If an app request call-back modifies any data associated with a resource,
then multiple threads can attempt to unsafely modify the data at the same time.
Lock the resource when calling the app request handler (as global_lock is
unlocked) to prevent concurrent changes to the resource information.
If the app request handler is definately known to not modify the resource
information, then COAP_RESOURCE_SAFE_REQUEST_HANDLER can be set in the flags
for coap_resource_init(). Usually if there is a PUT, POST, PATCH or IPATCH
handler it is unsafe to set this. Setting this will reduce lock contention.
Jon Shallow
39b79e23b4