Overview

Module sbroker

• Description
• Data Types
• Function Index
• Function Details

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 matched with a process in the other queue. The queues are managed using sbroker_queue callback module per queue so that 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. A broker also uses an sbroker_meter callback module to monitor the queue and processing delays of the broker.

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, [MeterSpec]}) or ignore. AskQueueSpec is the queue specification for the ask queue, AskRQueueSpec is the queue specification for the ask_r queue and MeterSpec is a meter specification. There can any number of meters but a meter module can only be included once. In the case of ignore the broker is not started and start_link returns ignore. As the callback modules are defined in the init/1 callback a broker supports the dynamic modules supervisor child specification.

Both queue and meter specifcations take the form: {Module, Args}. Module is the callback module and Args are its arguments.

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 = {sbroker_codel_queue, #{}},
      AskRQueueSpec = {sbroker_timeout_queue, #{}},
      MeterSpec = {sbroker_overload_meter, #{alarm => {overload, ?MODULE}}},
      {ok, {AskQueueSpec, AskRQueueSpec, [MeterSpec]}}.

Data Types

broker()

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

debug_option()

debug_option() = trace | log | {log, pos_integer()} | statistics | {log_to_file, file:filename()} | {install, {function(), any()}}

handler_spec()

handler_spec() = {module(), any()}

name()

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

start_option()

start_option() = {debug, debug_option()} | {timeout, timeout()} | {spawn_opt, [proc_lib:spawn_option()]} | {read_time_after, non_neg_integer() | infinity}

start_return()

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

Function Index

Function Details

ask/1

Equivalent to ask(Broker, self()).

ask/2

Send a match request, with value ReqValue, to try to match with a process calling ask_r/2 on the broker, Broker.

Returns {go, Ref, Value, RelativeTime, SojournTime} on a successful match or {drop, SojournTime}. value of the matched request sent by the counterparty process. RelativeTime is the approximate time differnece (in the broker's time unit) between when the request was sent and the matching request was sent. SojournTime is the approximate time spent in both the broker's message queue and internal queue.

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.

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.

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.

The sojourn time for matched process can be approximated by SojournTime minus RelativeTime.

ask_r/1

Equivalent to ask_r(Broker, self()).

ask_r/2

Tries to match with a process calling ask/2 on the same broker.

See also: ask/2.

async_ask/1

Equivalent to async_ask(Broker, self()).

async_ask/2

Monitors the broker and sends an asynchronous request to match with a process calling ask_r/2. Returns {await, Tag, Pid} or {drop, 0}.

Tag is a monitor reference() that uniquely identifies the reply containing the result of the request. Process, is the pid() of the monitored broker or {atom(), node()} if the broker is registered locally in another node. To cancel the request call cancel(Process, Tag).

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

Ref is the transaction reference, which is a reference(). Value is the value of the matched process. RelativeTime is the time spent waiting for a match after discounting time spent waiting for the broker to handle requests. SojournTime is the time spent in the broker's message queue.

Multiple asynchronous requests can be made from a single process to a broker and no guarantee is made of the order of replies. A process making multiple requests can reuse the monitor reference for subsequent requests to the same broker process (Process) using async_ask/3.

See also: async_ask/3, cancel/2.

async_ask/3

Sends an asynchronous request to match with a process calling ask_r/2. Returns {await, Tag, Pid}.

To is a tuple containing the process, pid(), to send the reply to and Tag, any(), that identifies the reply containing the result of the request. Process is the pid() of the broker or {atom(), node()} if the broker is registered locally on a different node. To cancel all requests identified by Tag on broker Process call cancel(Process, Tag).

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

Ref is the transaction reference, which is a reference(). Value is the value of the matched process. RelativeTime is the time spent waiting for a match after discounting time spent waiting for the broker to handle requests. SojournTime is the time spent in the broker's message queue.

Multiple asynchronous requests can be made from a single process to a broker and no guarantee is made of the order of replies. If the broker exits or is on a disconnected node there is no guarantee of a reply and so the caller should take appropriate steps to handle this scenario.

See also: cancel/2.

async_ask_r/1

Equivalent to async_ask_r(Broker, self()).

async_ask_r/2

Monitors the broker and sends an asynchronous request to match with a process calling ask/2.

See also: async_ask/2, cancel/2.

async_ask_r/3

Sends an asynchronous request to match with a process calling ask/2.

See also: async_ask/3, 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/2

Equivalent to cancel(Broker, Tag, infinity).

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/1

Equivalent to change_config(Broker, infinity).

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.

dirty_cancel/2

Cancels an asynchronous request.

See also: cancel/3.

dynamic_ask/1

Equivalent to dynamic_ask(Broker, self()).

dynamic_ask/2

Tries to match with a process calling ask_r/2 on the same broker. If no immediate match available the request is converted to an async_ask/2.

Returns {go, Ref, Value, RelativeTime, SojournTime} on a successful match or {await, Tag, BrokerPid}.

Ref is the transaction reference, which is a reference(). Value is the value of the matched process. RelativeTime is the time spent waiting for a match after discounting time spent waiting for the broker to handle requests. SojournTime is the time spent in the broker's message queue. Tag is a monitor reference and BrokerPid the pid() of the broker, as returned by async_ask/2.

See also: async_ask/2, nb_ask/2.

dynamic_ask_r/1

Equivalent to dynamic_ask_r(Broker, self()).

dynamic_ask_r/2

Tries to match with a process calling ask/2 on the same broker. If no immediate match available the request is converted to an async_ask_r/2.

See also: dynamic_ask/2.

len/1

Equivalent to len(Broker, infinity).

len/2

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

len_r/1

Equivalent to len_r(Broker, infinity).

len_r/2

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

nb_ask/1

Equivalent to nb_ask(Broker, self()).

nb_ask/2

Tries to match with a process calling ask_r/2 on the same broker but does not enqueue the request if no immediate match. Returns {go, Ref, Value, RelativeTime, SojournTime} on a successful match or {drop, SojournTime}.

Ref is the transaction reference, which is a reference(). Value is the value of the matched process. RelativeTime is the time spent waiting for a match after discounting time spent waiting for the broker to handle requests. SojournTime is the time spent in the broker's message queue.

See also: ask/2.

nb_ask_r/1

Equivalent to nb_ask_r(Broker, self()).

nb_ask_r/2

Tries to match with a process calling ask/2 on the same broker but does not enqueue the request if no immediate match.

See also: nb_ask/2.

start_link/3

Starts a broker with callback module Module and argument Args, and broker options Opts.

See also: gen_server:start_link/3.

start_link/4

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

See also: start_link/3.

Overview

Generated by EDoc, Oct 10 2016, 18:50:59.