/**
* openBranch opens and locks the branch for other writing
*
* @return GitCommit the head commit of the branch or null if empty branch
* @author The Young Shepherd
**/
public function setTip(GitCommit $commit)
{
$fBranch = fopen(sprintf('%s/refs/heads/%s', $this->git->getDir(), $this->branchName), 'a+b');
flock($fBranch, LOCK_EX);
$commit->write();
ftruncate($fBranch, 0);
fwrite($fBranch, $commit->getSha()->hex());
fclose($fBranch);
$this->tipCache = $commit;
}
