Properly lock solrInstances for reboot and restoration of embedded Solr

Putting a synchronization lock directly on the solrInstances property
was ineffective as it is assigned a new (unlocked) instance in these
operations.

source/net/yacy/search/index/Fulltext.java

@@ -40,6 +40,7 @@ import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.locks.ReentrantLock;
 import java.util.regex.Pattern;
 import java.util.zip.Deflater;
 import java.util.zip.GZIPOutputStream;
@@ -96,6 +97,10 @@ public final class Fulltext {
     private final File                    archivePath;
     private       Export                  exportthread; // will have a export thread assigned if exporter is running
     private       InstanceMirror          solrInstances;
+    
+    /** Synchronization lock for solrInstances property */
+    private ReentrantLock solrInstancesLock;
+    
     private final CollectionConfiguration collectionConfiguration;
     private final WebgraphConfiguration   webgraphConfiguration;
     private       boolean                 writeWebgraph;
@@ -106,6 +111,7 @@ public final class Fulltext {
         this.archivePath = archivePath;
         this.exportthread = null; // will have a export thread assigned if exporter is running
         this.solrInstances = new InstanceMirror();
+        this.solrInstancesLock = new ReentrantLock();
         this.collectionConfiguration = collectionConfiguration;
         this.webgraphConfiguration = webgraphConfiguration;
         this.writeWebgraph = false;
@@ -198,22 +204,35 @@ public final class Fulltext {
     }
     
     public EmbeddedInstance getEmbeddedInstance() {
-        synchronized (this.solrInstances) {
-            if (this.solrInstances.isConnectedEmbedded()) return this.solrInstances.getEmbedded();
+    	this.solrInstancesLock.lock();
+        try {
+            if (this.solrInstances.isConnectedEmbedded()) {
+            	return this.solrInstances.getEmbedded();
+            }
             return null;
+        } finally {
+        	this.solrInstancesLock.unlock();	
         }
     }
     
     public SolrConnector getDefaultConnector() {
-        synchronized (this.solrInstances) {
+    	this.solrInstancesLock.lock();
+        try {
             return this.solrInstances.getDefaultMirrorConnector();
+        } finally {
+        	this.solrInstancesLock.unlock();	
         }
     }
     
     public SolrConnector getWebgraphConnector() {
-        if (!this.writeWebgraph) return null;
-        synchronized (this.solrInstances) {
+        if (!this.writeWebgraph) {
+        	return null;
+        }
+    	this.solrInstancesLock.lock();
+        try {
             return this.solrInstances.getGenericMirrorConnector(WebgraphSchema.CORE_NAME);
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
     }
     
@@ -232,8 +251,11 @@ public final class Fulltext {
     }
 
     public void clearLocalSolr() throws IOException {
-        if (this.exportthread != null) this.exportthread.interrupt();
-        synchronized (this.solrInstances) {
+        if (this.exportthread != null) {
+        	this.exportthread.interrupt();
+        }
+    	this.solrInstancesLock.lock();
+        try {
             EmbeddedInstance instance = this.solrInstances.getEmbedded();
             if (instance != null) {
                 for (String name: instance.getCoreNames()) {
@@ -242,11 +264,14 @@ public final class Fulltext {
                 this.commit(false);
             }
             this.solrInstances.clearCaches();
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
     }
 
     public void clearRemoteSolr() throws IOException {
-        synchronized (this.solrInstances) {
+    	this.solrInstancesLock.lock();
+        try {
             ShardInstance instance = this.solrInstances.getRemote();
             if (instance != null) {
                 for (String name: instance.getCoreNames()) {
@@ -254,6 +279,8 @@ public final class Fulltext {
                 }
             }
             this.solrInstances.clearCaches();
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
     }
 
@@ -593,7 +620,8 @@ public final class Fulltext {
         }
         final File storagePath = esc.getContainerPath();
         final File zipOut = new File(this.archivePath, storagePath.getName() + "_" + GenericFormatter.SHORT_DAY_FORMATTER.format() + ".zip");
-        synchronized (this.solrInstances) {
+    	this.solrInstancesLock.lock();
+        try {
             this.disconnectLocalSolr();
             try {
                 ZIPWriter.zip(storagePath, zipOut);
@@ -606,6 +634,8 @@ public final class Fulltext {
                     ConcurrentLog.logException(e);
                 }
             }
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
         return zipOut;
     }
@@ -621,7 +651,8 @@ public final class Fulltext {
         	throw new SolrException(ErrorCode.SERVICE_UNAVAILABLE, "No embedded Solr available.");
         }
         final File storagePath = esc.getContainerPath();
-        synchronized (this.solrInstances) {
+    	this.solrInstancesLock.lock();
+        try {
             // this.disconnectLocalSolr(); // moved to (InstanceMirror) sorlInstances.close()
             this.solrInstances.close();
             try {
@@ -636,6 +667,8 @@ public final class Fulltext {
                     ConcurrentLog.logException(e);
                 }
             }
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
     }
 
@@ -654,7 +687,8 @@ public final class Fulltext {
      * Please check before that the local embedded Solr is enabled and no external remote Solr is attached.
      */
     public void rebootEmbeddedLocalSolr() {
-        synchronized (this.solrInstances) {
+    	this.solrInstancesLock.lock();
+        try {
             this.disconnectLocalSolr();
             // this.solrInstances.close(); // moved to (InstanceMirror) sorlInstances.close()
             this.solrInstances = new InstanceMirror();
@@ -663,6 +697,8 @@ public final class Fulltext {
             } catch (final IOException e) {
                 ConcurrentLog.logException(e);
             }
+        } finally {
+        	this.solrInstancesLock.unlock();
         }
     }