2008/10/2 David Empson <[EMAIL PROTECTED]> > Piero 74 wrote: > >I have to develop in my application a task which sends email on certain > events. The provide address will be programmed. > >I will use dns to resolve the provider address. > > > >After, i will try to connect to it: if server will be down for some > reason, my task will be block forever!!!! > > >I need to avoid blocking task... is there a work around? > > [Additional information from discussion in lwip-devel: this is using BSD > sockets.] > > The obvious solution would be to create another task to separate the > sending of e-mail from the normal function of your main task. You can use > some kind of queue mechanism to copy the e-mail from the main task to the > "send e-mail" task. >
yes... i have the same idea... because i saw that connect requested from client can block for 20 seconds if the server is down. > You may need to limit the queue size to deal with the "mail server offline" > scenario. The e-mail sending task would discard all pending messages if it > fails to connect to the server, and then try the connection again the next > time an e-mail send is requested by the main task. > interesting idea... but i have to consider RAM usage. > > Depending on memory constraints, you might be able to hold on to old > messages and try again after a reasonable delay, or perhaps keep a single > e-mail message which records the fact that you had to delete several due to > inability to connect to the mail server. > interesting idea too! > > Having a queue for sending multiple e-mail messages also has the advantage > that you might be able to send several at once in a single connection to the > mail server, if several notifiable events occur in quick succession. > Yes, you are all right, the only problem it could be RAM usage, but i'm thinking something like a list of predefined messages, and a email-book, so, messages exchanged on queue will have small size (just some indexes).... But, my real problem, it's a timeout for connect request: in my application all tasks cannot block for a long time, because i have a watchdog system which will reset the board if some task will be blocked for a long time (currently is working with 60s timeout). So, i have to be sure that connect doesn't block forever, or blocks always for a fixed time. I did a simple test, and i saw a 18 seconds block (time for sending 6 SYN packets with tcpiip retransmission delay policy) I have to other tests, but, it seems an acceptable behavior! (if i will put email manager in a specific task, as you said) Bye, Piero
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