Testing write lock contents

src/main/java/com/upserve/uppend/FileStore.java

@@ -8,6 +8,7 @@
 
 import java.io.*;
 import java.lang.invoke.MethodHandles;
+import java.nio.ByteBuffer;
 import java.nio.channels.*;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.*;
@@ -80,10 +81,21 @@ abstract class FileStore<T extends Partition> implements AutoCloseable, Register
 
         this.readOnly = readOnly;
         lockPath = readOnly ? dir.resolve("readLock") : dir.resolve("writeLock");
-
         try {
             lockChan = FileChannel.open(lockPath, StandardOpenOption.CREATE, StandardOpenOption.READ, StandardOpenOption.WRITE);
-            lock = readOnly ? lockChan.lock(0L, Long.MAX_VALUE, true) : lockChan.lock(); // Write lock is exclusive
+            if(readOnly) {
+                // this is a readLock
+                lock = lockChan.lock(0L, Long.MAX_VALUE, true);
+            } else {
+                // this is an exclusive writeLock
+                lock = lockChan.lock();
+                String writeLockContentString = builder.getWriteLockContentString();
+                if(writeLockContentString != null) {
+                    ByteBuffer byteBuf = ByteBuffer.wrap(writeLockContentString.getBytes());
+                    lockChan.write(byteBuf);
+                    lockChan.force(false);
+                }
+            }
         } catch (IOException e) {
             throw new UncheckedIOException("unable to open lock: " + lockPath, e);
         } catch (OverlappingFileLockException e) {

src/main/java/com/upserve/uppend/FileStoreBuilder.java

@@ -28,6 +28,8 @@ public class FileStoreBuilder<T extends FileStoreBuilder<T>> {
 
     private int targetBufferSize = TARGET_PRODUCTION_BUFFER_SIZE;
 
+    private String writeLockContentString = null;
+
     // Store Options
     public static final int DEFAULT_FLUSH_DELAY_SECONDS = 30;
     public static final int DEFAULT_FLUSH_THRESHOLD = 1000;
@@ -76,6 +78,12 @@ public T withTargetBufferSize(int targetBufferSize) {
         return (T) this;
     }
 
+    @SuppressWarnings("unchecked")
+    public T withWriteLockContentString(String writeLockContentString) {
+        this.writeLockContentString = writeLockContentString;
+        return (T) this;
+    }
+
     // Append Store Options
     @SuppressWarnings("unchecked")
     public T withStoreName(String storeName) {
@@ -179,6 +187,8 @@ public String getStoreName() {
 
     public String getMetricsRootName(){ return metricsRootName; }
 
+    public String getWriteLockContentString() { return writeLockContentString; }
+
     public LookupDataMetrics.Adders getLookupDataMetricsAdders(){ return lookupDataMetricsAdders; }
 
     public MutableBlobStoreMetrics.Adders getMutableBlobStoreMetricsAdders() { return mutableBlobStoreMetricsAdders; }
@@ -203,6 +213,7 @@ public String toString() {
                 ", storeMetrics=" + storeMetrics +
                 ", cacheMetricsRegistry=" + cacheMetricsRegistry +
                 ", cacheMetrics=" + cacheMetrics +
+                ", writeLockContentString='" + writeLockContentString + "'" +
                 '}';
     }
 }

src/test/java/com/upserve/uppend/FileStoreTest.java

@@ -7,7 +7,9 @@
 import java.nio.ByteBuffer;
 import java.nio.file.*;
 import java.util.*;
+import java.util.regex.Pattern;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 import static org.junit.Assert.*;
 
@@ -197,6 +199,28 @@ public void testCreateDirectoriesWithParentSymlink() throws Exception {
         SafeDeleting.removeDirectory(base);
     }
 
+    @Test
+    public void testLockFileAndContent_readWrite() throws IOException {
+        String expectedWriteLockContent = "write lock message";
+        MyFileStore v = new MyFileStore(path, 1, expectedWriteLockContent);
+        Path writeLockFilePath = Paths.get(path.toString(), "writeLock");
+        try (FileReader fr = new FileReader(writeLockFilePath.toString());
+             BufferedReader br = new BufferedReader(fr)) {
+            String writeLockContent = br.readLine();
+            assertTrue(Pattern.matches(expectedWriteLockContent, writeLockContent));
+        }
+        SafeDeleting.removeDirectory(path);
+    }
+
+    @Test
+    public void testLockFileAndContent_readOnly() throws IOException {
+        MyFileStore v = new MyFileStore(path, 1, true);
+        Path readLockFilePath = Paths.get(path.toString(), "readLock");
+        File file = readLockFilePath.toFile();
+        assertEquals(0, file.length());
+        SafeDeleting.removeDirectory(path);
+    }
+
     @Test
     public void testReaderWriter() throws InterruptedException {
 
@@ -253,5 +277,14 @@ private class MyFileStore extends FileAppendOnlyStore {
                     .withMetadataTTL(30)
             );
         }
+
+        MyFileStore(Path dir, int numPartitions, String writeLockContentString) {
+            super(false, new AppendOnlyStoreBuilder()
+                    .withDir(dir)
+                    .withPartitionCount(numPartitions)
+                    .withMetadataTTL(30)
+                    .withWriteLockContentString(writeLockContentString)
+            );
+        }
     }
 }