java 多线读文件是同步的吗

[iuoon]

按一行行读：
查看jdk中BufferedReader源码：这里面synchronized 的作用

 String readLine(boolean ignoreLF) throws IOException {
        StringBuffer s = null;
        int startChar;

        synchronized (lock) {
            ensureOpen();
            boolean omitLF = ignoreLF || skipLF;

        bufferLoop:
            for (;;) {
            //...省略
            }
    }

用nio文件通道方式读取，源码中也加上了synchronized ：

public FileChannel getChannel() {
        synchronized (this) {
            if (channel == null) {
                channel = FileChannelImpl.open(fd, path, true, false, this);
            }
            return channel;
        }
    }

测试代码：

public  String readFileByLines(String fileName) {
        File file = new File(fileName);
        BufferedReader reader = null;
        try {
             FileInputStream f=null;
            //   System.out.println("以行为单位读取文件内容，一次读一整行：");
            reader = new BufferedReader(new FileReader(file));
            String tempString;
            String mess="";
            // 一次读入一行，直到读入null为文件结束
            while ((tempString = reader.readLine()) != null) {
                mess+=tempString;
            }
            reader.close();
            return mess;
        } catch (IOException e) {
            return "read file error";
        } finally {
            if (reader != null) {
                try {
                    reader.close();
                } catch (IOException e1) {
                }
            }
        }
    }

当用loadrunner测试下，读本地文件的性能急剧下降
查看jvm日志如下：

Thread Execution Information:
-----------------------
Thread "http-thread-pool-8080(98)" thread-id: 837 thread-state: TIMED_WAITING Waiting on lock: java.lang.Object@583dadc8
	 at: java.lang.Object.wait(Native Method)
	 at: com.sun.grizzly.util.SyncThreadPool$SyncThreadWorker.getTask(SyncThreadPool.java:374)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:524)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	 at: java.lang.Thread.run(Thread.java:745)
Thread Synchronization Statistics:
-----------------------
Number of times this thread was blocked (to enter/reenter a Monitor): 4,582
Number of times this thread waited for a notification (i.e. it was in WAITING or TIMED_WAITING state): 4,522
Total CPU time for this thread: 1 seconds 189,494,744 nanoseconds.
User-level CPU time for this thread: 1 seconds 189,494,744 nanoseconds.
Object Monitors currently held or requested by this thread: []
Ownable Synchronizers (e.g. ReentrantLock and ReentrantReadWriteLock) held by this thread: []
--------------------------------------------------------------------------------
Thread Execution Information:
-----------------------
Thread "http-thread-pool-8080(97)" thread-id: 836 thread-state: TIMED_WAITING Waiting on lock: java.lang.Object@583dadc8
	 at: java.lang.Object.wait(Native Method)
	 at: com.sun.grizzly.util.SyncThreadPool$SyncThreadWorker.getTask(SyncThreadPool.java:374)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:524)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	 at: java.lang.Thread.run(Thread.java:745)
Thread Synchronization Statistics:
-----------------------
Number of times this thread was blocked (to enter/reenter a Monitor): 4,585
Number of times this thread waited for a notification (i.e. it was in WAITING or TIMED_WAITING state): 4,523
Total CPU time for this thread: 1 seconds 194,873,842 nanoseconds.
User-level CPU time for this thread: 1 seconds 194,873,842 nanoseconds.
Object Monitors currently held or requested by this thread: []
Ownable Synchronizers (e.g. ReentrantLock and ReentrantReadWriteLock) held by this thread: []
--------------------------------------------------------------------------------
Thread Execution Information:
-----------------------
Thread "http-thread-pool-8080(96)" thread-id: 835 thread-state: TIMED_WAITING Waiting on lock: java.lang.Object@583dadc8
	 at: java.lang.Object.wait(Native Method)
	 at: com.sun.grizzly.util.SyncThreadPool$SyncThreadWorker.getTask(SyncThreadPool.java:374)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:524)
	 at: com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	 at: java.lang.Thread.run(Thread.java:745)
Thread Synchronization Statistics:

所以问下，多线程读取文件是同步的吗，
如果是，java有其他高效多线读取文件的方法吗