NSThread: Fix threadPriority and setThreadPriority: on Android by using setpriority instead of pthread

[hmelder]

Android's pthread_setschedparam is currently broken, as it checks if the priority is in the range of the system's min and max priorities. The interval bounds are queried with sched_get_priority_min, and sched_get_priority_max which just return 0, regardless of the specified scheduling policy.

The solution is to use setpriority to set the thread priority. This is possible because on Linux, it is not a per-process setting as specified by POSIX but a per-thread setting (See the Bugs section in setpriority).

[rfm]

This makes perfect sense.

[hmelder]

Android's pthread_setschedparam is currently broken

I have to correct myself. It is not broken (as seen here). On Linux, SCHED_OTHER does not have additional priorities which means that sched_get_priority_min and sched_get_priority_max always return 0.

However, user-space threads, created with pthread_create, are a 1-to-1 mapping to Linux LWPs (Light Weight Process). Adjusting the nice value (with nice() or setpriority()) will change the way the thread is handled.

[hmelder]

After skimming through the newest Android Sources, I can indeed verify that setpriority is still used.

On Android there is setThreadPriority in android.os.Process which is implemented here.

The underlying function is called androidSetThreadPriority which in turn calls setpriority.

This is much better than interfacing with JNI.

[hmelder]

@rfm how about doing that on Linux as well? Currently we do not prioritise anything because of this.

[hmelder]

Here is a similar discussion: dotnet/runtime#91165

[triplef]

Another discussion about this in the NDK project: android/ndk#1255

If I understand it correctly it sounds like we should use setpriority().