shared-engine

Example: a SHARED engine shared with other native code

By default the plugin links SQLite statically, so libnscsqlite.so contains its own private copy. That is the right answer for almost every app.

Build the engine as a shared library instead when the app has other native code that must talk to the same SQLite — the same page cache, the same registered functions, the same sqlite3_auto_extension list. Two static copies in one process are two independent engines that merely happen to open the same files.

It also makes the engine swappable: in the prototype behind this example, the .so was replaced with a build of a different SQLite version without relinking the plugin, and all 33 APIs the plugin needs still resolved.

Setup

App_Resources/Android/nscsqlite/
  CMakeLists.txt
  sqlite/
    sqlite3.c
    sqlite3.h

Your other native target then links nscsqlite_sqlite the same way the plugin does, or declares its own SHARED IMPORTED target for libnscsqlite3.so.

What to check

• The library must reach the APK. It is produced by the same external native build as libnscsqlite.so, so AGP should package it alongside; confirm it once with unzip -l platforms/android/app/build/outputs/apk/debug/app-debug.apk | grep 'lib/'. If it is missing at run time the app fails at dlopen, not at build time.
• Symbols are exported on purpose here. libnscsqlite3.so has a dynamic symbol table with sqlite3_* in it — that is the point of the exercise, and it is the thing the static default avoids. Keeping the SONAME libnscsqlite3.so rather than libsqlite3.so is what stops an unrelated dependency from binding to it by accident.
• 16 KB alignment. The plugin passes -Wl,-z,max-page-size=16384 when it links its own library. If your NDK is older than r28 you may want the same flag on this target: target_link_options(nscsqlite_sqlite PRIVATE -Wl,-z,max-page-size=16384).
• SQLITE_API is not optional with C_VISIBILITY_PRESET hidden. The amalgamation defines SQLITE_API as nothing on ELF, so without the override in the CMakeLists.txt the library exports no symbols and the plugin fails to link.