信号处理pika/python

Question

我在使用者中使用pika.BlockingConnection，它为每条消息执行一些任务。我还添加了信号处理，以便消费者在完全执行所有任务后正常死亡。

在处理消息和接收信号时，我只是从函数中获得"signal received"，但代码并没有退出。所以，我决定检查在回调函数结束时接收到的信号。问题是，我要检查信号多少次，因为这段代码中会有更多的函数。有没有更好的方法来处理信号而不过度？

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，如果需要更多的细节，请告诉我。

Answer 1

我认为这正是您想要的：

#!/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contextmanager来处理阻塞信号，这样所有的逻辑都隐藏在回调本身之外。这也应该使代码的重用更加容易。只是为了澄清它是如何工作的，它相当于：

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()