[9fans] Tread and alarm

[9fans] Tread and alarm

[Adriano Verardo]

Hi, all

In a user space file server (9p(2)/9pfile(2)/...) I postpone the Rread
response if there are no available data,
in order to implement a suspensive read().

The client is (really?) suspended until Tread, but the read() sys call
cannot be interrupted by alarm().

It seems to me that the alarm note is received after Tread, as if the
process were totally freezed
waiting for the 9P transaction.

Could anyone kindly explain to me if this is correct and where is my
mistake ?

Thanks in advance

adriano

Re: [9fans] Tread and alarm

[Adriano Verardo]

Errata: ... alarm note is received after Rread, as if the ...

sorry :-)

Adriano Verardo wrote:
> Hi, all
>
> In a user space file server (9p(2)/9pfile(2)/...) I postpone the Rread
> response if there are no available data,
> in order to implement a suspensive read().
>
> The client is (really?) suspended until Tread, but the read() sys call
> cannot be interrupted by alarm().
>
> It seems to me that the alarm note is received after Tread, as if the
> process were totally freezed
> waiting for the 9P transaction.
>
> Could anyone kindly explain to me if this is correct and where is my
> mistake ?
>
> Thanks in advance
>
> adriano
>
>
>
>

Re: [9fans] Tread and alarm

[erik quanstrom]

> The client is (really?) suspended until Tread, but the read() sys call
> cannot be interrupted by alarm().

i didn't understand your errata, so to clarify,
read(2) is interruptable with a note (modulo the
file server, but that's a different story).  here's a
program that demonstrates:

; 8.readalarm
note: alarm
read -1
	interrupted

- erik

----

#include <u.h>
#include <libc.h>

void
nofun(void*, char *msg)
{
	print("note: %s\n", msg);
	if(strstr(msg, "alarm") != nil)
		noted(NCONT);
	else
		noted(NDFLT);
}

void
main(void)
{
	char buf[1024];
	int fd, n;

	fd = open("/net/log", OREAD);
	if(fd == -1)
		sysfatal("open: %r");
	notify(nofun);
	alarm(500);
	n = read(fd, buf, 1024);
	alarm(0);

	print("read %d\n", n);
	if(n < 0)
		print("	%r\n");
	exits("");
}

Re: [9fans] Tread and alarm

[cinap_lenrek]

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you have to implement flush in the 9p server.

--
cinap

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From: Adriano Verardo <a.verardo@tecmav.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
Subject: [9fans] Tread and alarm
Date: Wed, 27 Oct 2010 23:09:22 +0200
Message-ID: <4CC89502.8000304@tecmav.com>

Hi, all

In a user space file server (9p(2)/9pfile(2)/...) I postpone the Rread
response if there are no available data,
in order to implement a suspensive read().

The client is (really?) suspended until Tread, but the read() sys call
cannot be interrupted by alarm().

It seems to me that the alarm note is received after Tread, as if the
process were totally freezed
waiting for the 9P transaction.

Could anyone kindly explain to me if this is correct and where is my
mistake ?

Thanks in advance

adriano

Re: [9fans] Tread and alarm

[Adriano Verardo]

erik quanstrom wrote:
>> The client is (really?) suspended until Tread, but the read() sys call
>> cannot be interrupted by alarm().
>>
>
> i didn't understand your errata
If the are no available data, the file server doesn't do

r->ofcall.count = 0;
response(r, nil);

but just enqueue the Req and process it only when there are data to return.

The client exec alarm() and read(), exactly as in your example.
The alarm handler is the same too and I see the print only after the
server response:

r->ofcall.count = N (>0)
response(r, nil)

adriano
> , so to clarify,
> read(2) is interruptable with a note (modulo the
> file server, but that's a different story).  here's a
> program that demonstrates:
>
> ; 8.readalarm
> note: alarm
> read -1
> 	interrupted
>
> - erik
>
> ----
>
> #include <u.h>
> #include <libc.h>
>
> void
> nofun(void*, char *msg)
> {
> 	print("note: %s\n", msg);
> 	if(strstr(msg, "alarm") != nil)
> 		noted(NCONT);
> 	else
> 		noted(NDFLT);
> }
>
> void
> main(void)
> {
> 	char buf[1024];
> 	int fd, n;
>
> 	fd = open("/net/log", OREAD);
> 	if(fd == -1)
> 		sysfatal("open: %r");
> 	notify(nofun);
> 	alarm(500);
> 	n = read(fd, buf, 1024);
> 	alarm(0);
>
> 	print("read %d\n", n);
> 	if(n < 0)
> 		print("	%r\n");
> 	exits("");
> }
>
>
>
>

Re: [9fans] Tread and alarm

[Adriano Verardo]

cinap_lenrek@gmx.de wrote:
> you have to implement flush in the 9p server.
>
> --
> cinap
>
>
Ah ...

I've just (re)read the 9p(2) man page ... it seems clear now.

Thank you very much, cinap :-)
> ------------------------------------------------------------------------
>
> Subject:
> [9fans] Tread and alarm
> From:
> Adriano Verardo <a.verardo@tecmav.com>
> Date:
> Wed, 27 Oct 2010 23:09:22 +0200
> To:
> Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
>
> To:
> Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
>
>
> Hi, all
>
> In a user space file server (9p(2)/9pfile(2)/...) I postpone the Rread
> response if there are no available data,
> in order to implement a suspensive read().
>
> The client is (really?) suspended until Tread, but the read() sys call
> cannot be interrupted by alarm().
>
> It seems to me that the alarm note is received after Tread, as if the
> process were totally freezed
> waiting for the 9P transaction.
>
> Could anyone kindly explain to me if this is correct and where is my
> mistake ?
>
> Thanks in advance
>
> adriano
>