Examining Runs That Deadlock
The following listing shows a run of the dining philosophers program that results in an actual deadlock.
% cc -g -o din_philo din_philo.c % collect -r deadlock -o din_philo.1.er din_philo Creating experiment database din_philo.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 2: got right chopstick 2 Philosopher 3: got right chopstick 3 (hang) Execution terminated by pressing CTRL-C
Type the following commands to examine the experiment with er_print utility:
% er_print din_philo.1.er (er_print) deadlocks
Deadlock #1, Potential deadlock
Thread #2
Lock being held: 0x21380, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x21398, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #3
Lock being held: 0x21398, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213b0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #4
Lock being held: 0x213b0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213c8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #5
Lock being held: 0x213c8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213e0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #6
Lock being held: 0x213e0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x21380, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Deadlock #2, Actual deadlock
Thread #2
Lock being held: 0x21380, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x21398, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #3
Lock being held: 0x21398, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213b0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #4
Lock being held: 0x213b0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213c8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #5
Lock being held: 0x213c8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x213e0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Thread #6
Lock being held: 0x213e0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
Lock being requested: 0x21380, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
The following screen shot shows Thread Analyzer's presentation of the deadlock information.
Figure 3-2 Deadlock Detected in din_philo.c
Thread Analyzer reports two deadlocks for din_philo.c, one potential and the other actual. On closer inspection, you 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 view to see where in the source code Thread #2 acquired the lock at address 0x21380, and where in the source code it requested the lock at address 0x21398.
The following screen shot shows the Dual Source view for Thread #2. The top half of the screen shot shows that Thread #2 acquired the lock at address 0x21380 by calling pthread_mutex_lock() on line 105. The bottom half of the screen shot shows that the same thread requested the lock at address 0x21398 by calling pthread_mutex_lock() on line 105. Each of the two calls to pthread_mutex_lock() used a different lock as the argument. In general, the lock-acquire and lock-request operations might not be on the same source line.
The default metric (Exclusive Deadlocks metric) is shown to the left of each source line in the screen shot. This metric gives a count of the number of times a lock-acquire or lock-request operation, which was involved in a deadlock, was reported on that source line. Only source lines that are part of a deadlock chain would have a value for this metric that is larger than zero.
Figure 3-3 Potential Deadlock in din_philo.c
