Is it possible for libraries to share memory like the shared memory in linux?
(The shared memory feature adopted in System V and later adopted to linux)
Eg: When two apps are working simultaneously and both uses the OkHttp library, is the library loaded into memory twice?
The same shared memory feature is still present in Android, and it works on built-in shared libraries such as OpenGL ES, but it's not used for third-party libraries like you're asking about. Each app that uses a third-party library has to include the library in its APK file. These then aren't shared libraries (in the .so sense): they're just duplicate files which might happen to contain the same code. (Usually they won't contain the same code because different apps will have been built against different versions of the library.)
This avoids possible incompatibilities or security problems caused by updating libraries from different apps. Shared library incompatibilities are a huge problem in GNU/Linux systems. Distributions put a lot of effort into preventing them by testing different combinations of applications and libraries, but they still go wrong sometimes. In Android, where nobody is responsible for making sure that different apps work together, that kind of shared library system would result in apps often breaking when a shared library is updated. Security problems might come about in a system that used shared libraries in this way, because an app might update a shared library to a "newer version" that's actually hacked to leak information or control the app. The libraries would have to be treated as separate packages, signed by the author, just like apps are, and then there would have to be a complex process for handling version updates.
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