Do once

Purpose: Execute statements only once in a process.

  do-once
     <any statements>
     ...
  end-do-once

do-once will execute <any statements> only once in a single process regardless of how many requests that process serves. <any statements> end with end-do-once. The first time a process reaches do-once, <any statements> will execute; in all subsequent cases the program control will skip to immediately after end-do-once.

do-once cannot be nested, but otherwise can be used any number of times.

Typical use of do-once may be making any calls that need to be performed only once per process, or it may be a one-time setup of process-scoped variables, or anything else that needs to execute just once for all requests served by the same process.

<any statements> execute in the nested scope relative to the code surrounding do-once/end-do-once, except that any process-scoped variables are created in the same scope as the code surrounding do-once/end-do-once; this simplifies creation of process-scoped variables, if needed.

Examples

In this example, a process-scoped array (that is available to multiple requests of a single process) is created in the very first request a process serves and data is written to it; the subsequent requests do not create a new array but rather just write to it.

 ...
  do-once
     new-array my_array hash-size 1024 process-scope
  end-do-once
  write-array my_array key my_key value my_data
  ...