(PECL libevent >= 0.0.1)
Set the watermarks for read and write events
void event_buffer_watermark_set ( resource $bevent, int $events, int $lowmark, int $highmark )
Sets the watermarks for read and write events. Libevent does not invoke read callback unless there is at least lowmark bytes in the input buffer; if the read buffer is beyond the highmark, reading is stopped. On output, the write callback is invoked whenever