On how to select the right tool for a given task Post: 302249572

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Top Forums Shell Programming and Scripting On how to select the right tool for a given task Post 302249572 by neked on Tuesday 21st of October 2008 03:42:23 PM

10-21-2008

Registered User

Quote:

Originally Posted by neked

3) Even if you were a parameter substitution guru, and you used meaningful variable names and comments to make clearer what your parameter substitution tricks do, then future maintainers of the code might not be the same. This bit me a couple of days ago: I had to spend 20 minutes debugging a bash script riddled with those parameter substitution scripts. I estimate I would've spent closer to 5 minutes if the code was written using more obvious external tools (sed, basename, awk). This is about 15 minutes of human time wasted in order to save less than a few milliseconds of CPU time. Especially since the whole script runs only once a night, and does not exceed 0.030 seconds runtime on my modest 7 years old computer.

I've just substituted all occurrences of parameter substitutions with equivalent sed and basename commands in the script I refer to above, the execution time went up from an average of 0.030 seconds to 0.061 seconds. That means parameter substitution use shaved an average of 0.03 seconds per run. Considering that I've had to spend roughly 15 more minutes understanding the code to debug it, this means the code has to run 15*60/0.03 times to pay off the extra time I invested to debug it. That's 30,000 times. Considering that it runs once a night, this means we'll have to wait more than 80 years!

Even after 80 years, those 0.020 seconds shaved off CPU time per night are not as worthy to me as 15 minutes of my time which I could've spent aternative activity redacted

Last edited by Perderabo; 10-21-2008 at 05:49 PM.. Reason: clean up language

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LEARN ABOUT PHP

set_time_limit

SET_TIME_LIMIT(3)							 1							 SET_TIME_LIMIT(3)

set_time_limit - Limits the maximum execution time

SYNOPSIS

       bool set_time_limit (int  $seconds)

DESCRIPTION

	Set  the  number of seconds a script is allowed to run. If this is reached, the script returns a fatal error. The default limit is 30 sec-
       onds or, if it exists, the max_execution_time value defined in the php.ini.

	When called, set_time_limit(3) restarts the timeout counter from zero. In other words, if the timeout is the default 30  seconds,  and	25
       seconds into script execution a call such as set_time_limit(20) is made, the script will run for a total of 45 seconds before timing out.

PARAMETERS

	      o $seconds
		- The maximum execution time, in seconds. If set to zero, no time limit is imposed.

RETURN VALUES

	Returns TRUE on success, or FALSE on failure.

NOTES

       Warning

	       This  function  has no effect when PHP is running in safe mode. There is no workaround other than turning off safe mode or changing
	      the time limit in the php.ini.

       Note

	       The set_time_limit(3) function and the configuration directive max_execution_time only affect the  execution  time  of  the  script
	      itself.  Any  time  spent  on activity that happens outside the execution of the script such as system calls using system(3), stream
	      operations, database queries, etc. is not included when determining the maximum time that the script has been running. This  is  not
	      true on Windows where the measured time is real.

SEE ALSO

       max_execution_time, max_input_time.

PHP Documentation Group 													 SET_TIME_LIMIT(3)