Question

I need to write a sorting program in C and it would be nice if the file could be sorted in place to save disk space. The data is valuable, so I need to ensure that if the process is interrupted (ctrl-c) the file is not corrupted. I can guarantee the power cord on the machine will not be yanked.

Extra details: file is ~40GB, records are 128-bit, machine is 64-bit, OS is POSIX

Any hints on accomplishing this, or notes in general?

Thanks!

To clarify: I expect the user will want to ctrl-c the process. In this case, I want to exit gracefully and ensure that the data is safe. So this question is about handling interrupts and choosing a sort algorithm that can wrap up quickly if requested.

Following up (2 years later): Just for posterity, I have installed the SIGINT handler and it worked great. This does not protect me against power failure, but that is a risk I can handle. Code at https://code.google.com/p/pawnsbfs/source/browse/trunk/hsort.c and https://code.google.com/p/pawnsbfs/source/browse/trunk/qsort.c

Answer 1

Install a handler for SIGINT that just sets a “process should exit soon” flag.

In your sort, check the flag after every swap of two records (or after every N swaps). If the flag is set, bail out.