Add job throttle

README.md

@@ -138,6 +138,20 @@ Horarium guarantees that a job would run **exactly once**
 
 Every Horarium instance consults MongoDB about new jobs to run every 100ms (default), thus creating some load on the DB server. This interval can be changed in ```HorariumSettings```
 
+If you want to decrease load, you can use job throttling that will automatically increase interval if there are no jobs available after certain attempts. To enable this feature, pass `JobThrottleSettings` to `HorariumSettings` with property `UseJobThrottle` set to `true`.
+
+```csharp
+var settings = new HorariumSettings
+{
+    JobThrottleSettings = new JobThrottleSettings
+    {
+        UseJobThrottle = true
+    }
+};
+```
+
+For more information about configuration, see `JobThrottleSettings`
+
 ## Using Horarium with SimpleInjector
 
 To use Horarium with SimpleInjector one should implement its own `IJobFactory`, using `Container` from `SimpleInjector`. For example:

src/Horarium.Test/RunnerJobTest.cs

@@ -102,6 +102,123 @@ public async Task Start_WontRecoverBeforeIntervalTimeout_AfterFailedDB()
             jobRepositoryMock.Verify(r => r.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()), Times.Once);
         }
 
+        [Fact]
+        public async Task Start_ExecutionWithDelay_WithThrottle()
+        {
+            // Arrange
+            var jobRepositoryMock = new Mock<IJobRepository>();
+
+            var settings = new HorariumSettings
+            {
+                IntervalStartJob = TimeSpan.FromSeconds(1),
+                JobThrottleSettings = new JobThrottleSettings
+                {
+                    UseJobThrottle = true,
+                    IntervalMultiplier = 1,
+                    JobRetrievalAttempts = 1
+                }
+            };
+
+            var runnerJobs = new RunnerJobs(jobRepositoryMock.Object,
+                settings,
+                new JsonSerializerSettings(),
+                Mock.Of<IHorariumLogger>(),
+                Mock.Of<IExecutorJob>(),
+                Mock.Of<IUncompletedTaskList>());
+
+            // Act
+            runnerJobs.Start();
+            await Task.Delay(settings.IntervalStartJob - TimeSpan.FromMilliseconds(500));
+            jobRepositoryMock.Invocations.Clear();
+
+            await Task.Delay(settings.IntervalStartJob + settings.IntervalStartJob.Multiply(settings.JobThrottleSettings.IntervalMultiplier));
+
+            // Assert
+            jobRepositoryMock.Verify(r => r.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()), Times.Once);
+        }
+
+        [Fact]
+        public async Task Start_ExecutionWithDelay_IncreaseInterval()
+        {
+            // Arrange
+            var jobRepositoryMock = new Mock<IJobRepository>();
+
+            jobRepositoryMock.Setup(x => x.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()))
+                .ReturnsAsync(() => null);
+
+            var settings = new HorariumSettings
+            {
+                IntervalStartJob = TimeSpan.FromSeconds(1),
+                JobThrottleSettings = new JobThrottleSettings
+                {
+                    UseJobThrottle = true,
+                    IntervalMultiplier = 1,
+                    JobRetrievalAttempts = 1,
+                }
+            };
+
+            var runnerJobs = new RunnerJobs(jobRepositoryMock.Object,
+                settings,
+                new JsonSerializerSettings(),
+                Mock.Of<IHorariumLogger>(),
+                Mock.Of<IExecutorJob>(),
+                Mock.Of<IUncompletedTaskList>());
+
+            // Act
+            runnerJobs.Start();
+            await Task.Delay(settings.IntervalStartJob - TimeSpan.FromMilliseconds(500));
+            jobRepositoryMock.Invocations.Clear();
+
+            var interval = settings.IntervalStartJob +
+                           settings.IntervalStartJob.Multiply(settings.JobThrottleSettings.IntervalMultiplier);
+            await Task.Delay(interval);
+            interval += settings.IntervalStartJob.Multiply(settings.JobThrottleSettings.IntervalMultiplier);
+            await Task.Delay(interval);
+            interval += settings.IntervalStartJob.Multiply(settings.JobThrottleSettings.IntervalMultiplier);
+            await Task.Delay(interval);
+
+            // Assert
+            jobRepositoryMock.Verify(r => r.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()), Times.Exactly(3));
+        }
+
+        [Fact]
+        public async Task Start_ExecutionWithDelay_MaxInterval()
+        {
+            // Arrange
+            var jobRepositoryMock = new Mock<IJobRepository>();
+
+            jobRepositoryMock.Setup(x => x.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()))
+                .ReturnsAsync(() => null);
+
+            var settings = new HorariumSettings
+            {
+                IntervalStartJob = TimeSpan.FromSeconds(1),
+                JobThrottleSettings = new JobThrottleSettings
+                {
+                    UseJobThrottle = true,
+                    IntervalMultiplier = 1,
+                    JobRetrievalAttempts = 1,
+                    MaxJobThrottleInterval = TimeSpan.FromSeconds(1)
+                }
+            };
+
+            var runnerJobs = new RunnerJobs(jobRepositoryMock.Object,
+                settings,
+                new JsonSerializerSettings(),
+                Mock.Of<IHorariumLogger>(),
+                Mock.Of<IExecutorJob>(),
+                Mock.Of<IUncompletedTaskList>());
+
+            // Act
+            runnerJobs.Start();
+            await Task.Delay(settings.IntervalStartJob - TimeSpan.FromMilliseconds(500));
+            jobRepositoryMock.Invocations.Clear();
+
+            await Task.Delay(TimeSpan.FromSeconds(5));
+            // Assert
+            jobRepositoryMock.Verify(r => r.GetReadyJob(It.IsAny<string>(), It.IsAny<TimeSpan>()), Times.Exactly(5));
+        }
+
         [Fact]
         public async Task Start_NextJobStarted_AddsJobTaskToUncompletedTasks()
         {

src/Horarium/Handlers/RunnerJobs.cs

@@ -17,6 +17,8 @@ public class RunnerJobs : IRunnerJobs
         private readonly IExecutorJob _executorJob;
         private Task _runnerTask;
         private readonly IUncompletedTaskList _uncompletedTaskList;
+
+        private readonly TimeSpan _defaultJobThrottleInterval = TimeSpan.FromMilliseconds(100);
 
         private CancellationToken _cancellationToken;
         private readonly CancellationTokenSource _cancelTokenSource = new CancellationTokenSource();
@@ -100,11 +102,29 @@ private async Task<JobMetadata> GetReadyJob()
 
         private async Task StartRunnerInternal(CancellationToken cancellationToken)
         {
+            var jobWaitTime = _settings.IntervalStartJob;
+
             while (true)
+            {
+                var isJobRan = await TryRunJob(cancellationToken, jobWaitTime);
+                if (!_settings.JobThrottleSettings.UseJobThrottle)
+                {
+                    jobWaitTime = _settings.IntervalStartJob;
+                    continue;
+                }
+
+                jobWaitTime = !isJobRan ? GetNextIntervalStartJob(jobWaitTime) : _settings.IntervalStartJob;
+            }
+        }
+
+        private async Task<bool> TryRunJob(CancellationToken cancellationToken, TimeSpan waitTime)
+        {
+            for (var i = 0; i < _settings.JobThrottleSettings.JobRetrievalAttempts; i++)
             {
                 var job = await GetReadyJob();
+                var isJobReady = job != null;
 
-                if (job != null)
+                if (isJobReady)
                 {
                     _horariumLogger.Debug("Try to Run jobMetadata...");
 
@@ -117,11 +137,34 @@ private async Task StartRunnerInternal(CancellationToken cancellationToken)
                     throw new TaskCanceledException();
                 }
 
-                if (!_settings.IntervalStartJob.Equals(TimeSpan.Zero))
+                if (isJobReady)
                 {
-                    await Task.Delay(_settings.IntervalStartJob, cancellationToken);
+                    return true;
                 }
+
+                if (!waitTime.Equals(TimeSpan.Zero))
+                {
+                    await Task.Delay(waitTime, cancellationToken);
+                }
+            }
+
+            return false;
+        }
+
+        private TimeSpan GetNextIntervalStartJob(TimeSpan currentInterval)
+        {
+            if (currentInterval.Equals(TimeSpan.Zero))
+            {
+                return _defaultJobThrottleInterval;
             }
+
+            var nextInterval =
+                currentInterval +
+                TimeSpan.FromTicks((long) (currentInterval.Ticks * _settings.JobThrottleSettings.IntervalMultiplier));
+
+            var maxInterval = _settings.JobThrottleSettings.MaxJobThrottleInterval;
+
+            return nextInterval > maxInterval ? maxInterval : nextInterval;
         }
     }
 }

src/Horarium/HorariumSettings.cs

@@ -10,6 +10,8 @@ public class HorariumSettings
 
         public TimeSpan ObsoleteExecutingJob { get; set; } = TimeSpan.FromMinutes(5);
 
+        public JobThrottleSettings JobThrottleSettings { get; set; } = new JobThrottleSettings();
+
         public IJobScopeFactory JobScopeFactory { get; set; } = new DefaultJobScopeFactory();
 
         public IHorariumLogger Logger { get; set; } = new EmptyLogger();

src/Horarium/JobThrottleSettings.cs

@@ -0,0 +1,28 @@
+using System;
+
+namespace Horarium
+{
+    public class JobThrottleSettings
+    {
+        /// <summary>
+        /// When `true`, IntervalStartJob will automatically increase if there is no jobs available
+        /// </summary>
+        public bool UseJobThrottle { get; set; }
+
+        /// <summary>
+        /// After all attempts are exhausted, waiting interval is increased by formula:
+        /// <c>currentInterval + (currentInterval * intervalMultiplier)</c>
+        /// </summary>
+        public int JobRetrievalAttempts { get; set; } = 10;
+
+        /// <summary>
+        /// Multiplier to get the next waiting interval
+        /// </summary>
+        public double IntervalMultiplier { get; set; } = 0.25;
+
+        /// <summary>
+        /// Maximum waiting interval
+        /// </summary>
+        public TimeSpan MaxJobThrottleInterval { get; set; } = TimeSpan.FromSeconds(30);
+    }
+}