LFE Friday - c:i/0
This week's LFE Friday was translated with permission from the
Erlang Thursday
series by Steven Proctor.
This week's translator: Robert Virding.
Today's LFE Friday 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 1598 2392 0
init init:loop/1 2
<0.3.0> erlang:apply/2 6772 176779 0
erl_prim_loader erl_prim_loader:loop/3 6
<0.6.0> gen_event:init_it/6 376 223 0
error_logger gen_event:fetch_msg/5 8
<0.7.0> erlang:apply/2 987 404 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 73 0
application_master:loop_it/4 5
<0.11.0> supervisor:kernel/1 376 1891 0
kernel_sup gen_server:loop/6 9
<0.12.0> erlang:apply/2 6772 129164 0
code_server code_server:loop/1 3
<0.14.0> rpc:init/1 233 21 0
rex gen_server:loop/6 9
<0.15.0> global:init/1 233 45 0
global_name_server gen_server:loop/6 9
<0.16.0> erlang:apply/2 233 21 0
global:loop_the_locker/1 5
<0.17.0> erlang:apply/2 233 3 0
global:loop_the_registrar/0 2
<0.18.0> inet_db:init/1 376 236 0
inet_db gen_server:loop/6 9
<0.19.0> global_group:init/1 233 53 0
global_group gen_server:loop/6 9
<0.20.0> file_server:init/1 233 84 0
file_server_2 gen_server:loop/6 9
<0.21.0> supervisor_bridge:standard_error/ 233 34 0
standard_error_sup gen_server:loop/6 9
<0.22.0> erlang:apply/2 233 9 0
standard_error standard_error:server_loop/1 2
<0.23.0> supervisor_bridge:user_sup/1 233 69 0
gen_server:loop/6 9
<0.24.0> user_drv:server/2 1598 2064 0
user_drv user_drv:server_loop/6 9
<0.25.0> group:server/3 233 36 0
user group:server_loop/3 4
<0.26.0> group:server/3 987 11825 0
group:server_loop/3 4
<0.27.0> erlang:apply/2 233 360 0
lfe_shell:shell_eval/3 5
<0.28.0> erlang:apply/2 6772 17553 0
c:pinfo/1 38
<0.30.0> kernel_config:init/1 233 233 0
gen_server:loop/6 9
<0.31.0> supervisor:kernel/1 233 56 0
kernel_safe_sup gen_server:loop/6 9
Total 30252 343672 0
196
okWe 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 see a process related to the LFE repl lfe_shell. We can grab the pid of that process by calling c:i/3 which displays information about a process but can reference a pid by the three integer values that make up the process's pid.
> (c:i 0 27 0)
(#(current_function #(lfe_shell shell_eval 3))
#(initial_call #(erlang apply 2))
#(status waiting)
#(message_queue_len 0)
#(messages ())
#(links (<0.28.0> <0.26.0>))
#(dictionary ())
#(trap_exit true)
#(error_handler error_handler)
#(priority normal)
#(group_leader <0.26.0>)
#(total_heap_size 11334)
#(heap_size 10958)
#(stack_size 5)
#(reductions 1576)
#(garbage_collection
(#(min_bin_vheap_size 46422)
#(min_heap_size 233)
#(fullsweep_after 65535)
#(minor_gcs 6)))
#(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.
Note that the c:i/0 function prints out the data so it is intended to be called from the shell and not from another function. While the output is not as pretty as the observer application this function is very useful when you only have access to through a terminal.
The c:i/0 function gets the information about a process using the BIFs process_info/1 and process_info/2. These functions are very useful when need to access the process information from within a function or application.
> (process_info (pid 0 27 0))
(#(current_function #(lfe_shell shell_eval 3))
#(initial_call #(erlang apply 2))
#(status waiting)
#(message_queue_len 0)
#(messages ())
#(links (<0.38.0> <0.26.0>))
#(dictionary ())
#(trap_exit true)
#(error_handler error_handler)
#(priority normal)
#(group_leader <0.26.0>)
#(total_heap_size 57380)
#(heap_size 28690)
#(stack_size 5)
#(reductions 3770)
#(garbage_collection
(#(min_bin_vheap_size 46422)
#(min_heap_size 233)
#(fullsweep_after 65535)
#(minor_gcs 1)))
#(suspending ()))As with the c functions c:m/1 and c:regs/0 this function exists as an LFE repl built-in command which can be called from the repl with just (i).
-Proctor, Robert
