3.4.2 检查存在潜在死锁但仍可完成的运行

在提供足够大的休眠参数时，哲人进餐程序可避免实际死锁，并正常终止。但是，正常终止并不意味着程序可以完全避免死锁。它仅仅表示在一次特定的运行中，占用和请求的锁定不会构成死锁链。如果在其他运行中计时发生更改，则还会发生实际死锁。以下列表显示了正常终止的哲人进餐程序的一次运行。但是 er_print 实用程序和线程分析器会报告潜在死锁。

% cc din_philo.c -mt -g                


% collect -r deadlock a.out 40
Creating experiment database tha.2.er ...
Philosopher 0 is done thinking and now ready to eat.
Philosopher 2 is done thinking and now ready to eat.
Philosopher 1 is done thinking and now ready to eat.
Philosopher 3 is done thinking and now ready to eat.
Philosopher 2: got right  chopstick 2
Philosopher 3: got right  chopstick 3
Philosopher 0: got right  chopstick 0
Philosopher 4 is done thinking and now ready to eat.
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 3: got left chopstick 4
Philosopher 3: eating.
Philosopher 0: got right  chopstick 0
Philosopher 4: got right  chopstick 4
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 3: got right  chopstick 3
Philosopher 2: got right  chopstick 2
Philosopher 4: got left chopstick 0
Philosopher 4: eating.
Philosopher 0: got right  chopstick 0
Philosopher 3: got left chopstick 4
Philosopher 3: eating.
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 4: got right  chopstick 4
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
Philosopher 4: got left chopstick 0
Philosopher 4: eating.
Philosopher 3: got right  chopstick 3
Philosopher 2: got right  chopstick 2
Philosopher 0: got right  chopstick 0
Philosopher 3: got left chopstick 4
Philosopher 3: eating.
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
...
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 4: got right  chopstick 4
Philosopher 3: got right  chopstick 3
Philosopher 4: got left chopstick 0
Philosopher 4: eating.
Philosopher 0: got right  chopstick 0
Philosopher 3: got left chopstick 4
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 3: eating.
Philosopher 0: got right  chopstick 0
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 4: got right  chopstick 4
Philosopher 3: got right  chopstick 3
Philosopher 2: got right  chopstick 2
Philosopher 4: got left chopstick 0
Philosopher 4: eating.
Philosopher 4 is done eating.
Philosopher 3: got left chopstick 4
Philosopher 3: eating.
Philosopher 0: got right  chopstick 0
Philosopher 0: got left chopstick 1
Philosopher 0: eating.
Philosopher 3 is done eating.
Philosopher 2: got left chopstick 3
Philosopher 2: eating.
Philosopher 0 is done 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


% er_print tha.2.er 
(er_print) deadlocks

Deadlock #1, Potential deadlock
	Thread #2
		Lock being held:	0x215a8, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
		Lock being requested:	0x215c0, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
	Thread #3
		Lock being held:	0x215c0, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
		Lock being requested:	0x215d8, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
	Thread #4
		Lock being held:	0x215d8, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
		Lock being requested:	0x215f0, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
	Thread #5
		Lock being held:	0x215f0, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
		Lock being requested:	0x21608, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
	Thread #6
		Lock being held:	0x21608, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"
		Lock being requested:	0x215a8, at: grab_chopstick + 0x0000002C, line 101 in "din_philo.c"

Deadlocks List Summary: Experiment: tha.2.er Total Deadlocks: 1
(er_print) 
 

下面的屏幕抓图显示了线程分析器界面的潜在死锁信息：