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→C example
== C example ==
== C example ==
=== The Problem and the Code ===
=== The Problem and the Code ===
Consider the following simple, well-suited job for a cluster: comparison of independent Monte Carlo calculations of π. The following C-program implements random sampling of points withing a square bounding a circle. (The probability of landing inside the circle can be shown to be π/4)
<syntaxhighlight lang="c">
<syntaxhighlight lang="c">
#include <stdio.h>
#include <stdio.h>
Queue 50</pre>
Queue 50</pre>
The last line specifies that 50 instances should be scheduled on the cluster. The description file specifies the executable and the arguments passed to it during execution. (In this case we are requesting that all instances iterate 10e9 times in the program's sampling loop.) The requirement field insists that the job stay on the Statistics Cluster. (All statistics nodes are labeled with "stats group" in their Condor ClassAds) Output and error files are targets for standard out and standard error streams respectively. The log file is used to by Condor to record in real time the progress in job processing. Note that this setup labels output files by process number to prevent a job instance from overwritting files belonging to another. The current values imply that all files are to be found in the same directory as the description file.
The last line specifies that 50 instances should be scheduled on the cluster. The description file specifies the executable and the arguments passed to it during execution. (In this case we are requesting that all instances iterate 10e9 times in the program's sampling loop.) The requirement field insists that the job stay on the Statistics Cluster. (All statistics nodes are labeled with "stats group" in their Condor ClassAds) Output and error files are targets for standard out and standard error streams respectively. The log file is used by Condor to record in real time the progress in job processing. Note that this setup labels output files by process number to prevent a job instance from overwritting files belonging to another. The current values imply that all files are to be found in the same directory as the description file.
The <i>universe</i> variable specifies the condor runtime environment. For the purposes of these independent jobs, the simplest "vanilla" universe suffices. In a more complicated parallel task, with checkpointing and migration, MPI calls etc., more advanced run-time environments are employed, often requiring specilized linking of the binaries. The lines specifying transfer settings are important to avoid any assumptions about accessibility over nfs. They should be included whether or not any output files (aside from standard output and error) are necessary.
The <i>universe</i> variable specifies the condor runtime environment. For the purposes of these independent jobs, the simplest "vanilla" universe suffices. In a more complicated parallel task, with checkpointing and migration, MPI calls etc., more advanced run-time environments are employed, often requiring specilized linking of the binaries. The lines specifying transfer settings are important to avoid any assumptions about accessibility over nfs. They should be included whether or not any output files (aside from standard output and error) are necessary.
=== Job Submission and Management ===
=== Job Submission and Management ===
While logged in on stats, the job is submitted with:
<syntaxhighlight lang="bash">
<syntaxhighlight lang="bash">
condor_submit calcpi.condor
condor_submit calcpi.condor
pi=3.141797520000
pi=3.141797520000
...</pre>
...</pre>
== R example ==
== R example ==
=== The Problem and the Code ===
=== The Problem and the Code ===