add support for timeout in constructor

[russellpierce]

If you specify an incorrect address as it stands it seems as though RcppRedis will wait for a very long time (if not indefinitely) before throwing an error. This modification allows one to set a timeout in the constructor. If the connection has not been established by the timeout, it gives up and produces an error.

[eddelbuettel]

Sounds reasonable. But (just to think out aloud) should we not just always set it to, say, 500ms (or three seconds or whatnot) ?

Also, maybe supply the argument as a double and split into whole int and millisecond?

[eddelbuettel]

I think I just add that. Hold on ...

[russellpierce]

Do I set a smart default for the user or do I expose the interface? I went towards exposing the interface... but I do also love smart defaults. Regardless, you are right, if we expose the option it probably should take the double and split it up between seconds and microseconds. Two parenthetical thoughts... a) oddly not milliseconds - I wonder how they are doing their timing such that they imagine they get that level of time resolution ... b) does a user really care about resolution below the second level here?

This is just an initialization step, so it only happens once; so long as it times out before the user feels the need to tap their finger at it and say 'is this thing on?', no problem. The slippery slope argument from there is that perhaps all connection requests should just use redisConnectWithTimeout and we should select a sensible default value for all connections. I think it makes a certain amount of sense to do that, and then perhaps to accept an override value in the constructor if they aren't happy with our default.

[eddelbuettel]

I frankly never had the time out problem so 'shrugs'. Wait a min -- editing on train right now.

[eddelbuettel]

This should do, right?

    // set up a connection to Redis on the given machine and port
    void init(std::string host="127.0.0.1", int port=6379,
              std::string auth="", double timeout=0.0)  {
        if (timeout == 0) {
            prc_ = redisConnect(host.c_str(), port);
        } else {
            int second = static_cast<int>(timeout);
            int microseconds = static_cast<int>(1000*(timeout - second));
            struct timeval timeoutStruct = { timeout, microseconds };
            prc_ = redisConnectWithTimeout(host.c_str(), port, timeoutStruct);
        }

[russellpierce]

I think instead use 1000000*(timeout - second). You want microseconds. cf. https://github.com/redis/hiredis/blob/master/examples/example.c

[eddelbuettel]

Touche. Will fix.

I was also about to send you there for 'proper' defauls. Does it have any?

[russellpierce]

The example uses 1.5 seconds, but as far as I can tell redisConnectWithTimeout has no default time value.