throttle new downloads to one every 100ms. Helps with GitHub issue #90

core/src/main/groovy/com/muwire/core/download/DownloadManager.groovy

@@ -31,9 +31,11 @@ import com.muwire.core.collections.FileCollection
 import com.muwire.core.collections.FileCollectionItem
 import com.muwire.core.collections.UIDownloadCollectionEvent
 
+import java.util.concurrent.BlockingQueue
 import java.util.concurrent.ConcurrentHashMap
 import java.util.concurrent.Executor
 import java.util.concurrent.Executors
+import java.util.concurrent.LinkedBlockingQueue
 import java.util.logging.Level
 
 @Log
@@ -52,6 +54,10 @@ public class DownloadManager {
 
     private final Map<InfoHash, Downloader> downloaders = new ConcurrentHashMap<>()
     
+    private final BlockingQueue<DelayedStart> pendingStart = new LinkedBlockingQueue<>()
+    private volatile boolean shutdown
+    private final Thread pendingProcessor
+    
     public DownloadManager(EventBus eventBus, TrustService trustService, MeshManager meshManager, MuWireSettings muSettings,
         I2PConnector connector, File home, Persona me, ChatServer chatServer, FileManager fileManager) {
         this.eventBus = eventBus
@@ -70,6 +76,31 @@ public class DownloadManager {
             rv.setDaemon(true)
             rv
         })
+        
+        pendingProcessor = new Thread({processDelayed()} as Runnable)
+        pendingProcessor.setName("download-delayer")
+        pendingProcessor.setDaemon(true)
+        pendingProcessor.start()
+    }
+    
+    private void processDelayed() {
+        while(!shutdown) {
+            DelayedStart ds = pendingStart.poll()
+            if (ds != null) {
+                Downloader downloader = ds.downloader
+                if (!ds.resume) {
+                    if (!downloader.paused)
+                        executor.execute({ downloader.download() } as Runnable)
+                    eventBus.publish(new DownloadStartedEvent(downloader: downloader))
+                } else
+                    executor.execute({downloader.doResume() as Runnable})
+            }
+            Thread.sleep(100)
+        }
+    }
+    
+    void queueForResume(Downloader downloader) {
+        pendingStart.offer(new DelayedStart(downloader, true))
     }
 
 
@@ -143,8 +174,7 @@ public class DownloadManager {
         }
         downloaders.put(infoHash, downloader)
         persistDownloaders()
-        executor.execute({downloader.download()} as Runnable)
-        eventBus.publish(new DownloadStartedEvent(downloader : downloader))
+        pendingStart.offer(new DelayedStart(downloader, false))
     }
 
     public void onUIDownloadCancelledEvent(UIDownloadCancelledEvent e) {
@@ -232,15 +262,8 @@ public class DownloadManager {
             }
                 
                 
-            try {
-                if (!downloader.paused)
-                    downloader.download()
-                downloaders.put(infoHash, downloader)
-                eventBus.publish(new DownloadStartedEvent(downloader : downloader))
-            } catch (IllegalArgumentException bad) {
-                log.log(Level.WARNING,"cannot start downloader, skipping", bad)
-                return
-            }
+            downloaders.put(infoHash, downloader)
+            pendingStart.offer(new DelayedStart(downloader, false))
         }
     }
 
@@ -318,6 +341,8 @@ public class DownloadManager {
     }
 
     public void shutdown() {
+        shutdown = true
+        pendingProcessor.interrupt()
         downloaders.values().each { it.stop() }
         Downloader.executorService.shutdownNow()
     }
@@ -331,4 +356,13 @@ public class DownloadManager {
         downloaders.values().each { total += it.speed() }
         total
     }
+    
+    private static class DelayedStart {
+        final Downloader downloader
+        final boolean resume
+        DelayedStart(Downloader downloader, boolean resume) {
+            this.downloader = downloader
+            this.resume = resume
+        }
+    }
 }

core/src/main/groovy/com/muwire/core/download/DownloadSession.groovy

@@ -225,7 +225,7 @@ class DownloadSession {
                 System.arraycopy(infoHash.getHashList(), piece * 32, expected, 0, 32)
                 if (hash != expected) {
                     pieces.markPartial(piece, 0)
-                    throw new BadHashException("bad hash on piece $piece")
+                    throw new BadHashException("bad hash on piece $piece for infoHash " + Base64.encode(infoHash.getRoot()))
                 }
                 
                 eventBus.publish(new SourceVerifiedEvent(infoHash : infoHash, source : endpoint.destination))

core/src/main/groovy/com/muwire/core/download/Downloader.groovy

@@ -119,7 +119,7 @@ abstract class Downloader {
 
     public void resume() {
         paused = false
-        doResume()
+        downloadManager.queueForResume(this)
     }
     
     protected abstract void doResume();