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DIRECTIVES.md

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Using directives to modify behavior

Several of the parameters that can be given to the rwloadsim executable are used to modify the behavior of the RWL*Load Simulator. A few examples are that --statistics cause runtime statistics to be saved and that --startseconds can be used to set a value for the common starting time. These and many other settings can alternatively be modified using directives in your rwl source files. Directives are instructions to rwloadsim and are handled purely during scanning of your rwl sources files; they are not handled by the parser and are not "executed".

All directives have an initial $ followed by a string of characters without any white space. The characters are lower case letters and in a few cases contain numerals or punctuation. Many directive names are terminated by a : followed by a directive value such as a number. Directives are never upper case letters; $ followed by upper case are environment variables.

Many directives can be changed several times in your rwl source files, which means the actual value will be used on-wards during scanning and parsing. A directive set in one source file will be applied in subsequent sources files both when these are on the command line or as include files.

Some examples of directives are:

  • $statisitcs:basic which has the same effect as the --statistics option
  • $starseconds:<double> which has the same effect as the --startseconds option
  • $implicit:both which turns on implicit bind and define

Directives for creating useroptions are described in WORKING.md and all directives are documented at the rwlman directive page.

Conditional compilation

A set of directives, $if ... $then, $else, $endif are used to perform conditional compilation. The compile time expression between $if and $then, which can use global variables and a small subset of built in functions only, is evaluated during scanning, causing either the first or second part (after $else) to be parsed; $else and the second part can be omitted. The initial $if and $then parts and the compile time expression between them must be on the same source line, but there are otherwise no restrictions on how these are put in your rwl source file.

A small example of how this can be used is:

integer poolsize := 0; $useroption:poolsize

database mydb
  username "username"
  password "{password}"
  connect "//host/service";
  $if poolsize $then
    sessionpool 1 .. poolsize
  $else
    dedicated
  $endif
  default;

There are further examples in MODULAR.md.

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