maybe it's a problem with eof detection. I tried to reproduce it using a
threaded version (see attached), but it works correctly.
On Fri, Mar 31, 2017 at 5:29 PM arisawa <[email protected]> wrote:
> Hello,
>
> I was playing with an experimental code on pipe and met with a problem
> which I don’t understand.
>
> the program reads a file and writes it to one end of pipe and then reads
> it from another end of pipe.
> the buffer for writing pipe is named buf0, and for reading pipe is named
> buf.
> and I found the program does not finish unless sizeof(buf) > sizeof(buf0).
> is this a bug or feature of pipe?
>
> Kenji Arisawa
>
> === BEGIN a.c ===
> #include <u.h>
> #include <libc.h>
>
> char *argv0;
>
> void
> usage(void)
> {
> fprint(2,"usage: %s file\n",argv0);
> exits("usage");
> }
>
> void
> main(int argc, char *argv[])
> {
> int fd,pfd[2];
> char buf[256];
> char buf0[256];
> /* need to be sizeof(buf) > sizeof(buf0)
> * but this condition is very curious to me */
> int n;
> char *file;
> argv0 = argv[0];
> argc--;argv++;
> USED(argc);
> if(argv[0] == nil)
> usage();
> file = argv[0];
> fd = open(file,OREAD);
> if(fd < 0)
> sysfatal("no such file");
>
> if(pipe(pfd) < 0)
> sysfatal("pipe error");
> print("pfd: %d %d\n",pfd[0],pfd[1]);
>
> while((n = read(fd,buf0,sizeof(buf0))) > 0){
> print("read: %d %s\n",n,file);
> n = write(pfd[1],buf0,n);
> print("write: %d\n",n);
> }
> close(pfd[1]);
> while((n = read(pfd[0],buf,sizeof(buf))) > 0){
> buf[n] = 0;
> print("%d %s\n",n,buf);
> }
> print("%d\n",n);
>
> exits(nil);
> }
> === END a.c ===
>
#include <u.h>
#include <libc.h>
#include <thread.h>
void
copyfunc(void *v)
{
int *fd, n;
char buf[256];
int tot = 0;
fd = v;
while((n = read(fd[0], buf, sizeof buf)) > 0){
if(write(fd[1], buf, n) != n)
sysfatal("write: %r");
tot += n;
fprint(2, "copied %d byte chunk\n", n);
}
fprint(2, "total copied: %d\n", tot);
close(fd[0]);
close(fd[1]);
threadexits(nil);
}
/* copy stdin to stdout through a pipe. run like ./pipetest </lib/constitution >/dev/null */
void
threadmain(int argc, char *argv[])
{
int fd[4];
int pfd[2];
if(pipe(pfd) < 0)
sysfatal("pipe error");
fd[0] = 0;
fd[1] = pfd[0];
fd[2] = pfd[1];
fd[3] = 1;
proccreate(copyfunc, fd, 8192);
copyfunc(fd+2);
}
