PT(4) PT(4) NAME pt - interprocess I/O junctor files DESCRIPTION These special files, conventionally collected in directory /dev/pt, provide a facility for interprocess communication. The name `pt' comes from `pseudo-tty,' after vaguely similar mechanisms in other systems. Pt files come in even-odd pairs. If one process opens an odd numbered pt file, and another opens the corresponding even file, then data written on one file is available for reading on its partner, in symmetrical full-duplex fashion. `Record' boundaries are preserved, where a record is the information presented in one write call. Thus a reader attempting to read into a large buffer will receive chunks of data corresponding to the amounts generated by each call to write. The odd-numbered member of a pair is the master. Masters and slaves differ only in the rules for opening; IO is sym- metrical. Master pt files may be opened by at most one pro- cess. Thus the following strategy is appropriate for estab- lishing communications: one process searches the /dev/pt directory for an odd-numbered file it can open; when it finds one, it publishes the name in some way. Typically, it will either fork off a child process that knows the name by sharing variables, or place the name in some conventional place. Then one or more slave processes may open the corre- sponding even-numbered file and communicate with the master. Once both even- and odd-numbered members of a pair have been opened, the communications channel is shut down when the file on either side is closed for the last time. Thus a master process that expects several unrelated processes to open the even pt corresponding to its odd pt should keep the even pt open. Pt files are stream devices and line discipline modules (see stream(4)) may be attached to them. SEE ALSO stream(4), ptopen(3) BUGS Writes are not atomic, in general. However, several slow writers may write small messages to a fast reader and achieve the illusion of atomicity.