3.4.1 Examining Runs That Deadlock

The following listing shows a run of the dining philosophers program that results in an actual deadlock.

prompt% cc din_philo.c -mt -g             

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

Execution terminated by pressing CTRL-C


% er_print tha.1.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"

Deadlock #2, Actual 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.1.er Total Deadlocks: 2
(er_print) 

The following screen-shot shows the Thread Analyzer's presentation of the deadlock information:

The Thread Analyzer reports two deadlocks for din_philo.c, one potential and the other actual. On closer inspection, we find that the two deadlocks are identical. The circular chain involved in the deadlock is as follows:

Select the first thread in the chain (Thread #2) and then click on the Dual Source tab to see where in the source code Thread #2 held the lock at address 0x215a8, and where in the source code it requested the lock at address 0x215c0. The following screen-shot shows the Dual Source tab for thread number two. The default metric (Exclusive Deadlocks metric) is shown to the left of each source line. This metric gives a count of the number of times a lock-hold or lock-request operation, which was involved in a deadlock, was reported on that line.