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In the current implementation of supervisors, temporary children
should never be restarted. However, when a temporary child is
restarted as part of a one_for_all or rest_for_one strategy where
the failing process is not the temporary child, the supervisor
still tries to restart it.
Because the supervisor doesn't keep some of the MFA information
of temporary children, this causes the supervisor to hit its
restart limit and crash.
This patch fixes the behaviour by inserting a clause in
terminate_children/2-3 (private function) that will omit temporary
children when building a list of killed processes, to avoid having
the supervisor trying to restart them again.
Only supervisors in need of restarting children used the list, so
the change should be of no impact for the functions that called
terminate_children/2-3 only to kill all children.
The documentation has been modified to make this behaviour
more explicit.
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Since initial arguments of temporary children under simple_one_for_one
supervisors are not saved, only a list of pids was stored in such
supervisors. When adding/deleting many children, this would scale
badly. To avoid this the list is now changed to a set.
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supervisor:terminate_child/2 was not allowed if the supervisor used
restart strategy simple_one_for_one. This is now changed so that
children of this type of supervisors can be terminated by specifying
the child's Pid.
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terminates" and improved test suite
The bug fix supplied by Filipe David Manana <[email protected]>
did not cover all possible ways that a process may be terminated
as for instance with supervisor:terminate_child. Also there
was a bug in the base case of the patch returning a list of a list instead
of only the list.
Added a timeout for the test cases, eliminated unnecessary sleeps,
improved code.
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The temporary child specs are never removed from the supervisor's state, and
have they're MFA component set to {M, F, undefined} instead of the MFA passed
in the supervisor:start_child/2 call. Subsequent calls to supervisor:restart_child/2
may crash. Stack trace example:
{badarg,[{erlang,apply,[gen_server,start_link,undefined]},
{supervisor,do_start_child,2},{supervisor,handle_call,3},
{gen_server,handle_msg,5},
{proc_lib,init_p_do_apply,3}]}
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dialyzer spec.
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Previous commit changed the supervisor to not save
parameter lists for temporary processes supervised by simple-one-for-one
supervisors. But it is unnecessary to save them for any
temporary processes as they should not be restarted. Proably the
biggest gain is in the simple-one-for-one case.
Also changed the test case count_children_memory so it does
not test that which_children will produce garbage that must
be reclaimed later. This is a strange thing to test and it is no
longer true for all invocations of which_children.
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- Export two more types so that they can be used in other modules
- Correct some types and specs
- Add spec for behaviour_info/1
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* jn/supervisor_child_count_only:
Add count_children/1 to supervisor.erl to determine the number of
OTP-8436 Added supervisor:count_children/1 to count the number of children
being managed without the memory impact of which_children/1.
(Thanks to Jay Nelson.)
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children being managed without the memory impact of which_children/1
The function which_children/1 returns a list of the child processes
currently being supervised, but it has the penalty of creating a new
list thereby consuming more memory. In low memory situations it is
often desirable to know which supervisor may have generated many
processes, but the act of discovering the culprit should not cause the
node to crash (or worse a different node if the kernel kills one
randomly). The new function count_children/1 can give an indication
of which supervisor is taxing resources the most without adding to the
burden. Rather than creating a new list, it walks the supervisor's
internal children structure using an accumulator function so that any
used memory can be incrementally collected yet the resulting count can
still be obtained.
The return result of count_children/1 is a property list of counts
containing:
- {specs, Total_Num_Child_Specs}
- {active, Num_Active_Child_Processes_Of_Supervisor_Or_Worker_Type}
- {supervisors, Num_Supervisor_Type_Children_Including_Dead_Processes}
- {workers, Num_Worker_Type_Children_Including_Dead_Processes}
This patch was made in response to mailing list discussions of the
problem diagnosing heavily taxed production systems. I cannot find
the original request, but http://www.erlang.org/cgi-bin/ezmlm-cgi/4/35060
is my original post of the patch.
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