diff --git a/changelog/@unreleased/pr-309.v2.yml b/changelog/@unreleased/pr-309.v2.yml
new file mode 100644
index 0000000..7dff707
--- /dev/null
+++ b/changelog/@unreleased/pr-309.v2.yml
@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+ description: Implement DnsCacheTtl accessors
+ links:
+ - https://github.com/palantir/jvm-diagnostics/pull/309
diff --git a/jvm-diagnostics/build.gradle b/jvm-diagnostics/build.gradle
index 97005f0..289eca7 100644
--- a/jvm-diagnostics/build.gradle
+++ b/jvm-diagnostics/build.gradle
@@ -10,5 +10,8 @@ dependencies {
}
moduleJvmArgs {
- exports 'java.management/sun.management', 'java.base/jdk.internal.platform'
+ exports 'java.management/sun.management',
+ 'java.base/jdk.internal.platform',
+ // Required for access to 'sun.net.InetAddressCachePolicy' for DNS cache TTL
+ 'java.base/sun.net'
}
diff --git a/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/DnsCacheTtlAccessor.java b/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/DnsCacheTtlAccessor.java
new file mode 100644
index 0000000..281e811
--- /dev/null
+++ b/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/DnsCacheTtlAccessor.java
@@ -0,0 +1,33 @@
+/*
+ * (c) Copyright 2022 Palantir Technologies Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.palantir.jvm.diagnostics;
+
+public interface DnsCacheTtlAccessor {
+
+ /** Returns the number of seconds successful DNS results are cached before making another DNS request. */
+ int getPositiveSeconds();
+
+ /** Returns the number of seconds unsuccessful DNS results are cached before making another DNS request. */
+ int getNegativeSeconds();
+
+ /**
+ * The amount of time a previously successful DNS result will be used beyond {@link #getPositiveSeconds()} if
+ * subsequent DNS requests for the same hostname fail.
+ * Introduced in Java 21 by JDK-8306653.
+ */
+ int getStaleSeconds();
+}
diff --git a/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/JvmDiagnostics.java b/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/JvmDiagnostics.java
index 7b4382a..f0bcf07 100644
--- a/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/JvmDiagnostics.java
+++ b/jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/JvmDiagnostics.java
@@ -16,8 +16,10 @@
package com.palantir.jvm.diagnostics;
+import java.lang.reflect.Method;
import java.util.Optional;
import java.util.OptionalLong;
+import java.util.function.IntSupplier;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@@ -122,6 +124,20 @@ public static Optional cpuShares() {
}
}
+ /**
+ * Returns a {@link HotspotDnsCacheTtlAccessor}. This functionality is not supported on all java runtimes,
+ * and an {@link Optional#empty()} is returned in cases TTL information is not accessible.
+ */
+ public static Optional dnsCacheTtl() {
+ try {
+ HotspotDnsCacheTtlAccessor accessor = new HotspotDnsCacheTtlAccessor();
+ return accessor.isEnabled() ? Optional.of(accessor) : Optional.empty();
+ } catch (Throwable t) {
+ log.debug("Failed to create a HotspotDnsCacheTtlAccessor", t);
+ return Optional.empty();
+ }
+ }
+
private JvmDiagnostics() {}
private static final class HotspotSafepointTimeAccessor implements SafepointTimeAccessor {
@@ -209,4 +225,54 @@ public OptionalLong getCpuShares() {
return OptionalLong.of(result);
}
}
+
+ private static final class HotspotDnsCacheTtlAccessor implements DnsCacheTtlAccessor {
+
+ boolean isEnabled() {
+ try {
+ // Ensure invocations succeed. If sufficient exports aren't present, this will throw.
+ getPositiveSeconds();
+ return true;
+ } catch (Throwable t) {
+ return false;
+ }
+ }
+
+ private final IntSupplier staleAccessor = createStaleAccessor();
+
+ private static IntSupplier createStaleAccessor() {
+ if (Runtime.version().feature() >= 21) {
+ // Introduced in Java 21 by https://bugs.openjdk.org/browse/JDK-8306653
+ try {
+ Method getStale = sun.net.InetAddressCachePolicy.class.getMethod("getStale");
+ return () -> {
+ try {
+ return (Integer) getStale.invoke(null);
+ } catch (ReflectiveOperationException roe) {
+ log.debug("Failed to load stale InetAddressCachePolicy", roe);
+ return 0;
+ }
+ };
+ } catch (ReflectiveOperationException roe) {
+ log.debug("Failed to load stale InetAddressCachePolicy", roe);
+ }
+ }
+ return () -> 0;
+ }
+
+ @Override
+ public int getPositiveSeconds() {
+ return sun.net.InetAddressCachePolicy.get();
+ }
+
+ @Override
+ public int getNegativeSeconds() {
+ return sun.net.InetAddressCachePolicy.getNegative();
+ }
+
+ @Override
+ public int getStaleSeconds() {
+ return staleAccessor.getAsInt();
+ }
+ }
}
diff --git a/jvm-diagnostics/src/test/java/com/palantir/jvm/diagnostics/JvmDiagnosticsTest.java b/jvm-diagnostics/src/test/java/com/palantir/jvm/diagnostics/JvmDiagnosticsTest.java
index 4c2f145..02b1829 100644
--- a/jvm-diagnostics/src/test/java/com/palantir/jvm/diagnostics/JvmDiagnosticsTest.java
+++ b/jvm-diagnostics/src/test/java/com/palantir/jvm/diagnostics/JvmDiagnosticsTest.java
@@ -51,4 +51,11 @@ void testThreadUserTime() {
.getUserTimeNanoseconds(Thread.currentThread().getId()))
.isGreaterThan(0L);
}
+
+ @Test
+ void testDnsCacheTtl() {
+ assertThat(JvmDiagnostics.dnsCacheTtl().get().getPositiveSeconds()).isEqualTo(30);
+ assertThat(JvmDiagnostics.dnsCacheTtl().get().getNegativeSeconds()).isEqualTo(10);
+ assertThat(JvmDiagnostics.dnsCacheTtl().get().getStaleSeconds()).isEqualTo(0);
+ }
}