Can we use gevent.sleep() for precise timings?

问题

Can we use gevent.sleep() anywhere in our application or gevent.monkey.patch_time() on any third party libraries without an issue, especially precise timings takes place?

For example, some libraries use time.sleep() function in order to measure a couple of microseconds that is used to control an embedded (dot matrix LCD and such) device. Can we safely monkey patch such libraries without a problem?

回答1:

No. gevent.sleep() is not suitable for precise timings.

Here is the test code:

import gevent
import time


for i in range(10):
        test_duration = 0.1 ** i
        start_time = time.time()
        gevent.sleep(test_duration)
        end_time = time.time()

        gevent_duration = end_time - start_time

        err = (gevent_duration - test_duration) / test_duration
        print("test_duration: %.10f secs, err: %%%.10f" % (test_duration, err))

Here is the result:

ceremcem@cca-erik:gevent-timing-test$ python test.py 
test_duration: 1.0000000000 secs, err: %0.0009050369
test_duration: 0.1000000000 secs, err: %0.0037088394
test_duration: 0.0100000000 secs, err: %0.0192871094
test_duration: 0.0010000000 secs, err: %0.1119842529
test_duration: 0.0001000000 secs, err: %9.9791755676
test_duration: 0.0000100000 secs, err: %108.9109649658
test_duration: 0.0000010000 secs, err: %1095.0102081299
test_duration: 0.0000001000 secs, err: %10878.0397644043
test_duration: 0.0000000100 secs, err: %108407.9279174804
test_duration: 0.0000000010 secs, err: %1087902.9764404292
ceremcem@cca-erik:gevent-timing-test$ python test.py 
test_duration: 1.0000000000 secs, err: %0.0009670258
test_duration: 0.1000000000 secs, err: %0.0031008720
test_duration: 0.0100000000 secs, err: %0.0271072388
test_duration: 0.0010000000 secs, err: %0.1529922485
test_duration: 0.0001000000 secs, err: %10.1293792725
test_duration: 0.0000100000 secs, err: %117.3032989502
test_duration: 0.0000010000 secs, err: %1191.0928955078
test_duration: 0.0000001000 secs, err: %11898.4712829590
test_duration: 0.0000000100 secs, err: %119089.0802612304
test_duration: 0.0000000010 secs, err: %1188992.4539794917

As you can see, errors are also unpredictable.

That's why gevent.monkey.patch_all() should be used carefully in such situations.

来源：https://stackoverflow.com/questions/30584196/can-we-use-gevent-sleep-for-precise-timings

标签

python

real-time

embedded-linux

gevent