gevent-helpers 0.1.1

fork()

A workaround for gevent issue 154, until that issue is fixed.

BlockingDetector(timeout=1, raise_exc=AlarmInterrupt, aggressive=True)

Use operating system signals to detect blocking threads.

timeout=1 is the number of seconds to wait before considering the thread blocked (note: if signal.setitimer or the itimer package is available, this can be a real number; otherwise it will be rounded up to the nearest integer).

raise_exc=AlarmInterrupt controls which exception will be raised in the blocking thread. If raise_exc is False-ish, no exception will be raised (a log.warning message, including stack trace, will always be issued). NOTE: the default value, AlarmInterrupt, is a subclass of BaseException, so it will not be caught by except Exception: (it will be caught by dirt.runloop). For example:

# Don't raise an exception, only log a warning message and stack trace:
BlockingDetector(raise_exc=False)

# Raise ``MyException()`` and lot a warning message:
BlockingDetector(raise_exc=MyException())

# Raise ``MyException("blocking detected after timeout=...")`` and log
# a warning message:
BlockingDetector(raise_exc=MyException)

aggressive=True determines whether the blocking detector will reset as soon as it is triggered, or whether it will wait until the blocking thread yields before it resets. For example, if aggressive=True, raise_exc=False, and timeout=1, a log message will be written for every second that a thread blocks. However, if aggressive=False, only one log message will be written until the blocking thread yields, at which point the alarm will be reset.

Note: BlockingDetector overwrites the signal.SIGALRM handler and does not attempt to save the previous value.

For example:

>>> def spinblock():
...     while True:
...         pass
>>> gevent.spawn(BlockingDetector())
>>> gevent.sleep()
>>> spinblock()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in spinblock
  File ".../dirt/misc/gevent_.py", line 167, in alarm_handler
    raise exc
gevent_helpers.AlarmInterrupt: blocking detected after timeout=1