When encountering the error message "The forked VM terminated without saying properly goodbye. VM crash or System.exit called", developers are usually dealing with issues related to Maven-based Java projects where tests are executed in a separate VM forked from the main Maven process. This error generally points to an abrupt termination of the Virtual Machine (VM), caused either by a system crash, an unexpected error, or explicit termination command (System.exit) during the execution of Java tests or applications.

Understanding the Forked VM and Its Operations

In Maven projects, particularly when using plugins like Surefire or Failsafe, tests are often executed in a forked VM. This means Maven starts a new, separate virtual machine for executing tests to isolate them from the main build process. This approach has advantages such as preventing potential influences of test code on the Maven build and providing a clean environment for each test execution group.

Common Causes of "VM terminated without saying properly goodbye"

1. Explicit Calls to System.exit: If the test or any libraries used within invoked a System.exit, it would lead to an immediate termination of the JVM, thereby leading to this error. Usage of such commands in test environments is generally discouraged unless one is testing the system's response to such scenarios.
2. Unhandled Exceptions: An unhandled exception thrown during the test execution could cause the JVM to crash, leading to termination without proper closure. This might also be accompanied by other error logs which can give insights into what went wrong.
3. Out of Memory Error: Java applications require a certain amount of memory space, and if the forked VM is not allocated enough memory, an OutOfMemoryError may occur, potentially causing the JVM to crash.
4. JNI or Native Code Issues: Java Native Interface (JNI) or native libraries can cause issues if there are bugs in the native code or if the native code interacts unexpectedly with the JVM.
5. Concurrency Issues: Race conditions or deadlocks in multithreaded applications can lead the system into an unresponsive state, causing abrupt termination.

Diagnosis and Solutions

To diagnose and resolve the issue of the forked VM terminating abruptly, consider the following steps:

1. Review Test Code and Libraries: Check if any part of your codebase, including third-party libraries, calls System.exit. This should be removed or mocked during testing.
2. Increase Memory Allocation: Adjust the memory settings for Maven-Surefire or Failsafe plugin in your pom.xml to ensure that the forked VM has enough memory to perform its tasks.
3. Catch and Log Exceptions: Ensure all exceptions are properly caught and logged. This not only prevents unexpected exits but also helps in diagnosing issues through log analysis.
4. Examine Native Code: If using JNI or other native code, investigate any potential issues or compatibility problems with the JVM.
5. Check for Concurrency Issues: Try to identify and fix any potential concurrency problems in multithreaded tests.
6. Analyze Crash Logs: If a JVM crash is suspected, look for hs_err_pid logs, which Java generates in event of a crash. It can provide valuable insights into what caused the JVM to terminate.

Summary Table

Ultimately, the message "The forked VM terminated without saying properly goodbye" is indicative of deeper issues that need to be resolved to ensure reliable and robust test execution in a Maven-based Java environment. By methodically addressing each potential cause, one can significantly reduce the frequency of such errors.