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55 To aid the programmer in developing programs which are comprised of
57 processes, the different choices are discussed and a series of example
58 programs are presented. These programs
90 Pipes are another form of descriptor that have been used in UNIX
110 has necessitated some change in the way that descriptors are created.
120 available. These new possibilities are allowed in the Berkeley UNIX IPC
131 communication that are supported by Berkeley UNIX 4.4BSD.
132 A series of examples are presented that create processes that communicate
135 Finally, the calls that actually transfer data are reviewed.
140 for the programmer trying to construct programs which are comprised of
146 to the computation that occurs when the compiled statements are run.
149 various directions and then end. These are single process programs.
163 therefore, typically precede, or are included in, an if-statement.
166 The descriptors can represent open files or sockets (sockets are communication
167 objects that will be discussed below). Descriptors are referred to
168 by their index numbers in the table. The first three descriptors are often
170 These are the standard input, output and error.
173 (devices are also treated as files in UNIX), the child's input will
233 The two ends are not equivalent. The socket whose index is
260 If the parent and child are to have a two-way conversation,
266 is, all messages sent through the pipe are placed in order
269 stream, he is given as many bytes as are available, up
283 communication in both directions. Since socketpairs are
292 These are the parameters shown in the example.
308 The constants AF_UNIX and SOCK_STREAM are defined in
329 Pipes and socketpairs are a simple solution for communicating between
333 Neither standard UNIX pipes nor socketpairs are
339 also the case when the communicating processes are on separate machines.
347 There are several domains for sockets.
348 Two that will be used in the examples here are the UNIX domain (or AF_UNIX,
368 is reliable, error-free, and, as in pipes, no message boundaries are
379 be received, although this is not guaranteed. Often datagrams are
383 The individual datagrams will be kept separate when they are read, that
384 is, message boundaries are preserved.
402 keeps track of the names that are bound to sockets,
405 This code also keeps track of the names that are bound to sockets.
436 These sockets are in the UNIX domain.
453 Names in the UNIX domain are path names. Like file path names they may
455 Because these names are used to allow processes to rendezvous, relative
463 objects. The names are removed by calling \fIunlink()\fP or using
465 Names in the UNIX domain are only used for rendezvous. They are not used
467 contrast with the Internet domain, unbound sockets need not be (and are
468 not) automatically given addresses when they are connected.
488 The examples in Figure 6a and 6b are very close to the previous example
494 machine. These ports are managed by the system routines that implement
496 Unlike UNIX domain names, Internet socket names are not entered into
504 As a result, different protocols are allowed to use the same port numbers.
546 from 1 to 1023. Higher numbers are available to general users.
554 Note that port numbers are not automatically reported back to the user.
635 If there are several possible communicants,
663 Messages are read from the connection socket.
670 It avoids blocking when there are no pending connection requests by
681 file system. There are some differences, however, in the functionality of
703 The simplest calls are \fIread() \fP and \fIwrite().\fP \fIWrite()\fP
714 These calls are, therefore, quite flexible and may be used to
717 There are variations on \fIread() \fP and \fIwrite()\fP
720 both files and sockets. These are \fIreadv()\fP and \fI writev(),\fP
737 There are a pair of calls similar to \fIread\fP and \fIwrite\fP
739 and receiving OOB information; these are \fI send()\fP
741 These calls are used only with sockets; specifying a descriptor for a file will
759 Finally, there are a pair of calls that allow the sending and
761 recipient must be specified. These are \fIsendmsg()\fP and
763 These calls are actually quite general and have other uses,
767 The various options for reading and writing are shown in Figure 10,
831 Pipes have the advantage of portability, in that they are supported in all
832 UNIX systems. They also are relatively
850 as there are usually only 64 entries available in the open descriptor
854 teardown time can be unnecessarily long. Weighed against this are
876 In particular the following manual pages are relevant:
899 The views and conclusions contained in this document are those of the