Subversion Repositories planix.SVN

.TH IOPROC 2

.SH NAME

closeioproc,

iocall,

ioclose,

iointerrupt,

iodial,

ioopen,

ioproc,

ioread,

ioreadn,

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);

.XX

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 ,

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 .

It is an error to execute more than one call

at a time in an I/O proc.

.PP

.I Iointerrupt

interrupts the call currently executing in the I/O proc.

If no call is executing,

.IR iointerrupt

is a no-op.

.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 thread (2)