Os Io Epoll
DodaTech
1 min read
In this tutorial, you'll learn about How to Fix epoll Errors. We cover key concepts, practical examples, and best practices.
Fix epoll errors when edge-triggered epoll misses data if not loop-read completely.
Quick Fix
Wrong
import selectors
sel=selectors.DefaultSelector()
sel.register(fd, selectors.EVENT_READ)
# Edge-triggered: notification only on state change
# If data arrives between registration and first epoll call, notification missed!
Edge-triggered: no notification for existing data. Must read until EAGAIN. Loses data.
Right
import selectors
sel=selectors.DefaultSelector()
sel.register(fd, selectors.EVENT_READ)
def read_callback():
# Level-triggered (default): notified as long as data available
# Edge-triggered requires: read in loop until EAGAIN
data=os.read(fd, 4096)
while data:
process(data)
data=os.read(fd, 4096) # until EAGAIN
# Level-triggered is simpler. Use edge-triggered only when necessary.
# epoll with EPOLLONESHOT: re-arm after each event
# Correct edge-triggered setup:
import select
epoll=select.epoll()
epoll.register(fd, select.EPOLLIN | select.EPOLLET) # edge-triggered
# Must use non-blocking fd:
os.set_blocking(fd, False)
Level-triggered: no missed events. Edge-triggered: read in loop until EAGAIN.
Prevention
Level-triggered is simpler. Edge-triggered: read until EAGAIN in loop. Use non-blocking fd.
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