lPushx
Description
Adds the string value to the head (left) of the list if the list exists.
添加一个VALUE到LIST容器的顶部（左侧）如果这个LIST存在的话。
Parameters
key
value String, value to push in key
Return value
LONG The new length of the list in case of success, FALSE in case of Failure.
Examples
$redis->delete('key1');
$redis->lPushx('key1', 'A'); // returns 0
$redis->lPush('key1', 'A'); // returns 1
$redis->lPushx('key1', 'B'); // returns 2
$redis->lPushx('key1', 'C'); // returns 3
/* key1 now points to the following list: [ 'A', 'B', 'C' ] */