On Thu, Nov 11, 2010 at 12:03, Jelmer Vernooij <[email protected]> wrote:
> Hi Sebastian, > > On Thu, 2010-11-11 at 16:49 +0100, Sebastian Egner wrote: > > On 11.11.10 15:20, Jelmer Vernooij wrote: > > > We'd need an alternative way to determine whether there's data > available > > > from a subprocess. I'm not sure what the best way to do that is on > > > Windows. The subprocess module doesn't provide any hints about this. > > Your are right, of course. I checked: The object proc.stdout will be a > > Python 'file' object on Windows---and these don't come with a method of > > polling, unless the entire file is switched into asynchronous mode. > Switching the file to some sort of non-blocking mode should be fine, if > that gives you a way to poll whether there is data available. > > > However, from the source code I got the impression that it is sufficient > > to detect EOF because can_read() only checks if some bytes are waiting > > to be read, so the subsequent read() can still block on the second byte > > of the stream. This means, we can probably get away with a simple > > read-ahead mechanism: can_read() does a blocking read(1) and stores it, > > and the next Procotol.read(n) returns the stored byte appended with > > read(n-1). > This is not a file but a stream. Not being able to read from it does not > necessarily imply EOF. Attempting to read a single byte will mean > blocking until the other side provides that byte, while we could be > spending that time crunching data. The second byte could indeed block as > well, but because of the way the protocol works this will not be the > case (a packet is always at least 4 bytes). > FYI, there is also ReceivableProtocol.recv(), which is guaranteed to not block but may return zero bytes. > > I am attaching a hacked version of client.py, which implements the > > mechanism as an alternative SubprocessWrapper for the Windows platform. > > You can diff the file against dulwich 0.6.2. > Can you please attach diffs instead? They're much easier to read and > review. > > Cheers, > > Jelmer > > _______________________________________________ > Mailing list: https://launchpad.net/~dulwich-users > Post to : [email protected] > Unsubscribe : https://launchpad.net/~dulwich-users > More help : https://help.launchpad.net/ListHelp > >
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