信号处理 pika / python

Question

我在一个消费者中使用了 pika.BlockingConnection，这个消费者会对每条消息执行一些任务。我还添加了信号处理，这样消费者在完成所有任务后可以正常退出。

当我处理消息时，如果收到信号，我只会从函数中得到 "signal received" 的提示，但代码并没有退出。因此，我决定在回调函数的末尾也检查一下是否收到信号。我的问题是，我需要检查信号多少次，因为代码中会有很多其他函数。有没有更好的方法来处理信号，而不至于检查得太频繁呢？

import signal
import sys
import pika
from time import sleep

received_signal = False
all_over = False

def signal_handler(signal, frame):
    global received_signal
    print "signal received"
    received_signal = True

signal.signal(signal.SIGINT, signal_handler)
signal.signal(signal.SIGTERM, signal_handler)

mq_connection = pika.BlockingConnection(pika.ConnectionParameters(my_mq_server, virtual_host='test'))
mq_channel = mq_connection.channel()

def callback(ch, method, properties, body):
    if received_signal:
        print "Exiting, as a kill signal is already received"
        exit(0)
    print body
    sleep(50)
    mq_channel.basic_ack(delivery_tag=method.delivery_tag)
    print "Message consumption complete"

    if received_signal:
        print "Exiting, as a kill signal is already received"
        exit(0)

try:
    print ' [*] Waiting for messages. To exit press CTRL+C'
    mq_channel.basic_consume(callback, queue='test')
    mq_channel.start_consuming()
except Exception:
    mq_channel.close()
    exit()

这是我在这里的第一个问题，如果需要更多细节，请告诉我。

Answer 1

我觉得这个可以满足你的需求：

#!/usr/bin/python

import signal
import sys 
import pika
from contextlib import contextmanager

received_signal = False
processing_callback = False

def signal_handler(signal, frame):
    global received_signal
    print "signal received"
    received_signal = True
    if not processing_callback:
         sys.exit()

signal.signal(signal.SIGINT, signal_handler)
signal.signal(signal.SIGTERM, signal_handler)

@contextmanager
def block_signals():
    global processing_callback
    processing_callback = True
    try:
        yield
    finally:
        processing_callback = False
        if received_signal:
            sys.exit()

def callback(ch, method, properties, body):
    with block_signals:
        print body
        sum(xrange(0, 200050000)) # sleep gets interrupted by signals, this doesn't.
        mq_channel.basic_ack(delivery_tag=method.delivery_tag)
        print "Message consumption complete"

if __name__ == "__main__":    
    try:
        mq_connection = pika.BlockingConnection(pika.ConnectionParameters('localhost'))
        mq_channel = mq_connection.channel()
        print ' [*] Waiting for messages. To exit press CTRL+C'
        mq_channel.basic_consume(callback, queue='test')
        mq_channel.start_consuming()
    except Exception as e:
        mq_channel.close()
        sys.exit()

我使用了一个上下文管理器来处理信号的阻塞，这样所有的逻辑就隐藏在回调函数之外了。这也应该让代码更容易重复使用。为了让你更清楚它是怎么工作的，它其实和这个是一样的：

def callback(ch, method, properties, body):
    global processing_callback
    processing_callback = True
    try:
        print body
        sum(xrange(0, 200050000))
        mq_channel.basic_ack(delivery_tag=method.delivery_tag)
        print "Message consumption complete"
    finally:
        processing_callback = False
        if received_signal:
            sys.exit()