CTP is a C library that offers a pool thread, based on pthread, that is the only dependency.
While easy to use, it has some interesting features:

• Cross platform: Standard C; Windows, linux, bsd; 32/64 bit
• Can spawn the best number of threads according to detected cpu
• Lazy thread activation
• Ability to pause/resume
• Automatic/custom queue size
• Can block when adding work or discard if queue is full (best effort)
• Possibility to know how many threads were effectively spawned
• Dedicated API to query status in any moment (paused/idle/working)
• Easy transition from pthread, the work prototype has the same signature

Just compile the .c file and add it to your linker, as object or library. If using gcc/clang, remember to complie with -pthread and link with -lpthread

If you want to use visual studio, or other windows compiler, use package https://sourceware.org/pthreads-win32

While compiling ctp (The library, not the clients), you can pass these variables:

• CTP_DEFAULT_THREADS_NUM
• CTP_MULTIPLY_QUEUE_FACTOR
• CTP_MIN_QUEUE_SIZE

CTP_DEFAULT_THREADS_NUM is used only if you pass 0 to init, and ctp fails to detect core number.
In this case, CTP_DEFAULT_THREADS_NUM threads will be used. Default is 4.
If you pass 0 to init in the second parameter, the queue size will be calculated according to 3 parameters:
threads-num, CTP_MULTIPLY_QUEUE_FACTOR and CTP_MIN_QUEUE_SIZE. The formula is:
max(threads-num * CTP_MULTIPLY_QUEUE_FACTOR, CTP_MIN_QUEUE_SIZE)
The default value for CTP_MULTIPLY_QUEUE_FACTOR is 8.
The default value for CTP_MIN_QUEUE_SIZE is 256

For API details see header file. Test file may help too