[gmx-users] Potential bug in IMD implementation (Interactive Molecular Dynamics)

[Xavier Martinez]

Dear gmx users,

I came across a bug that is reproducible when using the IMD 
implementation in several versions of Gromacs including 2019.3 and 
different operating systems.

This bug occurs with the following steps:

- Run an IMD simulation (gmx mdrun -imdwait -imdpull -imdterm -s mysim.tpr)

- Connect to the simulation using VMD (or other visualization tool that 
implements the IMD protocol)

- Pause the simulation from VMD ("detach sim" button)

- Reconnect to the simulation

The expected behavior is to have the same performance before and after 
pausing the simulation.

The actual behavior is a slower and stuttering simulation. Note that 
this bug does not occur when using NAMD.

See an example of the bug here: 
https://www.youtube.com/watch?v=_gZ6wA7c4b8 
<https://www.youtube.com/watch?v=_gZ6wA7c4b8&feature=youtu.be>

An error line appears in the gromacs window: "IMD: Failed to shutdown 
socket. Did the client already disconnect?" and "IMD: Error in file 
gromacs-2019.3/src/gromacs/imd/imdsocket.cpp on line 293."

How should I proceed to help this bug getting fixed ?

Best regards,

Xavier Martinez, Ph.D

CNRS-IBPC LBT, Paris