fork.3f

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)fork.3f	8.1	9/11/90
.TH fork 3f VAX "" Unsupported
.SH Name
fork \- create a copy of this process
.SH Syntax
.B integer function fork()
.SH Description
.NXR "fork subroutine (FORTRAN)"
.NXR "process" "copying"
The
.PN fork
function creates a copy of the calling process.
The only distinction between the two processes is that the value
returned to one of them (referred to as the 'parent' process)
will be the process ID of the copy.
The copy is usually referred to as the 'child' process.
The value returned to the 'child' process will be zero.
.PP
All logical units open for writing are flushed before the fork to avoid
duplication of the contents of I/O buffers in the external file(s).
.PP
If the returned value is negative, it indicates an error and will be
the negation of the system error code.
See 
.MS perror 3f .
.PP
A corresponding
.PN exec
routine has not been provided because there is no satisfactory way to
retain open logical units across the exec.
However, the usual function of
.PN fork/exec
can be performed using
.MS system 3f .
.if 0 \{
A pipe can be opened to another process using the f77
.PN open
statement with
.sp 1
.ti +5
.B "file=\(fm\fIprocess\fB\(fm, status=\(fmpipe\(fm, access=\(fmread\(fm"
.br
or
.br
.ti +5
.B "file=\(fm\fIprocess\fB\(fm, status=\(fmpipe\(fm, access=\(fmwrite\(fm"
\}
.SH Files
.ie \nM /usr/ucb/lib/libU77.a
.el /usr/lib/libU77.a
.SH See Also
fork(2), kill(3f), perror(3f), system(3f), wait(3f)