Loop — Event loop

class pyuv.Loop

Instantiate a new event loop. The instantiated loop is not the default event loop. In order to instantiate the default event loop default_loop classmethod should be used.

classmethod default_loop()

Create the default event loop. Most applications should use this event loop if only a single loop is needed.

Parameters:mode (int) –

Specifies the mode in which the loop will run. It can take 3 different values:

  • UV_RUN_DEFAULT: Default mode. Run the event loop until there are no active handles or requests.
  • UV_RUN_ONCE: Run a single event loop iteration.
  • UV_RUN_NOWAIT: Run a single event loop iteration, but don’t block for io.

Run the event loop. Returns True if there are pending operations and run should be called again or False otherwise.


Stops a running event loop. The action won’t happen immediately, it will happen the next loop iteration, but if stop was called before blocking for i/o a 0 timeout poll will be performed, so the loop will not block for i/o on that iteration.


Manage event loop time. now will return the current event loop time in milliseconds. It expresses the time when the event loop began to process events.

After an operation which blocks the event loop for a long time the event loop may have lost track of time. In that case update_time should be called to query the kernel for the time.

This are advanced functions not be used in standard applications.

queue_work(work_callback[, done_callback])
  • work_callback (callable) – Function that will be called in the thread pool.
  • done_callback (callable) –

    Function that will be called in the caller thread after the given function has run in the thread pool.

    Callback signature: done_callback(errorno). Errorno indicates if the request was cancelled (UV_ECANCELLED) or None, if it was actually executed.

Run the given function in a thread from the internal thread pool. A WorkRequest object is returned, which has a cancel() method that can be called to avoid running the request, in case it didn’t already run.

Unix only: The size of the internal threadpool can be controlled with the UV_THREADPOOL_SIZE environment variable, which needs to be set before the first call to this function. The default size is 4 threads.

excepthook(type, value, traceback)

This function prints out a given traceback and exception to sys.stderr.

When an exception is raised and uncaught, the interpreter calls loop.excepthook with three arguments, the exception class, exception instance, and a traceback object. The handling of such top-level exceptions can be customized by assigning another three-argument function to loop.excepthook.


Returns the file descriptor of the polling backend.


Returns the poll timeout.


Read only

List of handles in this loop.


Read only

Checks whether the reference count, that is, the number of active handles or requests left in the event loop is non-zero aka if the loop is currently running.