thread-ring benchmark

[Alan Knowles]

try googling for "thread-limit.c proc"

There are a few /proc settings that enable more threads to be run, 
(basically you are running out of resources, and Phobos is hiding the 
real error - you need the error return from thread_start.)

I have got it up to quite a high number of threads.

However !!IMPORTANT!! - this is a horrible example on how to use 
threads, and for beginners it will confuse them horribly.

If you do make this code public anywhere, please put a note in it
"NEVER USE THREADS LIKE THIS!" - threads are intended to be used in 
pools, and re-used, if you write your application like this, it will 
ALWAYS crash eventually, whatever you do...

(As you may have guessed - I got caught by that one...)


Regards
Alan


bearophile wrote:
> This is the D thread-ring benchmark on the Shootout site:
> http://shootout.alioth.debian.org/gp4/benchmark.php?test=threadring&lang=dlang&id=0
> 
> For me on DMD 1.024 on Win it works, but it doesn't work on the site (it gives: Error: Thread error: failed to start), maybe it's a thread problem on Linux, so it may be a Phobos bug.
> 
> This is my shortened & simplified version, it uses a static array local to the main() (indent reduced to just 2 spaces):
> 
> // The Computer Language Benchmarks Game
> // http://shootout.alioth.debian.org/
> // contributed by Alexander Suhoverhov
> // Modified by bearophile
> 
> import std.thread: Thread;
> import std.conv: toInt;
> 
> int n;
> bool finished = false;
> 
> class MessageThread: Thread {
>   MessageThread next;
>   int message, name;
> 
>   int run() {
>     while (true) {
>       while (!message && !finished)
>         yield;
> 
>       if (finished)
>         return 0;
> 
>       if (message == n) {
>         finished = true;
>         printf("%d\n", name);
>         return 0;
>       }
> 
>       next.message = this.message + 1;
>       this.message = 0;
>     }
>     return 0;
>   }
> }
> 
> void main(char[][] args) {
>   const NUM_THREADS = 503;
>   MessageThread[NUM_THREADS] ring;
> 
>   n = args.length == 2 ? toInt(args[1]) : 100_000;
> 
>   foreach(i, ref mt; ring)
>     mt = new MessageThread;
> 
>   foreach(i, mt; ring) {
>     mt.name = i + 1;
>     mt.next = ring[(i + 1) % ring.length];
>     mt.start;
>   }
> 
>   ring[0].message = 1;
> 
>   foreach(mt; ring)
>     mt.wait;
> }
> 
> 
> The good thing is that it on my PC it runs faster than the Java6 version (the given n is 10 millions).
> The bad thing is that it doesn't print 361 (but probably one less, 360), so if you spot the problem you can suggest it.
> Note that the Java version doesn't use global variables like n and finished. There is a simple way to avoid the need of finished, using std.c.stdlib.exit, but the code requires more time to run.
> Note that  the Haskell version (that uses light threads) works in about 1/10 of the time... (The Erlang/Oz versions too are fast) so maybe the D threading of Phobos may become quite faster in the future, using similar "threads".
> 
> Bye,
> bearophile