Brew Interview Question:

What precautions should we take when I invoke INETMGR_GetHostByName() to perform DNS lookup?

Submitted by: Administrator

You must ensure that your app cancels its pending DNS callback, if any, using CALLBACK_Cancel() in all exit routes. This includes when the app is suspended and when the app is stopped (both via the End key and the Clear key).

For example, if you used the following code to lookup a DNS address:

CALLBACK_Init(&pMe->cbkLookup, GetHostByNameCB, pMe);
INETMGR_GetHostByName(pINetMgr,&pMe->dnsresult, hostName,
&pMe->cbkLookup);



You should use the following code to cancel the callback in all exit routes:


// Check if the callback can be cancelled. If NULL it has
// already happened and cannot be cancelled.
if(pMe->cbkLookup.pfnCancel != NULL) {
CALLBACK_Cancel(&pMe->cbkLookup);
}


The callback cancel code should be incorporated in the Suspend event handler code ( EVT_APP_SUSPEND), the app's FreeAppData function (which is called when the app is stopped, i.e. receives EVT_APP_STOP event), and in the Clear key event handler code (EVT_KEY and keycode AVK_CLR).

Note: Please note that your app will not pass TRUE BREW Testing if it does not properly cancel its pending DNS callback. Some symptoms that might indicate that your app is not canceling its p ending DNS callback are:,/p>

Phone crashes upon starting up app
Phone displays "Please Re-insert Battery" error upon starting up app

Both might imply that the previously running app did not cancel its pending DNS callback.
Submitted by: Administrator