feat: adds close state checking for snapshot reader and writer (#1114)

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotReader.java

@@ -22,7 +22,7 @@
 import com.alipay.sofa.jraft.entity.RaftOutter.SnapshotMeta;
 
 /**
- * Snapshot reader.
+ * Snapshot reader.<strong>Note: it's not thread-safe.</strong>
  *
  * @author boyan ([email protected])
  *

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/SnapshotWriter.java

@@ -24,7 +24,7 @@
 import com.google.protobuf.Message;
 
 /**
- * Snapshot writer.
+ * Snapshot writer. <strong>Note: it's not thread-safe.</strong>
  *
  * @author boyan ([email protected])
  *

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotReader.java

@@ -53,11 +53,21 @@ public class LocalSnapshotReader extends SnapshotReader {
     private final String                 path;
     private final LocalSnapshotStorage   snapshotStorage;
     private final SnapshotThrottle       snapshotThrottle;
+    private volatile boolean             closed;
 
     @Override
     public void close() throws IOException {
+        checkState();
         snapshotStorage.unref(this.getSnapshotIndex());
+
         this.destroyReaderInFileService();
+        this.closed = true;
+    }
+
+    private void checkState() {
+        if (this.closed) {
+            throw new IllegalStateException("Reader was closed");
+        }
     }
 
     public LocalSnapshotReader(LocalSnapshotStorage snapshotStorage, SnapshotThrottle snapshotThrottle, Endpoint addr,
@@ -68,6 +78,7 @@ public LocalSnapshotReader(LocalSnapshotStorage snapshotStorage, SnapshotThrottl
         this.addr = addr;
         this.path = path;
         this.readerId = 0;
+        this.closed = false;
         this.metaTable = new LocalSnapshotMetaTable(raftOptions);
     }
 
@@ -118,6 +129,7 @@ public SnapshotMeta load() {
 
     @Override
     public String generateURIForCopy() {
+        checkState();
         if (this.addr == null || this.addr.equals(new Endpoint(Utils.IP_ANY, 0))) {
             LOG.error("Address is not specified");
             return null;

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/LocalSnapshotWriter.java

@@ -47,12 +47,14 @@ public class LocalSnapshotWriter extends SnapshotWriter {
     private final LocalSnapshotMetaTable metaTable;
     private final String                 path;
     private final LocalSnapshotStorage   snapshotStorage;
+    private volatile boolean             closed;
 
     public LocalSnapshotWriter(String path, LocalSnapshotStorage snapshotStorage, RaftOptions raftOptions) {
         super();
         this.snapshotStorage = snapshotStorage;
         this.path = path;
         this.metaTable = new LocalSnapshotMetaTable(raftOptions);
+        this.closed = false;
     }
 
     @Override
@@ -95,21 +97,32 @@ public void close() throws IOException {
 
     @Override
     public void close(final boolean keepDataOnError) throws IOException {
+        checkState();
         this.snapshotStorage.close(this, keepDataOnError);
+        this.closed = true;
+    }
+
+    private void checkState() {
+        if (this.closed) {
+            throw new IllegalStateException("Writer was closed");
+        }
     }
 
     @Override
     public boolean saveMeta(final SnapshotMeta meta) {
+        checkState();
         this.metaTable.setMeta(meta);
         return true;
     }
 
     public boolean sync() throws IOException {
+        checkState();
         return this.metaTable.saveToFile(this.path + File.separator + JRAFT_SNAPSHOT_META_FILE);
     }
 
     @Override
     public boolean addFile(final String fileName, final Message fileMeta) {
+        checkState();
         final Builder metaBuilder = LocalFileMeta.newBuilder();
         if (fileMeta != null) {
             metaBuilder.mergeFrom(fileMeta);
@@ -120,6 +133,7 @@ public boolean addFile(final String fileName, final Message fileMeta) {
 
     @Override
     public boolean removeFile(final String fileName) {
+        checkState();
         return this.metaTable.removeFile(fileName);
     }
 

jraft-core/src/main/java/com/alipay/sofa/jraft/storage/snapshot/local/SnapshotFileReader.java

@@ -30,7 +30,7 @@
 import com.alipay.sofa.jraft.util.ByteBufferCollector;
 
 /**
- * Snapshot file reader
+ * Snapshot file reader. <strong>Note: it's not thread-safe.</strong>
  *
  * @author boyan ([email protected])
  *