Job-scoped resources and thread safety

Some resources (open database files, for example) are scoped to the activation group. For the purposes of this discussion, resources that are scoped to the activation group must be treated with the same considerations as job-scoped resources. All of the threads that use the activation group use these resources.

Your application can use appropriate synchronization techniques if threads in your application modify these resources when other threads are using them. You need to ensure a consistent view of the resources between your threads.

Here are some of the common job-scoped or activation-group-scoped resources:

• Heap, static, and global storage

  The most commonly shared resource. For more information, see Storage usage and threaded applications.

• Open files

  After you open a file, threads in a process can directly share integrated file system files and database files by passing the file handle pointer or file descriptor number to another thread. The working directory is always scoped to the process.

• Locales

  The locale of an application is an activation group resource. All threads share the locale. Changing the locale affects other threads with regard to collating sequences or other locale information.

• Coded character set identifier

  Changing the coded character set identifier (CCSID) of a job affects the current data translation or representation of all threads in that job.

• Environment variables

  Your application commonly uses environment variables for configuration and optional behavior. All the threads in the job share these environment variables.