Avoid startup freezes of OMJulia

[CSchoel]

Sometimes, OMJulia freezes when the first command is sent to the OMC, indefinitely waiting for an answer.

My current solution for this was to attempt to implement a timeout for ZMQ.recv, however this currently yields the following error:

┌ Warning: getVersion() timed out in avoidStartupFreeze
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/w5Lny/src/Simulation.jl:309
ERROR: LoadError: ZMQ.StateError("Operation cannot be accomplished in current state")
Stacktrace:
 [1] _send(::ZMQ.Socket, ::Base.RefValue{ZMQ._Message}, ::Bool) at /home/cslz90/.julia/packages/ZMQ/R3wSD/src/comm.jl:14
 [2] send(::ZMQ.Socket, ::String; more::Bool) at /home/cslz90/.julia/packages/ZMQ/R3wSD/src/comm.jl:45
 [3] send at /home/cslz90/.julia/packages/ZMQ/R3wSD/src/comm.jl:43 [inlined]
 [4] avoidStartupFreeze(::OMJulia.OMCSession) at /home/cslz90/.julia/packages/ModelicaScriptingTools/w5Lny/src/Simulation.jl:301
 [5] setupOMCSession(::String, ::String; quiet::Bool, checkunits::Bool) at /home/cslz90/.julia/packages/ModelicaScriptingTools/w5Lny/src/Simulation.jl:339
 [6] withOMC(::var"#53#54", ::String, ::String; quiet::Bool, checkunits::Bool) at /home/cslz90/.julia/packages/ModelicaScriptingTools/w5Lny/src/Simulation.jl:423
 [7] withOMC(::Function, ::String, ::String) at /home/cslz90/.julia/packages/ModelicaScriptingTools/w5Lny/src/Simulation.jl:423
 [8] top-level scope at /home/cslz90/Documents/Promotion/code/2019-schoelzel-inada/scripts/unittests.jl:14
in expression starting at /home/cslz90/Documents/Promotion/code/2019-schoelzel-inada/scripts/unittests.jl:14

I guess when ZMQ freezes during revc, it cannot change its state variables, which lead to a subsequent send operation triggering this StateError. A solution might be to simply restart the whole connection when this occurs.

[CSchoel]

The restart solution seems to work. I just got the following warnings:

┌ Warning: Discarding frozen connection to OMC with file descriptor 143 and starting new OMC instance. This may leave the old OMCinstance still running on your machine.
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/KpoFH/src/Simulation.jl:298
Closing OMC session
┌ Warning: Closing old OMC instance failed with the following error:
│ ZMQ.StateError("Operation cannot be accomplished in current state")
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/KpoFH/src/Simulation.jl:306

But no OMC instance was left open after the simulations finished.

[CSchoel]

Second time that i encountered a frozen connection with the new solution, still no dangling OMC instance. This seems to work reliably. 👍

[CSchoel]

Another interesting observation: It seems possible that the first warning is shown without the second warning, meaning that it is not unreasonable to hope, that closing the OMC will work smoothly. Also: Third occurrence of warning, still no dangling OMC processes. 🎉

[CSchoel]

New case report: Two warnings, one dangling OMC instance. This means that the warning message is also justified.

┌ Warning: Discarding frozen connection to OMC with file descriptor 61 and starting new OMC instance. This may leave the old OMCinstance still running on your machine.
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/cGAUx/src/Simulation.jl:298
Closing OMC session
┌ Warning: Closing old OMC instance failed with the following error:
│ ZMQ.StateError("Operation cannot be accomplished in current state")
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/cGAUx/src/Simulation.jl:306
┌ Warning: Discarding frozen connection to OMC with file descriptor 72 and starting new OMC instance. This may leave the old OMCinstance still running on your machine.
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/cGAUx/src/Simulation.jl:298
Closing OMC session
┌ Warning: Closing old OMC instance failed with the following error:
│ ZMQ.StateError("Operation cannot be accomplished in current state")
└ @ ModelicaScriptingTools ~/.julia/packages/ModelicaScriptingTools/cGAUx/src/Simulation.jl:306

[cslz90@cswork ~]$ ps -aux | grep omc
cslz90      6987  0.0  0.2 1287812 42072 pts/0   Sl+  11:35   0:00 omc --interactive=zmq +z=julia.xyzKRHj35I
cslz90      8727  0.0  0.0   6672  2468 pts/2    S+   11:39   0:00 grep --colour=auto omc