前面介绍过GNU Radio中协议数据包的传递方式之一——消息机制。仔细研究GNU Radio的源代码会发现，其中的消息机制是很重要的。几乎在所有实际的发送、接收中都会用到消息（message）：在GRC中的packet_encoder和packet_decoder、pkt.py中的pkd_mod和pkd_demod以及packet.py中的packet_encoder和packet_decoder、packet_mod、packet_demod等等都用到了message_source和message_sink。
下面是一个使用message的例子：
from gnuradio import gr,blocks
from time import sleep
class msg_blocks(gr.top_block):
def __init__(self):
gr.top_block.__init__(self, 'Message Blocks Test')
# initialize the queues
self.sink_queue = gr.msg_queue()
self.source_queue = gr.msg_queue()
# initialize the blocks
self.msg_source = blocks.message_source(gr.sizeof_char, self.source_queue)
self.msg_sink = blocks.message_sink(gr.sizeof_char, self.sink_queue, False)
self.connect((self.msg_source, 0), (self.msg_sink, 0))
def send_pkt(self, payload):
self.source_queue.insert_tail(gr.message_from_string(payload))
def recv_pkt(self):
pkt = ""
if self.sink_queue.count():
pkt = self.sink_queue.delete_head().to_string()
return pkt
if __name__=="__main__":
tb = msg_blocks()
tb.start()
# operate on queues directly
print 'operating on the queues directly'
print 'sink queue count:', tb.sink_queue.count()
print 'inserting:', 'a'
tb.source_queue.insert_tail(gr.message_from_string('a'))
sleep(1) # sleep to yield to tb thread
print 'sink queue count:', tb.sink_queue.count()
print 'received:', tb.sink_queue.delete_head().to_string()
# operate using methods
print 'operating with fuctions supplied by the top block'
print 'sending:', 'a'*512
tb.send_pkt('a'*512)
sleep(1)
print 'received:', tb.recv_pkt()运行结果：
