Env var to debug child processes. (#5305)

* adds env var to specify a port to wait for a debugger to connect to so child processes can be debugged in acceptance tests

---------

Signed-off-by: Justin Florentine <justin+github@florentine.us>

acceptance-tests/dsl/src/main/java/org/hyperledger/besu/tests/acceptance/dsl/node/ProcessBesuNodeRunner.java

@@ -421,6 +421,24 @@ public class ProcessBesuNodeRunner implements BesuNodeRunner {
                 + "acceptance-tests/tests/build/resources/test/acceptanceTesting.security");
     // add additional environment variables
     processBuilder.environment().putAll(node.getEnvironment());
+
+    try {
+      int debugPort = Integer.parseInt(System.getenv("BESU_DEBUG_CHILD_PROCESS_PORT"));
+      LOG.warn("Waiting for debugger to attach to SUSPENDED child process");
+      String debugOpts =
+          " -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=*:" + debugPort;
+      String prevJavaOpts = processBuilder.environment().get("JAVA_OPTS");
+      if (prevJavaOpts == null) {
+        processBuilder.environment().put("JAVA_OPTS", debugOpts);
+      } else {
+        processBuilder.environment().put("JAVA_OPTS", prevJavaOpts + debugOpts);
+      }
+
+    } catch (NumberFormatException e) {
+      LOG.debug(
+          "Child process may be attached to by exporting BESU_DEBUG_CHILD_PROCESS_PORT=<port> to env");
+    }
+
     try {
       checkState(
           isNotAliveOrphan(node.getName()),