Putting It All Together: the restartSpawn Example Program

The following code example, restartSpawn, illustrates many of the function calls covered in this and previous chapters. The example is provided as an overview of the restart mechanism and the use of persistent memory. Specific parts of the example could be used as the basis of a more complex user application that incorporates hot restart.

The restartSpawn example uses two restartable processes, a parent process, HR_parent.r and a child, HR_child.r which is spawned by the parent. Both processes should be compiled as supervisor processes. The source code for the two processes is provided in "Example Application Code". The example can be summarized as follows:

• The parent process uses a set of control structures stored in persistent memory. It spawns the child process using hrfexec() , then explicitly crashes, causing itself to be restarted by the system. The parent process restarts the child process indirectly each time it runs, through a call to hrfexec().

• The child process also uses a set of control structures stored in persistent memory. It executes a four-step loop which causes the following to be displayed:

  =========== Message ===========
   STEP 1  STEP 2  STEP 3  STEP 4
  ======== End of message========

The message is displayed independently of the number of times the parent process crashes, or the site is restarted.