erts_debug:get_internal_state是用來獲取Erlang執行期內部資訊的主要手段. 但是這個功能是用來給開發人員或者說需要了解系統內部細節的場合, 比如說系統調優.
在R13B04可以使用的選項有:
1. reds_left
2. node_and_dist_references
3. monitoring_nodes
4. next_pid
5. next_port
6. ‘DbTable_words’
7. check_io_debug
8. process_info_args
9. processes
10. processes_bif_info
11. max_atom_out_cache_index
12. nbalance
13. available_internal_state
14. force_heap_frags
15. {process_status, Pid}
16. {link_list, Pid} 或者 {link_list, Port} 或者 {link_list, Nodename}
17. {monitor_list, Pid} 或者 {monitor_list, Nodename}
18. {channel_number, Sysname}
19. {have_pending_exit, Pid}
20. {binary_info, Binary}
21. {dist_port, Sysname}
22. {atom_out_cache_index, Atom}
23. {fake_scheduler_bindings, How} How=spread | processor_spread | thread_spread | default_bind | no_node_processor_spread | no_node_thread_spread | no_spread | unbound

使用此功能的前提是先用erts_debug:set_internal_state(available_internal_state, true). 否者呼叫get_internal_state會提示失敗.
我們演示下:

[email protected]:~/otp/test# erl -sname x
Erlang R14A (erts-5.8)  [smp:2:2] [rq:2] [async-threads:0] [kernel-poll:false]

Eshell V5.8  (abort with ^G)
([email protected])1> erts_debug:get_internal_state(check_io_debug). 
** exception error: undefined function erts_debug:get_internal_state/1
(
 
[email protected])2> erts_debug:set_internal_state(available_internal_state, true).
false
=ERROR REPORT==== 7-Apr-2010::14:40:41 ===
Process <0.38.0> on node '[email protected]' enabled access to the emulator internal state.
NOTE: This is an erts internal test feature and should *only* be used by OTP test-suites.
(
 
[email protected])3> erts_debug:get_internal_state(check_io_debug). 
--- fds in pollset --------------------------------------
fd=0 type=chr driver_select ev=IN  inport=#Port<0.294> inname=tty_sl -c -e indrv=tty_sl 
fd=3 type=fifo internal ep_ev=IN
fd=4 type=fifo internal 
fd=7 type=sock driver_select ev=IN  inport=#Port<0.62> inname=tcp_inet indrv=tcp_inet 
fd=8 type=sock driver_select ev=IN  inport=#Port<0.65> inname=tcp_inet indrv=tcp_inet 
fd=9 type=fifo driver_select ev=IN  inport=#Port<0.486> inname=inet_gethost 4  indrv=spawn 
fd=10 type=sock driver_select ev=IN  inport=#Port<0.492> inname=tcp_inet indrv=tcp_inet 
fd=11 type=sock driver_select ev=IN  inport=#Port<0.495> inname=tcp_inet indrv=tcp_inet 

used fds=6
internal fds=2
---------------------------------------------------------
0
([email protected])4>  erts_debug:get_internal_state({process_status, self()}).
running

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