René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Detecting xruns in process callback","articleBody":"Hi and thanks for the great library, been using it for years!\r\n\r\n**What's the best way to detect if the last process callback lead to an xrun?** Here's my use case: I'm sending MIDI, which works 99% of the time. But when an xrun occurs, the MIDI events aren't sent to connected inputs and on the next process callback I clear the buffer and they're lost forever. Here's how I'm currently doing it:\r\n\r\n```python\r\njack_midi_event_write = jack._lib.jack_midi_event_write\r\n\r\njack_port_get_buffer = jack._lib.jack_port_get_buffer\r\n\r\n\r\nclass Process:\r\n    __slots__ = ('_before', '_buffer', '_client', '_port', '_xrun')\r\n\r\n    def __init__(self, client: jack.Client, port: jack.OwnMidiPort) -\u003e None:\r\n        self._before = 0;\r\n        self._buffer = jack.RingBuffer(2 ** 8)\r\n        self._xrun = threading.Event()\r\n        self._client = client\r\n        self._port = port\r\n\r\n    def process(self, frames: int) -\u003e None:\r\n        xrun = self._xrun\r\n        xrun_set = xrun.is_set()\r\n        port = self._port\r\n        client = port._client\r\n        last_frame_time = client.last_frame_time\r\n        blocksize = client.blocksize\r\n\r\n        if not xrun_set and last_frame_time - blocksize == self._before:\r\n            port.clear_buffer()\r\n        if xrun_set:\r\n            xrun.clear()\r\n\r\n        self._before = last_frame_time\r\n        src_buffer = self._buffer\r\n        space = src_buffer.read_space\r\n\r\n        if space != 0:\r\n            data = src_buffer.read(space)\r\n            dst_buffer = jack_port_get_buffer(port._ptr, blocksize)\r\n            i = 0\r\n            while i != space:\r\n                jack_midi_event_write(dst_buffer, 0, data[i : i + 3], 3)\r\n                i += 3\r\n\r\n    def handle_xrun(self, delay_usec: float) -\u003e None:\r\n        self._xrun.set()\r\n\r\n    def _append(self, event: Tuple[int, int, int]) -\u003e None:\r\n        self._buffer.write(bytes(event))\r\n\r\n    def note_on(self, note: int) -\u003e None:\r\n        self._append((0x99, note, 100))\r\n\r\n    def note_off(self, note: int) -\u003e None:\r\n        self._append((0x89, note, 0))\r\n```\r\nI'm doing two things:\r\n\r\n1. I'm comparing `last_frame_time - blocksize` to the `last_frame_time` on the previous process callback.\r\n\r\n2. Using the `set_xrun_callback` to set a `threading.Event()`\r\n\r\nI'm not sure if I'm doing any of this correctly, just experimenting to see what works. I know you're not meant to use Python for realtime, but it's working too well to justify moving to C++.\r\n\r\nThanks.\r\n","author":{"url":"https://github.com/dj-foxxy","@type":"Person","name":"dj-foxxy"},"datePublished":"2020-01-23T11:09:08.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":5},"url":"https://github.com/81/jackclient-python/issues/81"}