[review v3] Demangle minsyms in parallel

["Tom Tromey (Code Review)" <gerrit@gnutoolchain-gerrit.osci.io>]

Tom Tromey has posted comments on this change.

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/173
......................................................................


Patch Set 3:

(1 comment)

| --- /dev/null
| +++ gdb/gdbsupport/parallel-for.h
| @@ -1,0 +45,19 @@ parallel_for_each (RandomIt first, RandomIt last, RangeFunction callback)
| +#if CXX_STD_THREAD
| +  /* So we can use a local array below.  */
| +  const size_t local_max = 16;
| +  size_t n_threads = std::min (thread_pool::g_thread_pool->count (),
| +			       local_max);
| +  size_t n_actual_threads = 0;
| +  std::future<void> futures[local_max];
| +
| +  size_t n_elements = last - first;
| +  if (n_threads > 1 && 2 * n_threads <= n_elements)

PS3, Line 54:

I think this check doesn't really make sense -- if one has many
elements but also many threads available, the answer shouldn't be
to give up.

In the next revision, I've changed it to reduce the number of threads
used when there aren't many elements per thread.  I picked an
arbitrary cutoff of a minimum of 10 elements.

| +    {
| +      size_t elts_per_thread = n_elements / n_threads;
| +      n_actual_threads = n_threads - 1;
| +      for (int i = 0; i < n_actual_threads; ++i)
| +	{
| +	  RandomIt end = first + elts_per_thread;
| +	  auto task = [=] ()
| +		      {
| +			callback (first, end);

-- 
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I220341f70e94dd02df5dd424272c50a5afb64978
Gerrit-Change-Number: 173
Gerrit-PatchSet: 3
Gerrit-Owner: Tom Tromey <tromey@sourceware.org>
Gerrit-Reviewer: Christian Biesinger <cbiesinger@google.com>
Gerrit-Reviewer: Tom Tromey <tromey@sourceware.org>
Gerrit-Comment-Date: Fri, 22 Nov 2019 23:45:35 +0000
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