memory: allow concurrent backing reads

src/kernel/memory.cpp

@@ -21,6 +21,7 @@
 #include <map>
 #include <memory>
 #include <mutex>
+#include <shared_mutex>
 #include <vector>
 
 #if KYTY_PLATFORM == KYTY_PLATFORM_WINDOWS
@@ -168,6 +169,7 @@ static bool VirtualRangesOverlap(uint64_t left_start, uint64_t left_size, uint64
 #if defined(KYTY_VIRTUAL_MEMORY_ALLOCATION_TESTS)
 static uint32_t        g_test_backing_store_unmaps_before_failure = UINT32_MAX;
 static callback_func_t g_test_before_backing_map                   = nullptr;
+static callback_func_t g_test_backing_read                         = nullptr;
 #endif
 
 #include "memoryAddressSpace.inc"
@@ -3569,6 +3571,10 @@ void TestBeforeNextBackingMap(callback_func_t callback) {
 	g_test_before_backing_map = callback;
 }
 
+void TestSetBackingReadCallback(callback_func_t callback) {
+	g_test_backing_read = callback;
+}
+
 void TestFailNextPhysicalMemoryUnmap() {
 	TestFailPhysicalMemoryUnmapAfter(0);
 }