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Handle UnsupportedClassVersionError in ServiceLoader on jdk9 #7090

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merged 1 commit into from
Nov 8, 2022
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Handle UnsupportedClassVersionError in ServiceLoader on jdk9 #7090

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50 changes: 44 additions & 6 deletions javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/SafeServiceLoader.java
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Original file line number Diff line number Diff line change
Expand Up @@ -32,12 +32,11 @@ public final class SafeServiceLoader {
@SuppressWarnings("ForEachIterable")
public static <T> List<T> load(Class<T> serviceClass) {
List<T> result = new ArrayList<>();
java.util.ServiceLoader<T> services = ServiceLoader.load(serviceClass);
for (Iterator<T> iter = services.iterator(); iter.hasNext(); ) {
try {
result.add(iter.next());
} catch (UnsupportedClassVersionError e) {
logger.log(FINE, "Unable to load instrumentation class: {0}", e.getMessage());
ServiceLoader<T> services = ServiceLoader.load(serviceClass);
for (Iterator<T> iterator = new SafeIterator<>(services.iterator()); iterator.hasNext(); ) {
T service = iterator.next();
if (service != null) {
result.add(service);
}
}
return result;
Expand All @@ -54,4 +53,43 @@ public static <T extends Ordered> List<T> loadOrdered(Class<T> serviceClass) {
}

private SafeServiceLoader() {}

private static class SafeIterator<T> implements Iterator<T> {
private final Iterator<T> delegate;

SafeIterator(Iterator<T> iterator) {
delegate = iterator;
}

private static void handleUnsupportedClassVersionError(
UnsupportedClassVersionError unsupportedClassVersionError) {
logger.log(
FINE,
"Unable to load instrumentation class: {0}",
unsupportedClassVersionError.getMessage());
}

@Override
public boolean hasNext() {
// jdk9 and newer throw UnsupportedClassVersionError in hasNext()
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oh interesting, so we would have run into this problem on Java 11 if we introduced Java 17-only instrumentation

do you know if the underlying iterator will move on item hasNext when it throws exception, so that we will continue iterating over it from that point?

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I tested it manually and believe that hasNext will move to the next element on exception. Relevant code is in
https://github.com/openjdk/jdk11u/blob/b928a88fd564fab88f00086a62c0695ed5cc9353/src/java.base/share/classes/java/util/ServiceLoader.java#L1181 pending iterator is advanced before Class.forName

while (true) {
try {
return delegate.hasNext();
} catch (UnsupportedClassVersionError unsupportedClassVersionError) {
handleUnsupportedClassVersionError(unsupportedClassVersionError);
}
}
}

@Override
public T next() {
// jdk8 throws UnsupportedClassVersionError in next()
try {
return delegate.next();
} catch (UnsupportedClassVersionError unsupportedClassVersionError) {
handleUnsupportedClassVersionError(unsupportedClassVersionError);
return null;
}
}
}
}