Even Simpler Queue Service (ESQS)

Posted by stoyan

Like a part of my Erlang study, I decided to code a pure-man queues management service, similar to Amazon SQS – Even Simpler Queue Service (or Erlang SQS you decide ;) ). For now it’s just one file qserver.erl , but i hope to make it better. First I based my code on OTP ( gen_server ), but after this decided to write it from scratch. Lessons learned:

  • access to the processes by name, not by Pid is more human friendly
  • implement the whole API with simple cast (async) and call (sync) messages
  • one function with guards (do_q) is maybe better than several functions with different names
  • pg2: gave me better name service, then global:register/unreister
Usage: 
Erlang (BEAM) emulator version 5.5.3 [source] [async-threads:0] [hipe] [kernel-poll:false]
1> c(qserver).
{ok,qserver}
2> qserver:start('aa').
{ok,<0.38.0>}
3> qserver:start('bb').
{ok,<0.40.0>}
4> qserver:listq().    
[bb,aa]
5> qserver:inq('aa',123).
{ok,123}
6> qserver:lenq('aa').    
1
7> qserver:inq('aa',[1,2,3]).
{ok,[1,2,3]}
8> qserver:revq('aa').       
ok
9> qserver:outq('aa').
[1,2,3]
10> qserver:outq('aa').
123
11> qserver:outq('aa').
** exited: empty **
12> qserver:stop('aa').
ok
13> qserver:outq('aa').
{oops,{no_such_group,aa}}

There is still a lot to be done – data exchange with the queues (i want to use UBF for data transport format), more robust name service (pg2 is based on gen_server, so if the node with the database die, all names will be lost) – gen_server_cluster based , ACL to the queues etc.

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