[FIX] Invalid tmp dir on WAMP

When trying to set Post SMTP Setup > Settings > Advanced > Temporary Directory always has thrown an invalid error on WAMP since the couple of years I’ve been using this plugin. Looked into it today, and the fix that worked for me is this:

\plugins\post-smtp\Postman\PostmanUtils.php line 246

Change this:

static function deleteLockFile( $tempDirectory = null ) {
	$path = PostmanUtils::calculateTemporaryLockPath( $tempDirectory );
	$success = @unlink( $path );

To this:

static function deleteLockFile( $tempDirectory = null ) {
    $path = PostmanUtils::calculateTemporaryLockPath( $tempDirectory );
    #-->
    //$success = @unlink( $path );        
    # alx359: fix for tmp dir throwing an 'invalid' error on WAMP
    # https://stackoverflow.com/questions/43097799/
    $success = false;
    for( $trial = 0; $trial < 10; $trial++ ) {
        if( $success = @unlink( $path ) ) { break; }
        usleep( 250000 ); # Wait a short time
        clearstatcache(); # Maybe a concurrent script has deleted the file in the meantime
        if( !file_exists( $filename ) ) { $success = true; break; }
    }
    //error_log( var_export( $success .'|'. $path , true ) );
    #<--

While debugging noticed the test lock file throws a Resource temporarily unavailable during the unmasked unlink, and the file was referred twice after saving the path in the backend, which indeed suggests a concurrency issue somewhere. Anyway, the stackoverflow link in the comment explains the issue better, and their solution works.

Thanks.