similar to: [PATCH libnbd] examples: Fix theoretical cookie race in example.

This is working now, and incorporates all of the changes in Eric's review, *except* that it still doesn't retire commands (although this seems to make no obvious difference, except possibly a performance and memory impact). Rich.

** NOT WORKING ** This patch shows how to integrate libnbd and the glib main loop. Posted mainly as a point of discussion as it doesn't quite work yet. Rich.

There was a theoretic race in this example: If the server was very fast at handling commands then it's possible that in a call such as: cookie = nbd_aio_pread_callback (..., callback, ...); buffers[i].cookie = cookie; nbd_aio_pread_callback finished and calls the callback before returning. buffers[i].cookie would therefore not be set, but the callback() function was checking the list of

On 7/17/19 8:00 AM, Richard W.M. Jones wrote: > --- > .gitignore | 1 + > README | 2 + > configure.ac | 9 + > examples/Makefile.am | 22 ++ > examples/glib-main-loop.c | 511 ++++++++++++++++++++++++++++++++++++++ > 5 files changed, 545 insertions(+) Looks good. > > + revents = g_source_query_unix_fd

I think I've addressed everything that was raised in review. Some of the highlights: - Callbacks should be freed reliably along all exit paths. - There's a simple test of closure lifetimes. - I've tried to use VALID|FREE in all the places where I'm confident that it's safe and correct to do. There may be more places. Note this is an optimization and shouldn't

On 7/15/19 1:38 PM, Richard W.M. Jones wrote: > --- > .gitignore | 1 + > README | 2 + > configure.ac | 9 + > examples/Makefile.am | 22 ++ > examples/glib-main-loop.c | 501 ++++++++++++++++++++++++++++++++++++++ > 5 files changed, 535 insertions(+) > Rough review (since I've never used a glib main loop

--- .gitignore | 1 + README | 2 + configure.ac | 9 + examples/Makefile.am | 22 ++ examples/glib-main-loop.c | 511 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 545 insertions(+) diff --git a/.gitignore b/.gitignore index ce02aef..9a8ba37 100644 --- a/.gitignore +++ b/.gitignore @@ -41,6 +41,7 @@ Makefile.in

This implements most of what I wrote here: https://www.redhat.com/archives/libguestfs/2019-July/msg00213.html

v1 was here: https://www.redhat.com/archives/libguestfs/2019-July/thread.html#00231 The changes address everything that Eric picked up in his review of the first two patches. I have also added two more patches (4 and 5) which respectively fix docs and change int status -> unsigned status, as discussed. Passes make, check, check-valgrind. Rich.

On 8/13/19 5:36 PM, Richard W.M. Jones wrote: > The definition of functions that take a callback is changed so that > the callback and user_data are combined into a single structure, eg: > > int64_t nbd_aio_pread (struct nbd_handle *h, > void *buf, size_t count, uint64_t offset, > - int (*completion_callback) (/*..*/), void *user_data, > +

As proposed here: https://www.redhat.com/archives/libguestfs/2019-August/msg00130.html I didn't actually read Eric's replies to that yet because I've been concentrating on writing these patches all day. Anyway here they are and I'll look at what Eric said about the proposal next. Rich.

Patches 1 & 2 are rather complex, but the end result is that we pass closures + user_data + free function in single struct parameters as I described previously in this email: https://www.redhat.com/archives/libguestfs/2019-August/msg00210.html Patch 3 adds a convenient FREE_CALLBACK macro which seems a worthwhile simplification if you buy into 1 & 2. Patch 4 adds another macro which is

This applies on top of the OClosure v2 series posted a few minutes ago. Rich.

--- .gitignore | 1 + README | 2 + configure.ac | 9 + examples/Makefile.am | 22 ++ examples/glib-main-loop.c | 501 ++++++++++++++++++++++++++++++++++++++ 5 files changed, 535 insertions(+) diff --git a/.gitignore b/.gitignore index edbf941..79b95b5 100644 --- a/.gitignore +++ b/.gitignore @@ -41,6 +41,7 @@ Makefile.in

Previously closures had a crude flag which tells if they are persistent or transient. Transient closures (flag = false) last for the lifetime of the currently called libnbd function. Persistent closures had an indefinite lifetime which could last for as long as the handle. In language bindings handling persistent closures was wasteful as we needed to register a "close callback" to

As discussed in this thread, the parameter is an invitation to write code with race conditions: https://www.redhat.com/archives/libguestfs/2019-July/thread.html#00309 --- docs/libnbd.pod | 6 +- examples/glib-main-loop.c | 10 ++-- examples/strict-structured-reads.c | 2 +- generator/generator | 57

On 7/17/19 8:40 AM, Eric Blake wrote: > > It may be possible in rare situations that the libnbd state machine can > send() the command AND see data ready to recv() (perhaps from a previous > command still in flight), where it ends up read()ing until blocking and > happens to get the server's reply to this command and fire off the > callback, all prior to the

Previously closures had a crude flag which tells if they are persistent or transient. Transient closures (flag = false) last for the lifetime of the currently called libnbd function. Persistent closures had an indefinite lifetime which could last for as long as the handle. In language bindings handling persistent closures was wasteful as we needed to register a "close callback" to

Previously closures had a crude flag which tells if they are persistent or transient. Transient closures (flag = false) last for the lifetime of the currently called libnbd function. Persistent closures had an indefinite lifetime which could last for as long as the handle. In language bindings handling persistent closures was wasteful as we needed to register a "close callback" to

Patches 1-4 are basically uncontroversial, straightforward refactoring and IMHO we should just push them. Possibly 1-3 should be squashed together, but I posted them separately so they are easier to review. Patches 5 and 6 together implement OClosure. Patch 5 adds the feature and is simple to understand. Patch 6 changes the Closure completion callbacks into OClosure, but because it doesn't