zookeeper-curator-interprocessmutex

constructor

InterProcessMutex(CuratorFramework client, String path, String lockName, int maxLeases, LockInternalsDriver driver)
    {
        basePath = PathUtils.validatePath(path);
        internals = new LockInternals(client, driver, path, lockName, maxLeases);  //构建内部锁
    }

static class LockData

private static class LockData
    {
        final Thread owningThread;
        final String lockPath;
        final AtomicInteger lockCount = new AtomicInteger(1); //控制次数

        private LockData(Thread owningThread, String lockPath)
        {
            this.owningThread = owningThread;
            this.lockPath = lockPath;
        }
    }

LockInternals constructor

 LockInternals(CuratorFramework client, LockInternalsDriver driver, String path, String lockName, int maxLeases)
    {
        this.driver = driver;   //内部锁驱动
        this.lockName = lockName;  //锁名
        this.maxLeases = maxLeases;

        this.client = client.newWatcherRemoveCuratorFramework();  //curatorframeworkImpl 子类
        this.basePath = PathUtils.validatePath(path);
        this.path = ZKPaths.makePath(path, lockName);
    }

acquire

public void acquire() throws Exception
    {   //获取互斥锁，直到获取为止
        if ( !internalLock(-1, null) )
        {
            throw new IOException("Lost connection while trying to acquire lock: " + basePath);
        }
    }

internalLock

private boolean internalLock(long time, TimeUnit unit) throws Exception
    {
        /*
           Note on concurrency: a given lockData instance
           can be only acted on by a single thread so locking isn't necessary
           一个给定的lockdata实例的并发只能由单个线程执行，因此不需要锁定
        */

        Thread currentThread = Thread.currentThread();

        LockData lockData = threadData.get(currentThread);
        if ( lockData != null )   //如果lockdata 不为null，则已经是获取了zookeeper锁
        {
            // re-entering
            lockData.lockCount.incrementAndGet();   //获取锁计数+1
            return true;
        }
        //尝试获取锁 LockInternals    getLockNodeBytes // 默认为null 的实现
        String lockPath = internals.attemptLock(time, unit, getLockNodeBytes());
        if ( lockPath != null )
        {
            LockData newLockData = new LockData(currentThread, lockPath);
            threadData.put(currentThread, newLockData);
            return true;
        }

        return false;
    }

InterProcessLock attemptLock

 String attemptLock(long time, TimeUnit unit, byte[] lockNodeBytes) throws Exception
    {
        final long      startMillis = System.currentTimeMillis();  //记录开始时间，计算需要等待的时间
        final Long      millisToWait = (unit != null) ? unit.toMillis(time) : null;
        final byte[]    localLockNodeBytes = (revocable.get() != null) ? new byte[0] : lockNodeBytes;
        int             retryCount = 0;

        String          ourPath = null;
        boolean         hasTheLock = false;
        boolean         isDone = false;
        while ( !isDone )
        {
            isDone = true;

            try
            {       //path 为传入path/lockname
                   //driver 默认为 StandardLockInternalsDriver
                   //构建锁的节点，节点createModel为 EPHEMERAL_SEQUENTIAL
                  //our path : 创建protect的节点  /path/uuid - localname - sequence
                 // 只有相应uuid的节点才能修改此节点的信息
                ourPath = driver.createsTheLock(client, path, localLockNodeBytes);
                hasTheLock = internalLockLoop(startMillis, millisToWait, ourPath);
            }
            catch ( KeeperException.NoNodeException e )
            {
                // gets thrown by StandardLockInternalsDriver when it can't find the lock node
                // this can happen when the session expires, etc. So, if the retry allows, just try it all again
                if ( client.getZookeeperClient().getRetryPolicy().allowRetry(retryCount++, System.currentTimeMillis() - startMillis, RetryLoop.getDefaultRetrySleeper()) )
                {
                    isDone = false;
                }
                else
                {
                    throw e;
                }
            }
        }

        if ( hasTheLock )
        {
            return ourPath;
        }

        return null;
    }

StandardLockInternalsDriver createsTheLock

  @Override    //创建锁path，可自定义节点
    public String createsTheLock(CuratorFramework client, String path, byte[] lockNodeBytes) throws Exception
    {
        String ourPath;
        //our path  ：          /parent/uuid - children - sequence
        if ( lockNodeBytes != null )
        {
            ourPath = client.create().creatingParentContainersIfNeeded().withProtection().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath(path, lockNodeBytes);
        }
        else
        {
            ourPath = client.create().creatingParentContainersIfNeeded().withProtection().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath(path);
        }
        return ourPath;
    }

internalLockLoop

 private boolean internalLockLoop(long startMillis, Long millisToWait, String ourPath) throws Exception
    {
        boolean     haveTheLock = false;
        boolean     doDelete = false;
        try
        {
            if ( revocable.get() != null )
            {
                client.getData().usingWatcher(revocableWatcher).forPath(ourPath);
            }

            while ( (client.getState() == CuratorFrameworkState.STARTED) && !haveTheLock )
            {
                // uuid - localname - sequence
                // ourPath ：/path/uuid - localname - sequence
                //basePath ： /path
                //return 回来为 按照sequence 进行排序
                List        children = getSortedChildren();
                //sequenceNodeName ： uuid - localname - sequence
                String              sequenceNodeName = ourPath.substring(basePath.length() + 1); // +1 to include the slash

                //获取 getsTheLock:是否获取锁   pathToWatch:获取锁的 sequenceNode
                PredicateResults    predicateResults = driver.getsTheLock(client, children, sequenceNodeName, maxLeases);
                if ( predicateResults.getsTheLock() )
                {
                    haveTheLock = true;
                }
                else
                {
                    //  获取锁的path
                    String  previousSequencePath = basePath + "/" + predicateResults.getPathToWatch();

                    synchronized(this)
                    {
                        try 
                        {
                            // use getData() instead of exists() to avoid leaving unneeded watchers which is a type of resource leak
                            // 如果该节点变化，则使用watch
                            //notifyFromWatcher  唤醒所有的children，重新竞争
                            client.getData().usingWatcher(watcher).forPath(previousSequencePath);
                            if ( millisToWait != null )
                            {
                                millisToWait -= (System.currentTimeMillis() - startMillis);
                                startMillis = System.currentTimeMillis();
                                //时间超时，删除节点，不竞争下次锁
                                if ( millisToWait <= 0 )
                                {
                                    doDelete = true;    // timed out - delete our node
                                    break;
                                }

                                wait(millisToWait);  //睡眠相应的时间
                            }
                            else
                            {
                                //睡眠
                                wait();
                            }
                        }
                        catch ( KeeperException.NoNodeException e ) 
                        {
                            // it has been deleted (i.e. lock released). Try to acquire again
                        }
                    }
                }
            }
        }
        catch ( Exception e )
        {
            ThreadUtils.checkInterrupted(e);
            doDelete = true;
            throw e;
        }
        finally
        {
            //出现异常或者超时，删除此节点
            if ( doDelete )
            {
                deleteOurPath(ourPath);
            }
        }
        return haveTheLock;
    }

release

 public void release() throws Exception
    {
        /*
            Note on concurrency: a given lockData instance
            can be only acted on by a single thread so locking isn't necessary
         */

        Thread currentThread = Thread.currentThread();
        LockData lockData = threadData.get(currentThread);
        if ( lockData == null )
        {
            throw new IllegalMonitorStateException("You do not own the lock: " + basePath);
        }

        int newLockCount = lockData.lockCount.decrementAndGet();  //如果多次锁入，则需要多次释放
        if ( newLockCount > 0 )
        {
            return;
        }
        if ( newLockCount < 0 )
        {
            throw new IllegalMonitorStateException("Lock count has gone negative for lock: " + basePath);
        }
        try
        {
            //为0时，释放  删除path节点就ok了
            internals.releaseLock(lockData.lockPath);
        }
        finally
        {
            threadData.remove(currentThread);
        }
    }