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< Erlang ~ a null process? |
| yeejiun |
 Posted: Sun Sep 20, 2009 3:14 am |
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Joined: 20 Sep 2009
Posts: 2
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Hi, I'm new to Erlang and have a quick question: is there such a thing as a null process in Erlang? i.e., is there a special Pid that I can send messages to such that those msgs will just get dropped?
I realize that it's easy to create such a process, but I'd like to know if a predefined one exists. Thanks. |
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| Allan |
| Posted: Mon Sep 21, 2009 4:57 am |
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Joined: 29 Jun 2009
Posts: 30
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yeejiun wrote: is there such a thing as a null process in Erlang? i.e., is there a special Pid that I can send messages to such that those msgs will just get dropped?
There is no predefined one.
Create a valid PID by calling "spawn(fun() -> ok end).". Then you can send messages to that PID without wasting memory or cycles due to message queueing because messages sent to terminated processes are dropped. |
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| yeejiun |
| Posted: Mon Sep 21, 2009 5:19 am |
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| Mazen |
| Posted: Sun Sep 27, 2009 8:34 am |
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Joined: 20 Jul 2006
Posts: 164
Location: London
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Like:
Code:
Eshell V5.7.1 (abort with ^G)
1> NullPid = pid(0,0,0).
<0.0.0>
2> NullPid ! die.
die
3>
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| Allan |
| Posted: Sun Sep 27, 2009 2:05 pm |
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There is no BIF pid/3 outside the shell!
The documentation for c:pid/3 states: "This function should only be used when debugging.".
The documentation for list_to_pid/1 (that is used by c:pid/3) contains the warning "This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.".
Rickard Green wrote in msg#00017 in lang.erlang.general: "Note that list_to_pid/1 and c:pid/3 are only intended to be used for debugging and testing. They should not be used in application programs."
Do not use the PID generation functions in production code.
P.S.: On my single node shell, PID <0.0.0> belongs to init:loop/1. Maybe sending it arbitrary messages is not a good idea... ;) |
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| Mazen |
| Posted: Mon Sep 28, 2009 6:57 am |
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Allan wrote: There is no BIF pid/3 outside the shell!
The documentation for c:pid/3 states: " This function should only be used when debugging.".
The documentation for list_to_pid/1 (that is used by c:pid/3) contains the warning " This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.".
Rickard Green wrote in msg#00017 in lang.erlang.general: " Note that list_to_pid/1 and c:pid/3 are only intended to be used for debugging and testing. They should not be used in application programs."
Do not use the PID generation functions in production code.
P.S.: On my single node shell, PID <0.0.0> belongs to init:loop/1. Maybe sending it arbitrary messages is not a good idea... 
Hehe, you are 100% right, I would also use what you suggested. But for the sake of my dignity you can also do this:
Code: Eshell V5.7.1 (abort with ^G)
1> NullPid = pid(0,1,0).
<0.1.0>
2> NullPid ! die.
die
3>
For some reason pid 0.1.0 isn't used by anything, it is simply skipped. Probably it was used to bootstrap something or just do some initialization of something. Anyway, the concept is the same: Use a dead process' pid, thus using 0.1.0 has the same affect as what you proposed.
PS: Yes you would have to use the "BIF only intended for debugging"
phew |
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| rvirding |
| Posted: Wed Sep 30, 2009 6:16 pm |
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Location: Stockholm, Sweden
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It's even worse than just using "debugging" BIFs. There is no guarantee that the pid of a dead process will not be reused in the future! Albeit it might take a long time and many spawns but eventually pids get reused.
Do you intend to send it big messages? If not then create a null process which just loops receive and throws away the messages. You could even register it as 'null'. |
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| wuji |
| Posted: Wed Aug 22, 2012 7:28 am |
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| dongdongwu |
| Posted: Thu Sep 20, 2012 2:16 am |
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