Using and Administering

Examples

A sample program called para_api.c is provided in the samples/llpara subdirectory of the release directory, usually /usr/lpp/LoadL/full.

In order to run this example, you need to do the following:

1. Copy the sample Makefile and the sample program called para_api.c to your home directory.
2. Update the startCmd variable in para_api.c to reflect your home directory versus /usr/lpp/LoadL/full/samples/llpara. For example:

   char *startCmd = "/home/user/para_api -s";
   

3. Issue make to create the executable para_api.
4. Update your job command file as follows:

   
   

   #!/bin/ksh # @ initialdir = /home/user # @ executable = para_api # @ output = para_api.$(cluster).$(process).out # @ error = para_api.$(cluster).$(process).err # @ job_type = parallel # @ min_processors = 2 # @ max_processors = 2 # @ queue

5. Submit the job command file to LoadLeveler.

   The syntax to invoke the Parallel Master is:

     para_api
   

   The syntax to invoke the Parallel Slave is:

     para_api -s
   

   The Parallel Master does the following:

   • Acquires the hostlist through the ll_get_hostlist API and prints out the returned fields.
   • Starts a Parallel Slave task by executing the command specified in the StartCmd variable on all hosts returned in the hostlist.
   • Acquires the socket connected to the Parallel Slave's standard I/O (stdio).
   • Writes a command over the socket to verify stdin.
   • Reads acknowledgments over the socket to verify stderr and stdout.
   • Prints out host names and acknowledgments.
   Example output follows:

   num_nodes=2
    
   name=host1.kgn.ibm.com address=9.115.8.162 switch_number=-1
    
   name=host2.kgn.ibm.com address=9.115.8.164 switch_number=-1
    
   Connected to host1.kgn.ibm.com at sock 3
   Received acko "8000" and acke "10000" from host 0
    
   Connected to host2.kgn.ibm.com at sock 4
   Received acko "8001" and acke "10001" from host 1
    
   <Master Exiting>
   

   The Parallel Slave does the following:

   • Reads command from stdin.
   • Writes acknowledgment to stdout and stderr.