Is cout << msg an atomic action?

[Alex Vinokur]

void foo (int n)
{
std::ostringstream oss;
oss << "ABCD: " << n << std::endl;
std::cout << oss.str() << std::flush;
}

That function has been invoked in multiprocessing mode.
Output was something like:
ABCA: B1
C
etc.

Is cout << msg an atomic action?


Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Chris Thomasson]

"Alex Vinokur" <al****@users.sourceforge.netwrote in message
news:a8**********************************@1g2000hs l.googlegroups.com...

>

void foo (int n)
{
std::ostringstream oss;
oss << "ABCD: " << n << std::endl;
std::cout << oss.str() << std::flush;
}

That function has been invoked in multiprocessing mode.
Output was something like:
ABCA: B1
C
etc.

Is cout << msg an atomic action?

no:

http://groups.google.com/group/comp....37f881199c5133
(read all...)

[James Kanze]

On Feb 4, 6:17 am, Alex Vinokur <[e-mail]:

void foo (int n)
{
std::ostringstream oss;
oss << "ABCD: " << n << std::endl;
std::cout << oss.str() << std::flush;

}

That function has been invoked in multiprocessing mode.

Output was something like:
ABCA: B1
C
etc.

Is cout << msg an atomic action?

It depends on the implementation, but I would not normally
expect to be able to write to the same stream from two different
threads without some external synchronization. Both reading
from and writing to an iostream modify the object itself.

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[Alex Vinokur]

On Feb 4, 11:42*am, James Kanze <[e-mail]:

On Feb 4, 6:17 am,AlexVinokur<[e-mail]:

void foo (int n)
{
* std::ostringstream oss;
* oss << "ABCD: " << n << std::endl;
* std::cout << oss.str() << std::flush;

}
That function has been invoked in multiprocessing mode.
Output was something like:
ABCA: B1
C
etc.
Is cout << msg an atomic action?

It depends on the implementation, but I would not normally
expect to be able to write to the same stream from two different
threads without some external synchronization. *Both reading
from and writing to an iostream modify the object itself.

I realize that
cout << msg1 << msg2;
is not an atomic action.

But is
cout << msg1;
also not atomic one?

Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn

[Chris Thomasson]

"Alex Vinokur" <al****@users.sourceforge.netwrote in message

news:38**********************************@q39g2000 hsf.googlegroups.com...

On Feb 4, 11:42 am, James Kanze <[e-mail]:

On Feb 4, 6:17 am,AlexVinokur<[e-mail]:

void foo (int n)
{
std::ostringstream oss;
oss << "ABCD: " << n << std::endl;
std::cout << oss.str() << std::flush;

}

That function has been invoked in multiprocessing mode.

Output was something like:
ABCA: B1
C
etc.
Is cout << msg an atomic action?

It depends on the implementation, but I would not normally
expect to be able to write to the same stream from two different
threads without some external synchronization. Both reading
from and writing to an iostream modify the object itself.

I realize that
cout << msg1 << msg2;
is not an atomic action.

But is
cout << msg1;
also not atomic one?

On a single-threaded application yes; otherwise, well, good luck.

[peter koch]

On 4 Feb., 06:17, Alex Vinokur <[e-mail]:

void foo (int n)
{
* std::ostringstream oss;
* oss << "ABCD: " << n << std::endl;
* std::cout << oss.str() << std::flush;

}

That function has been invoked in multiprocessing mode.

Output was something like:
ABCA: B1
C
etc.

Is cout << msg an atomic action?

I would be most surprised if it was. In theory, an implementation
could make some of these operations atomic, but it would be quite a
stupid thing to do for the simple reason that the atomicity is at the
wrong level.
In case you have user provided operator << these will hardly be atomic
as they can't use the same syncronisation objects as std::cout.

/Peter

/Peter