On 08/19/2011 12:35 AM, Jonathan M Davis wrote:
On Thursday, August 18, 2011 14:33 jdrewsen wrote:
Den 17-08-2011 18:21, Timon Gehr skrev:
On 08/17/2011 05:58 PM, Jonathan M Davis wrote:
On Wednesday, August 17, 2011 11:30:06 Steven Schveighoffer wrote:
On Wed, 17 Aug 2011 11:05:56 -0400, jdrewsen<jdrew...@nospam.com> wrote:
Den 17-08-2011 15:51, Steven Schveighoffer skrev:
On Wed, 17 Aug 2011 05:43:00 -0400, Jonas Drewsen
<jdrew...@nospam.com>
wrote:
On 17/08/11 00.21, Jonathan M Davis wrote:
On Tuesday, August 16, 2011 12:32 Martin Nowak wrote:
On Tue, 16 Aug 2011 20:48:51 +0200,
jdrewsen<jdrew...@nospam.com>
wrote:
Den 16-08-2011 18:55, Martin Nowak skrev:
On Tue, 16 Aug 2011 15:13:40 +0200,
dsimcha<dsim...@yahoo.com>
wrote:
On 8/16/2011 7:48 AM, Jonas Drewsen wrote:
Hi all,
This is a review request for the curl wrapper. Please
read the
"known
issues" in the top of the source file and if possible
suggest a
solution.
We also need somebody for running the review process.
Anyone?
Code:
https://github.com/jcd/phobos/blob/curl-wrapper/etc/curl
.d
Docs:
http://freeze.steamwinter.com/D/web/phobos/etc_curl.html
Demolish!
/Jonas
From a quick look, this looks very well thought out. I'll
review
it
more thoroughly when I have more time. A few
questions/comments
from a
quick look at the docs:
Does the async stuff use D threads, or does Curl have its
own
async
API?
In your examples for postData, you have onReceive a
ubyte[] and
write
it out to console. Did you mean to cast this to some kind
of
string?
For onReceive, what's the purpose of the return value?
If/when this module makes it into Phobos, are we going to
start
including a libcurl binary with DMD distributions so that
std.curl
feels truly **standard** and requires zero extra
configuration?
I was also wondering about the async handling. In the
long-term
I'd like
to see a bigger picture for async handling in phobos
(offering
some kind
of futures, maybe event-loops etc.).
Though this is not a requirement for the curl wrapper now.
std.parallelism also has some kind of this stuff and file
reading
would
benefit from it too.
This has been discussed before and I also think this is very
important.
But before that I think some kind of package management should
be
prioritized (A DIP11 implementaion or a more traditional
solution).
One thing I spotted at a quick glance, sending to be filled
buffers to
another thread should not be done by casting to shared not
immutable.
I'm not entirely sure what you mean. There is no use of shared
buffers
in the wrapper. I do cast the buffer between mutable/immutable
because
only immutable or by value data can be passed using
std.concurrency.
Since the buffers are only used by the thread that currently
has the
buffer this is safe. I've previously asked for a non-cast
solution
(ie.
some kind of move between threads semantic for
std.concurrency) but
was
advised that this was the way to do it.
martin
Pardon the typo. What I meant is that AFAIK casting from
immutable to
mutable has undefined behavior.
The intended method for sending a uint[] buffer to another
thread is
to
cast that
buffer to shared (cast(shared(uint[])) and casting away the
shared
on the
receiving side.
It is allowed to send shared data using std.concurrency.
Casting away immutability and then altering data is undefined.
Actually
casting it away is defined. So, if you have data in one thread
that
you know
is unique, you can cast it to immutable (or
std.exception.assumeUnique to do
it) and then send it to another thread. On that thread, you can
then
cast it
to mutable and alter it.
However, you're circumventing the type system when you do this.
So,
you have
to be very careful. You're throwing away the guarantees that the
compiler
makes with regards to const and immutable. It _is_ guaranteed to
work
though.
And I'm not sure that there's really any difference between
casting
to shared
and back and casting to immutable and back. In both cases, you're
circumventing the type system. The main difference would be that
if
you
screwed up with immutable and cast away immutable on something
that
really was
immutable rather than something that you cast to immutable just to
send it to
another thread, then you could a segfault when you tried to alter
it,
since it
could be in ROM.
- Jonathan M Davis
Yeah I know you have to be careful when doing these kind of things.
I
ran into the problem of sending buffers between threads (using
std.concurrency) so that they could be reused. There isn't any "move
ownership" support in place so Andrei suggested I could do it by
casting immutable.
If anyone knows of a cleaner way to do this please tell.
casting to shared and back. Passing shared data should be supported
by std.concurrency, and casting away shared is defined as long as
you know
only one thread owns the data after casting.
-Steve
Why is this cleaner than casting to immutable and back?
Once it's immutable, it can never be mutable again. Casting to
immutable is a one-way street. Yes, you can cast to mutable, but you
still can't change the data unless you want undefined behavior.
Shared is not like that, an item can be thread-local, then shared, then
thread local again, all the time being mutable. It also reflects better
what the process is (I'm sharing this data with another thread, then
that
thread is taking ownership). There's still the possibility to screw up,
but at least you are not in undefined territory in the
correctly-implemented case.
Are you sure? As I understand it, there's no real difference between
casting to
immutable and back and casting to shared and back. Both circumvent the
type
system. In the one case, the type system guarantees that the data
can't be
altered, and you're breaking that guarantee, because you know that it
_can_
be, since you created the data and know that it's actually mutable.
No. As soon as the data is typed as immutable anywhere it cannot be
changed anymore. You only break guarantees if you actually try to change
the data (otherwise std.typecons.assumeUnique would perform its job
outside defined behavior btw)
I'm thinking down the same lines as Jonathan. Is the behavior for
immutable casts that you describe specified in the language reference
somewhere?
I have no problem with using shared casts instead of immutable - I just
want make sure it is really needed.
The behavior of casting a way const or immutable on a value and then mutating
it is undefined by the language, because you're breaking the language's
guarantees and what happens depends entirely on whether the actual object was
actually immutable. However, in the case of casting to immutable and then
casting back, you _know_ that the object is mutable, so there's no problem.
You're just circumventing the type system which throws away the guarantees
that it gives you about immutability, which could screw up optimizations if
you had actually did more than just pass the variable around. But that's just
not happening here.
As for casting to and from shared and mutating the object, I don't see how it
is any more defined than casting to and from immutable and then mutating the
object is. In both cases, you circumvented the type system, which breaks the
compiler's guarantees and risks bugs if you actually do more than just pass
the variable around before casting it back to being thread-local and mutable.
- Jonathan M Davis
As long as the data is not being shared between multiple threads after
it's sharedness has been cast away, you are well in defined area,
because you are NOT breaking anything.
The crucial difference between immutable and shared is, that something
that is immutable will always be immutable, but being shared or not may
change dynamically.
Casting to immutable is a one-way-street, while casting to shared is not.
