From 2967e07c8b5e16018dbd68b3f78199e75e865bd3 Mon Sep 17 00:00:00 2001
From: Mike Hearn <mike@plan99.net>
Date: Thu, 18 Dec 2014 13:59:28 +0100
Subject: [PATCH] Change how DownloadProgressTracker waits for progress to
 avoid possible deadlocks.

---
 .../core/DownloadProgressTracker.java         | 33 +++++++++++++------
 1 file changed, 23 insertions(+), 10 deletions(-)

diff --git a/core/src/main/java/org/bitcoinj/core/DownloadProgressTracker.java b/core/src/main/java/org/bitcoinj/core/DownloadProgressTracker.java
index 920dda0c..dea4e7ac 100644
--- a/core/src/main/java/org/bitcoinj/core/DownloadProgressTracker.java
+++ b/core/src/main/java/org/bitcoinj/core/DownloadProgressTracker.java
@@ -17,11 +17,13 @@
 
 package org.bitcoinj.core;
 
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.common.util.concurrent.SettableFuture;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import java.util.Date;
-import java.util.concurrent.Semaphore;
+import java.util.concurrent.ExecutionException;
 
 /**
  * <p>An implementation of {@link AbstractPeerEventListener} that listens to chain download events and tracks progress
@@ -32,12 +34,13 @@ public class DownloadProgressTracker extends AbstractPeerEventListener {
     private static final Logger log = LoggerFactory.getLogger(DownloadProgressTracker.class);
     private int originalBlocksLeft = -1;
     private int lastPercent = 0;
-    private Semaphore done = new Semaphore(0);
+    private SettableFuture<Long> future = SettableFuture.create();
     private boolean caughtUp = false;
 
     @Override
     public void onChainDownloadStarted(Peer peer, int blocksLeft) {
-        startDownload(blocksLeft);
+        if (blocksLeft > 0 && originalBlocksLeft == -1)
+            startDownload(blocksLeft);
         // Only mark this the first time, because this method can be called more than once during a chain download
         // if we switch peers during it.
         if (originalBlocksLeft == -1)
@@ -46,7 +49,7 @@ public class DownloadProgressTracker extends AbstractPeerEventListener {
             log.info("Chain download switched to {}", peer);
         if (blocksLeft == 0) {
             doneDownload();
-            done.release();
+            future.set(peer.getBestHeight());
         }
     }
 
@@ -58,7 +61,7 @@ public class DownloadProgressTracker extends AbstractPeerEventListener {
         if (blocksLeft == 0) {
             caughtUp = true;
             doneDownload();
-            done.release();
+            future.set(peer.getBestHeight());
         }
 
         if (blocksLeft < 0 || originalBlocksLeft <= 0)
@@ -88,10 +91,8 @@ public class DownloadProgressTracker extends AbstractPeerEventListener {
      * @param blocks the number of blocks to download, estimated
      */
     protected void startDownload(int blocks) {
-        if (blocks > 0 && originalBlocksLeft == -1)
-            log.info("Downloading block chain of size " + blocks + ". " +
-                    (blocks > 1000 ? "This may take a while." : ""));
-
+        log.info("Downloading block chain of size " + blocks + ". " +
+                (blocks > 1000 ? "This may take a while." : ""));
     }
 
     /**
@@ -104,6 +105,18 @@ public class DownloadProgressTracker extends AbstractPeerEventListener {
      * Wait for the chain to be downloaded.
      */
     public void await() throws InterruptedException {
-        done.acquire();
+        try {
+            future.get();
+        } catch (ExecutionException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    /**
+     * Returns a listenable future that completes with the height of the best chain (as reported by the peer) once chain
+     * download seems to be finished.
+     */
+    public ListenableFuture<Long> getFuture() {
+        return future;
     }
 }