Skip to content

logger_flush_task()

uvent::task::Awaitable<void> logger_flush_task();

logger_flush_task() is the only piece of code that actually touches I/O.

You must launch exactly one instance of it, usually right after ulog::init():

ulog::init(cfg);
usub::uvent::system::co_spawn(ulog::logger_flush_task());

// ... then start uvent loop
usub::Uvent uvent(/*workers=*/4);
uvent.run();

What it does

Inside its loop:

  1. Calls Logger::flush_once_batch()

    • Pulls up to batch_size log records from the global MPMC queue.
    • Groups them by level.
    • Optionally rotates the destination file (if size limit exceeded).
    • Writes the batch to disk/stdout in as few write() syscalls as possible.

  2. co_await sleep_for(flush_interval_ns)

    • Gives control back to the uvent scheduler.
    • No busy-waiting.

Rotation happens here

Log rotation is done only inside this coroutine, right before writing each per-level batch:

  • Producers never rotate.
  • Producers never close FDs.
  • Producers never rename files.

This means:

  • No races between logging threads and I/O.
  • No partial rename while someone else is writing.
  • Either the full batch lands in the "old" file, or the entire batch lands in the "new" file after rotation.

Shutdown

When you call ulog::shutdown():

  • The logger sets an internal shutdown flag.
  • The flush logic drains the queue completely.
  • After the queue is empty, all sinks are fsync()'d and closed (or flushed if stdout).
  • After that point, logging calls are no longer expected to be used.

You should call ulog::shutdown() after the uvent loop exits.