CODEWITHSUNDEEP
androidc++multithreadingc++11android-ndk
iammilind
iammilind

Reputation: 69988

c++11 multithreading issues with Android where some threads are not scheduled properly

I am developing a VoIP based application which is multithreaded. For every socket there is a c++11 std::thread (including SSL read & write). The core module for data communication is in C++ which is called through JNI interface.

My observation is that, once initializing the application after few seconds, some threads which were running earlier normally are not getting running time. If a certain thread is running then it keeps running for a while ranging from 3-4 seconds to 30-40 seconds.

After referring change native thread priority on Android, I also tried changing "nice" value to -10 for all the threads, but no luck. Important to note that exactly same C++ code is working perfectly fine for iOS.

Is there an issue with Android Native thread scheduling, or am I missing something?

Upvotes: 4

Views: 1570

Answers (1)

wessel
wessel

Reputation: 564

while (...) {
 int selectResult = select( fd, ...);
 if ( selectResult > 0 ) DoSomeWork( fd );
 else nanosleep(...); /* this is the new line which solved my stalling threads */
}

I had a similar problem, and found that for my case the solution was to verify that those threads that have an eternal loop (constantly performing select until there is something on a socket to spawn a handler thread), always call nanosleep at least once in their loop.

Like you, I experienced this issue on Android, and no issue on iOS.

I can only hypothesise that the JVM on Android sometimes would give full priority to one thread which is only polling a socket without pausing, such that other threads which had actual work to be done would stall. But I wouldn't know how to verify that hypothesis.

It's also weird that my solution works, given that select already uses a user-chosen timeout, such that I would think it internally sleeps anyway. Apparently not on Android.

Upvotes: 1

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