Before you delve into the fundamentals of Web applications, you need to understand the concept of Micro Focus run units and sessions.
Many COBOL applications are single-user programs, so adapting these programs into a multi-user Java environment can be problematic. You may experience a problem such as file locking or memory isolation breaking down because the same resource set is being used by many users. Often, fixing this contention requires a significant rewriting of code.
Micro Focus solves this with a construct called a run unit, and is specified by the JVM COBOL runtime class com.microfocus.cobol.runtimeservices.RunUnit. Each run unit is a new session object, and contains its own memory space and file lock table. A JVM COBOL program in one run unit will not normally access the memory of a program in another run unit. There is isolation between them. In addition, file locks are held for each run unit. If a program in one run unit holds a file lock, it will not be accessible to a file handling program in another run unit in the same process.
This feature is implemented using the concept of a Run Unit Manager. Each manager controls the life-cycle of run unit objects in Java environments with a notion of a session. A manager:
The class com.microfocus.cobol.runtimeservices.servlet.ServletRunUnitManager in the JVM COBOL runtime exists to handle the life-cycle of run units in the context of servlet API HttpSession objects.