How to use BitCaskLock in java
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Order
This paper mainly studies BitCaskLock.
BitCaskLock
Bitcask-java/src/main/java/com/trifork/bitcask/BitCaskLock.java
Public class BitCaskLock {public static enum Stale {OK, NOT_STALE} public static enum Type {WRITE, MERGE; private String type_name () {if (this = = MERGE) return "merge"; if (this = = WRITE) return "write" Throw new RuntimeException ();}} private RandomAccessFile file; private boolean is_write_lock; private File filename; private BitCaskLock (RandomAccessFile file, File filename, boolean isWriteLock) {this.file = file; this.filename = filename; this.is_write_lock = isWriteLock } public static BitCaskLock acquire (Type type, File dirname) throws IOException {File lock_filename = lock_filename (type, dirname); foo: do {try {BitCaskLock lock = lock_acquire (lock_filename, true) String lock_contents = Integer.toString (OS.getpid ()) + "\ n"; lock.write_data (ByteString.copyFromUtf8 (lock_contents)); return lock } catch (FileAlreadyExistsException e) {delete_stale_lock (lock_filename); continue foo;}} while (false); return null } public void release () throws IOException {if (file! = null) {if (is_write_lock) {file.close (); filename.delete () }} file = null;} / /.}
The acquire method of BitCaskLock first obtains BitCaskLock through lock_acquire, and if FileAlreadyExistsException occurs, executes delete_stale_lock; and its release method executes file.close () and filename.delete () against is_write_lock.
Lock_acquire
Bitcask-java/src/main/java/com/trifork/bitcask/BitCaskLock.java
Private static BitCaskLock lock_acquire (File lockFilename, boolean is_write_lock) throws IOException {if (is_write_lock) {if (lockFilename.createNewFile () = = false) {/ / file already exists, so we fail! Throw new FileAlreadyExistsException (lockFilename);}} RandomAccessFile f = new RandomAccessFile (lockFilename, is_write_lock? "rws": "r"); return new BitCaskLock (f, lockFilename, is_write_lock);}
The lock_acquire method executes lockFilename.createNewFile () against is_write_lock, and throws FileAlreadyExistsException if it is false
Delete_stale_lock
Bitcask-java/src/main/java/com/trifork/bitcask/BitCaskLock.java
Public static Stale delete_stale_lock (Type type, File dirname) throws IOException {return delete_stale_lock (lock_filename (type, dirname));} private static Stale delete_stale_lock (File lockFilename) throws IOException {BitCaskLock l = null; try {l = lock_acquire (lockFilename, false) } catch (FileNotFoundException e) {return Stale.OK;} catch (IOException e) {return Stale.NOT_STALE;} try {int pid = l.read_lock_data_pid () If (OS.pid_exists (pid)) {return Stale.NOT_STALE;} else {lockFilename.delete (); return Stale.OK } catch (IOException e) {return Stale.NOT_STALE;} finally {l.release ();}}
The delete_stale_lock method executes lock_acquire first, returns Stale.OK if FileNotFoundException occurs, returns Stale.NOT_STALE; if IOException occurs, otherwise gets pid through l.read_lock_data_pid (), returns Stale.NOT_STALE if OS.pid_exists (pid), executes lockFilename.delete () otherwise, returns Stale.OK; and finally executes l.release ()
Summary
The acquire method of BitCaskLock first obtains BitCaskLock through lock_acquire, and if FileAlreadyExistsException occurs, executes delete_stale_lock; and its release method executes file.close () and filename.delete () against is_write_lock.
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