test

Oracle Solaris Studio 12.2：线程分析器用户指南

3.3.2 为 1 号哲学家引入一段休眠时间

一种避免死锁的方法是让 1 号哲学家在拿起他的筷子之前等待一段时间。就代码而言，可让他在拿起自己的筷子之前休眠指定的一段时间 (sleep_seconds)。如果他休眠的时间足够长，该程序就可能会完成而不发生任何实际死锁。可以将他休眠的秒数指定为可执行程序的参数。如果不指定参数，该哲学家就不会休眠。

以下伪代码显示了每位哲学家的逻辑：

   while (there is still food on the table)
      {
        if (sleep argument is specified and I am philosopher #1)
           {
             sleep specified amount of time
           }

        grab right fork
        grab left fork
        eat some food
        put down left fork
        put down right fork 
      }

下面列出了该程序的一次运行，在这次运行中 1 号哲学家在拿起他的筷子之前等待 30 秒。该程序运行至完成，所有五位哲学家都吃到了面条。


% a.out 30
Philosopher 0 is done thinking and now ready to eat.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 4 is done thinking and now ready to eat.
Philosopher 4: got right  chopstick 4
Philosopher 3 is done thinking and now ready to eat.
Philosopher 3: got right  chopstick 3
Philosopher 0: eating.
Philosopher 2 is done thinking and now ready to eat.
Philosopher 2: got right  chopstick 2
Philosopher 1 is done thinking and now ready to eat.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
...
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0 is done eating.
Philosopher 4: got left chopstick 0
Philosopher 4: eating.
Philosopher 4 is done eating.
Philosopher 3: got left chopstick 4
Philosopher 3: eating.
Philosopher 3 is done eating.
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
Philosopher 2 is done eating.
Philosopher 1: got right  chopstick 1
Philosopher 1: got left chopstick 2
Philosopher 1: eating.
Philosopher 1 is done eating.
%

Execution terminated normally

尝试多次运行该程序，并指定不同的休眠参数。如果 1 号哲学家在拿起他的筷子之前仅等待很短的一段时间，那么发生什么情况呢？如果他等待的时间更长一些，又会怎么样？尝试为可执行程序 a.out 指定不同的休眠参数。在使用或不使用休眠参数的情况下多次重新运行该程序。该程序有时会挂起，而有时又可以运行至完成。程序是否挂起取决于线程的调度情况以及线程进行锁请求的时间。