Thread safety in Android libraries

Question

I'm trying to implement a native shared library(.so) for the Android system. Naturally, there are some code blocks that need to be thread-safe.

I found out here that pthreads locks, mutexes, or condition variables are not supported.

I'd like to know what is usually used at the library level to achieve thread-safety?

Answer 1

How this can be achieves depends on whether you just want it to be thread safe when accessed by Java level threads, or you need to synchronize native threads with Java threads.

There are two ways to synchronize only Java level threads:

1.The easiest way is to add the synchronized keyword to the native methods that be accessed by multiple thread, i.e.

public native synchronized int sharedAccess();

2.Synchronization from the native side:

(*env)->MonitorEnter(env, obj);
...                      /* synchronized block */
(*env)->MonitorExit(env, obj);

Refer here on how to synchronize native threads with Java threads