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Oracle Solaris Studio 12.2：线程分析器用户指南

3.5 了解死锁实验结果

本节说明如何使用线程分析器检查哲学家就餐程序中的死锁。

3.5.1 检查出现死锁的运行

下面列出了导致实际死锁的哲学家就餐程序的一次运行。


% 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

键入以下命令以使用 er_print 实用程序检查实验：


% er_print din_philo.1.er
(er_print) deadlocks

Deadlock #1, Potential deadlock
  Thread #2
    Lock being held:        0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #3
    Lock being held:        0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #4
    Lock being held:        0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #5
    Lock being held:        0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #6
    Lock being held:        0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"

Deadlock #2, Actual deadlock
  Thread #2
    Lock being held:        0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #3
    Lock being held:        0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #4
    Lock being held:        0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #5
    Lock being held:        0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #6
    Lock being held:        0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested:   0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"

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

以下屏幕抓图显示了线程分析器中显示的死锁信息。

图 3–2 din_philo.c 中检测到的死锁

线程分析器窗口的屏幕抓图，显示了实际的死锁。

线程分析器报告了 din_philo.c 的两个死锁，一个是潜在死锁，另一个是实际死锁。通过进一步检查，可以发现两个死锁是相同的。

该死锁涉及的循环链如下：

线程 2：在地址 0x215a0 持有锁，在地址 0x215b8 请求锁

线程 3：在地址 0x215b8 持有锁，在地址 0x215d0 请求锁

线程 4：在地址 0x215d0 持有锁，在地址 0x215e8 请求锁

线程 5：在地址 0x215e8 持有锁，在地址 0x21600 请求锁

线程 6：在地址 0x21600 持有锁，在地址 0x215a0 请求锁

选择循环链中的第一个线程（线程 2），然后单击 "Dual Source"（双源）标签，可以在源代码中看到，线程 2 在地址 0x215a0 持有锁，在源代码中也可以看到，该线程在地址 0x215b8 请求锁。以下屏幕抓图显示了对应于线程 2 的 "Dual Source"（双源）标签。每个源代码行的左侧会显示缺省的度量："Exclusive Deadlocks"（互斥死锁）度量。此度量显示了该行上报告的（死锁涉及的）锁持有或锁请求操作的总次数。

图 3–3 din_philo.c 中的潜在死锁

线程分析器 "Dual Source"（双源）标签的屏幕抓图，显示了潜在的死锁。

3.5.2 检查存在潜在死锁但仍可完成的运行

如果提供足够大的休眠参数，哲学家就餐程序就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。它仅仅表示在给定的一次运行中，持有和请求的锁未形成死锁链。如果在其他运行中出现了时间变化，则仍可能会发生实际死锁。下面列出了由于引入 40 秒休眠时间而正常终止的哲学家就餐程序的一次运行。但是，er_print 实用程序和线程分析器会报告潜在死锁。


% cc -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

键入下列以粗体显示的命令以使用 er_print 实用程序检查实验：


% er_print din_philo_pt.1.er
(er_print) deadlocks
Deadlock #1, Potential deadlock
  Thread #2
    Lock being held:      0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #3
    Lock being held:      0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #4
    Lock being held:      0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #5
    Lock being held:      0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #6
    Lock being held:      0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"

Deadlocks List Summary: Experiment: din_philo_pt.1.er Total Deadlocks: 1
(er_print)
 
Deadlock #1, Potential deadlock
  Thread #2
    Lock being held:      0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #3
    Lock being held:      0x215b8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #4
    Lock being held:      0x215d0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #5
    Lock being held:      0x215e8, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
  Thread #6
    Lock being held:      0x21600, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"
    Lock being requested: 0x215a0, at: grab_chopstick + 0x0000002C, line 106 in "din_philo.c"

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

以下屏幕抓图显示了线程分析器界面中的潜在死锁信息。

图 3–4 din_philo.c 中的潜在死锁

线程分析器窗口的屏幕抓图，显示了潜在的死锁。