test: add failing spec for JDK HttpClient thread leak

Author: naborka

http-client-jdk/src/test/groovy/io/micronaut/http/client/jdk/JdkBlockingHttpClientThreadLeakSpec.groovy

@@ -0,0 +1,60 @@
+package io.micronaut.http.client.jdk
+
+import io.micronaut.context.ApplicationContext
+import io.micronaut.context.annotation.Requires
+import io.micronaut.http.annotation.Controller
+import io.micronaut.http.annotation.Get
+import io.micronaut.http.client.annotation.Client
+import io.micronaut.runtime.server.EmbeddedServer
+import spock.lang.AutoCleanup
+import spock.lang.Shared
+import spock.lang.Specification
+
+import java.util.regex.Pattern
+
+class JdkBlockingHttpClientThreadLeakSpec extends Specification {
+
+    private static final Pattern JDK_HTTP_CLIENT_SELECTOR = Pattern.compile(/HttpClient-\d+-SelectorManager/)
+
+    @Shared @AutoCleanup
+    EmbeddedServer server = ApplicationContext.run(EmbeddedServer, [
+        'spec.name': 'JdkBlockingHttpClientThreadLeakSpec'
+    ])
+
+    @Shared @AutoCleanup
+    ApplicationContext clientCtx = ApplicationContext.run([
+        'spec.name': 'JdkBlockingHttpClientThreadLeakSpec',
+        'micronaut.http.services.leakspec.url': server.URL.toString()
+    ])
+
+    def "synchronous declarative @Client does not spawn a new JDK HttpClient per call"() {
+        given:
+        LeakClient client = clientCtx.getBean(LeakClient)
+        int baseline = countSelectorThreads()
+
+        when:
+        500.times { client.ping() }
+
+        then: 'thread count is measured immediately, before GC can reap leaked clients'
+        int after = countSelectorThreads()
+        (after - baseline) <= 1
+    }
+
+    private static int countSelectorThreads() {
+        Thread.getAllStackTraces().keySet().count { JDK_HTTP_CLIENT_SELECTOR.matcher(it.name).matches() } as int
+    }
+
+    @Requires(property = 'spec.name', value = 'JdkBlockingHttpClientThreadLeakSpec')
+    @Client('leakspec')
+    static interface LeakClient {
+        @Get('/leak/ping')
+        String ping()
+    }
+
+    @Requires(property = 'spec.name', value = 'JdkBlockingHttpClientThreadLeakSpec')
+    @Controller('/leak')
+    static class LeakController {
+        @Get('/ping')
+        String ping() { 'pong' }
+    }
+}