.TH IOPROC 2
.SH NAME
closeioproc,
iocall,
ioclose,
ioflush,
iointerrupt,
iodial,
ioopen,
ioproc,
ioread,
ioreadn,
iosleep,
iowrite \- slave I/O processes for threaded programs
.SH SYNOPSIS
.PP
.de XX
.ift .sp 0.5
.ifn .sp
..
.EX
.ta \w'Ioproc* 'u
#include <u.h>
#include <libc.h>
#include <thread.h>
.sp
typedef struct Ioproc Ioproc;
.sp
Ioproc*	ioproc(void);
.XX
int	ioopen(Ioproc *io, char *file, int omode);
int	ioclose(Ioproc *io, int fd);
long	ioread(Ioproc *io, int fd, void *a, long n);
long	ioreadn(Ioproc *io, int fd, void *a, long n);
long	iowrite(Ioproc *io, int fd, void *a, long n);
int	iodial(Ioproc *io, char *addr, char *local, char *dir, char *cdfp);
int	iosleep(Ioproc *io, long n);
.XX
int	ioflush(Ioproc *io);
void	iointerrupt(Ioproc *io);
void	closeioproc(Ioproc *io);
.XX
long	iocall(Ioproc *io, long (*op)(va_list *arg), ...);
.EE
.SH DESCRIPTION
.PP
These routines provide access to I/O in slave procs.
Since the I/O itself is done in a slave proc, other threads
in the calling proc can run while the calling thread
waits for the I/O to complete.
.PP
.I Ioproc
forks a new slave proc and returns a pointer to the
.B Ioproc
associated with it.
.I Ioproc
uses
.I mallocz
and
.IR proccreate ;
if either fails, it calls
.I sysfatal
rather than return an error.
.PP
.IR Ioopen ,
.IR ioclose ,
.IR ioread ,
.IR ioreadn ,
.IR iowrite ,
.IR iosleep ,
and
.IR iodial
execute the
similarly named library or system calls
(see
.IR open (2),
.IR read (2),
and
.IR dial (2))
in the slave process associated with
.IR io .
.PP
.I Iointerrupt
interrupts the next or currently executing call in the I/O proc.  If
there was no call executing, the interrupt will stay pending and the
next I/O call will get interrupted.
.PP
.I Ioflush
executes a non-op in the I/O proc. It is commonly called after
.IR iointerrupt
to clear a pending interrupt.
.PP
.I Closeioproc
terminates the I/O proc and frees the associated
.B Ioproc .
.PP
.I Iocall
is a primitive that may be used to implement
more slave I/O routines.
.I Iocall
arranges for
.I op
to be called in
.IR io 's
proc, with
.I arg
set to the variable parameter list,
returning the value that
.I op
returns.
.SH EXAMPLE
Relay messages between two file descriptors,
counting the total number of bytes seen:
.IP
.EX
.ta +\w'xxxx'u +\w'xxxx'u +\w'xxxx'u
int tot;

void
relaythread(void *v)
{
	int *fd, n;
	char buf[1024];
	Ioproc *io;

	fd = v;
	io = ioproc();
	while((n = ioread(io, fd[0], buf, sizeof buf)) > 0){
		if(iowrite(io, fd[1], buf, n) != n)
			sysfatal("iowrite: %r");
		tot += n;
	}
	closeioproc(io);
}

void
relay(int fd0, int fd1)
{
	int fd[4];

	fd[0] = fd[3] = fd0;
	fd[1] = fd[2] = fd1;
	threadcreate(relaythread, fd, 8192);
	threadcreate(relaythread, fd+2, 8192);
}
.EE
.LP
If the two
.I relaythread
instances were running in different procs, the
common access to
.I tot
would be unsafe.
.PP
Implement
.IR ioread :
.IP
.EX
static long
_ioread(va_list *arg)
{
	int fd;
	void *a;
	long n;

	fd = va_arg(*arg, int);
	a = va_arg(*arg, void*);
	n = va_arg(*arg, long);
	return read(fd, a, n);
}

long
ioread(Ioproc *io, int fd, void *a, long n)
{
	return iocall(io, _ioread, fd, a, n);
}
.EE
.SH SOURCE
.B /sys/src/libthread/io*.c
.SH SEE ALSO
.IR dial (2),
.IR open (2),
.IR read (2),
.IR sleep (2),
.IR thread (2)