Re: [lwip-users] connect block for ever?? (i need a workaround)

[David Empson]

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.

 

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.

 

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.

 

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.