Overview

Module sbroker

• Description
• Data Types
• Function Index
• Function Details

Behaviours: gen_fsm.

This module defines the sbroker behaviour.
Required callback functions: init/1.

Description

This module provides a process match making service. A process joins one of two queues and is matcheid with a process in the other queue. The queues can be actively managed using an squeue callback module, and passively managed using head or tail drop. A different strategy can be used for both queues. Processes that die while in a queue are automatically removed to prevent matching with a process that is nolonger alive.

There are two functions to join a queue: ask/1 and ask_r/1. Processes that call ask/1 are matched against processes that call ask_r/1. If no match is immediately avaliable a process is queued in the relevant queue until a match becomes avaliable. If queue management is used processes may be dropped without a match.

Processes calling ask/1 try to match with/dequeue a process in the ask_r queue. If no process exists they are queued in the ask queue and await a process to call ask_r/1.

Similarly processes calling ask_r/1 try to match with/dequeue a process in the ask queue. If no process exists they are queued in the ask_r queue and await a process to call ask/1.

A broker requires a callback module. The callback modules implements one callback, init/1, with single argument Args. init/1 should return {ok, {AskQueueSpec, AskRQueueSpec, Interval}) or ignore. AskQueuSpec is the queue specification for the ask queue and AskRQueueSpec is the queue specification for the ask_r queue. Interval is the interval in milliseconds that the active queue is polled. This ensures that the active queue management strategy is applied even if no processes are enqueued/dequeued. In the case of ignore the broker is not started and start_link returns ignore.

A queue specifcation takes the following form: {Module, Args, Out, Size, Drop}. Module is the squeue callback module and Args are its arguments. The queue is created using squeue:new(Time, Module, Args), where Time is chte current time in native time units. Out defines the method of dequeuing, it is either the atom out (dequeue items from the head, i.e. FIFO), or the atom out_r (dequeue items from the tail, i.e. LIFO). Size is the maximum size of the queue, it is either a non_neg_integer() or infinity. Drop defines the strategy to take when the maximum size, Size, of the queue is exceeded. It is either the atom drop (drop from the head of the queue, i.e. head drop) or drop_r (drop from the tail of the queue, i.e. tail drop).

For example:

  -module(sbroker_example).
 
  -behaviour(sbroker).
 
  -export([start_link/0]).
  -export([ask/0]).
  -export([ask_r/1]).
  -export([init/1]).
 
  start_link() ->
      sbroker:start_link({local, ?MODULE}, ?MODULE, []).
 
  ask() ->
      sbroker:ask(?MODULE).
 
  ask_r() ->
      sbroker:ask_r(?MODULE).
 
  init([]) ->
      AskQueueSpec = {squeue_codel, {5, 100}, out, 64, drop},
      AskRQueueSpec = {squeue_timeout, 5000, out_r, infinity, drop},
      Interval = 200,
      {ok, {AskQueueSpec, AskRQueueSpec, Interval}}.

Data Types

broker()

broker() = pid() | atom() | {atom(), node()} | {global, any()} | {via, module(), any()}

name()

name() = {local, atom()} | {global, any()} | {via, module(), any()}

queue_spec()

queue_spec() = {module(), any(), out | out_r, non_neg_integer() | infinity, drop | drop_r}

start_return()

start_return() = {ok, pid()} | ignore | {error, any()}

Function Index

Function Details

ask/1

Tries to match with a process calling ask_r/1 on the same broker. Returns {go, Ref, Pid, RelativeTime, SojournTime} on a successful match or {drop, SojournTime}.

Ref is the transaction reference, which is a reference(). Pid is the matched process. RelativeTime is the time (in native time units) spent waiting for a match after discounting time spent waiting for the broker to handle requests. SojournTime is the time spent in both the broker's message queue and internal queue, in native time units.

RelativeTime represents the SojournTime without the overhead of the broker. The value measures the level of queue congestion without being effected by the load of the broker.

If RelativeTime is positive, the request was enqueued in the internal queue awaiting a match with another request sent approximately RelativeTime after this request was sent. Therefore SojournTime minus RelativeTime is the latency, or overhead, of the broker in native time units.

If RelativeTime is negative, the request dequeued a request in the internal queue that was sent approximately RelativeTime before this request was sent. Therefore SojournTime is the latency, or overhead, of the broker in native time units.

If RelativeTime is 0, the request was matched with a request sent at approximately the same time. Therefore SojournTime is the latency, or overhead, of the broker in native time units.

ask_r/1

Tries to match with a process calling ask/1 on the same broker.

See also: ask/1.

async_ask/1

Monitors the broker and sends an asynchronous request to match with a process calling ask_r/1. Returns {await, Tag, Pid}.

Tag is a monitor reference() that uniquely identifies the reply containing the result of the request. Pid, is the pid (pid()) of the monitored broker. To cancel the request call cancel(Pid, Tag).

The reply is of the form {Tag, {go, Ref, Pid, RelativeTime, SojournTime} or {Tag, {drop, SojournTime}}.

See also: async_ask/2, cancel/2.

async_ask/2

Sends an asynchronous request to match with a process calling ask_r/1. Returns {await, Tag, Pid}.

Tag is a any() that identifies the reply containing the result of the request. Pid, is the pid (pid()) of the broker. To cancel all requests identified by Tag on broker Pid call cancel(Pid, Tag).

The reply is of the form {Tag, {go, Ref, Pid, RelativeTime, SojournTime} or {Tag, {drop, SojournTime}}.

See also: cancel/2.

async_ask_r/1

Monitors the broker and sends an asynchronous request to match with a process calling ask/1.

See also: async_ask/1, cancel/2.

async_ask_r/2

Sends an asynchronous request to match with a process calling ask/1.

See also: async_ask/2, cancel/2.

await/2

Await the response to an asynchronous request identified by Tag.

Exits if a response is not received after Timeout milliseconds.

See also: async_ask/2, async_ask_r/2.

cancel/3

Cancels an asynchronous request. Returns the number of cancelled requests or false if no requests exist. In the later case a caller may wish to check its message queue for an existing reply.

See also: async_ask/1, async_ask_r/1.

change_config/2

Change the configuration of the broker. Returns ok on success and {error, Reason} on failure, where Reason, is the reason for failure.

len/2

Get the length of the ask queue in the broker, Broker.

len_r/2

Get the length of the ask_r queue in the broker, Broker.

nb_ask/1

Tries to match with a process calling ask_r/1 on the same broker but does not enqueue the request if no immediate match. Returns {go, Ref, Pid, RelativeTime, SojournTime} on a successful match or {retry, SojournTime}.

See also: ask/1.

nb_ask_r/1

Tries to match with a process calling ask/1 on the same broker but does not enqueue the request if no immediate match.

See also: nb_ask/1.

start_link/2

Starts a broker with callback module Module and argument Args.

start_link/3

Starts a broker with name Name, callback module Module and argument Args.

Overview

Generated by EDoc, May 1 2015, 11:53:46.