Help Topic: Poking the MOOSDB

Maintained by: mikerb@mit.edu         Get PDF

Poking the MOOSDB

Poking refers to the idea of publishing a variable-value pair to the MOOSDB. Many apps publish to the MOOSDB during the course of normal operation. Poking implies a publication that perhaps was not planned, or outside the normal mode of business. It is often very useful for debugging. Here we describe the uPokeDB tool.

Where to get more information:

    Or simply: 

 $ uPokeDB --web

Poking the MOOSDB with uPokeDB    [top]

uPokeDB is a command-line tool for poking the MOOSDB with one or more variable-value pairs. Poking the MOOSDB requires knowing where the MOOSDB is running in terms of its IP address, (ServerHost parameter), and port number, (ServerPort parameter). These may be specified on the command line to uPokeDB, but for our purposes here we assume the existence of a mission file, alpha.moos with this information: 

  // (wget http://oceanai.mit.edu/2.680/examples/alpha.moos)
  ServerHost = localhost
  ServerPort = 9000
  Community  = alpha

Your goals in this part are:

  1. Open two terminal windows and launch the MOOSDB and uXMS as done previously: 
 $ MOOSDB alpha.moos
 $ uXMS alpha.moos --all

Now open a third terminal window for poking the MOOSDB as follows: 

 $ uPokeDB DEPLOY=true SPEED=2 alpha.moos

Note the two new variables, DEPLOY and SPEED, appearing in the uXMS window. It should look something like: 

 ==============================================================
 uXMS_655                                              0/0(204)
 ==============================================================
 VarName     (S)  (T)  (C)  VarValue (SCOPING:EVENTS)
 ----------  ---  ---  ---  -------------------------
 DB_CLIENTS                 "uXMS_655,"
 DB_TIME                    1386249435.276804
 DB_UPTIME                  46.213629
 DEPLOY                     "true"
 SPEED                      2
  1. Note the variable values in uXMS. DEPLOY has the value "true" with double quotes, indicating that it is a string. The variable SPEED is of type double, indicated by the lack of quotes. The types were inferred by uPokeDB by heuristically checking whether the arguments are numerical or not. But sometimes you do want to publish a string with a numerical value. Try posting the variable HEIGHT with the string value of "192", noting the colon-equals instead of equals: 
 $ uPokeDB HEIGHT:=192 alpha.moos

Note the new variable, HEIGHT, appearing in the uXMS window. It should look something like the below output, where in this case, the (S)ource column is expanded to show the source of the postings. 

 ==============================================================
 uXMS_655                                              0/0(347)
 ==============================================================
 VarName     (S)ource     (T)  (C)  VarValue (SCOPING:EVENTS)
 ----------  ---------    ---  ---  -------------------------
 DB_CLIENTS  MOOSDB_alpha           "uXMS_655,"
 DB_TIME     MOOSDB_alpha           1386250092.847527
 DB_UPTIME   MOOSDB_alpha           703.784353
 DEPLOY      uPokeDB                "true"
 HEIGHT      uPokeDB                "192"
 SPEED       uPokeDB                2

Further things to try Using uPokeDB    [top]

Here's some other things to consider and try:

  1. Trying poking the DEPLOY variable to the MOOSDB a second time, this time with: 
 $ uPokeDB DEPLOY=100 alpha.moos

Does the value of DEPLOY change? If not, why not?

  1. Create a simple script of pokes on the command line as follows: 
 $ uPokeDB APPLES=1 alpha.moos; sleep 5; uPokeDB APPLES=2 alpha.moos;

If you're new to the command line environment, the semicolon above separates successful command line invocations. The sleep command is a common shell utilitity that will simply pause a given number of seconds before completing.

  1. Another way to execute the same simple script as above is to store the above three commands in a file named, for example, myscript: 
 uPokeDB APPLES=1 alpha.moos
 sleep 5
 uPokeDB APPLES=2 alpha.moos

With the above file you can make the two successive pokes to the MOOSDB, with five seconds in between, with: 

 $ source myscript

There are many other ways of poking the MOOSDB. All MOOS apps that publish anything are examples. Of course many MOOS applications publish a fixed set of variables that are not easily changeable without re-coding. But certain apps like uTimerScript and pMarineViewer have built-in configuration file parameters for poking the MOOSDB in user configurable ways.

Page built from LaTeX source using texwiki, developed at MIT. Errata to issues@moos-ivp.org. Get PDF