java.nio.channels.FileChannel中lock()与tryLock()方法的区别（Android Studio代码环境）

FileChannel中的lock()与tryLock()方法都是尝试去获取在某一文件上的独有锁（以下简称独有锁），可以实现进程间操作的互斥。区别在于lock()会阻塞（blocking）方法的执行，tryLock()则不会。

如果进程在执行lock()或tryLock()后获取到独有锁（return a FileLock object），那么进程会一直持有该锁到被释放（文件流被关闭 或 调用release() ）。

如果进程P（A）持有独有锁：

1、进程P（B）执行lock()获取独有锁，则lock()所在方法会一直阻塞，直到独有锁被进程P（A）释放。

2、进程P（B）执行tryLock()获取独有锁，则tryLock()会抛出异常java.io.IOException: fcntl failed: EAGAIN (Try again)异常

测试代码：

private void processLockTest() {
try {
File file = new File(getFilesDir().getAbsolutePath() + File.separator + "lock.lock");
FileOutputStream fos = new FileOutputStream(file);
FileLock fl = null;
boolean loop = true;
int time = 0;
LogUtil.log(android.os.Process.myPid() + "   " + "while start" + "  " + file.getAbsolutePath());
while (loop) {
time++;
LogUtil.log(android.os.Process.myPid() + "   " + "loop 次数:" + time);
if (fl == null) {
LogUtil.log(android.os.Process.myPid() + "   " + "tryLock before" + " " + file.getAbsolutePath());
try {
fl = fos.getChannel().tryLock();
} catch (Exception e) {
e.printStackTrace();
LogUtil.log(android.os.Process.myPid() + "   " + "tryLock IOException" + " " + e.toString());
}
LogUtil.log(android.os.Process.myPid() + "   " + "tryLock after" + " " + file.getAbsolutePath());
}
if (fl != null) {
while (loop) {
Thread.sleep(2000);
time++;
if (time == 5) {
fl.release();
}
if (time == 10) {
loop = false;
}
if (fl != null) {
LogUtil.log(System.currentTimeMillis() + "  " + android.os.Process.myPid() + "  " + "got");
} else {
LogUtil.log(System.currentTimeMillis() + "  " + android.os.Process.myPid() + "  " + "fl is null");
}
}
} else {
LogUtil.log(System.currentTimeMillis() + "  " + android.os.Process.myPid() + "  " + "ungot");
}
Thread.sleep(2000);
}
LogUtil.log(android.os.Process.myPid() + "   " + "while over");
} catch (Throwable t) {

}
}

在两个进程中同时执行代码：

new Thread(new Runnable() {
@Override
public void run() {
LogUtil.log(android.os.Process.myPid() + "   " + "processLockTest start");
processLockTest();
LogUtil.log(android.os.Process.myPid() + "   " + "processLockTest over");
}
}).start();

打印结果：

06-29 16:51:15.199 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   processLockTest start
06-29 16:51:15.199 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   while start  /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.200 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   loop 次数:1
06-29 16:51:15.200 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.200 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.211 25971-25971/com.ak.testerdemo:myservice E/liangyanmiao: MyService onCreate
06-29 16:51:15.211 25971-25971/com.ak.testerdemo:myservice E/liangyanmiao: MyService onStartCommand
06-29 16:51:15.211 25971-25971/com.ak.testerdemo:myservice E/liangyanmiao: MyService onStartCommand
06-29 16:51:15.212 25971-25971/com.ak.testerdemo:myservice E/liangyanmiao: MyService onStartCommand
06-29 16:51:15.216 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   processLockTest start
06-29 16:51:15.216 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   while start  /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.216 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   loop 次数:1
06-29 16:51:15.216 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.218 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock IOException java.io.IOException: fcntl failed: EAGAIN (Try again)
06-29 16:51:15.219 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:15.221 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726275219  25971  ungot
06-29 16:51:17.201 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726277201  25998  got
06-29 16:51:17.222 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   loop 次数:2
06-29 16:51:17.223 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:17.224 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock IOException java.io.IOException: fcntl failed: EAGAIN (Try again)
06-29 16:51:17.224 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:17.224 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726277224  25971  ungot
06-29 16:51:19.201 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726279201  25998  got
06-29 16:51:19.224 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   loop 次数:3
06-29 16:51:19.225 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:19.226 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock IOException java.io.IOException: fcntl failed: EAGAIN (Try again)
06-29 16:51:19.226 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:19.226 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726279226  25971  ungot
06-29 16:51:21.203 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726281202  25998  got
06-29 16:51:21.226 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   loop 次数:4
06-29 16:51:21.227 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:21.231 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock IOException java.io.IOException: fcntl failed: EAGAIN (Try again)
06-29 16:51:21.231 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:21.232 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726281232  25971  ungot
06-29 16:51:23.203 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726283203  25998  got
06-29 16:51:23.232 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   loop 次数:5
06-29 16:51:23.233 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock before /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:23.234 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   tryLock after /data/data/com.ak.testerdemo/files/lock.lock
06-29 16:51:25.204 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726285204  25998  got
06-29 16:51:25.235 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726285234  25971  got
06-29 16:51:27.205 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726287205  25998  got
06-29 16:51:27.235 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726287235  25971  got
06-29 16:51:29.207 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726289207  25998  got
06-29 16:51:29.237 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726289237  25971  got
06-29 16:51:31.221 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726291221  25998  got
06-29 16:51:31.238 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726291237  25971  got
06-29 16:51:33.223 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 1498726293223  25998  got
06-29 16:51:33.239 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 1498726293238  25971  got
06-29 16:51:35.224 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   while over
06-29 16:51:35.225 25998-26150/com.ak.testerdemo:myservice2 E/liangyanmiao: 25998   processLockTest over
06-29 16:51:35.240 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   while over
06-29 16:51:35.240 25971-26152/com.ak.testerdemo:myservice E/liangyanmiao: 25971   processLockTest over

可以修改测试代码验证上述结论。