Motivation:
In #10630, field substitutions were introduced for NetUtil.LOCALHOST4, NetUtil.LOCALHOST6 and NetUtil.LOCALHOST fields. They were required to allow a native image be built with most of Netty (including NetUtil) initialized at build time.
The substitutions created in #10630 only define getters, so the 3 fields can only be read in a native image.
But when NetUtil is initialized at run-time (this is what happens in #10797), its static initialization block is executed, and this block writes to all 3 fields. As the substitutions do not provide any setters, field stores are not valid, and such builds fail.
Modifications:
- Add netty-testsuite-native-image-client-runtime-init Maven module that builds a native image deferring NetUtil class initialization till run-time; this module is used to demonstrate the problem and verify the problem is gone with the fix
- Add no-op setters to substitutions for NetUtil.LOCALHOST4, NetUtil.LOCALHOST6 and NetUtil.LOCALHOST
Result:
A native image initializing NetUtil at run-time builds successfully.
Fixes#10797
Motivation:
Since GraalVM version 19.3.0, instances of java.net.InetAddress (and its subclasses Inet4Address and Inet6Address) are not allowed in native image heap (that is, they cannot be stored in static fields of classes initialized at build time or be reachable through static fields of such classes). When building a native image, it makes sense to initialize at build time as many classes as possible.
But some fields of some classes in Netty (for example, NetUtil.LOCALHOST4) contain InetAddress instances. If a program is using code path that makes it possible to reach such fields at build time initialization, it becomes impossible to build a native image initializing core Netty classes initialized at runtime. An example of such a program is a client that uses netty-dns.
Modifications:
- Add netty-testsuite-native-image-client Maven module to test that such an example program can be built after the corresponding fixes
- Add native-image.properties to resolver-dns module to move initialization of some classes to runtime (some of them are parsing configuration during initialization, so it makes no sense to initialize them at build time; for others, it's needed to avoid InetAddress reachability at build time)
- Add substitutions for NetUtil.LOCALHOST4, NetUtil.LOCALHOST6 and NetUtil.LOCALHOST to overcome the InetAddress-related prohibition
- Extract some initialization code from NetUtil to NetUtilInitializations to allow it to be used by the substitutions
Result:
A client program using netty-dns with --initialize-at-build-time=io.netty builds successfully
