Application using VI Server suddenly crashes. Why is it ?

Question

Hi everyone !
I´m developing an application which makes extensive use ov VI Server. I´m going to give a short explanation of it before going ahead.
This application is supposed to run, simultaneously, on three different PCs, namely, ESTACAO_A, ESTACAO_B and ESTACAO_C, which share an Ethernet network. One feature of it is that it has a master / client architecture which means that, when one of the named PCs is the master, the others are the slaves. Anytime the user operating a slave PC can require command from that operating the master PC and, if this user acquiesces it, it becomes the new master.
This application communicates with an PLC using LabVIEW DSC and the master / client architecture was necessary because the application must run on three diferent computers, as said before, and each one of the slaves must monitor the state of the process under surveillance. That´s when VI Server gets in ! I found it was easier to implement this architecture using it than if I decided to use the TCP/IP VIs. The problem is that when I run the application on the PCs ESTACAO_A and ESTACAO_B only, ESTACAO_A and ESTACAO_C only and on the PCs ESTACAO_B and ESTACAO_C it works quite well but, when it is executed on the three PCs, and the user of ESTACAO_B requires to become the master, sometimes the application will crash on ESTACAO_B, and that will make the application crash on the other two PCs, since they won´t be able to communicate with the PC which was supposed to become the new master, in this case, ESTACAO_B. For the sake of information I tell you that when I ping the other machines on ESTACAO_B it takes a longer time to respond than that taken when I ping the other machines on ESTACAO_A and ESTACAO_C. I´m beginning to think it has something to do with it.
Any help will be deeply appreciated.

Answer 1

Thanks for the interest in helping me solve my problem, Philip !
Sorry for the delay but here is the library file containing the VIs used to implement the MASTER / SLAVE architecture I've talked about. Also, I decided that it would be a great help if I provided you with the additional information :
Below follows a short explanation of the most important VIs found on the attached .llb file.
PROTOTIPO_TESTE_PEDINDO.vi : it´s the main VI and implements a state machine architecture to handle the required features of the application.
The state machine is composed of the following states :
"Tenta ser MESTRE" : the PC in question tries to become the MASTER station.
"Envia comandos para o PLC" : in this state the application sends and receives data from the PLC and, when necessary, exhibits a window when another station has required to become the new MASTER, asking for the acquiescence of the user currently operating the actual MASTER station.
"Leitura de dados do MESTRE" : here the station first tries to identify which one of the stations - that is, ESTACAO_A, ESTACAO_B, ESTACAO_C and ESTACAO_D - is the actual MASTER. In case that there´s a MASTER, it´ll read data from the MASTER station through some VI Server subVIs I´ve created. Also, it´ll send a cluster consisting of a string specifying the current station address and a boolean value indicating that it has required command of the system.
"Fim da supervisão" : This is the last state before the aplication ends.
Escreve_Serial.vi : Sends a command to a switch connected to a serial port of the current station to swith to the port connected to it.
COM_PLC.vi : Initializes the Tag Engine, so that the Lookout driver can be loade to allow data exchange with the PLC.
ATIVA_DESATIVA.vi : Disables or enables the controls of the front panel, depending of the state of execution of the station in question, that is, SLAVE or MASTER.
CONTROLE_DA_VI.vi : This subVI sends a command to run another VI or to change the value of a boolean control named FIM to true, both commands are sent through VI Server.
CRIA_MENSAGEM.vi and MENSAGEM.vi : The first one creates a message telling which one of the currently SLAVE stations want to be the new MASTER and the last one shows it on the screen.
IDENTIFICA_MESTRE.vi : Identifies which station is the actual MASTER; if there´s a MASTER, it´s output will be a string composed of its address, if not it´s output will be a NIL string.
LEITURA.vi : Through the VI Server, this VI reads the values of controls and indicators of the MASTER station and assigns them to their correspondents on the SLAVE station by means of controls and indicators references.
PEDIDO_DE_COMANDO.vi : Sends a data cluster consisting of a string specifying which station required command of the system and a boolean value of true to the specified station.
Attachments:
PROTOTIPO_TESTE_PEDINDO.llb ‏2360 KB