Safely writing to the same file in parallel foreach loop

[Joseph Rushton Wakeling]

On 11/14/2012 10:17 PM, Jonathan M Davis wrote:
> I would point out though that given how expensive disk writes are, unless
> you're doing a lot of work within the parallel foreach loop, there's a good
> chance that it would be more efficient to use std.concurrency and pass the
> writes to another thread to do the writing. And the loop itself should still
> be able to be a parallel foreach, so you wouldn't have to change much
> otherwise. But with the synchronized block, you'll probably end up with each
> thread spending a lot of its time waiting on the lock, which will end up
> making the whole thing effectively single-threaded.

Do you mean that the synchronized {} blocks have to all be completed before the 
threads can all be terminated?

In the end the solution I came to was something like this:

     enum N = 16;   // number of cases
     shared real[N+1] results;

     foreach(i; parallel(iota(0, N+1)))
     {
         // ... do a lot of calculation ...
         results[i] = // result of calculation
     }

     // and now at the end we write out all the data

... which seems to work, although I'm not 100% confident about its safety.