2.x: Add scheduler creation factories (#5002)

* Add scheduler creation factories

Resolves #4993

This is a pretty vanilla copy from RxJava 1's implementation. Note that I had to tune NewThread scheduler to not be a singleton to support this.

We had talked about borrowing from project reactor's APIs for different overloads, let me know if you think we should add more fine-grained controls through these.

* Add `@since` info

* Change failure string to "is null"

* Move to RxJavaPlugins

* Remove no-arg overloads

* Rename to make it clearer about creation

Added scheduler because we're not in Scheduler anymore. Changed to "create" because "newNewThread" was weird

* Add tests (WIP)

* Remove unnecessary nullcheck

* Remove double try

* Fix tests, make them more robust with integration flow

* Shut down custom schedulers when done

src/main/java/io/reactivex/internal/schedulers/ComputationScheduler.java

@@ -15,20 +15,20 @@
  */
 package io.reactivex.internal.schedulers;
 
-import java.util.concurrent.*;
-import java.util.concurrent.atomic.AtomicReference;
-
 import io.reactivex.Scheduler;
 import io.reactivex.disposables.*;
 import io.reactivex.internal.disposables.*;
 
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicReference;
+
 /**
  * Holds a fixed pool of worker threads and assigns them
  * to requested Scheduler.Workers in a round-robin fashion.
  */
 public final class ComputationScheduler extends Scheduler {
     /** This will indicate no pool is active. */
-    static final FixedSchedulerPool NONE = new FixedSchedulerPool(0);
+    static final FixedSchedulerPool NONE;
     /** Manages a fixed number of workers. */
     private static final String THREAD_NAME_PREFIX = "RxComputationThreadPool";
     static final RxThreadFactory THREAD_FACTORY;
@@ -42,6 +42,7 @@ public final class ComputationScheduler extends Scheduler {
 
     static final PoolWorker SHUTDOWN_WORKER;
 
+    final ThreadFactory threadFactory;
     final AtomicReference<FixedSchedulerPool> pool;
     /** The name of the system property for setting the thread priority for this Scheduler. */
     private static final String KEY_COMPUTATION_PRIORITY = "rx2.computation-priority";
@@ -56,6 +57,9 @@ public final class ComputationScheduler extends Scheduler {
                 Integer.getInteger(KEY_COMPUTATION_PRIORITY, Thread.NORM_PRIORITY)));
 
         THREAD_FACTORY = new RxThreadFactory(THREAD_NAME_PREFIX, priority);
+
+        NONE = new FixedSchedulerPool(0, THREAD_FACTORY);
+        NONE.shutdown();
     }
 
     static int cap(int cpuCount, int paramThreads) {
@@ -68,12 +72,12 @@ static final class FixedSchedulerPool {
         final PoolWorker[] eventLoops;
         long n;
 
-        FixedSchedulerPool(int maxThreads) {
+        FixedSchedulerPool(int maxThreads, ThreadFactory threadFactory) {
             // initialize event loops
             this.cores = maxThreads;
             this.eventLoops = new PoolWorker[maxThreads];
             for (int i = 0; i < maxThreads; i++) {
-                this.eventLoops[i] = new PoolWorker(THREAD_FACTORY);
+                this.eventLoops[i] = new PoolWorker(threadFactory);
             }
         }
 
@@ -98,6 +102,18 @@ public void shutdown() {
      * count and using least-recent worker selection policy.
      */
     public ComputationScheduler() {
+        this(THREAD_FACTORY);
+    }
+
+    /**
+     * Create a scheduler with pool size equal to the available processor
+     * count and using least-recent worker selection policy.
+     *
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     */
+    public ComputationScheduler(ThreadFactory threadFactory) {
+        this.threadFactory = threadFactory;
         this.pool = new AtomicReference<FixedSchedulerPool>(NONE);
         start();
     }
@@ -121,7 +137,7 @@ public Disposable schedulePeriodicallyDirect(Runnable run, long initialDelay, lo
 
     @Override
     public void start() {
-        FixedSchedulerPool update = new FixedSchedulerPool(MAX_THREADS);
+        FixedSchedulerPool update = new FixedSchedulerPool(MAX_THREADS, threadFactory);
         if (!pool.compareAndSet(NONE, update)) {
             update.shutdown();
         }

src/main/java/io/reactivex/internal/schedulers/IoScheduler.java

@@ -16,13 +16,13 @@
 
 package io.reactivex.internal.schedulers;
 
-import java.util.concurrent.*;
-import java.util.concurrent.atomic.*;
-
 import io.reactivex.Scheduler;
 import io.reactivex.disposables.*;
 import io.reactivex.internal.disposables.EmptyDisposable;
 
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.*;
+
 /**
  * Scheduler that creates and caches a set of thread pools and reuses them if possible.
  */
@@ -37,16 +37,14 @@ public final class IoScheduler extends Scheduler {
     private static final TimeUnit KEEP_ALIVE_UNIT = TimeUnit.SECONDS;
 
     static final ThreadWorker SHUTDOWN_THREAD_WORKER;
+    final ThreadFactory threadFactory;
     final AtomicReference<CachedWorkerPool> pool;
 
     /** The name of the system property for setting the thread priority for this Scheduler. */
     private static final String KEY_IO_PRIORITY = "rx2.io-priority";
 
     static final CachedWorkerPool NONE;
     static {
-        NONE = new CachedWorkerPool(0, null);
-        NONE.shutdown();
-
         SHUTDOWN_THREAD_WORKER = new ThreadWorker(new RxThreadFactory("RxCachedThreadSchedulerShutdown"));
         SHUTDOWN_THREAD_WORKER.dispose();
 
@@ -56,6 +54,9 @@ public final class IoScheduler extends Scheduler {
         WORKER_THREAD_FACTORY = new RxThreadFactory(WORKER_THREAD_NAME_PREFIX, priority);
 
         EVICTOR_THREAD_FACTORY = new RxThreadFactory(EVICTOR_THREAD_NAME_PREFIX, priority);
+
+        NONE = new CachedWorkerPool(0, null, WORKER_THREAD_FACTORY);
+        NONE.shutdown();
     }
 
     static final class CachedWorkerPool implements Runnable {
@@ -64,11 +65,13 @@ static final class CachedWorkerPool implements Runnable {
         final CompositeDisposable allWorkers;
         private final ScheduledExecutorService evictorService;
         private final Future<?> evictorTask;
+        private final ThreadFactory threadFactory;
 
-        CachedWorkerPool(long keepAliveTime, TimeUnit unit) {
+        CachedWorkerPool(long keepAliveTime, TimeUnit unit, ThreadFactory threadFactory) {
             this.keepAliveTime = unit != null ? unit.toNanos(keepAliveTime) : 0L;
             this.expiringWorkerQueue = new ConcurrentLinkedQueue<ThreadWorker>();
             this.allWorkers = new CompositeDisposable();
+            this.threadFactory = threadFactory;
 
             ScheduledExecutorService evictor = null;
             Future<?> task = null;
@@ -97,7 +100,7 @@ ThreadWorker get() {
             }
 
             // No cached worker found, so create a new one.
-            ThreadWorker w = new ThreadWorker(WORKER_THREAD_FACTORY);
+            ThreadWorker w = new ThreadWorker(threadFactory);
             allWorkers.add(w);
             return w;
         }
@@ -143,13 +146,22 @@ void shutdown() {
     }
 
     public IoScheduler() {
+        this(WORKER_THREAD_FACTORY);
+    }
+
+    /**
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     */
+    public IoScheduler(ThreadFactory threadFactory) {
+        this.threadFactory = threadFactory;
         this.pool = new AtomicReference<CachedWorkerPool>(NONE);
         start();
     }
 
     @Override
     public void start() {
-        CachedWorkerPool update = new CachedWorkerPool(KEEP_ALIVE_TIME, KEEP_ALIVE_UNIT);
+        CachedWorkerPool update = new CachedWorkerPool(KEEP_ALIVE_TIME, KEEP_ALIVE_UNIT, threadFactory);
         if (!pool.compareAndSet(NONE, update)) {
             update.shutdown();
         }

src/main/java/io/reactivex/internal/schedulers/NewThreadScheduler.java

@@ -18,16 +18,18 @@
 
 import io.reactivex.Scheduler;
 
+import java.util.concurrent.ThreadFactory;
+
 /**
  * Schedules work on a new thread.
  */
 public final class NewThreadScheduler extends Scheduler {
 
+    final ThreadFactory threadFactory;
+
     private static final String THREAD_NAME_PREFIX = "RxNewThreadScheduler";
     private static final RxThreadFactory THREAD_FACTORY;
 
-    private static final NewThreadScheduler INSTANCE = new NewThreadScheduler();
-
     /** The name of the system property for setting the thread priority for this Scheduler. */
     private static final String KEY_NEWTHREAD_PRIORITY = "rx2.newthread-priority";
 
@@ -38,16 +40,16 @@ public final class NewThreadScheduler extends Scheduler {
         THREAD_FACTORY = new RxThreadFactory(THREAD_NAME_PREFIX, priority);
     }
 
-    public static NewThreadScheduler instance() {
-        return INSTANCE;
+    public NewThreadScheduler() {
+        this(THREAD_FACTORY);
     }
 
-    private NewThreadScheduler() {
-
+    public NewThreadScheduler(ThreadFactory threadFactory) {
+        this.threadFactory = threadFactory;
     }
 
     @Override
     public Worker createWorker() {
-        return new NewThreadWorker(THREAD_FACTORY);
+        return new NewThreadWorker(threadFactory);
     }
 }

src/main/java/io/reactivex/internal/schedulers/SingleScheduler.java

@@ -12,20 +12,21 @@
  */
 package io.reactivex.internal.schedulers;
 
-import java.util.concurrent.*;
-import java.util.concurrent.atomic.AtomicReference;
-
 import io.reactivex.Scheduler;
 import io.reactivex.disposables.*;
 import io.reactivex.internal.disposables.EmptyDisposable;
 import io.reactivex.plugins.RxJavaPlugins;
 
+import java.util.concurrent.*;
+import java.util.concurrent.atomic.AtomicReference;
+
 /**
  * A scheduler with a shared, single threaded underlying ScheduledExecutorService.
  * @since 2.0
  */
 public final class SingleScheduler extends Scheduler {
 
+    final ThreadFactory threadFactory;
     final AtomicReference<ScheduledExecutorService> executor = new AtomicReference<ScheduledExecutorService>();
 
     /** The name of the system property for setting the thread priority for this Scheduler. */
@@ -47,11 +48,20 @@ public final class SingleScheduler extends Scheduler {
     }
 
     public SingleScheduler() {
-        executor.lazySet(createExecutor());
+        this(SINGLE_THREAD_FACTORY);
+    }
+
+    /**
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     */
+    public SingleScheduler(ThreadFactory threadFactory) {
+        this.threadFactory = threadFactory;
+        executor.lazySet(createExecutor(threadFactory));
     }
 
-    static ScheduledExecutorService createExecutor() {
-        return SchedulerPoolFactory.create(SINGLE_THREAD_FACTORY);
+    static ScheduledExecutorService createExecutor(ThreadFactory threadFactory) {
+        return SchedulerPoolFactory.create(threadFactory);
     }
 
     @Override
@@ -66,7 +76,7 @@ public void start() {
                 return;
             }
             if (next == null) {
-                next = createExecutor();
+                next = createExecutor(threadFactory);
             }
             if (executor.compareAndSet(current, next)) {
                 return;

src/main/java/io/reactivex/plugins/RxJavaPlugins.java

@@ -12,17 +12,19 @@
  */
 package io.reactivex.plugins;
 
-import java.lang.Thread.UncaughtExceptionHandler;
-import java.util.concurrent.Callable;
-
-import io.reactivex.internal.functions.ObjectHelper;
-import org.reactivestreams.Subscriber;
-
 import io.reactivex.*;
+import io.reactivex.annotations.Experimental;
 import io.reactivex.flowables.ConnectableFlowable;
 import io.reactivex.functions.*;
+import io.reactivex.internal.functions.ObjectHelper;
+import io.reactivex.internal.schedulers.*;
 import io.reactivex.internal.util.ExceptionHelper;
 import io.reactivex.observables.ConnectableObservable;
+import io.reactivex.schedulers.Schedulers;
+import org.reactivestreams.Subscriber;
+
+import java.lang.Thread.UncaughtExceptionHandler;
+import java.util.concurrent.*;
 
 /**
  * Utility class to inject handlers to certain standard RxJava operations.
@@ -926,6 +928,58 @@ public static Completable onAssembly(Completable source) {
         return source;
     }
 
+    /**
+     * Create an instance of the default {@link Scheduler} used for {@link Schedulers#computation()}
+     * except using {@code threadFactory} for thread creation.
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     * @return the created Scheduler instance
+     * @since 2.0.5 - experimental
+     */
+    @Experimental
+    public static Scheduler createComputationScheduler(ThreadFactory threadFactory) {
+        return new ComputationScheduler(ObjectHelper.requireNonNull(threadFactory, "threadFactory is null"));
+    }
+
+    /**
+     * Create an instance of the default {@link Scheduler} used for {@link Schedulers#io()}
+     * except using {@code threadFactory} for thread creation.
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     * @return the created Scheduler instance
+     * @since 2.0.5 - experimental
+     */
+    @Experimental
+    public static Scheduler createIoScheduler(ThreadFactory threadFactory) {
+        return new IoScheduler(ObjectHelper.requireNonNull(threadFactory, "threadFactory is null"));
+    }
+
+    /**
+     * Create an instance of the default {@link Scheduler} used for {@link Schedulers#newThread()}
+     * except using {@code threadFactory} for thread creation.
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     * @return the created Scheduler instance
+     * @since 2.0.5 - experimental
+     */
+    @Experimental
+    public static Scheduler createNewThreadScheduler(ThreadFactory threadFactory) {
+        return new NewThreadScheduler(ObjectHelper.requireNonNull(threadFactory, "threadFactory is null"));
+    }
+
+    /**
+     * Create an instance of the default {@link Scheduler} used for {@link Schedulers#single()}
+     * except using {@code threadFactory} for thread creation.
+     * @param threadFactory thread factory to use for creating worker threads. Note that this takes precedence over any
+     *                      system properties for configuring new thread creation. Cannot be null.
+     * @return the created Scheduler instance
+     * @since 2.0.5 - experimental
+     */
+    @Experimental
+    public static Scheduler createSingleScheduler(ThreadFactory threadFactory) {
+        return new SingleScheduler(ObjectHelper.requireNonNull(threadFactory, "threadFactory is null"));
+    }
+
     /**
      * Wraps the call to the function in try-catch and propagates thrown
      * checked exceptions as RuntimeException.

src/main/java/io/reactivex/schedulers/Schedulers.java

@@ -13,13 +13,12 @@
 
 package io.reactivex.schedulers;
 
-import java.util.concurrent.Callable;
-import java.util.concurrent.Executor;
-
 import io.reactivex.Scheduler;
 import io.reactivex.internal.schedulers.*;
 import io.reactivex.plugins.RxJavaPlugins;
 
+import java.util.concurrent.*;
+
 /**
  * Static factory methods for returning standard Scheduler instances.
  * <p>
@@ -58,7 +57,7 @@ static final class IoHolder {
     }
 
     static final class NewThreadHolder {
-        static final Scheduler DEFAULT = NewThreadScheduler.instance();
+        static final Scheduler DEFAULT = new NewThreadScheduler();
     }
 
     static {