Add debug logging when diagnostics cannot be loaded (#12)

changelog/@unreleased/pr-12.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: Add debug logging when diagnostics cannot be loaded
+  links:
+  - https://github.com/palantir/jvm-diagnostics/pull/12

jvm-diagnostics/build.gradle

@@ -1,7 +1,9 @@
 apply from: "$rootDir/gradle/publish-jar.gradle"
 
 dependencies {
-    // No main dependencies
+    // Minimal main dependencies
+    implementation 'org.slf4j:slf4j-api'
+
     testImplementation 'org.junit.jupiter:junit-jupiter'
     testImplementation 'org.assertj:assertj-core'
-}
+}

jvm-diagnostics/src/main/java/com/palantir/jvm/diagnostics/JvmDiagnostics.java

@@ -17,6 +17,8 @@
 package com.palantir.jvm.diagnostics;
 
 import java.util.Optional;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * This utility class provides accessors to individual diagnostic getters. Every method should
@@ -25,20 +27,27 @@
  */
 public final class JvmDiagnostics {
 
+    private static final Logger log = LoggerFactory.getLogger(JvmDiagnostics.class);
+
     /**
      * Returns an {@link SafepointTimeAccessor} which provides safepoint information. This functionality
      * is not supported on all java runtimes, and an {@link Optional#empty()} is returned in cases
      * safepoint data is unavailable.
      *
      * The resulting instance should be reused rather than calling this factory each time a
      * value is needed.
+     *
+     * Currently this supports up to java 16 assuming {@code --illegal-access=deny} is not used, and java 17+
+     * only when the {@code --illegal-access=permit} paramter is provided. Once a safe, suitable replacement is
+     * found, we will likely use a multi-release jar to leverage the new functionality.
      */
     public static Optional<SafepointTimeAccessor> totalSafepointTime() {
         try {
             // Classes used by HotspotSafepointTimeAccessor are not guaranteed to exist at runtime on all JREs
             // so we must fail gracefully.
             return Optional.of(new HotspotSafepointTimeAccessor());
         } catch (Throwable t) {
+            log.debug("Failed to create a HotspotSafepointTimeAccessor", t);
             return Optional.empty();
         }
     }

versions.lock

@@ -1,4 +1,5 @@
 # Run ./gradlew --write-locks to regenerate this file
+org.slf4j:slf4j-api:1.7.30 (1 constraints: 3d05453b)
 
 [Test dependencies]
 org.apiguardian:apiguardian-api:1.1.0 (5 constraints: 0654a8a8)

versions.props

@@ -1,2 +1,3 @@
+org.slf4j:* = 1.7.30
 org.junit.jupiter:* = 5.7.1
 org.assertj:assertj-core = 3.19.0