# Reverse client-server connection fails with more than one MPI process

**URL:** https://discourse.paraview.org/t/reverse-client-server-connection-fails-with-more-than-one-mpi-process/3207
**Category:** ParaView Support
**Created:** [December 18, 2019, 5:00pm UTC](https://discourse.paraview.org/t/reverse-client-server-connection-fails-with-more-than-one-mpi-process/3207 "2019-12-18T17:00:42Z")
**Posts on this page:** 1
**Showing post:** 3

<div class="post-metadata">

### Author: ![XavierStuvw](https://discourse.paraview.org/user_avatar/discourse.paraview.org/xavierstuvw/32/2619_2.png) [@XavierStuvw](https://discourse.paraview.org/u/XavierStuvw)
#### Post date: [January 13, 2020, 3:44pm UTC](https://discourse.paraview.org/t/reverse-client-server-connection-fails-with-more-than-one-mpi-process/3207/3 "2020-01-13T15:44:54Z")

</div>

## 1. MPI compatibility

Following the suggestion of @Dave_DeMarle, I have made sure that both client and server sides are built with the flag `USE_SYSTEM_mpi=ON` so that when I launch a command

> mpirun -np 4 $PV570DIR/bin/pvserver --hostname=$(hostname -a) -rc --client-host=[client-url] --disable-xdisplay-test --timeout=1

the mpirun version at run time is the same as at compile time. Also, client and server tap from the same pool of programs and shared libraries.

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## 2. cmake settings

The external cache variables in CMakeCache.txt are the same in one setting. In another setting they differ because the client has **qt5** , the server **elg**. In both settings problems occur.

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## 3. setting qt5+elg with `--disable-xdisplay-test`

### 3.1 server starts

I receive the following messages

> Connecting to client (reverse connection requested)…  
> Connection URL: csrc://[client-url]:11111  
> Connecting to client (reverse connection requested)…  
> Connection URL: csrc://[client-url]:11111  
> Connecting to client (reverse connection requested)…  
> Connection URL: csrc://[client-url]:11111  
> Connecting to client (reverse connection requested)…  
> Connection URL: csrc://[client-url]:11111

### 3.2 client connects

At the client side I see the notifications

> Accepting connection(s): [client-hostname]:11111  
> Accepting connection(s): [client-hostname]:11111

At the server side

> [31m( 26.150s) [pvserver]vtkSocketCommunicator.c:808 ERR| vtkSocketCommunicator (0x56537cb0bff0): Could not receive tag. 1010580540  
> [31m( 26.150s) [pvserver]vtkSocketCommunicator.c:557 ERR| vtkSocketCommunicator (0x56537cb0bff0): Endian handshake failed.  
> Client connected.  
> [31m( 26.150s) [pvserver]vtkTCPNetworkAccessMana:333 ERR| vtkTCPNetworkAccessManager (0x56537c975b60):

> Connection failed during handshake. vtkSocketCommunicator::GetVersion()  
> returns different values on the two connecting processes  
> (Current value: 100).  
> Exiting…

So one connection works and the other exits. The other two idle connections continue to loop over the sequence 472-51-396

> [31m( 25.176s) [pvserver] vtkSocket.cxx:472 ERR| vtkClientSocket (0x5622bf734610): Socket error in call to connect. Connection refused.  
> [31m( 25.176s) [pvserver] vtkClientSocket.cxx:51 ERR| vtkClientSocket (0x5622bf734610): Failed to connect to server [client-url]:11111  
> [33m( 25.176s) [pvserver]vtkTCPNetworkAccessMana:396 WARN| vtkTCPNetworkAccessManager (0x5622becadb60): Connect failed. Retrying for 34.9704 more seconds.

until time-out, while the client operates.

### 3.3 clients works

I manage to operate at the client side and load the data from the server side. At the server there is one process `pvserver` at work. Effectively a sequential job.

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## 4. setting qt5+elg without `--disable-xdisplay-test`

At the point of connection I have 1 working connection (hence a pvserver process), 3 rapid exits and 0 timeouts. The threefold exit message is again

> Connection failed during handshake. vtkSocketCommunicator::GetVersion() returns different values on the two connecting processes (Current value: 100).

and `pvserver` works sequentially as in Sec. 3.3.

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## 5. setting qt5+qt5 with `--disable-xdisplay-test`

In this case I also set the cache variable `Qt5_DIR` to where I could locate the file `sb-qt5-configure.cmake`.

### 5.1 server starts

At the server side I see that `prgep pvserver` lists four process IDs.

### 5.2 client connects

However, of the four processes only one connects to the client and the other three keep on trying.

### 5.3 client does not work

When I try to load data from the server the connection at the server side crashes with the message

> X Error of failed request: BadValue (integer parameter out of range for operation)  
> Major opcode of failed request: 154 (GLX)  
> Minor opcode of failed request: 3 (X\_GLXCreateContext)  
> Value in failed request: 0x0  
> Serial number of failed request: 52  
> Current serial number in output stream: 53
> 
> Primary job terminated normally, but 1 process returned a non-zero exit code. Per user-direction, the job has been aborted.

with three SIGTERMS and finally with

> mpirun detected that one or more processes exited with non-zero status, thus causing the job to be terminated. The first process to do so was:  
> Process name: [[64131,1],3]  
> Exit code: 1

These errors are why I moved to the qt5+egl configuration, see [top post](https://discourse.paraview.org/t/reverse-client-server-connection-fails-with-more-than-one-mpi-process/3207) .

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## 6. setting qt5+qt5 without `--disable-xdisplay-test`

One connection works. The other one exits with the same connection-failed-during-handshake as in Sec 4, and then the system crashes with the X-error, 3 SIGTERMs and the MPI job termination as in Sec 5.3.

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## 7. similar issues reported?

- [Client / Server configuration](https://discourse.paraview.org/t/client-server-configuration/69)
- [Cannot connect to Catalyst Live visualization on Mac OS X](https://discourse.paraview.org/t/cannot-connect-to-catalyst-live-visualization-on-mac-os-x/301/)
- [ParaView version](https://discourse.paraview.org/t/paraview-version/2214)
- [[Paraview] Connecting to pvserver](https://paraview.paraview.narkive.com/ogEJvINP/connecting-to-pvserver)

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## 8. questions

Where could the problem be?  
How to get pvserver working parallel in full glory?  
Tips and/or directions?

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