picire 21.8

Common settings

• --parallel: Enables Picire to run in multiprocess mode. (Otherwise, the original single-process variant will run.)

• -j <num>: Defines the maximum number of parallel jobs.

• --combine-loops: The base algorithm had a dependency between subset and complement-based reduce loops, but because of the sequential nature of its implementation, it had no effect on efficiency. However, in parallel mode, this separation becomes a potential sub-optimality. With this option, the two reduce loops run combined for additional performance. Further details about the algorithm variants are available in the cited papers.

• --complement-first: For some input types, subset-based reduce is not as effective as the complement-based one (sometimes, aggressively removing too big parts of the input eliminates the interestingness as well). By default, Picire performs subset-based reduce before complement-based reduce, which can result in many superfluous checks for such inputs. This flag forces to start with complement checks.

• --subset-iterator / --complement-iterator: Guide the iteration strategies of the subset and complement-based reduce loops.

  • forward: Start investigating subsets (or complements) from the beginning of the input.

  • backward: Start investigating subsets (or complements) from the end of the input. The goal is to reduce the number of semantic violations (assuming that definitions - like variable declarations - appear before uses).

  • skip: Completely avoids the subset or complement checks (mostly used with --subset-iterator).

For the detailed options, see picire --help.

Tester script

The tester script is expected to take one command line argument, the path of a test case, and it has to exit with 0 if the test is interesting and with non-zero otherwise. An example tester script that runs an arbitrary target application and checks if it fails on an assertion might look like the one below:

#! /bin/bash
timeout --foreground 10 <path/to/the/target/application> $1 2>&1 | grep -q "Assertion failed";

Remarks:

• The <path/to/the/target/application> should either be an absolute path to the target application or the application should be on the search path (i.e., $PATH).

• $1 is the single and mandatory command line argument containing the path of a test case.

• If the target application is not guaranteed to exit, then it’s worth running it with timeout to limit the amount of time waiting for producing the expected behaviour.

• If the target is run with timeout then the --foreground flag can also be useful as it allows forwarding the KILL signals (used by the parallel implementation) through the timeout’s process group. This enables us to stop all alive parallel processes when a new interesting configuration is found already.

• If the interestingness decision is based on the content of the output then using grep (perhaps with -q or --quiet) might be a right choice, since it returns 0 if the pattern was found and 1 if not. Exactly the return value Picire expects.

A common form of Picire’s usage:

picire --input=<path/to/the/input> --test=<path/to/the/tester> \
       --parallel --subset-iterator=skip --complement-iterator=backward