Post by nic on Sept 22, 2016 11:41:34 GMT
One of the recent iOS updates has seen the appearance of some unexpected behaviour with MidiBus library powered apps (although other non MidiBus apps are affected also).
The problem occurs on newer version of iOS 9 (and 10 we think) where music apps crash on startup (or running) when the iDevice is connected to a wifi network, but this network is not connected to the Internet. This would be a common scenario in a live situation.
Technically what is happening is that the app is trying to resolve a host using DNS on the main thread. This will time out (this is normal behaviour), but the recent iOS versions do not like the amount of time the main thread is sitting waiting for a response and believe the app has hung and simply terminate it without warning.
The MidiBus library has been patched to address this and developers who use the MidiBus library are encouraged to build against v1.37 (or higher) - currently 1.37 is a pre-release but is working fine. Developers not using the MidiBus library should ensure that all calls to functions that do DNS lookups (eg. gethostbyname()) are called from a background thread.
One workaround is to run up all the apps first while connected to a network that has Internet connectivity so they can do their lookups and leave them running before the gig. The iDevice will then cache (for a limited time) those lookups and the apps will not crash. However, once the cache is cleared (not sure how long) then any app that makes a DNS lookup will crash again. NB. (pre 1.37) MidiBus powered apps will only do the lookup at app start so should not crash subsequently even after the DNS cache is cleared.
Regards, Nic.
The problem occurs on newer version of iOS 9 (and 10 we think) where music apps crash on startup (or running) when the iDevice is connected to a wifi network, but this network is not connected to the Internet. This would be a common scenario in a live situation.
Technically what is happening is that the app is trying to resolve a host using DNS on the main thread. This will time out (this is normal behaviour), but the recent iOS versions do not like the amount of time the main thread is sitting waiting for a response and believe the app has hung and simply terminate it without warning.
The MidiBus library has been patched to address this and developers who use the MidiBus library are encouraged to build against v1.37 (or higher) - currently 1.37 is a pre-release but is working fine. Developers not using the MidiBus library should ensure that all calls to functions that do DNS lookups (eg. gethostbyname()) are called from a background thread.
One workaround is to run up all the apps first while connected to a network that has Internet connectivity so they can do their lookups and leave them running before the gig. The iDevice will then cache (for a limited time) those lookups and the apps will not crash. However, once the cache is cleared (not sure how long) then any app that makes a DNS lookup will crash again. NB. (pre 1.37) MidiBus powered apps will only do the lookup at app start so should not crash subsequently even after the DNS cache is cleared.
Regards, Nic.
