Add structured-concurrency-final module: StructuredTaskScope final in JDK 28 (JEP 543), run on 28-ea, 27, 26 and 25

Runnable demos for the ankurm.com structured-concurrency-java article: the ExecutorService thread leak and its fix, every built-in Joiner, structure violations, timeouts, a custom Joiner, JSON thread dumps (in-process and jcmd), scoped values, javap diffs of the API on 25, 26, 27 and 28-ea, compiler output for six pieces of 25/26-era code, and the preview class-file trap between 27 and 28. Transcripts in output/. Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01CifR2BE7PBvRy5hT8TS9oz
2026-10-26 02:01:31 +00:00
parent 2e25042a68
commit c93a1fffbb
37 changed files with 1351 additions and 0 deletions
@@ -0,0 +1,53 @@
+import com.sun.management.HotSpotDiagnosticMXBean;
+import java.lang.management.ManagementFactory;
+import java.nio.file.*;
+import java.util.concurrent.*;
+import java.util.concurrent.StructuredTaskScope.Joiner;
+
+/** The thread dump shows the scope as a container, its owner, and the threads forked in it. */
+public class ThreadDump {
+    public static void main(String[] args) throws Exception {
+        if (args.length > 0 && args[0].equals("hold")) {      // used by run.sh: hold nested scopes open so jcmd can dump them
+            try (var scope = StructuredTaskScope.open(Joiner.<String>awaitAllSuccessfulOrThrow(), cf -> cf.withName("orders"))) {
+                scope.fork(() -> { Thread.sleep(6000); return "A"; });
+                scope.fork(() -> {                                 // subtask B opens a child scope of its own
+                    try (var child = StructuredTaskScope.open(Joiner.<String>awaitAllSuccessfulOrThrow(), cf -> cf.withName("inventory"))) {
+                        child.fork(() -> { Thread.sleep(6000); return "B1"; });
+                        child.join();
+                    }
+                    return "B";
+                });
+                scope.join();
+            }
+            return;
+        }
+        Path file = Files.createTempFile("dump", ".json"); Files.delete(file);
+        try (var scope = StructuredTaskScope.open(Joiner.<String>awaitAllSuccessfulOrThrow(), cf -> cf.withName("orders"))) {
+            for (int i = 0; i < 2; i++) {
+                int n = i;
+                scope.fork(() -> { Thread.sleep(1500); return "task-" + n; });
+            }
+            Thread.sleep(300);        // let the subtasks start and block
+            ManagementFactory.getPlatformMXBean(HotSpotDiagnosticMXBean.class)
+                .dumpThreads(file.toString(), HotSpotDiagnosticMXBean.ThreadDumpFormat.JSON);
+            scope.join();
+        }
+        String json = Files.readString(file);
+        int at = json.indexOf("\"container\": \"orders");
+        int start = json.lastIndexOf('{', at);
+        int end = json.indexOf("\"threadCount\"", at);
+        String block = json.substring(start, end);
+        // identity hashes, thread ids and timestamps change between runs: mask them so the transcript is stable
+        block = block.replaceAll("@[0-9a-f]+", "@<hash>").replaceAll("\"tid\": \\d+", "\"tid\": <n>").replaceAll("\"owner\": \\d+", "\"owner\": <n>");
+        // keep the lines that show the hierarchy: the scope, its parent and owner, and each forked thread with its own frame
+        for (String line : block.split("\n")) {
+            String l = line.trim();
+            if (l.startsWith("\"container\"") || l.startsWith("\"parent\"") || l.startsWith("\"owner\"")
+                    || l.startsWith("\"tid\"") || l.startsWith("\"virtual\"") || l.startsWith("\"state\"")
+                    || l.contains("ThreadDump.lambda")) {
+                System.out.println(l);
+            }
+        }
+        Files.deleteIfExists(file);
+    }
+}