Synchronization functions are now thread pool specific

[marwankallal]

Instead of using pthread_kill() to send signals, we can use pthread_sigqueue() to pass a pointer of the pausing threadpool to the signal handler. From there, I've kept the previous sleep(1) loop to wait for thpool_resume()

(fix for #13)

[Pithikos]

Thanks for the work! I did try the fix and it seems to work. The only annoying thing is the warnings during compilation and as I found out this works only if we include #define _GNU_SOURCE in the top of the source code which unfortunately means that the code stops being POSIX compliant.

You think there is a way to rework this implementation to not deviate from the POSIX standard?

[marwankallal]

That is true, I'll try to find a POSIX compliant way and add it to this PR.

[Pithikos]

I close this since there are not any new updates. Feel free to re-open if anything changes.