Option for disabling parallel execution

[vaclav-easymarkit]

It could be helpful especially for the machines with weak CPU performance. I could try to prepare pull-request if you like to.

[zdenekdrahos]

I wouldn't specify number of tasks. I see two main use cases:

• run everything in parallel (current behaviour)
• don't use parallelism at all

So I think that simple switch would be good enough. Just like in --output:

# run parallel tasks
phpqa
phpqa --execution parallel

# don't use parallelism
phpqa --execution single
phpqa --execution something_else_than_word_parallel

If --execution equals parallel then ParallelExec is used. Otherwise tasks are executed sequentially with ExecStack.

No BC is introduced (parallel execution is default option) and the solution is extensible in the future (if --execution is integer then it can be used as number of parallel processes). It's simple change compared to dividing processes into parallel groups.

[vaclav-easymarkit]

Yes, you are right, it will be sufficient.