潜在的デッドロックがあるにもかかわらず完了した実行の検証

十分に大きな休眠引数を指定した場合、食事する哲学者プログラムは、実デッドロックを回避でき、通常どおりに終了します。ただし、通常どおりに終了したからといって、プログラムにデッドロックがないことを意味するわけではありません。単に、保持されたロックと要求されたロックが、所与の実行中にデッドロックチェーンを形成しなかったことを意味するだけです。他の実行でタイミングが変更すれば、実デッドロックが生じる可能性があります。次のリストは、40 秒の休眠時間によって、通常どおりに終了する食事する哲学者プログラムの実行を示しています。ただし、er_print ユーティリティーとスレッドアナライザは潜在的デッドロックを報告します。

% cc -g -o din_philo_pt din_philo.c
% collect -r deadlock -o din_philo_pt.1.er din_philo_pt 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 left chopstick 1
Philosopher 0: eating.
Philosopher 0: got right  chopstick 0
Philosopher 2: got left chopstick 3
Philosopher 2: 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

プロンプトで次のコマンドを入力して、er_print ユーティリティーで実験結果を検証します。

% er_print din_philo_pt.1.er
(er_print) deadlocks
Deadlock #1, Potential deadlock
        Thread #2
                Lock being held:        0x21388, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
                Lock being requested:   0x213a0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
        Thread #3
                Lock being held:        0x213a0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
                Lock being requested:   0x213b8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
        Thread #4
                Lock being held:        0x213b8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
                Lock being requested:   0x213d0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
        Thread #5
                Lock being held:        0x213d0, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
                Lock being requested:   0x213e8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
        Thread #6
                Lock being held:        0x213e8, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"
                Lock being requested:   0x21388, at: grab_chopstick + 0x00000024, line 105 in "din_philo.c"

Deadlocks List Summary: Experiment: din_philo_pt.1.er Total Deadlocks: 1

次のスクリーンショットには、スレッドアナライザでの潜在的デッドロック情報が示されています。

図 3-4  din_philo.c での潜在的デッドロック