libshbuf 0.0.3

libshbuf introduces a new IPC concept: the "shared buffer", a more flexible and faster alternative for standard Unix FIFOs.
Take some shared memory, flavour it with semaphore-based locking and change notifications, and refine it with an easy-to-use API and you get libshbufs "shared buffers".
Main features:
- Normally better latency and throughput
- Full access to the buffer at any time
- Connecting processes need not to be children of each other
- Arbitrary buffer lengths
- Memory mapped
- Backlog
The implementation is based on SysV shared memory, semaphores and message queues. It makes use of POSIX pthreads.
Both an easy understandable C library and a basic Python module are provided.
Version 0.0.3 is stable and feature complete.
The concept of "shared buffers" is explicitly designed for high thoughput, low latency streaming of data (e.g. audio) between two processes, where a Unix FIFO is not enough. Thus it is optimized for exactly two connecting peers, a minimum of locking and minimum of copying of memory.
For each shared buffer two shared memory blocks, a semaphore and a messages queue are created. The first shared memory block (aka "control memory block") contains some watermark information about the shared buffer. The second contains the buffer itself.
The semaphore is used for locking access to the control block. The message queue is used for signalling the other side on changes of the buffer.
A shared buffer provider is a process which creates it with with shbuf_create(). A new key for it will be registered (the key is an integer value, the key_t of the control shm). A shared buffer client is the other side of the buffer: it opens an existing buffer with shbuf_open(key).
Only one client and one provider may be connected at once. When using the notifying feature of libshbuf a background thread is started, which listens on the message queue for certain messages. It forwards these messages to a classic FIFO. The main program may listen on this FIFO with a standard select() or poll().