Use modern Logback for Java 21+ tests with better Virtual Threads support.

dd-java-agent/instrumentation/java/java-concurrent/java-concurrent-21.0/build.gradle

@@ -1,6 +1,4 @@
 apply from: "$rootDir/gradle/java.gradle"
-// Use slf4j-simple as default; logback has a high chance of getting stuck in a deadlock on CI.
-apply from: "$rootDir/gradle/slf4j-simple.gradle"
 apply plugin: 'idea'
 
 testJvmConstraints {
@@ -49,6 +47,13 @@ tasks.named("check") {
   dependsOn "previewTest"
 }
 
+// Use latest logback for Java 21+ tests with better virtual thread support.
+configurations.named("testRuntimeClasspath") {
+  resolutionStrategy {
+    force libs.logback.classic.latest
+  }
+}
+
 dependencies {
   testImplementation project(':dd-java-agent:instrumentation:datadog:tracing:trace-annotation')
 }

dd-java-agent/instrumentation/java/java-concurrent/java-concurrent-25.0/build.gradle

@@ -1,7 +1,24 @@
+plugins {
+  id 'idea'
+}
+
 apply from: "$rootDir/gradle/java.gradle"
 
 muzzle {
   pass {
     coreJdk('25')
   }
 }
+
+idea {
+  module {
+    jdkName = '25'
+  }
+}
+
+// Use latest logback for Java 21+ tests with better virtual thread support.
+configurations.named("testRuntimeClasspath") {
+  resolutionStrategy {
+    force libs.logback.classic.latest
+  }
+}

dd-java-agent/instrumentation/java/java-lang/java-lang-21.0/build.gradle

@@ -3,8 +3,6 @@ plugins {
 }
 
 apply from: "$rootDir/gradle/java.gradle"
-// Use slf4j-simple as default; logback has a high chance of getting stuck in a deadlock on CI.
-apply from: "$rootDir/gradle/slf4j-simple.gradle"
 
 testJvmConstraints {
   minJavaVersion = JavaVersion.VERSION_21
@@ -30,3 +28,11 @@ tasks.named("compileTestJava", JavaCompile) {
 dependencies {
   testImplementation project(':dd-java-agent:instrumentation:datadog:tracing:trace-annotation')
 }
+
+// Use latest logback for Java 21+ tests with better virtual thread support.
+configurations.named("testRuntimeClasspath") {
+  resolutionStrategy {
+    force libs.logback.classic.latest
+  }
+}
+

gradle/libs.versions.toml

@@ -57,6 +57,7 @@ lz4 = "1.7.1"
 # Logging
 slf4j = "1.7.30"
 logback = "1.2.13"
+logback-latest = "1.5.27"
 
 # JSON
 jackson = "2.20.0"
@@ -134,6 +135,7 @@ lz4 = { module = "org.lz4:lz4-java", version.ref = "lz4" }
 
 # Logging
 logback-classic = { module = "ch.qos.logback:logback-classic", version.ref = "logback" }
+logback-classic-latest = { module = "ch.qos.logback:logback-classic", version.ref = "logback-latest" }
 logback-core = { module = "ch.qos.logback:logback-core", version.ref = "logback" }
 log4j-over-slf4j = { module = "org.slf4j:log4j-over-slf4j", version.ref = "slf4j" }
 jcl-over-slf4j = { module = "org.slf4j:jcl-over-slf4j", version.ref = "slf4j" }