- Each sendmsg() transmits no more than port->max_size payload data.
- Longer buffers are fragmented and send using multiple sendmsg() calls.
- On receive side, buffers are connected in chain.
- Number of handler calls is the same as number of nxt_port_socket_write()
calls.
- nxt_buf_make_plain() function introduced to make single plain buffer from
the chain.
Use counter helps to simplify logic around port and application free.
Port 'post' function introduced to simplify post execution of particular
function to original port engine's thread.
Write message queue is protected by mutex which makes port write operation
thread safe.
To allow use port from different threads, the first step is to avoid using
port's memory pool for temporary allocations required to send data through
the port. Including but not limited by:
- buffers for data;
- send message structures;
- new mmap fd notifications;
It is still safe to use port memory pool for incoming buffers allocations
because recieve operation bound to single thread.
