An interesting module, and implemented well. As constructive critisim, there's two things I'd like to mention.

First, and simplest, you document a return value of undef on timeout but you actually return 0. This can trip people up so you might want to fix it.

Second, I think that, perhaps, you're handling nested time_limit()'s incorrectly (not that I really know what I mean by "correct"). Consider:

#!/usr/bin/perl -w

use TimeLimit;

$outter1 = time;
time_limit {
  $inner1 = time;
  time_limit { sleep 7 } 5;
  $inner2 = time;
} 3;
$outter2 = time;

$elapsed_outter = $outter2-$outter1;
$elapsed_inner  = $inner2-$inner1;
print "Seconds elapsed for outter limit: $elapsed_outter\n";
print "Seconds elapsed for inner limit:  $elapsed_inner\n";
[download]

The output of this test program is:

Seconds elapsed for outter limit: 5
Seconds elapsed for inner limit:  5
[download]

Whereas anyone looking at the outter time_limit() would think that it should return no more than 3s later. (Imagine the inner time_limit() call being burried in a called subroutine...)

Further, what if the code you expected to cause a timeout was after the inner time_limit() call? Because your code actually resets the alarm(), it could take even longer.

Of course, for most applications where you would want to time_limit() some code, you wouldn't really care if it takes a little bit longer to time out than you expected, so it shouldn't matter much. Also, I can't think of a very elegant solution that would handle such cases. I never did understand why they limited it to one alarm per process...

Well, I hope that at least gives you some ideas to work with. In fact, I think I might just have to look into writing a module that would offer a more robust replacement for alarm. :-) And again, congrats on a good module.

Happy coding.

bbfu
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