make sqlite storage more resilient to sporadic errors

- catch SQLite exceptions and report them
- failed statements are ignored, we're really just caching here, so if it fails we're handling it gracefully elsewhere
- handle cases where the database file goes away after we opened it
- handle cases where the schema wasn't created after the database file was opened successfully
- add tests

2 files changed, 5 insertions, 1 deletions

diff --git a/include/mbgl/platform/log.hpp b/include/mbgl/platform/log.hpp
index 5d287eb572..d6f3cd1ab4 100644
--- a/include/mbgl/platform/log.hpp
+++ b/include/mbgl/platform/log.hpp
@@ -4,6 +4,7 @@
 #include <mbgl/platform/event.hpp>
 
 #include <mbgl/util/std.hpp>
+#include <mbgl/util/noncopyable.hpp>
 
 #include <memory>
 #include <string>
@@ -12,7 +13,7 @@ namespace mbgl {
 
 class Log {
 public:
-    class Observer {
+    class Observer : private util::noncopyable {
     public:
         virtual ~Observer() = default;
 
@@ -22,6 +23,7 @@ public:
     };
 
     static void setObserver(std::unique_ptr<Observer> Observer);
+    static std::unique_ptr<Observer> removeObserver();
 
 private:
     template <typename T, size_t N>
diff --git a/include/mbgl/storage/default/sqlite_cache.hpp b/include/mbgl/storage/default/sqlite_cache.hpp
index 8f2746561c..fe80a41b52 100644
--- a/include/mbgl/storage/default/sqlite_cache.hpp
+++ b/include/mbgl/storage/default/sqlite_cache.hpp
@@ -38,6 +38,7 @@ private:
     void process(StopAction &action);
 
     void createDatabase();
+    void createSchema();
 
     const std::string path;
     uv_loop_t *loop = nullptr;
@@ -45,6 +46,7 @@ private:
     std::thread thread;
     std::unique_ptr<::mapbox::sqlite::Database> db;
     std::unique_ptr<::mapbox::sqlite::Statement> getStmt, putStmt, refreshStmt;
+    bool schema = false;
 };
 
 }