I'm tryin to use the sleep() function simultaneously in two threads. Now I d
o
understand this probably won't ever work since "Sleep may be implemented wit
h
SIGALRM" yadda yadda. So I was wondering if anyone had a workaround for this
?

Am I just suppose to "while ( time < timeImWaitingFor ) {yield}" or is 
there a
better way to do this?

Thanks!
Jeff

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"Jeff Rodriguez" <newsgroup1@gurugeek.EXAMPLENOSPAM.com> wrote in message
news:D386c.102848$h23.52201@fed1read06...
> I'm tryin to use the sleep() function simultaneously in two threads. Now I
do
> understand this probably won't ever work since "Sleep may be implemented
with
> SIGALRM" yadda yadda. So I was wondering if anyone had a workaround for
this?
>
> Am I just suppose to "while ( time < timeImWaitingFor ) {yield}" or is[/color
]
there a
> better way to do this?
>
> Thanks!
> Jeff

You're right, the problem is that sleep and any other system call that uses
signals isn't appropriate for use in more than one thread at a time, because
of the way signals are delivered. So, one way to do this that comes to mind
if you need N threads to sleep is to sleep in just one, block SIGALRM from
all threads but that one, and wait on a condition variable in the other N-1
threads that's signaled (with pthread_cond_signal) when the one sleeping
thread wakes up.

I'm sure some others here will suggest alternatives.

--
Marc Rochkind
"Advanced UNIX Programming" (publishing April 2004)
www.basepath.com/aup

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"Marc Rochkind" <rochkind@basepath.com> writes:

> "Jeff Rodriguez" <newsgroup1@gurugeek.EXAMPLENOSPAM.com> wrote in message
> news:D386c.102848$h23.52201@fed1read06... 
> do 
> with 
> this? 
> there a 
>
> You're right, the problem is that sleep and any other system call that use
s
> signals isn't appropriate for use in more than one thread at a time, becau
se
> of the way signals are delivered. So, one way to do this that comes to min
d
> if you need N threads to sleep is to sleep in just one, block SIGALRM from
> all threads but that one, and wait on a condition variable in the other N-
1
> threads that's signaled (with pthread_cond_signal) when the one sleeping
> thread wakes up.
>
> I'm sure some others here will suggest alternatives.

You can use nanosleep() if your system has it.

Otherwise, you can always fall back on

select(0, NULL, NULL, NULL, &timeval).

-SEan

[ Post a follow-up to this message ]

Sean Burke wrote:

> "Marc Rochkind" <rochkind@basepath.com> writes:
--SNIP--
>
>
> You can use nanosleep() if your system has it.
>
> Otherwise, you can always fall back on
>
>   select(0, NULL, NULL, NULL, &timeval).
>
> -SEan
>


How's portability on nanosleep() and select() acorss the various unicies?

I know FreeBSD has both, but what about systems like Linux, HURD, Solaris, e
tc.

Are there any potential problems with these two methods?

Thanks again,
Jeff

[ Post a follow-up to this message ]

Jeff Rodriguez <newsgroup1@gurugeek.EXAMPLENOSPAM.com> writes:

> Sean Burke wrote:
> 
> --SNIP-- 
>
>
> How's portability on nanosleep() and select() acorss the various unicies?
>
> I know FreeBSD has both, but what about systems like Linux, HURD, Solaris,
 etc.
>
> Are there any potential problems with these two methods?

For portability, select() is definitely your best choice.
nanosleep() is available on Solaris 8 and Linux of recent
vintage, but I'm not sure how far back it goes.

As for caveats, both calls can be interrupted by a
signal, so if it's important to sleep out the full
interval, you'll need to check for that.

-SEan

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"Sean Burke" <foobar@mystery.org> wrote in message
news:x765d2fw67.fsf@bolo.xenadyne.com...

> For portability, select() is definitely your best choice.
> nanosleep() is available on Solaris 8 and Linux of recent
> vintage, but I'm not sure how far back it goes.
>
> As for caveats, both calls can be interrupted by a
> signal, so if it's important to sleep out the full
> interval, you'll need to check for that.
>
> -SEan


Here's what the 'Sleep' function in one of my portable libraries looks
like. It does have one caveat however, for full portability you are only
supposed to use it to sleep for intervals less than a second or in units of
full seconds (because of the fallback to sleep/usleep). It does not
guarantee to sleep for the full time nor does it tell you whether it was
interrupted or not. It's here just as an example.

void Sleep(unsigned milliseconds)
{
#if defined(PTH)
pth_yield(NULL);
pth_usleep(milliseconds*1000);
#elif defined(NANOSLEEP)
struct timespec t;
t.tv_sec=milliseconds/1000;
t.tv_nsec=(milliseconds%1000);
t.tv_nsec*=1000000ul;
nanosleep(&t, NULL);
#elif defined(OSF1)
struct timespec t;
t.tv_sec=milliseconds/1000;
t.tv_nsec=(milliseconds%1000);
t.tv_nsec*=1000000ul;
pthread_delay_np(&t);
#elif defined(NO_USLEEP)
struct timeval t;
t.tv_sec=milliseconds/1000;
t.tv_usec=(milliseconds%1000)*1000;
select(0, NULL, NULL, NULL, &t);
#else
int seconds, microseconds;
seconds=milliseconds/1000;
microseconds=(milliseconds%1000)*1000;
if(seconds) sleep(seconds);
if(microseconds) usleep(microseconds);
#endif
}

DS

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"David Schwartz" <davids@webmaster.com> writes:

[snip]

>     Here's what the 'Sleep' function in one of my portable libraries looks
> like. It does have one caveat however, for full portability you are only
> supposed to use it to sleep for intervals less than a second or in units o
f
> full seconds (because of the fallback to sleep/usleep). It does not
> guarantee to sleep for the full time nor does it tell you whether it was
> interrupted or not. It's here just as an example.
>
> void Sleep(unsigned milliseconds)
> {
> #if defined(PTH)
>  pth_yield(NULL);
>  pth_usleep(milliseconds*1000);

[snipped the rest]

Just out of curiosity and not knowing anything about PTH, are you really
supposed to yield your executing before going to sleep? Or does pth_yield()
behave differently?

Bye, Dragan

--
Dragan Cvetkovic,

To be or not to be is true. G. Boole      No it isn't.  L. E. J. Brouwer

!!! Sender/From address is bogus. Use reply-to one !!!

[ Post a follow-up to this message ]

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"Dragan Cvetkovic" <me@privacy.net> wrote in message
news:lmhdwmb09o.fsf@privacy.net... 
>
> [snipped the rest]
>
> Just out of curiosity and not knowing anything about PTH, are you really
> supposed to yield your executing before going to sleep? Or does
> pth_yield()
> behave differently?


I believe this was so the 'Sleep(0);' would do the same thing on PTH as
it does on other threading platforms. My recollection is that
'pth_usleep(0);' would not yield. On PTH, yielding is important because any
ready-to-run thread can be yielded to. (On POSIX threads, for example, a
ready-to-run thread may be running on another CPU and hence can't be yielded
to.)

Some code in other places does the equivalent of:

Lock();

if(ResourceIsAvailable()) UseIt();

else

{

Unlock() Sleep(0); Lock();

if(ResourceIsAvailable()) UseIt();

else DoThingsTheHardWay();

}

Unlock();

Without that change, on PTH, the second test was never true and we
always did things the hard way.

DS

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"David Schwartz" <davids@webmaster.com> writes:

> "Dragan Cvetkovic" <me@privacy.net> wrote in message
> news:lmhdwmb09o.fsf@privacy.net... 
>
>
>     I believe this was so the 'Sleep(0);' would do the same thing on PTH a
s
> it does on other threading platforms. My recollection is that
> 'pth_usleep(0);' would not yield.

Thanks for the explanation David.

Bye, Dragan

--
Dragan Cvetkovic,

To be or not to be is true. G. Boole      No it isn't.  L. E. J. Brouwer

!!! Sender/From address is bogus. Use reply-to one !!!

[ Post a follow-up to this message ]

"Marc Rochkind" <rochkind@basepath.com> wrote, on Thu, 18 Mar 2004:
 
> do 
> with 
> this?

> You're right, the problem is that sleep and any other system call that use
s
> signals isn't appropriate for use in more than one thread at a time, becau
se
> of the way signals are delivered.

POSIX requires sleep() to be thread-safe (on implementations that
support threads).  The "sleep may be implemented with SIGALRM" thing
only applies to non-threads implementations.

--
Geoff Clare <nospam@gclare.org.uk>

[ Post a follow-up to this message ]