ABL accesses named pipes using unbuffered I/O. This means that processes that read from and write to the same named pipe synchronize their reads and writes with each other. In ABL, this is true for opening as well as reading and writing named pipes. When an ABL process opens a named pipe for input, it blocks (waits) until another process opens the same named pipe for output. The reverse is also true—when an ABL process opens a named pipe for output, it blocks until another process opens the same named pipe for input.

When a process writes to a named pipe, the process blocks until another process reads from the named pipe. Similarly, when a process attempts to read from a named pipe, but there is nothing to read, the process blocks until something is written to the named pipe.