Threads, Fibers, and subprocess commands, like spawn, fork, backtick and exec,
log the source code location that invoked them. This location can now be
filtered based on a configuration option.

The default is to filter the Ruby core library location. But when a utility
library is used, the location will always show the same utility library source
code. Adding a custom filter that excludes the library locations allows the
client source code location to be logged instead.

The following configuration options designate the source filters:

  -Xmachine.thread.log.filter (default '^core/.*$')
  -Xmachine.fiber.log.filter (default '^core/.*$')
  -Xsystem.log.filter (default '^core/.*$')

The filter must match the entire source code line to exclude it. The first
non-matching source code line will be logged.

The filter expression uses the C++ regex facility and ECMAScript syntax.

The configuration options can come from five different locations:

  1. The file $HOME/.rbxconfig if $HOME is defined.
  2. The file .rbxconfig in the current working directory.
  3. The RBXOPT environment variable.
  4. The command line options.
  5. The default values.

This may cause ambiguity about what configuration options are in effect when a
process runs. The -Xsystem.log.config (default: yes) option prints the
configuration options that were parsed to the log file.