Retrieve full source items list in a unified way

Hi All,

I'm trying to figure out a way to extract all source item ids list in a unified way for all sourceList classes.

$migration = Migration::getInstance($migration_name);
$source = $migration->getSource();

Source is a iterator so I should be able to loop:

foreach ($source as $row) {
  // Do stuff
}

But I get this exception: Call to a member function getMap() on a non-object in /sites/all/modules/contrib/migrate/includes/source.inc on line 253
(I'm using a MigrateSourceXML class).

Digging into code the reason is that the MigrateSource implementation of rewind uses the current Migration:

public function rewind() {
    $this->activeMigration = Migration::currentMigration();
    $this->activeMap = $this->activeMigration->getMap();
    ... 
}

The current migration variable is set and unset after the method is called in some Migration & MigrationBase methods like:

- beginProcess:

protected function beginProcess($newStatus) {
    // So hook_watchdog() knows what migration (if any) is running
    self::$currentMigration = $this;

- Analyze:

analyze() {
    // The source needs this to find the map table.
    self::$currentMigration = $this;
}

Is there any way to set the currentMigration using current api?

Is there any other approach to loop into source list?

Thanks!