# Insert messages in queues? **URL:** \ **Category:** GNU Radio\ **Created:** [April 12, 2015, 5:53am UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530 "2015-04-12T05:53:54Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [April 12, 2015, 5:53am UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530/1 "2015-04-12T05:53:54Z")
If I’m using a block that has a message port output, is there a way to put those messages into a message queue? For instance: self.message\_queue = gr.msg\_queue() self.msg\_connect((self.gsm\_control\_channels\_decoder, ‘msgs’), (???message\_queue???, 0)) I have used gr.msg\_queue() with blocks.message\_sink() but that only accepts items such as complex, float, etc. I need to take the messages generated by any old block and parse them outside the flowgraph. From what I have read, I thought all blocks that handle messages have queues, so shouldn’t I be able to pop them directly out of that block? I guess I’m confused. Are there two type of message passing; an old one that uses queues, and a new one that uses PMT? Thanks, Lou – View this message in context: [http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272.html](http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![madengr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ec9cab/32.png) [@madengr](https://www.ruby-forum.com/u/madengr)\ **Post date:** [April 12, 2015, 6:27pm UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530/2 "2015-04-12T18:27:36Z")
On 11.04.2015 20:38, madengr wrote: > From what I have read, I thought all blocks that handle messages have > queues, so shouldn’t I be able to pop them directly out of that block? I > guess I’m confused. Are there two type of message passing; an old one that > uses queues, and a new one that uses PMT? Hey Louis, Yes, there are two ways, and they’re completely different. The old message queues will be deprecated soon, so anything with gr.msg\_queue() in there will, at one point in the future, stop working. Look at the Python output of some of the message examples we provide, also check out this manual page: [http://gnuradio.org/doc/doxygen/page\_msg\_passing.html](http://gnuradio.org/doc/doxygen/page_msg_passing.html) M ---
**Author:** ![madengr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ec9cab/32.png) [@madengr](https://www.ruby-forum.com/u/madengr)\ **Post date:** [April 13, 2015, 12:38am UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530/3 "2015-04-13T00:38:31Z")
Thanks Martin. Looking at the gr-blocks/examples/msg\_passing, the tutorial link, and qa\_msg, I only find examples of posting messages. Those make sense, but is there an equivalent to \_post method that pulls messages? > **[GNU Radio Manual and C++ API Reference: gr::basic\_block Class Reference](https://www.gnuradio.org/doc/doxygen/classgr_1_1basic__block.html)** From the above docs, I see the delete\_head\_blocking, which is maybe what I want. If I have a tagged stream to PDU like below, how do I pull the message? sink=blocks.tagged\_stream\_to\_pdu(blocks.float\_t, “packet\_len”) sink.to\_basic\_block.??? Lou Martin B.-2 wrote > M > > * * * > > Discuss-gnuradio mailing list > Discuss-gnuradio@ > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) – View this message in context: [http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272p53277.html](http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272p53277.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![madengr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ec9cab/32.png) [@madengr](https://www.ruby-forum.com/u/madengr)\ **Post date:** [April 13, 2015, 4:57pm UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530/4 "2015-04-13T16:57:14Z")
Martin, Yes, pop them outside the block, but also outside of the flow graph. Exactly reverse of the last example “Posting from External Sources” here: [http://gnuradio.org/doc/doxygen/page\_msg\_passing.html](http://gnuradio.org/doc/doxygen/page_msg_passing.html) “The last feature of the message passing architecture to discuss here is how it can be used to take in messages from an external source. We can call a block’s gr::basic\_block::\_post method directly and pass it a message. So any block with an input message port can receive messages from the outside in this way.” I want to take any block with an output message port and \_pull that message to the outside (of the flow so I can process it in Python). Presently, with the old queued messaging system, I can use blocks.message\_sink() to take an item into a message queue I can access outside the flow. Since this will be deprecated, I’d want to use blocks.tagged\_stream\_to\_pdu() to generate a message, but don’t see a way to get those messages stored into a FIFO (queue) and access them outside the flow. As you suggest, maybe the solution is to develop a block, with an input message port, that performs the callback and stores those messages in a FIFO. From browsing the documentation, it looks like the message\_debug block will store up messages (I haven’t attempted to read those messages), but I’d be worried about overflows. I guess the ideal was to do it without developing or modifying any blocks. Though looking at line 278 of usrp\_spectrum\_sense.py, when the message queues are deprecated, what would you do to get the data out of the flow? I assume blocks.bin\_statistics\_f() would have to be re-written to have a message port output, but then how do you get that message out of the flow? [https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/examples/python/usrp\_spectrum\_sense.py#L278](https://github.com/gnuradio/gnuradio/blob/master/gr-uhd/examples/python/usrp_spectrum_sense.py#L278) Thanks, Lou Martin B.-2 wrote > Cheers, > M – View this message in context: [http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272p53279.html](http://gnuradio.4.n7.nabble.com/Insert-messages-in-queues-tp53272p53279.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![madengr](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ec9cab/32.png) [@madengr](https://www.ruby-forum.com/u/madengr)\ **Post date:** [April 13, 2015, 8:34am UTC](https://www.ruby-forum.com/t/insert-messages-in-queues/241530/5 "2015-04-13T08:34:43Z")
On 12.04.2015 15:22, madengr wrote: > sink=blocks.tagged\_stream\_to\_pdu(blocks.float\_t, “packet\_len”) > sink.to\_basic\_block.??? So you want pop messages from outside the block, right? Is the original block written in C++? delete\_head\_block() should work, but this seems unusual. Typically, we have two mechanisms of handling messages: Dedicated message handler callbacks, or we pop the queue ourselves in work() using delete\_head(). If you’re popping messages outside of the block, the block itself would never see or use those messages – which is why I’m surprised. You might be better of writing a mini-Python-block that handles the messages. Cheers, M