[Xcb] xcb recursive write not protected in all cases?

Roland Mainz roland.mainz at nrubsig.org
Mon Dec 23 23:09:15 PST 2013

On Tue, Dec 24, 2013 at 6:23 AM, Keith Packard <keithp at keithp.com> wrote:
> Josh Triplett <josh at joshtriplett.org> writes:
>> On Mon, Dec 23, 2013 at 05:00:46PM -0800, Keith Packard wrote:
>>> I think we need to check out.writing closer to the actual use of the
>>> out.queue; perhaps it would suffice to check that down inside
>>> send_request itself? That would certainly offer the surest guarantee
>>> that iolock wasn't dropped between the check for out.writing and the use
>>> of out.queue.
>> Based on your analysis, that sounds like the best plan indeed: check
>> while holding the lock in send_request, where there's no way we can
>> subsequently drop it before sending the request.
> I ran into another issue in the same area -- while waiting for
> out.writing, we can lose the socket back to Xlib, append some data to
> the request buffer and then Xlib comes along and tries to write another
> request to the socket and *bam* another assertion failure in write_vec.
> I think we have to block until we have the socket *and* out.writing is
> false.
> Something like this:

Just curious: Does XCB have something similar like EAGAIN ?



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