Compilation error due to ExecutorService API change in JDK 19

[cushon]

Version

3b16da4

Bug description

Starting in JDK 19, ExecutorService implements AutoCloseable: openjdk/jdk@00e6c63#diff-139913957207a1eeaa338c35b269f2c566b358590ae62dd2a8063e98bb5b0456

This change causes a compilation error in mina-sshd.

Actual behavior

cd ~/sshd-common
mvn clean package -Djava.sdk.version=19
...
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.1:compile (default-compile) on project sshd-common: Compilation failure: Compilation failure:
[ERROR] /usr/local/google/home/cushon/src/mina-sshd/sshd-common/src/main/java/org/apache/sshd/common/util/threads/NoCloseExecutor.java:[43,8] org.apache.sshd.common.util.threads.NoCloseExecutor is not abstract and does not override abstract method close() in java.nio.channels.Channel
[ERROR] /usr/local/google/home/cushon/src/mina-sshd/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java:[29,8] types java.util.concurrent.ExecutorService and org.apache.sshd.common.Closeable are incompatible;
[ERROR]   interface org.apache.sshd.common.util.threads.CloseableExecutorService inherits unrelated defaults for close() from types java.util.concurrent.ExecutorService and org.apache.sshd.common.Closeable
[ERROR] /usr/local/google/home/cushon/src/mina-sshd/sshd-common/src/main/java/org/apache/sshd/common/util/threads/SshThreadPoolExecutor.java:[35,8] types org.apache.sshd.common.Closeable and java.util.concurrent.ExecutorService are incompatible;
[ERROR]   class org.apache.sshd.common.util.threads.SshThreadPoolExecutor inherits unrelated defaults for close() from types org.apache.sshd.common.Closeable and java.util.concurrent.ExecutorService
[ERROR] -> [Help 1]

Expected behavior

I expected the project to compile

Relevant log output

Apache Maven 3.8.6
Maven home: /usr/share/maven
Java version: 19.0.1, vendor: Oracle Corporation
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", arch: "amd64", family: "unix"

Other information

No response

[tomaswolf]

Ooof. An API break in the JDK that's not even mentioned in the change notes. (At least I didn't see it there.)

That's going to be "fun" to sort out. It's the kind of fun I could do without.

The immediate issue seems to be that org.apache.sshd.common.Closeable has a default method for close(), and now the ExecutorService also does. Additionally org.apache.sshd.common.Closeable wrongly extends java.nio.channels.Channel. Just having an isOpen() and a close() method doesn't make it a channel.

[cushon]

The CSR for the change (https://bugs.openjdk.org/browse/JDK-8285450) does at least acknowledge this could happen:

The introduced methods are in public classes and interfaces for which it is conceivable but highly unlikely that users have clashing existing methods in implementation classes or subclasses

Based on some testing I've been doing with 19 this problem does seem to be very rare.

[cushon]

I'm still seeing a compilation error:

$ mvn clean package -Djava.sdk.version=19
...
[ERROR] /usr/local/google/home/cushon/src/mina-sshd/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java:[37,18] close() in org.apache.sshd.common.util.threads.CloseableExecutorService clashes with close() in java.util.concurrent.ExecutorService
[ERROR]   overridden method does not throw java.io.IOException

One option might be to rethrow as UncheckedIOException to avoid the clash:

diff --git a/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java b/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java
index cc7a81b9..3f4bf77d 100644
--- a/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java
+++ b/sshd-common/src/main/java/org/apache/sshd/common/util/threads/CloseableExecutorService.java
@@ -20,6 +20,7 @@
 package org.apache.sshd.common.util.threads;

 import java.io.IOException;
+import java.io.UncheckedIOException;
 import java.time.Duration;
 import java.util.Objects;
 import java.util.concurrent.ExecutorService;
@@ -34,7 +35,11 @@ public interface CloseableExecutorService extends ExecutorService, Closeable {
     }

     @Override
-    default void close() throws IOException {
-        Closeable.super.close();
+    default void close() {
+        try {
+            Closeable.super.close();
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
     }
 }

[tomaswolf]

Want to provide a pull request?

[tomaswolf]

Thank you, Liam!