Java exit a program without quitting JVM

Question

I want to exit a java process and free all the resources before it finishes its normal running, if a certain condition is meet. I dont however want to quit JVM, as I have other java programs running at the same time. Does return; do the above, or is there a better way to do it?

Thanks.

Answer 1

There is one JVM process per running Java application. If you exit that application, the process's JVM gets shut down. However, this does not affect other Java processes.

Answer 2

You need to understand the JVM mechanism and clarify the terminology.

Let's use the following as datum for the terminology.

• Threads are divisions of concurrently processed flows within a process.

• A process is an OS level thread. The OS manages the processes. A process is terminated by sending a termination signal to the OS management. The signal may be sent by the process itself or by another process that has the applicable privilege.

• Within a process, you can create process level threads. Process level threads are normally facilitated by the process management of the OS, but they are initiated by the process and terminated by the process. Therefore, process level threads are not the same as processes.

• An application is a collection of systems, programs and/or threads that cooperate in various forms. A program or process within an application may terminate without terminating the whole application.

Within the context of JVM terminology, program may be one of the following.

• A program is run per JVM process. Each program consumes one JVM process and is invoked by supplying the classpath of java bytecode and specifying the main entry point found in the classpath. When you terminate a java program, the whole jvm process that ran that program also terminates.

• A program is run per process level thread. For example, an application run within a tomcat or JEE server is run as a thread within the JEE process. The JEE process is itself a program consuming one JVM process. When you terminate an application program, the JEE process does not terminate.

You may initiate process level threads within a java program. You may write code that terminates a thread but that would not terminate the process (unless it is the last and only running thread in the process). The JVM garbage collection would take care of freeing of resources and you do not need to free resources yourself after a process level thread is terminated.

The above response is simplified for comprehension. Please read up on OS design and threading to facilitate a better understanding of processes and the JVM mechanism.