Threads on i5/OS™

All programs have at least one thread, referred to as the initial thread. In a program with multiple threads, each thread runs its code independently of the other threads in the program.

A process is the container for the memory and resources of the program. On IBM^® iSeries™ systems, a job represents a process. Each process has at least one thread (task) in which the program runs its code. The first thread in a process is referred to as the initial thread. Some processes are capable of supporting additional threads, which are called secondary threads.

The concepts that are described here pertain to all programming languages. For details about how each language enables a concept, refer to the programmer's guide for that specific language.

• Thread models
  There are different models of thread usage: user threads and kernel threads.
• Thread program models
  There are different models for creating multithread programs.
• Jobs and job resources
  A job is a container for storage and other resources. A job cannot run by itself.
• Thread-private data and thread-specific data
  Threads cannot share certain resources. Data that threads cannot share between themselves are called thread-private data.
• Multithreaded program startup commands
  To call a multithreaded Integrated Language Environment^® (ILE) program, the job in which the program is called must be capable of supporting multiple threads (multithread-capable). Multithreaded Java™ programs can be called in most jobs (some system jobs restrict the types of programs that can be called).
• Activation groups and threads
  All programs and service programs are activated within a substructure of a job that is called an activation group. This substructure contains the resources necessary to run the programs, including static and heap storage, and temporary data management resources.
• Communications considerations for multithreaded programming
  The only threadsafe communications protocol supported on i5/OS™ is sockets.
• Database considerations for multithreaded programming
  You should consider these items when using databases in multithreaded programs.
• Data management considerations for multithreaded programming
  You should consider several topics when managing data in a multithreaded program.
• File system considerations for multithreaded programming
  You should consider several topics when working with file systems in multithreaded programs.
• Printer file considerations for multithreaded programming
  Only printer files opened with SPOOL(*YES) are allowed in a job that is capable of multithread operations.