Bazel: Support building with Java 9

[davido]

Fixes: #4256.

Bazel@HEAD supports Java 9.

The current code has one single issue with Java 9 compliance: the usage
of sun.misc package. We add sun.misc module with --add-modules compiler
option for now. Long term, the usage of non poblic API should be
avoided.

To build (or test) with Java 9, build custom bazel version and issue:

$ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build
--javacopt='--release 9'
--java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9
:protobuf_java

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[davido]

@cushon

Unfortunately, it still doesn't work:

$ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 :protobuf_java
INFO: Analysed target //:protobuf_java (0 packages loaded).
INFO: Found 1 target...
ERROR: /home/davido/projects/davido_protobuf/BUILD:615:1: Building libprotobuf_java.jar (78 source files, 1 source jar) failed (Exit 1)
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:44: error: package sun.misc does not exist
  private static final sun.misc.Unsafe UNSAFE = getUnsafe();
                               ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:290: error: package sun.misc does not exist
  private static sun.misc.Unsafe getUnsafe() {
                         ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:427: error: package sun.misc does not exist
    sun.misc.Unsafe unsafe;
            ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:429: error: package sun.misc does not exist
    MemoryAccessor(sun.misc.Unsafe unsafe) {
                           ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:506: error: package sun.misc does not exist
    JvmMemoryAccessor(sun.misc.Unsafe unsafe) {
                              ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:291: error: package sun.misc does not exist
    sun.misc.Unsafe unsafe = null;
            ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:295: error: package sun.misc does not exist
              new PrivilegedExceptionAction<sun.misc.Unsafe>() {
                                                    ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:297: error: package sun.misc does not exist
                public sun.misc.Unsafe run() throws Exception {
                               ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:298: error: package sun.misc does not exist
                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                                ^
java/core/src/main/java/com/google/protobuf/UnsafeUtil.java:298: error: package sun.misc does not exist
                  Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class;
                                                     ^
Target //:protobuf_java failed to build
Use --verbose_failures to see the command lines of failed build steps.
INFO: Elapsed time: 3.871s, Critical Path: 3.68s
FAILED: Build did NOT complete successfully

Any clue, why passing: --add-modules=jdk.unsupported option has not fixed it?

[davido]

I wonder, if sun.misc.Unsafe can be replaced with https://github.com/jnr/jffi/blob/master/src/main/java/com/kenai/jffi/MemoryIO.java, to not mess around with internal/unsupported JDK API altogether. Another resource: https://blog.dripstat.com/removal-of-sun-misc-unsafe-a-disaster-in-the-making .

[davido]

Unfortunately, it still doesn't work: [...]

Never mind, I missed that --release 9 javacopt is now obligatory on Bazel@HEAD:

  $ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build --javacopt='--release 9' --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 :protobuf_java
.
INFO: Analysed target //:protobuf_java (10 packages loaded).
INFO: Found 1 target...
Target //:protobuf_java up-to-date:
  bazel-bin/libprotobuf_java.jar
INFO: Elapsed time: 17.899s, Critical Path: 12.86s
INFO: Build completed successfully, 3 total actions

I've updated the commit message correspondingly.

[xfxyjwf]

Can you add the jdk.unsupported flag but keep "-source 7" and "-target 7"? We don't want to introduce Java 8 or Java 9 only features regardless which javac is used.

[davido]

Done.

I removed explicit "-target 9" version, but --add-modules only works on java 9 release. That why to work on java 9, the Bazel mus be invoked like this:

  $ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build --javacopt='--release 9' --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 :protobuf_java

I added the command to the commit message.

But the good news is: this patch is backwards compatible. It still works, on Java 7,8,9 and uses "-source 7", "-target 7" option, if the user doesn't switch to java 9 toolcain.

[xfxyjwf]

Thanks! I'll merge after the tests pass.

[davido]

Thanks! I'll merge after the tests pass.

Thanks. Would you mind to create a new release in the next days?

[davido]

I only improved the commit message a bit in the latest push.