Due to the nature of PHP's implementation of
pcntl_exec(), Blackfire has no way to continue profiling when
pcntl_exec() is called. As a result, Blackfire is currently unable to continue profiling the process.
This means that some tools which use
pcntl_exec() are not compatible with Blackfire.
One well known tool that uses
pcntl_exec() is Drush. One solution for getting Blackfire to run with Drush is to add
pcntl_exec to disable_functions in your
php.ini file. Drush uses
pcntl_exec() is not available.