Add store-store fence when writing to possibly shared symbol cache

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/capi/CApiContext.java

@@ -48,6 +48,7 @@
 
 import java.io.IOException;
 import java.io.PrintStream;
+import java.lang.invoke.VarHandle;
 import java.nio.file.LinkOption;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -469,7 +470,9 @@ private static Object lookupNativeSymbol(Object[] nativeSymbolCache, NativeCAPIS
         String name = symbol.getName();
         try {
             Object nativeSymbol = InteropLibrary.getUncached().readMember(PythonContext.get(null).getCApiContext().getLLVMLibrary(), name);
-            return nativeSymbolCache[symbol.ordinal()] = CExtContext.ensureExecutable(nativeSymbol, symbol);
+            nativeSymbol = CExtContext.ensureExecutable(nativeSymbol, symbol);
+            VarHandle.storeStoreFence();
+            return nativeSymbolCache[symbol.ordinal()] = nativeSymbol;
         } catch (UnsupportedMessageException | UnknownIdentifierException e) {
             throw CompilerDirectives.shouldNotReachHere(e);
         }