Erlang Process monitoring: Link and monitor

Erlang was the first language to be developed for telecom products, and because of that, it decided her strict requirements for error handling. In addition to providing syntax such as Exception,try catch, Erlang also supports the mechanism of link and monitor two monitoring processes so that all processes can be joined together to form a whole. When a process exits with an error, the other process receives a message notification that the process exits. With these features, it is not difficult to build a simple, robust system using Erlang.

Process bidirectional monitoring-link

The link method establishes a two-way link relationship between processes, and when one of the processes exits, another process receives a message that the process exits.

Example 1:

[Plain]View Plaincopy

2. -module (Test).
4. -export ([start/0]).
8. Start ()
10. Pid = Spawn (Fun ()->loop () end),
12. Pid2 = Spawn (Fun ()->loop_link (Pid) end),
14. Io:format ("Pid ~p~npid2 ~p~n", [Pid,pid2]).
18. Loop_link (Pid)
20. Process_flag (Trap_exit, True),
22. Erlang:link (Pid),
24. Receive
26. MSG-
28. Io:format ("pid exit: ~p~n", [MSG])
30. End.
34. Loop ()
36. Process_flag (Trap_exit, True),
38. Receive
40. MSG-
42. Io:format ("Pid2 exit: ~p~n", [MSG])
44. End.

To run the code:

[Plain]View Plaincopy < param name= "wmode" value= "Transparent" >

1. 1> Test:start ().
2. Pid <0.63.0>
3. Pid2 <0.64.0>
4. Ok
5. Percent kill PID process, process PID2 receive notification
6. 2> exit (PID (0,63,0), kill).
7. PID exit: {' exit ', <0.63.0>,killed}
8. True
10. 3> Test:start ().
11. Pid <0.67.0>
12. Pid2 <0.68.0>
13. Ok
14. Percent kill PID2 process, process PID receive notification
15. 4> exit (PID (0,68,0), kill).
16. Pid2 exit: {' exit ', <0.68.0>,killed}
17. True

Note: The Erlang process does not capture the exit signal by default, and you can use Process_flag (Trap_exit, true) to change this default behavior.

Note 2: Remove link monitoring with Erlang:unlink (PID)

Process one-way monitoring-monitor

The monitor mode realizes one-way monitoring of the process, and when the monitored process exits, the monitoring process receives a message that the process exits.

Example 2:

[Plain]View Plaincopy

2. -module (Test).
6. -export ([start/0]).
10. Start ()
12. Pid = Spawn (Fun ()->loop () end),
14. Pid3 = Spawn (Fun ()->loop_monitor (Pid) end),
16. Io:format ("Pid ~p~npid3 ~p~n", [PID,PID3]).
20. Loop_monitor (Pid)
22. _monitorref = Erlang:monitor (process, Pid),
24. Receive
26. MSG-
28. Io:format ("pid exit: ~p~n", [MSG])
30. End.
34. Loop ()
36. Receive
38. MSG-
40. Io:format ("Pid3 exit: ~p~n", [MSG])
42. End.

To run the code:

[Plain]View Plaincopy < param name= "wmode" value= "Transparent" >

1. 1> Test:start ().
2. Pid <0.39.0>
3. PID3 <0.40.0>
4. Ok
5. Percent kill PID process, process PID3 receive notification
6. 2> exit (PID (0,39,0), kill).
7. PID exit: {' Down ', #Ref <0.0.0.80>,process,<0.39.0>,killed}
8. True
10. 3> Test:start ().
11. Pid <0.43.0>
12. PID3 <0.44.0>
13. Ok
14. Percent kill PID3 process, process PID not received notification
15. 4> exit (PID (0,44,0), kill).
16. True

Note: Remove monitor monitoring with Erlang:demonitor (MONITORREF)

If the process exits as normal, Erlang will not issue a process exit notification

[Plain]View Plaincopy

1. 10> exit (PID (0,70,0), normal).
2. True

Transferred from: http://blog.csdn.net/mycwq/article/details/13171117

Erlang Process monitoring: Link and monitor