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QUESTION
I'd like to use nanomsg/nng as the communication basis of a fully distributed peer-to-peer multi-node network, to help construct the dynamic ability of topological discovery and maintenance. Now I get stuck in its Golang package mangos.
The same work has been done in Python and pynng (which is a python binding for nanomsg), but when I use Go and invoke the corresponding methods by mangos instead, their behaviors are totally different. The puzzle is mainly threefold:
- The bus-type-Socket's Recv() acts in a blocking mode by default and seems not to be configurable to the non-blocking mode. Documents says:
OptionRecvDeadline is the time until the next Recv times out. The value is a time.Duration. Zero value may be passed to indicate that no timeout should be applied. A negative value indicates a non-blocking operation. By default there is no timeout.
I tried a negative value accordingly, but Recv() was still blocking. What else should I do? and how to understand the difference between "Zero-timeout" and "non-blocking"?
- The
dialerreturned by(s *socket) NewDialer(...)seems to linger on after callingdialer.Close(), since an error will occur when calling a nextdialer.Dial()reporting it's still "address in use". But when I tried toClose()thedialeragain, error occurs as well reporting it's already closed. I also tried different combinations of the following options, but all the attempts failed
ANSWER
Answered 2021-Jun-30 at 14:33I don't usually monitor stackoverflow or reddit for questions like this -- we do have a discord channel (link from the mangos and NNG home pages), as well as a mailing list.
Having said that, let me see if I can help (I'm the author for both NNG and mangos):
- OptionRecvDeadline is supported for bus. However, you're correct that it doesn't support non-blocking mode with a negative value, instead the negative value is treated the same as zero, and acts as blocking. This is a documentation bug. To achieve a logical non-blocking, use the value "1", which means one nanosecond, and that will logically equate to non-blocking, although the granularity may be limited by the scheduler latency. (In this case it would be like doing a "go close(channel); <-channel" -- very nearly non-blocking.
I'll see about fixing the documentation.
Calling Close() on the dialer is the right thing to do. It will linger until the pipes are closed, which it does automatically. It is possible that your use of a very short redial time might confound this -- I'll be honest in saying that I had not considered tiny redial times -- usually it's bad form to do this because it means that if the peer is not available your code will spin hard on the processor trying to reconnect. I usually recommend at minimum a 10 millisecond retry interval cap. (mangos.OptionMaxReconnectTime)
I think you're seeing the effect of queueing, but I'm not 100% certain -- I'd need to see a test case reproducing this. Definitely the bus protocol is best effort delivery, and if there are no connected peers then the message is dropped on the floor. (Just rechecked that to be certain.)
QUESTION
I'm upgrading our build machine (from Windows Server 2008 to Windows 10) and have a build that ran fine on the old machine (using Visual Studio). I had some problems getting it to run with VS Build Tools (I'm trying to avoid needing a VS license) on the new machine, so I'm porting it to use Clang.
The build uses Flatbuffers, which I have upgraded from 1.4.0 to 1.12.0. I'm getting the following error during the build:
...ANSWER
Answered 2020-Jul-17 at 14:15Turned out that I had in my include path a version of stdint.h that specifies it was for use "only with Microsoft Visual C++ compilers!". Unsurprisingly, it turns out it doesn't work with Clang. You'd expect it to either fail catastrophically or else just work anyway (it does define PTRDIFF_MAX), but I guess it just causes Clang to be very very confused.
Anyway, if I remove it from my include path, things start working.
QUESTION
I'm working on a "server" thread, which takes care of some IO calls for a bunch of "clients".
The communication is done using pynng v0.5.0, the server has its own asyncio loop.
Each client "registers" by sending a first request, and then loops receiving the results and sending back READY messages.
On the server, the goal is to treat the first message of each client as a registration request, and to create a dedicated worker task which will loop doing IO stuff, sending the result and waiting for the READY message of that particular client.
To implement this, I'm trying to leverage the Context feature of REP0 sockets.
Side notes
I would have liked to tag this question with nng and pynng, but I don't have enough reputation.
Although I'm an avid consumer of this site, it's my first question :)
I do know about the PUB/SUB pattern, let's just say that for self-instructional purposes, I chose not to use it for this service.
Problem:
After a few iterations, some READY messages are intercepted by the registration coroutine of the server, instead of being routed to the proper worker task.
Since I can't share the code, I wrote a reproducer for my issue and included it below.
Worse, as you can see in the output, some result messages are sent to the wrong client (ERROR:root:: worker/client mismatch, exiting.).
It looks like a bug, but I'm not entirely sure I understand how to use the contexts correctly, so any help would be appreciated.
Environment:
- winpython-3.8.2
- pynng v0.5.0+dev (46fbbcb2), with nng v1.3.0 (ff99ee51)
Code:
...ANSWER
Answered 2020-Apr-18 at 07:24After digging into the sources of both nng and pynng, and confirming my understanding with the maintainers, I can now answer my own question.
When using a context on a REP0 socket, there are a few things to be aware of.
As advertised, send/asend() is guaranteed to be routed to the same peer you last received from.
The data from the next recv/arecv() on this same context, however, is NOT guaranteed to be coming from the same peer.
Actually, the underlying nng call to rep0_ctx_recv() merely reads the next socket pipe with available data, so there's no guarantee that said data is coming from the same peer than the last recv/send pair.
In the reproducer above, I was concurrently calling arecv() both on a new context (in the Server._new_client_handler() coroutine), and on each worker context (in the Server._worker() coroutine).
So what I had previously described as the next request being "intercepted" by the main coroutine was merely a race condition.
One solution would be to only receive from the Server._new_client_handler() coroutine, and have the workers only handle one request. Note that in this case, the workers are no longer dedicated to a particular peer. If this behavior is needed, the routing of incoming requests must be handled at application level.
QUESTION
context: I have an code where I have functions based on MsgID's, all these functions corresponding to MSGID's will be kept in MAP which is in different class. MSGID's would be received in different class and I am trying to pass to MAP which is in other class for getting the function pointer and call the function with parameters.
...ANSWER
Answered 2020-Feb-06 at 08:52define your function pointer as member function pointer like
QUESTION
I am new to CMake, but I used to use qmake. In my qmake, I have the following for adding a static library that is inside a folder called bin, inside the project folder:
...ANSWER
Answered 2020-Feb-04 at 16:32If you want to use a pre-built static library in your CMake, you can declare a STATIC IMPORTED CMake target:
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