Travis CI (Linux:gcc, Linux:clang, Mac OS X:clang)

TAIL

Interview Q&A task: write a command line program that outputs the last five lines of a file and provide the corresponding set of automated test cases.

Implementation

The two strategies were choosen:

1. For regular files the program search new-lines backwards though the files, using the sliding window. Two distinct implementations for mapping file into window in the memory: with mmap regions and with malloc+read_seek. It is expected that mmap implementation will be little faster (NB: which is not happen however).

2. For secial files, sockets, fifos, pipes the program reads the whole file and stores the 5 last new-lines position into the ring buffer. The file context is also stored in ring buffer, that is freed dynamicaly.

So the program can operate in three modes: mmap, read and pipe.

How to build and build system

CMake was choosen as the primary build system.

Also the autoconf solution (configure+Makefile) exists as the poorman fallback. The tests automation however is implemented only for CMake. Autoconf only build the program.

So the way to compile everything is:

mkdir build; cd build; cmake ..; cmake --build .

To run tests use:

ctest

To run benchmarks:

cd tests; ./bench.sh

Testing

The helper in c lanuage gen_text was developed that can generate files with fixed and/or random content with given number of lines with a given length.

CTest checks that program can be started at all and then starts Python/Behave tests. Behave tests generates lot of test files with random content and compares the output of out "Tail" program with the output of POSIX tail utility. We are considering that tests pass it the output is the same.

Coverage

I'm testing the cases for 1-7 lines in a file. Also I'm specifically testing for the cases when input file does not ends with newline. I'm also test files with line length for 0 to 10000 chars.

Benchmarking

Each working mode is benchmarking on the files from 1 to 10000 lines with line length in range [1:10000]. Each benchmark runs several times (currently 3). I choose not start benchmarks in parallel to simplify integration with Travis and to get more steady results.

Tail in 'pipe' mode

Tail in 'mmap' mode

Tail in 'read' mode

Integration

The project is hosted in GitHub, I set up the continious integration with the open service Travis CI. On every git commit it builds the program and run the tests on Linux (gcc and clang) and MacOS (clang) environment. I also integrate the project with cloud code analitic service "coverity scan".

Possible Improvements

1. Integration with MyDash (CTest)
2. Store Behave results in jUnit format, parse it and represent in a form of table.
3. Push graphs with benchmarks results from Travis CI worker back to GitHub.
4. CI with Windows (AppVeyor)