Thread 2 is made to heartbeat

Now consider the case where Thread 2 is made to heartbeat. A HAM will automatically detect when the thread is unresponsive and can terminate it and/or perform recovery.

Thread 1                             Thread 2

...                                  ...
(Run at high priority)               (Run at low priority)
while true                           while true
do                                   do
    obtain lock a                        obtain lock a
                                             send heartbeat
        (compute section1)                   (compute section1)
    release lock a                       release lock a
done                                 done
...                                  ...

Here Thread 2 is expected to send heartbeats to a HAM. By placing the heartbeat call within the inside loop, the HAM detects when Thread 2 begins to starve.

The threads will execute as described earlier, but eventually Thread 2 will starve. We'll wait for a reasonable amount of time (some seconds) until it does. The threads write a simple execution log in /dev/shmem/mutex-starvation-heartbeat.log. The HAM detects that the thread has stopped heartbeating and terminates the process, after saving its state for postmortem analysis.

Let's look at what happens:

  1. Waiting for some time.

    Here's the current state of the threads in process 753682 and the state of mutex-starvation when it missed heartbeats:

         pid tid name               prio STATE       Blocked
      753682   1 t/mutex-starvation  10r JOIN        4
      753682   2 t/mutex-starvation  63r RECEIVE     1
      753682   3 t/mutex-starvation   1r MUTEX       753682-04 #-2147
      753682   4 t/mutex-starvation  63r NANOSLEEP
        Entity state from HAM
    Path            : mutex-starvation
    Entity Pid      : 753682
    Num conditions  : 1
    Condition type  : ATTACHEDSELF
    HeartBeat Period: 1000000000
    HB Low Mark     : 5
    HB High Mark    : 5
    Last Heartbeat  : 2001/09/03 14:44:37:796119160
    HeartBeat State : MISSEDHIGH
    Created         : 2001/09/03 14:44:34:780239800
    Num Restarts    : 0

    And here's the tail from the threads' log file:

    Thread 1: Unlocking lock a
    Thread 1: Locking lock a
    Thread 1: Unlocking lock a
    Thread 1: Locking lock a
    Thread 1: Unlocking lock a
    Thread 1: Locking lock a
    Thread 1: Unlocking lock a
    Thread 1: Locking lock a
    Thread 1: Unlocking lock a
    Thread 1: Locking lock a
  2. Extracting core current process information:
     processor=ARM num_cpus=2
      cpu 1 cpu=602370 name=604e speed=299
       flags=0xc0000001 FPU MMU EAR
      cpu 2 cpu=602370 name=604e speed=299
       flags=0xc0000001 FPU MMU EAR
     cyc/sec=16666666 tod_adj=999522656000000000 nsec=5627098907040 inc=999960
     boot=999522656 epoch=1970 intr=-2147483648
     rate=600000024 scale=-16 load=16666
       MACHINE="mtx604-smp" HOSTNAME="localhost"
     pretend_cpu=0 init_msr=36866 
    pid=753682 parent=729105 child=0 pgrp=753682 sid=1
     flags=0x000300 umask=0 base_addr=0x48040000 init_stack=0x4803f9f0
     ruid=0 euid=0 suid=0  rgid=0 egid=0 sgid=0
     ign=0000000006801000 queue=ff00000000000000 pending=0000000000000000
     fds=5 threads=4 timers=1 chans=4
     thread 1 REQUESTED
      ip=0xfe32f8c8 sp=0x4803f880 stkbase=0x47fbf000 stksize=528384
      state=JOIN flags=0 last_cpu=2 timeout=00000000
      pri=10 realpri=10 policy=RR
     thread 2
      ip=0xfe32f1a8 sp=0x47fbef50 stkbase=0x47f9e000 stksize=135168
      state=RECEIVE flags=4000000 last_cpu=2 timeout=00000000
      pri=63 realpri=63 policy=RR
     thread 3
      ip=0xfe32f838 sp=0x47f9df80 stkbase=0x47f7d000 stksize=135168
      state=MUTEX flags=4000000 last_cpu=2 timeout=00000000
      pri=1 realpri=1 policy=RR
     thread 4
      ip=0xfe32f9a0 sp=0x47f7cf20 stkbase=0x47f5c000 stksize=135168
      state=NANOSLEEP flags=4000000 last_cpu=1 timeout=0x1001000
      pri=63 realpri=63 policy=RR