java中BitCaskKeyDir的用法
这篇文章主要介绍"java中BitCaskKeyDir的用法"，在日常操作中，相信很多人在java中BitCaskKeyDir的用法问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"java中BitCaskKeyDir的用法"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
序
本文主要研究一下BitCaskKeyDir
BitCaskKeyDir
bitcask-java/src/main/java/com/trifork/bitcask/BitCaskKeyDir.java
public class BitCaskKeyDir { Map map = new HashMap(); ReadWriteLock rwl = new ReentrantReadWriteLock(); private boolean is_ready; public boolean put(ByteString key, BitCaskEntry ent) { Lock writeLock = rwl.writeLock(); writeLock.lock(); try { BitCaskEntry old = map.get(key); if (old == null) { map.put(key, ent); return true; } else if (ent.is_newer_than(old)) { map.put(key, ent); return true; } else { return false; } } finally { writeLock.unlock(); } } public BitCaskEntry get(ByteString key) { Lock readLock = rwl.readLock(); readLock.lock(); try { return map.get(key); } finally { readLock.unlock(); } } //......} BitCaskKeyDir提供了map来存放BitCaskEntry；其put方法使用writeLock.lock()，对于old值为null的或者新值大于old值的才put进去，否则返回false，最后writeLock.unlock()；其get方法使用readLock.lock()从map读取指定key的值，最后readLock.unlock()
key_dirs
bitcask-java/src/main/java/com/trifork/bitcask/BitCaskKeyDir.java
public class BitCaskKeyDir { public static Map key_dirs = new HashMap(); public static Lock keydir_lock = new ReentrantLock(); public static BitCaskKeyDir keydir_new(File dirname, int openTimeoutSecs) throws IOException { File abs_name = dirname.getAbsoluteFile(); BitCaskKeyDir dir; keydir_lock.lock(); try { dir = key_dirs.get(abs_name); if (dir == null) { dir = new BitCaskKeyDir(); key_dirs.put(abs_name, dir); return dir; } } finally { keydir_lock.unlock(); } if (dir.wait_for_ready(openTimeoutSecs)) { return dir; } else { throw new IOException("timeout while waiting for keydir"); } } public synchronized boolean is_ready() { return is_ready; } public synchronized void mark_ready() { is_ready = true; this.notifyAll(); } public synchronized boolean wait_for_ready(int timeout_secs) { long now = System.currentTimeMillis(); long abs_timeout = now + (timeout_secs * 1000); while (!is_ready && now < abs_timeout) { try { wait(); } catch (InterruptedException e) { // ignore } now = System.currentTimeMillis(); } return is_ready; }} BitCaskKeyDir定义了static的key_dirs，用于存放指定File的BitCaskKeyDir；其keydir_new会针对不存在的BitCaskKeyDir进行创建，最后通过dir.wait_for_ready(openTimeoutSecs)等待ready
小结
BitCaskKeyDir提供了map来存放BitCaskEntry；其put方法使用writeLock.lock()，对于old值为null的或者新值大于old值的才put进去，否则返回false，最后writeLock.unlock()；其get方法使用readLock.lock()从map读取指定key的值，最后readLock.unlock()
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