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Tue, 4 Aug 2020 16:14:54 +0000 (UTC) Date: Tue, 4 Aug 2020 17:14:52 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Subject: Re: [PATCH v6 06/12] monitor: Make current monitor a per-coroutine property Message-ID: <20200804161440.GL4020825@redhat.com> References: <20200528153742.274164-1-kwolf@redhat.com> <20200528153742.274164-7-kwolf@redhat.com> <87tuxia5a9.fsf@dusky.pond.sub.org> MIME-Version: 1.0 In-Reply-To: <87tuxia5a9.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/04 01:28:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Kevin Wolf , marcandre.lureau@gmail.com, qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Aug 04, 2020 at 03:50:54PM +0200, Markus Armbruster wrote: > Kevin Wolf writes: > > > This way, a monitor command handler will still be able to access the > > current monitor, but when it yields, all other code code will correctly > > get NULL from monitor_cur(). > > > > Outside of coroutine context, qemu_coroutine_self() returns the leader > > coroutine of the current thread. > > Unsaid: you use it as a hash table key to map from coroutine to monitor, > and for that you need it to return a value unique to the coroutine in > coroutine context, and a value unique to the thread outside coroutine > context. Which qemu_coroutine_self() does. Correct? > > The hash table works, but I hate it just as much as I hate > pthread_getspecific() / pthread_setspecific(). > > What we have here is a need for coroutine-local data. Feels like a > perfectly natural concept to me. > > Are we going to create another hash table whenever we need another piece > of coroutine-local data? Or shall we reuse the hash table, suitably > renamed and moved to another file? > > Why not simply associate an opaque pointer with each coroutine? All it > takes is one more member of struct Coroutine. Whatever creates the > coroutine decides what to use it for. The monitor coroutine would use > it to point to the monitor. Possible benefit of having the coroutine-local data stored in the coroutine stack is that we can probably make it lock-less. Using the hash table in monitor.c results in a serialization of across all coroutines & threads. Also, by providing a GDestroyNotify against the coroutine-local data we can easily guarantee cleanup with the coroutine is freed. Since we'll have a limited number of data items, we could make do with a simple array in the coroutine struct, instead of a hashtable. eg enum CoroutineLocalKeys { CO_LOCAL_CUR_MONITOR = 0, CO_LOCAL_LAST, }; struct Coroutine { ... gpointer localData[CO_LOCAL_LAST]; GDestroyNotify localDataFree[CO_LOCAL_LAST]; }; Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|