8 files changed, 498 insertions, 0 deletions
diff --git a/src/main/java/io/trygvis/queue/AsyncService.java b/src/main/java/io/trygvis/queue/AsyncService.java
new file mode 100755
index 0000000..c12f794
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/AsyncService.java
@@ -0,0 +1,27 @@
+package io.trygvis.queue;
+
+import java.util.*;
+
+public interface AsyncService {
+
+    /**
+     * @param name
+     * @param interval how often the queue should be polled for missed tasks in seconds.
+     */
+    Queue registerQueue(String name, int interval, AsyncCallable callable);
+
+    void stopQueue(Queue queue);
+
+    Queue getQueue(String name);
+
+    TaskRef schedule(Queue queue, String... args);
+
+    /**
+     * Polls for a new state of the execution.
+     */
+    Task update(Task ref);
+
+    interface AsyncCallable {
+        void run(List<String> args) throws Exception;
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/JdbcAsyncService.java b/src/main/java/io/trygvis/queue/JdbcAsyncService.java
new file mode 100644
index 0000000..ae6cdba
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/JdbcAsyncService.java
@@ -0,0 +1,253 @@
+package io.trygvis.queue;
+
+import org.slf4j.*;
+import org.springframework.jdbc.core.*;
+import org.springframework.transaction.*;
+import org.springframework.transaction.annotation.*;
+import org.springframework.transaction.support.*;
+
+import javax.sql.*;
+import java.util.*;
+import java.util.concurrent.*;
+
+import static java.util.Arrays.*;
+import static java.util.concurrent.TimeUnit.*;
+import static org.springframework.transaction.annotation.Propagation.MANDATORY;
+import static org.springframework.transaction.support.TransactionSynchronizationManager.registerSynchronization;
+
+public class JdbcAsyncService implements AsyncService {
+    private final Logger log = LoggerFactory.getLogger(getClass());
+
+    private final ScheduledThreadPoolExecutor executor = new ScheduledThreadPoolExecutor(10, Executors.defaultThreadFactory());
+
+    private final Map<String, QueueThread> queues = new HashMap<>();
+
+    private final TransactionTemplate transactionTemplate;
+
+    private final QueueDao queueDao;
+
+    private final TaskDao taskDao;
+
+    /**
+     * Accessed from all the queue threads.
+     */
+    private final Map<Long, TaskRef> taskRefs = Collections.synchronizedMap(new WeakHashMap<Long, TaskRef>());
+
+    public JdbcAsyncService(DataSource dataSource, PlatformTransactionManager transactionManager) {
+        this.transactionTemplate = new TransactionTemplate(transactionManager);
+        this.queueDao = new QueueDao(new JdbcTemplate(dataSource));
+        this.taskDao = new TaskDao(new JdbcTemplate(dataSource));
+    }
+
+    @Transactional(propagation = MANDATORY)
+    public Queue registerQueue(final String name, final int interval, AsyncCallable callable)  {
+        log.info("registerQueue: ENTER");
+
+        Queue q = queueDao.findByName(name);
+
+        log.info("q = {}", q);
+
+        final long interval_;
+        if (q == null) {
+            q = new Queue(name, interval * 1000);
+            queueDao.insert(q);
+            interval_ = interval;
+        } else {
+            // Found an existing queue. Use the Settings from the database.
+            interval_ = q.interval;
+        }
+
+        final QueueThread queueThread = new QueueThread(q, callable);
+        queues.put(name, queueThread);
+
+        registerSynchronization(new TransactionSynchronizationAdapter() {
+            public void afterCompletion(int status) {
+                log.info("status = {}", status);
+                if (status == TransactionSynchronization.STATUS_COMMITTED) {
+                    executor.scheduleAtFixedRate(new Runnable() {
+                        public void run() {
+                            queueThread.ping();
+                        }
+                    }, 1000, 1000 * interval_, MILLISECONDS);
+//                    Thread thread = new Thread(queueThread, name);
+//                    thread.setDaemon(true);
+//                    thread.start();
+                    queueThread.start();
+                }
+            }
+        });
+
+        log.info("registerQueue: LEAVE");
+        return q;
+    }
+
+    public void stopQueue(Queue queue) {
+        QueueThread queueThread = queues.get(queue.name);
+
+        if (queueThread == null) {
+            throw new RuntimeException("No such queue: '" + queue.name + "'.");
+        }
+
+        queueThread.shutdown();
+    }
+
+    public Queue getQueue(String name) {
+        QueueThread queueThread = queues.get(name);
+
+        if (queueThread == null) {
+            throw new RuntimeException("No such queue: '" + name + "'.");
+        }
+
+        return queueThread.queue;
+    }
+
+    @Transactional(propagation = MANDATORY)
+    public TaskRef schedule(Queue queue, String... args) {
+        log.info("schedule: ENTER");
+
+        Date scheduled = new Date();
+
+        StringBuilder arguments = new StringBuilder();
+        for (String arg : args) {
+            arguments.append(arg).append(' ');
+        }
+
+        long id = taskDao.insert(queue.name, scheduled, arguments.toString());
+        Task task = new Task(id, queue.name, scheduled, null, 0, null, asList(args));
+        log.info("task = {}", task);
+        queues.get(queue.name).ping();
+//        try {
+//            Thread.sleep(500);
+//        } catch (InterruptedException e) {
+//            e.printStackTrace();
+//        }
+
+        log.info("schedule: LEAVE");
+        TaskRef taskRef = new TaskRef(task);
+        taskRefs.put(task.id, taskRef);
+        return taskRef;
+    }
+
+    @Transactional(readOnly = true)
+    public Task update(Task ref) {
+        return taskDao.findById(ref.id);
+    }
+
+    class QueueThread extends Thread {
+        public boolean shouldRun = true;
+
+        public final Queue queue;
+
+        private final AsyncCallable callable;
+
+        QueueThread(Queue queue, AsyncCallable callable) {
+            super(queue.name);
+            this.queue = queue;
+            this.callable = callable;
+        }
+
+        public void ping() {
+            log.info("Sending ping to " + queue);
+            synchronized (this) {
+                notify();
+            }
+        }
+
+        public void run() {
+            while (shouldRun) {
+                List<Task> tasks = taskDao.findByNameAndCompletedIsNull(queue.name);
+
+                log.info("Found {} tasks on queue {}", tasks.size(), queue.name);
+
+                try {
+                    for (final Task task : tasks) {
+                        try {
+                            executeTask(task);
+                        } catch (TransactionException | TaskFailureException e) {
+                            log.warn("Task execution failed", e);
+                        }
+                    }
+                } catch (Exception e) {
+                    if (!isInterrupted() && !shouldRun) {
+                        log.warn("Error while executing tasks.", e);
+                    } else {
+                        log.warn("Error because queue was signalled to shut down.", e);
+                    }
+                }
+
+                synchronized (this) {
+                    try {
+                        wait();
+                    } catch (InterruptedException e) {
+                        // ignore
+                    }
+                }
+            }
+
+            log.info("Queue has stopped");
+
+            synchronized (this) {
+                this.notify();
+            }
+        }
+
+        private void executeTask(final Task task) {
+            final Date run = new Date();
+            log.info("Setting last run on task. date = {}, task = {}", run, task);
+            transactionTemplate.execute(new TransactionCallbackWithoutResult() {
+                protected void doInTransactionWithoutResult(TransactionStatus status) {
+                    taskDao.update(task.registerRun());
+                }
+            });
+
+            transactionTemplate.execute(new TransactionCallbackWithoutResult() {
+                protected void doInTransactionWithoutResult(TransactionStatus status) {
+                    Task t;
+
+                    try {
+                        callable.run(task.arguments);
+                        Date completed = new Date();
+                        t = task.registerComplete(completed);
+                        log.info("Completed task: {}", t);
+                        taskDao.update(t);
+                    } catch (Exception e) {
+                        throw new TaskFailureException(e);
+                    }
+
+                    TaskRef taskRef = taskRefs.get(task.id);
+
+                    if (taskRef != null) {
+                        log.info("Notifying listeners on task: {}", t);
+                        //noinspection SynchronizationOnLocalVariableOrMethodParameter
+                        synchronized (taskRef) {
+                            taskRef.notifyAll();
+                        }
+                    }
+                }
+            });
+        }
+
+        public void shutdown() {
+            log.info("Shutting down queue");
+            shouldRun = false;
+            synchronized (this) {
+                this.interrupt();
+            }
+            while (isAlive()) {
+                synchronized (this) {
+                    try {
+                        this.wait(100);
+                    } catch (InterruptedException e) {
+                        // ignore
+                    }
+                }
+            }
+        }
+    }
+
+    private static class TaskFailureException extends RuntimeException {
+        public TaskFailureException(Exception e) {
+            super(e);
+        }
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/Queue.java b/src/main/java/io/trygvis/queue/Queue.java
new file mode 100755
index 0000000..7e1fbff
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/Queue.java
@@ -0,0 +1,28 @@
+package io.trygvis.queue;
+
+/**
+ * TODO: concurrency control. min/max number of consumers.
+ * TODO: check interval. How often should the fallback check the queue. Resolution in seconds.
+ */
+public class Queue<A, B> {
+
+    public final String name;
+
+    public final long interval;
+
+    public Queue(String name, long interval) {
+        this.name = name;
+        this.interval = interval;
+    }
+
+    public Queue withInterval(int interval) {
+        return new Queue(name, interval);
+    }
+
+    public String toString() {
+        return "Queue{" +
+                "name='" + name + '\'' +
+                ", interval=" + interval +
+                '}';
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/QueueDao.java b/src/main/java/io/trygvis/queue/QueueDao.java
new file mode 100644
index 0000000..fcf975f
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/QueueDao.java
@@ -0,0 +1,36 @@
+package io.trygvis.queue;
+
+import org.springframework.beans.factory.annotation.*;
+import org.springframework.jdbc.core.*;
+import org.springframework.stereotype.*;
+
+import java.sql.*;
+
+import static org.springframework.dao.support.DataAccessUtils.*;
+
+public class QueueDao {
+
+    private final JdbcTemplate jdbcTemplate;
+
+    public QueueDao(JdbcTemplate jdbcTemplate) {
+        this.jdbcTemplate = jdbcTemplate;
+    }
+
+    public Queue findByName(String name) {
+        return singleResult(jdbcTemplate.query("SELECT name, interval FROM queue WHERE name=?", new QueueRowMapper(), name));
+    }
+
+    public void insert(Queue q) {
+        jdbcTemplate.update("INSERT INTO queue(name, interval) VALUES(?, ?)", q.name, q.interval);
+    }
+
+    public void update(Queue q) {
+        jdbcTemplate.update("UPDATE queue SET interval=? WHERE name=?", q.interval, q.name);
+    }
+
+    private class QueueRowMapper implements RowMapper<Queue> {
+        public Queue mapRow(ResultSet rs, int rowNum) throws SQLException {
+            return new Queue(rs.getString(1), rs.getLong(2));
+        }
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/Task.java b/src/main/java/io/trygvis/queue/Task.java
new file mode 100755
index 0000000..2a061bd
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/Task.java
@@ -0,0 +1,60 @@
+package io.trygvis.queue;
+
+import java.util.*;
+
+import static java.util.Collections.unmodifiableList;
+
+/**
+ * TODO: next run on failures. A default strategy from the queue, let the task be able to re-schedule itself.
+ */
+public class Task {
+
+    public final long id;
+
+    public final String queue;
+
+    public final Date scheduled;
+
+    public final Date lastRun;
+
+    public final int runCount;
+
+    public final Date completed;
+
+    public final List<String> arguments;
+
+    Task(long id, String queue, Date scheduled, Date lastRun, int runCount, Date completed, List<String> arguments) {
+        this.id = id;
+        this.queue = queue;
+        this.scheduled = scheduled;
+        this.lastRun = lastRun;
+        this.runCount = runCount;
+        this.completed = completed;
+
+        this.arguments = unmodifiableList(new ArrayList<>(arguments));
+    }
+
+    public Task registerRun() {
+        return new Task(id, queue, scheduled, new Date(), runCount + 1, completed, arguments);
+    }
+
+    public Task registerComplete(Date completed) {
+        return new Task(id, queue, scheduled, lastRun, runCount, new Date(), arguments);
+    }
+
+    public String toString() {
+        return "Task{" +
+                "id=" + id +
+                ", queue=" + queue +
+                ", scheduled=" + scheduled +
+                ", lastRun=" + lastRun +
+                ", runCount=" + runCount +
+                ", completed=" + completed +
+                ", arguments='" + arguments + '\'' +
+                '}';
+    }
+
+    public boolean isDone() {
+        return completed != null;
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/TaskDao.java b/src/main/java/io/trygvis/queue/TaskDao.java
new file mode 100644
index 0000000..84ce958
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/TaskDao.java
@@ -0,0 +1,54 @@
+package io.trygvis.queue;
+
+import org.springframework.jdbc.core.*;
+
+import java.sql.*;
+import java.util.Date;
+import java.util.*;
+
+import static java.util.Arrays.*;
+
+public class TaskDao {
+
+    private final JdbcTemplate jdbcTemplate;
+
+    public TaskDao(JdbcTemplate jdbcTemplate) {
+        this.jdbcTemplate = jdbcTemplate;
+    }
+
+    public long insert(String queue, Date scheduled, String arguments) {
+        jdbcTemplate.update("INSERT INTO task(id, run_count, queue, scheduled, arguments) " +
+                "VALUES(nextval('task_seq'), 0, ?, ?, ?)", queue, scheduled, arguments);
+        return jdbcTemplate.queryForObject("SELECT currval('task_seq')", Long.class);
+    }
+
+    public Task findById(long id) {
+        return jdbcTemplate.queryForObject("SELECT " + TaskRowMapper.fields + " FROM task WHERE id=?",
+                new TaskRowMapper(), id);
+    }
+
+    public List<Task> findByNameAndCompletedIsNull(String name) {
+        return jdbcTemplate.query("SELECT " + TaskRowMapper.fields + " FROM task WHERE queue=? AND completed IS NULL",
+                new TaskRowMapper(), name);
+    }
+
+    public void update(Task task) {
+        jdbcTemplate.update("UPDATE task SET scheduled=?, last_run=?, run_count=?, completed=? WHERE id=?",
+                task.scheduled, task.lastRun, task.runCount, task.completed, task.id);
+    }
+
+    private class TaskRowMapper implements RowMapper<Task> {
+        public static final String fields = "id, queue, scheduled, last_run, run_count, completed, arguments";
+
+        public Task mapRow(ResultSet rs, int rowNum) throws SQLException {
+            return new Task(
+                    rs.getLong(1),
+                    rs.getString(2),
+                    rs.getTimestamp(3),
+                    rs.getTimestamp(4),
+                    rs.getInt(5),
+                    rs.getTimestamp(6),
+                    asList(rs.getString(7).split(" ")));
+        }
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/TaskRef.java b/src/main/java/io/trygvis/queue/TaskRef.java
new file mode 100644
index 0000000..e465ee7
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/TaskRef.java
@@ -0,0 +1,23 @@
+package io.trygvis.queue;
+
+/**
+ * TODO: Implement waitForSuccess(). Rename waitFor to waitForAny(). Let waitForAny() throw TargetInvocationException
+ * which contains the exception that the task threw.
+ */
+public class TaskRef {
+    private Task task;
+
+    public TaskRef(Task task) {
+        this.task = task;
+    }
+
+    public Task getTask() {
+        return task;
+    }
+
+    public void waitFor(int timeout) throws InterruptedException {
+        synchronized (this) {
+            wait(timeout);
+        }
+    }
+}
diff --git a/src/main/java/io/trygvis/queue/spring/QueueSpringConfig.java b/src/main/java/io/trygvis/queue/spring/QueueSpringConfig.java
new file mode 100644
index 0000000..0eb7695
--- /dev/null
+++ b/src/main/java/io/trygvis/queue/spring/QueueSpringConfig.java
@@ -0,0 +1,17 @@
+package io.trygvis.queue.spring;
+
+import io.trygvis.queue.*;
+import org.springframework.context.annotation.*;
+import org.springframework.transaction.*;
+import org.springframework.transaction.annotation.*;
+
+import javax.sql.*;
+
+@Configuration
+@EnableTransactionManagement
+public class QueueSpringConfig {
+    @Bean
+    public AsyncService asyncService(DataSource dataSource, PlatformTransactionManager platformTransactionManager) {
+        return new JdbcAsyncService(dataSource, platformTransactionManager);
+    }
+}