site_archiver@lists.apple.com Delivered-To: macnetworkprog@lists.apple.com Sincerely, Jerry Krinock _______________________________________________ Do not post admin requests to the list. They will be ignored. Macnetworkprog mailing list (Macnetworkprog@lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/macnetworkprog/site_archiver%40lists.... During 2005 I wrote an bookmark-checking application which iterates through a user's bookmarks (typically Safari bookmarks), sends a GET request to each using an asynchronous NSURLConnection, then cancels and releases the connection after it gets the header. (The reason I don't send a HEAD request is that some sites don't give the expected response.) Anyhow, I spent quite a bit of time testing back then, and found that I could send 20 or even 50 requests per second on my residential DSL line, and although this would slow down web browsing and gaming performance by other apps and/or other computers, it still worked. But in the last year or so I've noticed a kind of nonlinear behavior. Typically, after several hundred requests, sent at 5-20 per second (i.e. 1-3 minutes), all further requests end in a timeout. It doesn't matter if I set the timeout at 20 or 60 seconds. Like the spigot gets closed -- all packets are dropped. I've verified in the debugger that -cancel and -dealloc are being sent to the NSURLConnections. Now, my app is set to limit the number of outstanding requests to 64, so when these timeouts start happening, the request rate slows down. Then after a minute or so, suddenly, requests start getting responses again. But then as my app piles them up, after another minute or so, the spigot closes again -- all requests time out. A couple users have reported this, and at first I thought it was something changed in the Mac OS. I see it on both 10.4 and 10.5, but I know that Apple often updates the URL Loading System in older OS dot releases too. But just now I verified that another Mac on the network will also fail to load web pages during the period when I'm getting timeouts. So now it's looking more like ISPs are doing this. (Mine here is Earthlink with PPPoE.) Two things seem odd... 1. The shutoff seems to be triggered by too many connections, not by too many bits per second. Sending, say, 5 requests per second and receiving, say, one 1500-byte packet with each one, is a rather modest 60 Kb/sec. 2. The shutoff is not just limiting my bit rate, it's a complete shutdown for a minute or so. Like "You were bad so we're going to drop all of your packets for a minute or so." If anyone has any experience with this which could confirm that this is indeed the work of ISPs and not something that the Mac OS is doing, that would be great. I established the limit of 64 outstanding NSURLConnections by noting that if I had no limit, things would crash if there were more than about 700 outstanding, and allowing more than 64 did not speed up the process. Does anyone know how many ports an NSURLConnection should consume? I notice that the marginal increase in the number of ports I'm reported using in Activity Monitor is about 4 per NSURLConnection. Does that make sense? Maybe redirects add to it also? Yes, I need to write a little test tool and get some data with different internet connections, but I'd appreciate if someone could help me understand where I should be "pushing". Or maybe some resources for further reading! This email sent to site_archiver@lists.apple.com