Erlang Thursday – c:i/0

Today’s Erlang Thursday continues with another function in the c module, c:i/0.

c:i/0 reports the system information, displaying information about all the processes on a given node.

c:i().
% Pid                   Initial Call                          Heap     Reds Msgs
% Registered            Current Function                     Stack
% <0.0.0>               otp_ring0:start/2                      987     4987    0
% init                  init:loop/1                              2
% <0.3.0>               erlang:apply/2                        6772   823443    0
% erl_prim_loader       erl_prim_loader:loop/3                   6
% <0.6.0>               gen_event:init_it/6                    376      220    0
% error_logger          gen_event:fetch_msg/5                    8
% <0.7.0>               erlang:apply/2                        1598      463    0
% application_controlle gen_server:loop/6                        7
% <0.9.0>               application_master:init/4              376       44    0
%                       application_master:main_loop/2           6
% <0.10.0>              application_master:start_it/4          233       69    0
%                       application_master:loop_it/4             5
% <0.11.0>              supervisor:kernel/1                   4185    49109    0
% kernel_sup            gen_server:loop/6                        9
% <0.12.0>              rpc:init/1                             233       35    0
% rex                   gen_server:loop/6                        9
% <0.13.0>              global:init/1                          233       51    0
% global_name_server    gen_server:loop/6                        9
% <0.14.0>              erlang:apply/2                         233       19    0
%                       global:loop_the_locker/1                 5
% <0.15.0>              erlang:apply/2                         233        3    0
%                       global:loop_the_registrar/0              2
% <0.16.0>              inet_db:init/1                         233      206    0
% inet_db               gen_server:loop/6                        9
% <0.17.0>              global_group:init/1                    233       59    0
% global_group          gen_server:loop/6                        9
% <0.18.0>              file_server:init/1                    2586     2562    0
% file_server_2         gen_server:loop/6                        9
% <0.19.0>              erlang:apply/2                        2586   155919    0
% code_server           code_server:loop/1                       3
% <0.20.0>              supervisor_bridge:standard_error/      233       41    0
% standard_error_sup    gen_server:loop/6                        9
% <0.21.0>              erlang:apply/2                         233        9    0
% standard_error        standard_error:server_loop/1             2
% <0.22.0>              supervisor_bridge:user_sup/1           610       87    0
%                       gen_server:loop/6                        9
% <0.23.0>              erlang:apply/2                         233       24    0
% user                  user:server_loop/2                       5
% <0.24.0>              kernel_config:init/1                   233      286    0
%                       gen_server:loop/6                        9
% <0.25.0>              supervisor:kernel/1                    233       58    0
% kernel_safe_sup       gen_server:loop/6                        9
% <0.29.0>              kjell_profile:init/1                   987    27100    0
% kjell_profile         gen_server:loop/6                        9
% <0.30.0>              kjell_extension:init/1                2586     3903    0
% kjell_extension       gen_server:loop/6                        9
% <0.45.0>              k_user_drv:server/2                    987     2218    0
% user_drv              k_user_drv:server_loop/5                 8
% <0.46.0>              k_group:server/3                       987    14541    0
%                       k_group:server_loop/3                    4
% <0.47.0>              erlang:apply/2                       28690     4406    0
%                       kjell:shell_rep/4                       17
% <0.48.0>              erlang:apply/2                        1598    20585    0
%                       c:pinfo/1                               49
% Total                                                      58707  1110447    0
%                                                              237
% ok

We can see that it returns the process id (pid), the initial function that started the process, the size of the heap, the number of reductions, the number of messages in the message queue, the registered name, the current function the process is in, and the stack size.

c:i/0 also includes a total of the total heap size, reductions, message queue size and stack size.

There c module also includes a c:ni/0, that reports the system information above across all nodes.

Looking at the process info, we can find a couple of processes related to kjell, which I used instead of erl for ease of finding their process information.

Looking at one of the kjell related processes, we can grab that pid, and do a deeper inspection of that process by calling c:i/3, which displays information about a process, but can reference the pid by the 3 integer values that make up the process’s pid.

c:i(0, 47, 0).
% [{current_function,{kjell,shell_rep,4}},
%  {initial_call,{erlang,apply,2}},
%  {status,waiting},
%  {message_queue_len,0},
%  {messages,[]},
%  {links,[<0.48.0>,<0.46.0>]},
%  {dictionary,[{{result,1},ok},
%               {{command,1},[{call,1,{remote,1,{atom,1,c},{atom,1,i}},[]}]},
%               {evaluator,<0.48.0>}]},
%  {trap_exit,true},
%  {error_handler,error_handler},
%  {priority,normal},
%  {group_leader,<0.46.0>},
%  {total_heap_size,46421},
%  {heap_size,28690},
%  {stack_size,17},
%  {reductions,4479},
%  {garbage_collection,[{min_bin_vheap_size,46422},
%                       {min_heap_size,233},
%                       {fullsweep_after,65535},
%                       {minor_gcs,2}]},
%  {suspending,[]}]

When looking at the information related to a specific process, we can see it shows the linked process, messages and message queue length, heap and stack information, ad various other settings that could be of use.

Again, this is not as pretty as the observer application, but they come in handy when you don’t have access past a terminal, as in working from a jump box, but it gives you a good idea of what is going on in your running Erlang node.

–Proctor

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