.TRACE_PROVIDER_INSTANCE_INFO*)&providerInfos[1];
+                int processId = unchecked((int)Interop.Kernel32.GetCurrentProcessId());
+                // iterate over the instances of the EventProvider in all processes
+                for (int i = 0; i < providerInfos->InstanceCount; i++)
                 {
-                    hr = Interop.Advapi32.EnumerateTraceGuidsEx(Interop.Advapi32.TRACE_QUERY_INFO_CLASS.TraceGuidQueryInfo,
-                        provider, sizeof(Guid), buffer, buffSize, out buffSize);
+                    if (providerInstance->Pid == processId)
+                    {
+                        var enabledInfos = (Interop.Advapi32.TRACE_ENABLE_INFO*)&providerInstance[1];
+                        // iterate over the list of active ETW sessions "listening" to the current provider
+                        for (int j = 0; j < providerInstance->EnableCount; j++)
+                            action(enabledInfos[j].LoggerId, enabledInfos[j].MatchAllKeyword, ref sessionList);
+                    }
+                    if (providerInstance->NextOffset == 0)
+                        break;
+                    Debug.Assert(0 <= providerInstance->NextOffset && providerInstance->NextOffset < buffSize);
+                    byte* structBase = (byte*)providerInstance;
+                    providerInstance = (Interop.Advapi32.TRACE_PROVIDER_INSTANCE_INFO*)&structBase[providerInstance->NextOffset];
                 }
-                if (hr == 0)
-                    break;
-                if (hr != Interop.Errors.ERROR_INSUFFICIENT_BUFFER)
-                    return;
             }
-
-            var providerInfos = (Interop.Advapi32.TRACE_GUID_INFO*)buffer;
-            var providerInstance = (Interop.Advapi32.TRACE_PROVIDER_INSTANCE_INFO*)&providerInfos[1];
-            int processId = unchecked((int)Interop.Kernel32.GetCurrentProcessId());
-            // iterate over the instances of the EventProvider in all processes
-            for (int i = 0; i < providerInfos->InstanceCount; i++)
+            finally
             {
-                if (providerInstance->Pid == processId)
+                if (buffer != null && buffer != stackSpace)
                 {
-                    var enabledInfos = (Interop.Advapi32.TRACE_ENABLE_INFO*)&providerInstance[1];
-                    // iterate over the list of active ETW sessions "listening" to the current provider
-                    for (int j = 0; j < providerInstance->EnableCount; j++)
-                        action(enabledInfos[j].LoggerId, enabledInfos[j].MatchAllKeyword, ref sessionList);
+                    Marshal.FreeHGlobal((IntPtr)buffer);
                 }
-                if (providerInstance->NextOffset == 0)
-                    break;
-                Debug.Assert(0 <= providerInstance->NextOffset && providerInstance->NextOffset < buffSize);
-                byte* structBase = (byte*)providerInstance;
-                providerInstance = (Interop.Advapi32.TRACE_PROVIDER_INSTANCE_INFO*)&structBase[providerInstance->NextOffset];
             }
 #else
 #if !ES_BUILD_PCL && TARGET_WINDOWS  // TODO command arguments don't work on PCL builds...

diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.TryGetProperty.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.TryGetProperty.cs
@@ -140,6 +140,7 @@ private bool TryGetNamedPropertyValue(
             out JsonElement value)
         {
             ReadOnlySpan<byte> documentSpan = _utf8Json.Span;
+            Span<byte> utf8UnescapedStack = stackalloc byte[JsonConstants.StackallocThreshold];
 
             // Move to the row before the EndObject
             int index = endIndex - DbRow.Size;
@@ -184,8 +185,8 @@ private bool TryGetNamedPropertyValue(
 
                             try
                             {
-                                Span<byte> utf8Unescaped = remaining <= JsonConstants.StackallocThreshold ?
-                                    stackalloc byte[remaining] :
+                                Span<byte> utf8Unescaped = remaining <= utf8UnescapedStack.Length ?
+                                    utf8UnescapedStack :
                                     (rented = ArrayPool<byte>.Shared.Rent(remaining));
 
                                 // Only unescape the part we haven't processed.