monitors

这又是啥!!! 今天看面试题的时候看到 monitors VS semaphore, 简直就是这是啥! monitors是啥! 啥啥啥...
让你不好好看书!搜索了一发于是来写总结...

monitors是比较high-level的控制多线程的结构, 素这样的

Typical implementation: each monitor has one lock. Acquire lockwhen begin a monitor operation, and Release lock when operationfinishes. Optimization: reader/writer locks. Statically identifyoperations that only read data, then allow these read-only operationsto go concurrently. Writers get mutual exclusion with respect to otherwriters and to readers. Standard synchronization mechanism for accessing shared data.

结构素这样的

monitor { 
  Condition *bufferAvail, *dataAvail;
  int num = 0;
  int data[10];

  Produce(v) { 
    while (num == 10) { /* Mesa semantics */
      bufferAvail->Wait();  
    }
    put v into data array
    num++;
    dataAvail->Signal(); 
 }
  Consume(v) { 
    while (num == 0) { /* Mesa Semantics */
      dataAvail->Wait();
    } 
    put next data array value into v
    num--; 
    bufferAvail->Signal(); 
  }
}

这不就是mutex么, 互斥锁啊...论两家都有一只狗, 只有一个花园, 狗见狗, 狗咬狗, 放个mutex万事大吉...

等等, 那还用个java啊! mutex还不够么

不够啊, mutex是对一个进程一个进程进行处理, 如果想批量操作, 请用monitors...论一边是基佬们, 一边是百合们, 只有一个花园, 我们要烧死异性恋, 嗯, 用monitors!

那...那monitors和semaphore啥区别, monitors是共享可见的啊少女! 然后看到了这个解释

A monitor is like a public toilet. Only one person can enter at a time. They lock the door to prevent anyone else coming in, do their stuff, and then unlock it when they leave.

A semaphore is like a bike hire place. They have a certain number of bikes. If you try and hire a bike and they have one free then you can take it, otherwise you must wait. When someone returns their bike then someone else can take it. If you have a bike then you can give it to someone else to return --- the bike hire place doesn't care who returns it, as long as they get their bike back.

monitors是全局共享可见, 比较high-level, semaphore由自己定义, 有自己的作用域, 可以用semaphore实现monitors

噢...

还是不会用, 还要研究研究怎么用.

引用:

http://people.csail.mit.edu/rinard/osnotes/h14.html

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