From 61e0abceb9a7816b8f1f301aa1462351e8d46983 Mon Sep 17 00:00:00 2001
From: James Crosswell <jamescrosswell@users.noreply.github.com>
Date: Wed, 7 Oct 2026 16:20:51 +1300
Subject: [PATCH] perf: counting discarded telemetry for client reports no
 longer allocates

ThreadsafeCounterDictionary.Add and Increment passed a new CounterItem to
GetOrAdd, allocating 24 B on every call even when the counter already
existed. Use the factory overload so the item is only created for a new key.

Closes #5686

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../Internal/ThreadsafeCounterDictionary.cs   |  4 ++--
 .../ThreadsafeCounterDictionaryTests.cs       | 19 +++++++++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/Sentry/Internal/ThreadsafeCounterDictionary.cs b/src/Sentry/Internal/ThreadsafeCounterDictionary.cs
index 0265fba7b6..0f10e6a244 100644
--- a/src/Sentry/Internal/ThreadsafeCounterDictionary.cs
+++ b/src/Sentry/Internal/ThreadsafeCounterDictionary.cs
@@ -24,13 +24,13 @@ private class CounterItem
     /// </summary>
     /// <param name="key">The key of the counter to increment.</param>
     /// <param name="quantity">The amount to add to the counter.</param>
-    public void Add(TKey key, int quantity) => _items.GetOrAdd(key, new CounterItem()).Add(quantity);
+    public void Add(TKey key, int quantity) => _items.GetOrAdd(key, static _ => new CounterItem()).Add(quantity);
 
     /// <summary>
     /// Atomically increments a counter based on the key provided, creating the counter if necessary.
     /// </summary>
     /// <param name="key">The key of the counter to increment.</param>
-    public void Increment(TKey key) => _items.GetOrAdd(key, new CounterItem()).Increment();
+    public void Increment(TKey key) => _items.GetOrAdd(key, static _ => new CounterItem()).Increment();
 
     /// <summary>
     /// Gets a single counter's value while atomically resetting it to zero.
diff --git a/test/Sentry.Tests/Internals/ThreadsafeCounterDictionaryTests.cs b/test/Sentry.Tests/Internals/ThreadsafeCounterDictionaryTests.cs
index fec7004088..09735f9940 100644
--- a/test/Sentry.Tests/Internals/ThreadsafeCounterDictionaryTests.cs
+++ b/test/Sentry.Tests/Internals/ThreadsafeCounterDictionaryTests.cs
@@ -275,4 +275,23 @@ void ReadAndAddToGrandTotal()
         const int expectedGrandTotal = numCounters * numThreadsPerCounter * numIterationsPerThread;
         Assert.Equal(expectedGrandTotal, grandTotal);
     }
+
+#if NET5_0_OR_GREATER && !__MOBILE__
+    [Fact]
+    public void AddAndIncrement_ExistingCounter_DoNotAllocate()
+    {
+        var key = DiscardReason.CallbackError.WithCategory(DataCategory.LogItem);
+        var counters = new ThreadsafeCounterDictionary<DiscardReasonWithCategory>();
+        counters.Add(key, 1);
+        counters.Increment(key);
+
+        var before = GC.GetAllocatedBytesForCurrentThread();
+        counters.Add(key, 1);
+        counters.Increment(key);
+        var allocated = GC.GetAllocatedBytesForCurrentThread() - before;
+
+        Assert.Equal(0, allocated);
+        Assert.Equal(4, counters[key]);
+    }
+#endif
 }