Is this function pure?

[Nathan Reed]

Bill Baxter wrote:
> On the other hand the support for concurrency may consist of little more 
> than a global mutex.  That means that the performance benefits of 
> launching multiple threads might not be so great since they'll all just 
> end up in a queued waiting for their turn to malloc.
> 
> I have no idea what they do in practice though.  Do typical malloc 
> systems actually allow simultaneous allocations in multiple threads?
> 
> --bb

On a multicore system the allocator might conceivably have a heap for 
each core or something like that.

However, even if this is not the case, allocation in a garbage-collected 
language is very quick and the mutex would only need to be held for the 
duration of the allocation.

With a pure function that does some allocation and then a bunch of 
computation, all the computations could proceed in parallel once each 
thread's memory had been allocated.  Synchronized allocations certainly 
need not negate the benefits of parallelism.

Thanks,
Nathan Reed