Erlang timed out processing

Erlang timed out processing

Before we improve the messager program, let's learn some basic principles together. R ecall that when "ping" ends, it sends a message to "pong" with an atomic value finished to notify "pong" to end the program. A nother way to end "pong" is to exit the program when "pong" does not receive a message from "ping" for a certain period of time. W e can add a time-out to pong to implement it:

-module(tut19).

-export([start_ping/1, start_pong/0,  ping/2, pong/0]).

ping(0, Pong_Node) ->
    io:format("ping finished~n", []);

ping(N, Pong_Node) ->
    {pong, Pong_Node} ! {ping, self()},
    receive
        pong ->
            io:format("Ping received pong~n", [])
    end,
    ping(N - 1, Pong_Node).

pong() ->
    receive
        {ping, Ping_PID} ->
            io:format("Pong received ping~n", []),
            Ping_PID ! pong,
            pong()
    after 5000 ->
            io:format("Pong timed out~n", [])
    end.

start_pong() ->
    register(pong, spawn(tut19, pong, [])).

start_ping(Pong_Node) ->
    spawn(tut19, ping, [3, Pong_Node]).

Compile the above code and copy the resulting tut19.beam file to a directory, and here is the output pong@kosken node:

true
Pong received ping
Pong received ping
Pong received ping
Pong timed out

The output on ping@gollum node is:

(ping@gollum)1> tut19:start_ping(pong@kosken).
<0.36.0>
Ping received pong
Ping received pong
Ping received pong
ping finished 

time-out is set at:

pong() ->
    receive
        {ping, Ping_PID} ->
            io:format("Pong received ping~n", []),
            Ping_PID ! pong,
            pong()
    after 5000 ->
            io:format("Pong timed out~n", [])
    end.

When recieve is executed, the time-out timer (5000 ms) starts, and the time-out timer is canceled as soon as it receives a message for .ping, Ping_PID. I f you don't receive a Ping_PID," the program that follows time-out is executed after 5000 milliseconds. A fter must be the last in recieve, that is, all other messages in recieve receive processing over time-out messages. I f there is a function that returns a value of integer values, we can call the function after after to set its return value to a time-out value, as follows:

after pong_timeout() ->

In general, there are many better ways to implement monitoring in addition to using timeouts to monitor the divisions of a distributed Erlang system. T imeouts are useful for monitoring events from outside the system, for example, when you want to receive messages from an external system within a specified time. For example, we can use timeouts to find that a user has left the messenger system, for example, when the user has not accessed the system for 10 minutes, and thinks that he or she has left the system.