ThreadMonitor

ThreadMonitor.kt

import kotlin.math.min

/**
 * Prints useful information about all threads in our process. Information includes
 * [Thread.getName], [Thread.getState] and the stacktrace of the [Thread] up to 10 items.
 *
 * To stop thread call [interrupt].
 *
 * Things to look for:
 *
 * - Too many threads.
 * - Rx IO threads that are not blocking on I/O (see their stack trace).
 * - Computation threads that are not idle (see their stack trace).
 * - Duplicate thread names because thread-pools are not being reused (for example more than one
 *   Glide or root OkHttpClient instance)
 */
class ThreadMonitor constructor(
        // Default is to run every 2 minutes.
        private val intervalMs: Long = 120000,
        private val maxStack: Int = 10
) : Thread("ThreadMonitor") {
    init {
        // Use MAX_PRIORITY so that we can see what other threads are doing without waiting for
        // them to go to idle.
        priority = Thread.MAX_PRIORITY
    }

    override fun run() {
        try {
            while (!Thread.currentThread().isInterrupted) {
                // Get all the threads and sort them by name
                val threads = Thread.getAllStackTraces()
                        .toList()
                        .sortedBy { (thread, _) ->
                            thread.name
                        }
                // For each thread, we get the index, name and stacktrace up to 10 items
                // and log them
                for (i in 0 until threads.size) {
                    val (thread, stacktrace) = threads[i]
                    val stack = stacktrace.toList().subList(0, min(maxStack, stacktrace.size))
                    System.out.println("Thread status %s %s (%s) > %s",
                            (i + 1), thread.name, thread.state, stack)
                }

                Thread.sleep(intervalMs)
            }
        } catch (interrupted: InterruptedException) {
            System.out.println("Thread monitor was interrupted")
        }
    }
}