Request engine lock from null provider crash

[asmirnov]

Environment

The client is using AdblockWebView as drop-in replacement for android WebView.
However it just crashes sometime with attached stacktraces.
Tested on some of recent versions of libadblockplus-android, most likely 1416d0ca58f92c0542f131888c72ea46437bc84a.

How to reproduce

Exact steps to reproduce are unclear.
It crashes on multiple devices (not single vendor) on multiple android versions.

Observed behaviour

Crash while trying to access engine lock from null provider.

Expected behaviour

No crash happens.

[asmirnov]

This is the only line where provider fields is written (set):
​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L249

It's called synchronously BTW.

This is the only line where setProvider is called from AdblockWebView:
​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1139 and it does not pass null for sure.

So the only ways to get null there are:

1) it's not yet set
It should be set as it'sensureProvider() is called from initAbpLoading().
​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1130
called).

And initAbpLoading is called in the very beginning of everything:

• in loadData() ​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1249
• in loadDataWithBaseURL() ​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1263
• in loadUrl() ​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1223
• in loadUrl(..) ​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1236
• in reload() ​https://github.com/adblockplus/libadblockplus-android/blob/master/adblock-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java#L1210

2) setProvider() is called with null argument intentionally.