On Jun 16, 2013, at 8:27 AM, Gary Willoughby <d...@kalekold.net> wrote:
> I'm writing a little program in D to perform some database operations and
> have a small question about design.
>
> Part of my program watches a log file for changes and this involves code
> which is wrapped up in a class. So the usage is something like this:
>
> auto fileWatcher = new FileWatcher(fileName);
> fileWatcher.onChange(delegate);
> fileWatcher.start();
>
> Once the start method is called a loop is entered within the class and the
> file is watched. Changes are handle through calling the registered delegate.
> The loop uses different watch methods for different platforms.
>
> What i need to be able to do is to stop the current watch and change the
> watched file.
>
> Because this is in an infinite loop, i can't check externally i.e. outside of
> the class, if i need to break from the loop simply because control never
> returns to the caller of the start() method.
>
> Am i missing something simple here? Any advice is welcome. I thought about
> threading and message passing but that's maybe overkill for something as
> simple as this?
Some form of concurrency is probably what you want here. But be aware that
your delegate may have to be made thread-safe, depending on what it does.
Regan suggested using Thread, and you can use spawn as well:
import std.concurrency;
import std.conv;
import std.datetime;
import std.stdio;
import core.thread;
void main()
{
auto tid = spawn(&fileWatcher, "file0");
foreach (i; 1 .. 5)
{
Thread.sleep(dur!"msecs"(300)); // sleep for a bit to
simulate work
send(tid, "file" ~ to!string(i));
}
}
void fileWatcher(string fileName)
{
while (true)
{
receiveTimeout(dur!"msecs"(0),
(string n) => fileName = n);
writefln("checking %s", fileName);
Thread.sleep(dur!"msecs"(100)); // sleep for a bit to
simulate work
}
writeln("bye!");
}
