use better hash function for better distribution in IoBuffer g_MappingLocks (#370)

* use better hash function for better distribution in IoBuffer g_MappingLocks
* changelog

2 files changed, 11 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 50535d9bf..b55b37448 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@
 - Improvement: Windows: Cache process handles for FormatPackageMessage reducing function execution time from 100+us to ~1 us
 - Improvement: Skip upstream logic early if we have no upstream endpoints
 - Improvement: Cachestore logging of CbObjects are now async
+- Improvement: Use better hashing algorithm for instance pointers when using shared lock in IoBufferExtendedCore::Materialize
 - Improvement: Use tsl/robin-map/robin-set in compactcas and projectstore for 30% faster GC
 
 ## 0.2.16
diff --git a/src/zencore/iobuffer.cpp b/src/zencore/iobuffer.cpp
index f53d80778..22bc61395 100644
--- a/src/zencore/iobuffer.cpp
+++ b/src/zencore/iobuffer.cpp
@@ -249,11 +249,20 @@ static_assert(IsPow2(MappingLockCount), "MappingLockCount must be power of two")
 
 static RwLock g_MappingLocks[MappingLockCount];
 
+static uint64_t
+HashPtr64(uint64_t x)
+{
+	x = (x ^ (x >> 30)) * UINT64_C(0xbf58476d1ce4e5b9);
+	x = (x ^ (x >> 27)) * UINT64_C(0x94d049bb133111eb);
+	x = x ^ (x >> 31);
+	return x;
+}
+
 static RwLock&
 MappingLockForInstance(const IoBufferExtendedCore* instance)
 {
 	intptr_t base		= (intptr_t)instance;
-	size_t	 lock_index = ((base >> 5) ^ (base >> 13)) & (MappingLockCount - 1u);
+	uint32_t lock_index = uint32_t(HashPtr64(uint64_t(base)) & (MappingLockCount - 1u));
 	return g_MappingLocks[lock_index];
 }