installation during install profile can cause problems due to hook_init() starting poorman's cron process

If you have Ultimate Cron as one of a large enough number of modules (say > 100) in an install profile, having hook_init triggering during the batch task of module enabling will cause all sorts of intermittent and highly variable issues and crashes and timeouts. Once a background task and poormans cron is going against a foreground of ajax calls and serial module installation, who knows what's possible.

A smaller set of modules culled from the same general project here (~50 modules) generally installs ok as an installation profile, even though it's including Ultimate Cron, and the background process for poorman's cron is running. So most people probably won't see this happen.

If you look at what background_process is doing in background_process_init(), something very similar should be in ultimate_cron_init():

  // Only determine when installation of site is finished
  if (!variable_get('install_profile', FALSE)) {
    return;
  }

The workaround we use for now is to add a step into the install profile (/profiles/myprofile/myprofile.profile) in which we disable that poorman's cron launch.

/**
 * Implements hook_install_tasks_alter().
 */
function myprofile_install_tasks_alter(&$tasks, $install_state) {
  $new_tasks = array();
  foreach ($tasks as $name => $task) {
    $new_tasks[$name] = $task;
    if ($name == 'install_bootstrap_full') {
      // we must insert after install_bootstrap_full if we want variable_get/set to work

      // add an invisible task to prepare for module installation
      $new_tasks['install_prepare_for_install_profile_modules'] = array(
        'run' => INSTALL_TASK_RUN_IF_NOT_COMPLETED,
        'function' => 'myprofile_install_prepare_for_install_profile_modules',
      );
    }
  }
  $tasks = $new_tasks;
}

/**
 * Callback for the myprofile_install_prepare_for_install_profile_modules step.
 */
function myprofile_install_prepare_for_install_profile_modules(&$install_state) {
  // this will stop Ultimate Cron from launching a background process following install.
  variable_set('ultimate_cron_poorman', FALSE);
}