site_archiver@lists.apple.com Delivered-To: darwin-kernel@lists.apple.com Hi everyone, for (i = 0; i <= max; i++) { // ... some code left out ... result = ctl_enqueuedata( ctlref, unit, &packed, sizeof(packed), i < max ? CTL_DATA_NOWAKEUP : CTL_DATA_EOR ); // ... some code left out ... } for (;;) { if ( recv( KextSocket, &packed, sizeof(packed), MSG_WAITALL ) != sizeof(packed) ) { // ... handle short read ... } // ... process read data ... } -- Best Regards, Markus Hanauska _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-kernel mailing list (Darwin-kernel@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-kernel/site_archiver%40lists.a... CTL_DATA_NOWAKEUP does not work as expected after reading the documentation. The documentation implies that this flag only means whether a thread blocking on a recv call is woken up or not. Let me show you some code Since I'm sending two packets to user space (in this example max == 1), each represented by packed struct, I don't want the user space process waiting on recv to wake up before both packages are there. I'd assume after en-queuing the data, the data is copied to the receive buffer of the socket, however on the first call the data is just copied there, on the second call the data is copied there as well and this time the thread is woken up. So far this works as expected. After both packets are enqueued the recv call in user space unblocks (it won't unblock after the first packet is enqueued). However, the code looks like this: I want to read the packets one by one, not all of them at once. What happens is, it wakes up and reads the first of the two enqueued packets. But when it tries to read the second packets, it blocks again. Why? The data for two packets is there(!), it should be able to run recv call above twice *WITHOUT* blocking. When I always use CTL_DATA_EOR, it can read both as expected, but then it will already wake up after the first enqueued packet. So does using several enqueue calls with CTL_DATA_NOWAKEUP and finally one without that flag only works if the receiver side then reads all the enqueued data in ONE call? As that is not clear from the documentation. Also I fail to see how CTL_DATA_NOWAKEUP should have any influence if no thread is blocked by the socket at all. If the thread is currently processing something else and I add data with CTL_DATA_NOWAKEUP to the socket, I'd expect that if it later gets back to the recv call, it can read the data at once without blocking, as a thread should never block on a socket if it has data ready to read and it has data ready to read (I just asked the kernel to not wake up blocking threads, but there were no threads blocking for this socket). I tried the above example with a bigger max. When I enqueue 10 packets, using CTL_DATA_NOWAKEUP on all, but the last packet, the thread wakes up, can read the first one and then blocks again, till some other data is enqueued without CTL_DATA_NOWAKEUP flag. After the whole process runs twice, I have enqueued 20 pakets, the user space process has read 2 of them, 18 should still be in the queue and it blocks on the recv call. This email sent to site_archiver@lists.apple.com