Redis subscribe does not really do anything, according to Swoole examples

[paveljanda]

• What did you do? If possible, provide a simple script for reproducing the error.
  • I tried to implement a redis pub-sub client behaviour using Swoole\Couroutine\Redis
• What did you expect to see?
  • A pub-sub behaviour (publishing into a channel using native redis-cli client will display published message in cli and vice-versa)
• What did you see instead?
  • According to the documentation, I saw only a true repeatedly (200k times a second) showing in cli even there was no message published in the channel
• What version of Swoole are you using (show your php --ri swoole)?
  • 4.4.3
• What is your machine environment used (including version of kernel & php & gcc) ?
  • Kernel: MacOS Mojave, version 10.14.6
  • PHP: 7.3.6
  • gcc: 4.2.1 (I think - gcc --version)

Code in documentation (https://github.com/swoole/swoole-src/blob/master/examples/coroutine/redis/sub.php):

go(function () {
    $redis = new Swoole\Coroutine\Redis();
    $redis->connect('127.0.0.1', 6379);
    //while (true) 
    {
        $msg = $redis->subscribe(array("msg_1"));
        var_dump($msg);
    }
});

I think it should be like this:

go(function() {
    $redis = new Redis;

    $redis->connect('127.0.0.1', 6379);

    $redis->subscribe(['channel'])

    while ($message = $redis->recv()) {
        var_dump($message);
    }
});

Thanks a lot

[doubaokun]

@paveljanda

Swoole\Coroutine\Redis is the coroutine version of Redis client.

The following code works as a Redis subscription:

<?php
go(function () {
    $redis = new Swoole\Coroutine\Redis();
    $redis->connect('127.0.0.1', 6379);
    while (true) 
    {
        $msg = $redis->subscribe(array("msg_1"));
        var_dump($msg);
    }
});

[paveljanda]

Actually I don't rally think this is true. You should not be calling Redis::subscribe each time you receive a message. You should be calling the example I gave you above:

go(function() {
    $redis = new Redis;

    $redis->connect('127.0.0.1', 6379);

    $redis->subscribe(['channel'])

    while ($message = $redis->recv()) {
        var_dump($message);
    }
});

[paveljanda]

Wtf?

I showed you correct behaviour. You can try those examples by yourself. Your example is wrong. Your example is repeatedly "var_dumping" true even it has not receive any message from the channel. My example subscribes to the channel "channel" only one time and then it receives the message only when there is a message published into this channel.

Please correct the documentation to prevent people directing a dead end.

[paveljanda]

cc @matyhtf @twose

[doubaokun]

@paveljanda you are using a block version redis client which is blocking the whole process which should not be used in the context of coroutine.

Please try the following example with php cli and PUBLISH msg_1 a and PUBLISH msg_2 b in redis client.

You should be able to understand how the redis sub works in Swoole:

<?php
go(function () {
    $redis = new Swoole\Coroutine\Redis();
    $redis->connect('127.0.0.1', 6379);
    while (true) 
    {
        $msg = $redis->subscribe(array("msg_1"));
        var_dump($msg);
    }

});

go(function () {
    $redis = new Swoole\Coroutine\Redis();
    $redis->connect('127.0.0.1', 6379);
    while (true) 
    {
        $msg = $redis->subscribe(array("msg_2"));
        var_dump($msg);
    }
});

Btw, please stop using the word Wtf.

[paveljanda]

I used the word because you suddenly closed the issue. Sorry for that but please, don't close this issue yet. I don't think it is resolved.

On my machine, your code is var_dumping true 900474 times in 5 seconds to cli. I don't think this is really correct behaviour. I think the process should wait for a message to be received from redis. You are not var_dumping the message but result of subscribe command.

My example is actually not blocking. I tried it. Or what am I missing?

[paveljanda]

Try this:

go(function() {
    $redis = new Redis;

    $connectResult = $redis->connect('127.0.0.1', 6379);

    if ($redis->subscribe(['channel-1'])) {
        while ($message = $redis->recv()) {
            var_dump($message);
        }
    } else {
        throw new \RuntimeException('Could not subscribe');
    }
});

go(function() {
    $redis = new Redis;

    $connectResult = $redis->connect('127.0.0.1', 6379);

    if ($redis->subscribe(['channel-2'])) {
        while ($message = $redis->recv()) {
            var_dump($message);
        }
    } else {
        throw new \RuntimeException('Could not subscribe');
    }
});

[paveljanda]

Result of my code:

array(3) {             
  [0]=>                
  string(9) "subscribe"
  [1]=>                
  string(9) "channel-1"
  [2]=>                
  int(1)               
}                      
array(3) {             
  [0]=>                
  string(9) "subscribe"
  [1]=>                
  string(9) "channel-2"
  [2]=>                
  int(1)               
}                      
array(3) {             
  [0]=>                
  string(7) "message"  
  [1]=>                
  string(9) "channel-1"
  [2]=>                
  string(3) "foo"      
}                      
array(3) {             
  [0]=>                
  string(7) "message"  
  [1]=>                
  string(9) "channel-1"
  [2]=>                
  string(3) "bar"      
}                      

Result fo your code:

true
true
true
true
true
true
true
true
true (200k times a second..)

[doubaokun]

@paveljanda when reporting bugs please follow the template like the other people:

Please answer these questions before submitting your issue. Thanks!

1. What did you do? If possible, provide a simple script for reproducing the error.

2. What did you expect to see?

3. What did you see instead?

4. What version of Swoole are you using (show your php --ri swoole)?

5. What is your machine environment used (including version of kernel & php & gcc) ?

[paveljanda]

Ok, sorry, will update the first comment. 👍

[paveljanda]

@doubaokun Updated. 👍

[doubaokun]

@paveljanda the example is updated for version > 4.4.0. Closing this thread now.

[paveljanda]

Thanks a lot, appreciate it.