fix: Don't allow multiple runs

Author: linkdotnet

src/LinkDotNet.Blog.Web/Features/TransformBlogPostRecordsService.cs

@@ -12,6 +12,7 @@ namespace LinkDotNet.Blog.Web.Features;
 
 public sealed partial class TransformBlogPostRecordsService : IJob
 {
+    private static readonly SemaphoreSlim Semaphore = new(1, 1);
     private readonly IRepository<BlogPost> blogPostRepository;
     private readonly IRepository<UserRecord> userRecordRepository;
     private readonly IRepository<BlogPostRecord> blogPostRecordRepository;
@@ -31,9 +32,25 @@ public TransformBlogPostRecordsService(
 
     public async Task RunAsync(JobExecutionContext context, CancellationToken token)
     {
-        LogTransformStarted();
-        await TransformRecordsAsync();
-        LogTransformStopped();
+        // In the future version of NCronJob we don't need this here,
+        // but can configure it via the AddCronJob method or similar ways
+        var hasLock = await Semaphore.WaitAsync(0, token);
+        if (!hasLock)
+        {
+            LogSkippingRun();
+            return;
+        }
+
+        try
+        {
+            LogTransformStarted();
+            await TransformRecordsAsync();
+            LogTransformStopped();
+        }
+        finally
+        {
+            Semaphore.Release();
+        }
     }
 
     private static IEnumerable<BlogPostRecord> GetBlogPostRecords(
@@ -112,4 +129,7 @@ private async Task TransformRecordsAsync()
 
     [LoggerMessage(Level = LogLevel.Information, Message = "Deleted records from UserRecord-Table")]
     private partial void LogDeletedUserRecords();
+
+    [LoggerMessage(Level = LogLevel.Information, Message = "There is already a running job. Skipping this run.")]
+    private partial void LogSkippingRun();
 }