问题
I am having problem with 'spawn' in erlang, it seems processes just die after awhile. Here's the simple code:
-module(simple).
-export([server/1, client/1, owner/1, spawn_n/2, start/1, main/1]).
server(State) ->
receive
{request,Return_PID} ->
io:format("SERVER ~w: Client request recieved from ~w~n", [self(),Return_PID]),
NewState = State + 1,
Return_PID ! {hit_count,NewState},
server(NewState);
{server_owner,Owner_PID} ->
io:format("SERVER ~w: Owner request recieved from ~w~n", [self(), Owner_PID]),
Owner_PID ! {hit_count,State},
server(State);
reset ->
io:format("SERVER ~w: State reset to zero.~n", [self()]),
server(0)
end.
client(Server_Address) ->
Server_Address ! {request, self()},
receive
{hit_count,Number} ->
io:format("CLIENT ~w: Hit count was ~w~n", [self(),Number])
end.
owner(Server_PID) ->
timer:sleep(random:uniform(100)),
Server_PID ! {server_owner,self()},
receive
{hit_count,Number} when Number > 5 ->
io:format("OWNER: Hit count is ~w , reseting counter. ~n", [Number]),
Server_PID ! reset,
owner(Server_PID);
{hit_count,Number} when Number < 5 ->
io:format("OWNER ~w: Hit count was ~w~n", [self(), Number]),
owner(Server_PID)
end.
spawn_n(N, Server_PID) ->
if
N>0 ->
spawn(simple,client,[Server_PID]),
timer:sleep(random:uniform(100)),
spawn_n(N-1,Server_PID);
N==0 ->
io:format("Last client spawned. ~n")
end.
start(N) ->
Server_PID = spawn(simple,server,[0]),
spawn(simple,owner,[Server_PID]),
spawn(simple,spawn_n,[N,Server_PID]).
main([Arg]) ->
N = list_to_integer(atom_to_list(Arg)),
start(N),
init:stop().
Here's an example I get when running it:
erl -noshell -s simple main 20
SERVER <0.28.0>: Client request recieved from <0.31.0>
CLIENT <0.31.0>: Hit count was 1
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.32.0>
OWNER <0.29.0>: Hit count was 1
CLIENT <0.32.0>: Hit count was 2
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.33.0>
OWNER <0.29.0>: Hit count was 2
CLIENT <0.33.0>: Hit count was 3
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.34.0>
OWNER <0.29.0>: Hit count was 3
CLIENT <0.34.0>: Hit count was 4
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.35.0>
OWNER <0.29.0>: Hit count was 4
CLIENT <0.35.0>: Hit count was 5
SERVER <0.28.0>: Owner request recieved from <0.29.0>
SERVER <0.28.0>: Client request recieved from <0.36.0>
CLIENT <0.36.0>: Hit count was 6
SERVER <0.28.0>: Client request recieved from <0.37.0>
CLIENT <0.37.0>: Hit count was 7
SERVER <0.28.0>: Client request recieved from <0.38.0>
CLIENT <0.38.0>: Hit count was 8
SERVER <0.28.0>: Client request recieved from <0.39.0>
CLIENT <0.39.0>: Hit count was 9
SERVER <0.28.0>: Client request recieved from <0.40.0>
CLIENT <0.40.0>: Hit count was 10
SERVER <0.28.0>: Client request recieved from <0.41.0>
CLIENT <0.41.0>: Hit count was 11
SERVER <0.28.0>: Client request recieved from <0.42.0>
CLIENT <0.42.0>: Hit count was 12
SERVER <0.28.0>: Client request recieved from <0.43.0>
CLIENT <0.43.0>: Hit count was 13
SERVER <0.28.0>: Client request recieved from <0.44.0>
CLIENT <0.44.0>: Hit count was 14
SERVER <0.28.0>: Client request recieved from <0.45.0>
CLIENT <0.45.0>: Hit count was 15
SERVER <0.28.0>: Client request recieved from <0.46.0>
CLIENT <0.46.0>: Hit count was 16
SERVER <0.28.0>: Client request recieved from <0.47.0>
CLIENT <0.47.0>: Hit count was 17
SERVER <0.28.0>: Client request recieved from <0.48.0>
CLIENT <0.48.0>: Hit count was 18
{error_logger,{{2011,6,27},{12,57,8}},"~s~n",["Error in process <0.28.0> with ex
it value: {terminated,[{io,format,[<0.22.0>,\"SERVER ~w: Client request recieved
from ~w~n\",[<0.28.0>,<0.49.0>]]},{simple,server,1}]}\n"]}
I don't get it. The processes just die or something? It shouldnt terminate! I am running on windows 7 if it might be something windows-related.
Thanks
EDIT: heres what happens by doing application:start(sasl). before:
C:\Program Files\erl5.8.4\bin>erl
Eshell V5.8.4 (abort with ^G)
1> application:start(sasl).
ok
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
supervisor: {local,sasl_safe_sup}
started: [{pid,<0.37.0>},
{name,alarm_handler},
{mfargs,{alarm_handler,start_link,[]}},
{restart_type,permanent},
{shutdown,2000},
{child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
supervisor: {local,sasl_safe_sup}
started: [{pid,<0.38.0>},
{name,overload},
{mfargs,{overload,start_link,[]}},
{restart_type,permanent},
{shutdown,2000},
{child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
supervisor: {local,sasl_sup}
started: [{pid,<0.36.0>},
{name,sasl_safe_sup},
{mfargs,
{supervisor,start_link,
[{local,sasl_safe_sup},sasl,safe
{restart_type,permanent},
{shutdown,infinity},
{child_type,supervisor}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
supervisor: {local,sasl_sup}
started: [{pid,<0.39.0>},
{name,release_handler},
{mfargs,{release_handler,start_link,[]}}
{restart_type,permanent},
{shutdown,2000},
{child_type,worker}]
2>
=PROGRESS REPORT==== 27-Jun-2011::16:03:55 ===
application: sasl
started_at: nonode@nohost
2> simple:main(['20']).
ok
SERVER <0.42.0>: Client request recieved from <0.45.0>
3> CLIENT <0.45.0>: Hit count was 1
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.47.0>
3> OWNER <0.43.0>: Hit count was 1
3> CLIENT <0.47.0>: Hit count was 2
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.48.0>
3> OWNER <0.43.0>: Hit count was 2
3> CLIENT <0.48.0>: Hit count was 3
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.49.0>
3> OWNER <0.43.0>: Hit count was 3
3> CLIENT <0.49.0>: Hit count was 4
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.50.0>
3> OWNER <0.43.0>: Hit count was 4
3> CLIENT <0.50.0>: Hit count was 5
3> SERVER <0.42.0>: Owner request recieved from <0.43.0>
3> SERVER <0.42.0>: Client request recieved from <0.51.0>
3> CLIENT <0.51.0>: Hit count was 6
3> SERVER <0.42.0>: Client request recieved from <0.52.0>
3> CLIENT <0.52.0>: Hit count was 7
3> SERVER <0.42.0>: Client request recieved from <0.53.0>
3> CLIENT <0.53.0>: Hit count was 8
3> SERVER <0.42.0>: Client request recieved from <0.54.0>
3> CLIENT <0.54.0>: Hit count was 9
3> SERVER <0.42.0>: Client request recieved from <0.55.0>
3> CLIENT <0.55.0>: Hit count was 10
3> SERVER <0.42.0>: Client request recieved from <0.56.0>
3> CLIENT <0.56.0>: Hit count was 11
3> SERVER <0.42.0>: Client request recieved from <0.57.0>
3> CLIENT <0.57.0>: Hit count was 12
3> SERVER <0.42.0>: Client request recieved from <0.58.0>
3> CLIENT <0.58.0>: Hit count was 13
3> SERVER <0.42.0>: Client request recieved from <0.59.0>
3> CLIENT <0.59.0>: Hit count was 14
3> SERVER <0.42.0>: Client request recieved from <0.60.0>
3> CLIENT <0.60.0>: Hit count was 15
3> SERVER <0.42.0>: Client request recieved from <0.61.0>
3> CLIENT <0.61.0>: Hit count was 16
3> SERVER <0.42.0>: Client request recieved from <0.62.0>
3> CLIENT <0.62.0>: Hit count was 17
3> SERVER <0.42.0>: Client request recieved from <0.63.0>
3> CLIENT <0.63.0>: Hit count was 18
3> {error_logger,{{2011,6,27},{16,3,58}},"~s~n",["Error in proc
exit value: {terminated,[{io,format,[<0.23.0>,\"SERVER ~w: Cli
ved from ~w~n\",[<0.42.0>,<0.64.0>]]},{simple,server,1}]}\n"]}
回答1:
You are calling init:stop() immediately after your spawns. How are you going to make sure all your processes are properly finished? You probably need to block on receive in main and notify main process when others are done.
回答2:
The other answer is correct, but it doesn't explain why.
It's a tricky question, and the answer is (sort of) in your log output:
{error_logger,{{2011,6,27},{12,57,8}},"~s~n",["Error in process <0.28.0> with exit value: {terminated,[{io,format,[<0.22.0>,\"SERVER ~w: Client request recieved from ~w~n\",[<0.28.0>,<0.49.0>]]},{simple,server,1}]}\n"]}
The first clue is that io:format/3 exits with 'terminated' and some data.
Looking at the documentation and searching for terminated gives ... nothing. Looking inside io.erl gives us the answer though.
Line 456 and 462 of io.erl returns {error, terminated} when the io device is down. So now we know that io:format can potentially exit with status terminated. Looking further we can see that this return value turns into the above error message on line 74 (with context):
case request(Io, Request) of
{error, Reason} ->
[_Name | Args] = tuple_to_list(to_tuple(Request)),
{'EXIT',{undef,[_Current|Mfas]}} = (catch erlang:error(undef)),
MFA = {io, Func, [Io | Args]},
exit({conv_reason(Func, Reason),[MFA|Mfas]});
If you follow the call path for request/2 you will find that one possible branch is at the {error, terminated} mentioned earlier.
So, long story short, standard out is down.
Most likely since you killed your system with init:stop().
来源：https://stackoverflow.com/questions/6491897/erlang-spawn-problems