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本文次要钻研一下BitCaskKeyDir

BitCaskKeyDir

bitcask-java/src/main/java/com/trifork/bitcask/BitCaskKeyDir.java

public class BitCaskKeyDir {    Map<ByteString, BitCaskEntry> map = new HashMap<ByteString, BitCaskEntry>();    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来寄存BitCaskEntry；其put办法应用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，最初writeLock.unlock()；其get办法应用readLock.lock()从map读取指定key的值，最初readLock.unlock()

key_dirs

bitcask-java/src/main/java/com/trifork/bitcask/BitCaskKeyDir.java

public class BitCaskKeyDir {    public static Map<File,BitCaskKeyDir> key_dirs = new HashMap<File, BitCaskKeyDir>();    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，用于寄存指定File的BitCaskKeyDir；其keydir_new会针对不存在的BitCaskKeyDir进行创立，最初通过dir.wait_for_ready(openTimeoutSecs)期待ready

小结

BitCaskKeyDir提供了map来寄存BitCaskEntry；其put办法应用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，最初writeLock.unlock()；其get办法应用readLock.lock()从map读取指定key的值，最初readLock.unlock()

doc

  • BitCaskKeyDir