added retry executor

src/main/java/net/woggioni/jwo/JWO.java

@@ -47,6 +47,10 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.ServiceConfigurationError;
 import java.util.ServiceLoader;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.function.Consumer;
@@ -928,4 +932,56 @@ public class JWO {
         if (!opt1.isPresent() || !opt2.isPresent()) return Optional.empty();
         else return Optional.ofNullable(cb.apply(opt1.get(), opt2.get()));
     }
+
+
+    public static Executor delayedExecutor(long delay, TimeUnit unit,
+                                            Executor executor) {
+        if (unit == null || executor == null)
+            throw new NullPointerException();
+        return new DelayedExecutor(delay, unit, executor);
+    }
+    private static final class Delayer {
+        private static ScheduledFuture<?> delay(Runnable command, long delay,
+                                                TimeUnit unit) {
+            return delayer.schedule(command, delay, unit);
+        }
+
+        private static final class DaemonThreadFactory implements ThreadFactory {
+            public Thread newThread(Runnable r) {
+                Thread t = new Thread(r);
+                t.setDaemon(true);
+                t.setName("CompletableFutureDelayScheduler");
+                return t;
+            }
+        }
+
+        private static final ScheduledThreadPoolExecutor delayer;
+        static {
+            (delayer = new ScheduledThreadPoolExecutor(
+                1, new DaemonThreadFactory())).
+                setRemoveOnCancelPolicy(true);
+        }
+    }
+
+    private static final class DelayedExecutor implements Executor {
+        final long delay;
+        final TimeUnit unit;
+        final Executor executor;
+        private DelayedExecutor(long delay, TimeUnit unit, Executor executor) {
+            this.delay = delay; this.unit = unit; this.executor = executor;
+        }
+        public void execute(Runnable r) {
+            Delayer.delay(new TaskSubmitter(executor, r), delay, unit);
+        }
+    }
+
+    private static final class TaskSubmitter implements Runnable {
+        final Executor executor;
+        final Runnable action;
+        TaskSubmitter(Executor executor, Runnable action) {
+            this.executor = executor;
+            this.action = action;
+        }
+        public void run() { executor.execute(action); }
+    }
 }

src/main/java/net/woggioni/jwo/RetryExecutor.java

@@ -0,0 +1,167 @@
+package net.woggioni.jwo;
+
+import lombok.Builder;
+
+import java.time.Duration;
+import java.util.Optional;
+import java.util.concurrent.Callable;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ForkJoinPool;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
+
+import static net.woggioni.jwo.JWO.delayedExecutor;
+import static net.woggioni.jwo.JWO.newThrowable;
+
+@Builder
+public class RetryExecutor {
+    @Builder.Default
+    private final int maxAttempts = 5;
+
+    @Builder.Default
+    private final Duration initialDelay = Duration.ofSeconds(1);
+
+    @Builder.Default
+    private final Double exp = 1.0;
+
+    @Builder.Default
+    private final ExceptionHandler exceptionHandler = err -> ExceptionHandlerOutcome.CONTINUE;
+
+    @Builder.Default
+    private final ExecutorService executorService = ForkJoinPool.commonPool();
+
+    public enum ExceptionHandlerOutcome {
+        THROW, CONTINUE
+    }
+
+    public interface ExceptionHandler {
+        ExceptionHandlerOutcome handleError(Throwable t);
+    }
+
+    public CompletableFuture<Void> submit(Runnable cb) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public CompletableFuture<Void> submit(
+        Runnable cb,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public CompletableFuture<Void> submit(
+        Runnable cb,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public CompletableFuture<Void> submit(
+        Runnable cb,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public CompletableFuture<Void> submit(
+        Runnable cb,
+        Duration initialDelay,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+    public static CompletableFuture<Void> submit(
+        Runnable cb,
+        int maxAttempts,
+        Duration initialDelay,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(() -> {
+            cb.run();
+            return null;
+        }, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public <T> CompletableFuture<T> submit(Callable<T> cb) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public <T> CompletableFuture<T> submit(
+        Callable<T> cb,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public <T> CompletableFuture<T> submit(
+        Callable<T> cb,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public <T> CompletableFuture<T> submit(
+        Callable<T> cb,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public <T> CompletableFuture<T> submit(
+        Callable<T> cb,
+        Duration initialDelay,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        return submit(cb, maxAttempts, initialDelay, exp, exceptionHandler, executorService);
+    }
+
+    public static <T> CompletableFuture<T> submit(
+        Callable<T> cb,
+        int maxAttempts,
+        Duration initialDelay,
+        Double exp,
+        ExceptionHandler exceptionHandler,
+        ExecutorService executorService) {
+        CompletableFuture<T> result = CompletableFuture.supplyAsync((Sup<T>) cb::call, executorService);
+        double delay = initialDelay.toMillis();
+        for(int i = 1; i <= maxAttempts; i++) {
+            int attempt = i;
+            double thisAttemptDelay = delay;
+            result = result.handleAsync((BiFun<T, Throwable, CompletableFuture<T>>) (value, err) -> {
+                Optional<Throwable> causeOpt = Optional.ofNullable(err).map(Throwable::getCause);
+                if(!causeOpt.isPresent()) {
+                    return CompletableFuture.completedFuture(value);
+                } else if(attempt == maxAttempts) {
+                    throw causeOpt.get();
+                } else {
+                    Throwable cause = causeOpt.get();
+                    ExceptionHandlerOutcome eho = exceptionHandler.handleError(cause);
+                    switch (eho) {
+                        case THROW:
+                            throw cause;
+                        case CONTINUE:
+                            Executor delayedExecutor = delayedExecutor(
+                                (long) thisAttemptDelay,
+                                TimeUnit.MILLISECONDS,
+                                executorService
+                            );
+                            return CompletableFuture.supplyAsync((Sup<T>) cb::call, delayedExecutor);
+                        default:
+                            throw newThrowable(UnsupportedOperationException.class,
+                                "Unsupported value for enum %s: '%s'",
+                                ExceptionHandlerOutcome.class.getName(),
+                                eho
+                            );
+                    }
+                }
+            }, executorService).thenComposeAsync(Function.identity(), executorService);
+            delay *= exp;
+        }
+        return result;
+    }
+}

src/main/java9/module-info.java

@@ -1,4 +1,5 @@
 module net.woggioni.jwo {
+    requires static lombok;
     requires org.slf4j;
     exports net.woggioni.jwo;
     exports net.woggioni.jwo.exception;