IOPROC(2) IOPROC(2)
NAME
closeioproc, iocall, ioclose, iointerrupt, iodial, ioopen,
ioproc, ioread, ioreadn, iowrite - slave I/O processes for
threaded programs
SYNOPSIS
#include <u.h>
#include <libc.h>
#include <thread.h>
typedef struct Ioproc Ioproc;
Ioproc* ioproc(void);
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);
void iointerrupt(Ioproc *io);
void closeioproc(Ioproc *io);
long iocall(Ioproc *io, long (*op)(va_list *arg), ...);
DESCRIPTION
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.
Ioproc forks a new slave proc and returns a pointer to the
Ioproc associated with it. Ioproc uses mallocz and
proccreate; if either fails, it calls sysfatal rather than
return an error.
Ioopen, ioclose, ioread, ioreadn, iowrite, and iodial exe-
cute the similarly named library or system calls (see
open(2), read(2), and dial(2)) in the slave process associ-
ated with io. It is an error to execute more than one call
at a time in an I/O proc.
Iointerrupt interrupts the call currently executing in the
I/O proc. If no call is executing, iointerrupt is a no-op.
Closeioproc terminates the I/O proc and frees the associated
Ioproc .
Iocall is a primitive that may be used to implement more
Page 1 Plan 9 (printed 12/21/24)
IOPROC(2) IOPROC(2)
slave I/O routines. Iocall arranges for op to be called in
io's proc, with arg set to the variable parameter list,
returning the value that op returns.
EXAMPLE
Relay messages between two file descriptors, counting the
total number of bytes seen:
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);
}
If the two relaythread instances were running in different
procs, the common access to tot would be unsafe.
Implement ioread:
static long
_ioread(va_list *arg)
{
int fd;
void *a;
long n;
fd = va_arg(*arg, int);
a = va_arg(*arg, void*);
Page 2 Plan 9 (printed 12/21/24)
IOPROC(2) IOPROC(2)
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);
}
SOURCE
/sys/src/libthread/io*.c
SEE ALSO
dial(2), open(2), read(2), thread(2)
Page 3 Plan 9 (printed 12/21/24)