java线程--提升"锁"的效率

1.减小锁的持有时间

案例jdk 中Pattern类代码片断

双重检查,减小锁的持有时间

/**
     * Creates a matcher that will match the given input against this pattern.
     *
     * @param  input
     *         The character sequence to be matched
     *
     * @return  A new matcher for this pattern
     */
    public Matcher matcher(CharSequence input) {
        if (!compiled) {
            synchronized(this) {
                if (!compiled)
                    compile();
            }
        }
        Matcher m = new Matcher(this, input);
        return m;
    }

2.减少锁粒度

3.读写分离

4.锁分离

案例jdk 中LinkedBlockingQueue类代码片断

/** Lock held by take, poll, etc */
    private final ReentrantLock takeLock = new ReentrantLock();

    /** Wait queue for waiting takes */
    private final Condition notEmpty = takeLock.newCondition();

    /** Lock held by put, offer, etc */
    private final ReentrantLock putLock = new ReentrantLock();

    /** Wait queue for waiting puts */
    private final Condition notFull = putLock.newCondition();

5.锁粗化